Study on Safe Usage of Bamboo and Mixed Scaffoldings

Occupational Safety & Health Council 2016

Study on Safe Usage of Bamboo and Mixed Scaffoldings

Table of contents

TITLE PAGE i

TABLE OF CONTENTS ii

LIST OF FIGURES v

LIST OF TABLES viii

Chapter 1 Introduction ...... 1

1.1 Background ...... 1

1.2 Research plan and methodology ...... 1

Chapter 2 Anchorage for Bamboo Scaffolding: Regional Reinforcement ...... 3

2.1 Mechanical properties of connection in bamboo scaffolding ...... 4

2.1.1 Connection resistance with and without nodes ...... 5

2.1.2 Slipping stiffness of connection without nodes ...... 6

2.1.3 Rotational stiffness of connection ...... 6

2.2 Modeling of bamboo scaffolding ...... 8

2.2.1 Description of bamboo scaffolding ...... 8

2.2.2 Finite element modeling of bamboo scaffolding ...... 9

2.3 Regional reinforcement of bamboo scaffolding...... 10

2.3.1 Option 1 - Ledger reinforcement ...... 10

2.3.2 Option 2 - Reinforcing two adjacent ledgers ...... 11

2.3.3 Option 3 - Platform reinforcement ...... 13

2.3.4 Personal energy absorber (PEA) lanyard and self-retracting lifeline

(SRL)...... 15

2.3.5 Critical cases for experimental test ...... 16

2.4 Full-scale bamboo scaffolding test ...... 17

2.4.1 Description of the scaffolding ...... 18

2.4.2 Test arrangement ...... 18

ii Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

2.4.3 Static point load test ...... 19

2.4.4 Drop load test ...... 21

2.5 Scaffoldings with different configuration and dimensions ...... 22

2.6 Multiple anchorages for Option 2 regional reinforcement ...... 23

Chapter 3 Anchorage for Bamboo Scaffolding: Other Options ...... 65

3.1 A safer scaffolding erection process...... 65

3.2 Anchorages for bamboo scaffolding above roof level ...... 66

3.3 Anchorages for bamboo scaffolding below roof level ...... 68

Chapter 4 Use of Mixed Scaffolding ...... 72

4.1 Mechanical properties of connection ...... 72

4.1.1 Normal steel tube-bamboo connection ...... 72

4.1.2 Anti-sliding steel tube-bamboo/normal steel tube connection ...... 74

4.1.3 Normal steel tube-normal steel tube connection ...... 75

4.1.4 Thermal effect of steel tube on connection ...... 76

4.2 Design and modeling of mixed scaffolding ...... 77

4.2.1 Design of mixed scaffolding ...... 77

4.2.2 Modeling of mixed scaffolding ...... 77

4.3 Comparison among three types of mixed scaffolding ...... 78

4.3.1 Construction cost and time...... 79

4.3.2 Weight and weight distribution ...... 81

4.3.3 Load-carrying capacity ...... 81

4.3.4 Summary ...... 85

4.4 Full-scale mixed scaffolding test ...... 87

4.4.1 Description of the scaffolding ...... 87

4.4.2 Test arrangement ...... 88

4.4.3 UDL test on platform ...... 88

4.4.4 Static point load test on connection ...... 90

4.5 Anchorages for mixed scaffolding ...... 92

iii Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Chapter 5 Use of Different Materials for the Working Platform ...... 135

5.1 Types for the working platform ...... 135

5.2 Mechanical properties of wooden boards and iron planks ...... 135

5.3 Full-scale test of working platform ...... 136

5.3.1 Test arrangement ...... 137

5.3.2 Test results...... 138

Chapter 6 Conclusions and Recommendations ...... 150

Appendix ...... 152

Appendix A Other types of connection and test fixture ...... 152

A1 Column (or beam/bracing) splice test ...... 152

A2 A special type of connection called “打戒指” ...... 154

A3 Fixture for beam-column connection test ...... 155

Appendix B Material properties of bamboo and steel tube ...... 161

B1 Mechanical properties of bamboo ...... 161

B2 Mechanical properties of steel tube ...... 162

B3 Tube specimens and fixture for tensile test ...... 163

Appendix C Column buckling of structural bamboo in bamboo scaffoldings .. 170

C1 Effective length of the post in bamboo scaffoldings [10] ...... 171

C2 Non-prismatic parameter 휶 [34] ...... 173

C3 Working example: column buckling of bamboo post using Kao Jue ... 174

Appendix D Allowable compressive load on metal post in mixed scaffoldings 176

References ...... 178

iv Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Lists of figures

Fig. 2-1 Setup of bamboo connection test ...... 24

Fig. 2-2 Two failure modes for connection with node ...... 25

Fig. 2-3 Typical load-displacement curve for conection test with node ...... 25

Fig. 2-4 Slippage failure for connection test without node ...... 25

Fig. 2-5 Vertical testing curves of BP-BP connection...... 26

Fig. 2-6 Modeling of slippage stiffness for bamboo connection ...... 27

Fig. 2-7 Setup of rotational stiffness test ...... 27

Fig. 2-8 Rotational test curves of BP-BP connection ...... 28

Fig. 2-9 Modeling of rotational stiffness for bamboo connection ...... 29

Fig. 2-10 Two typical arrangements and configuration of DLBS ...... 30

Fig. 2-11 Modeling of bamboo scaffolding ...... 30

Fig. 2-12 Deformation of scaffolding after reinforcement ...... 31

Fig. 2-13 Reinforcement option: combining two adjacent ledgers with steel tubes .... 31

Fig. 2-14 Load-carrying capacities and moment distribution diagrams ...... 32

Fig. 2-15 Modeling of contact surface with couplers ...... 32

Fig. 2-16 Load cases for Option 2 ...... 33

Fig. 2-17 Deformation of load case (2) at the position closest to the edge...... 33

Fig. 2-18 Reinforcement option: installing steel tubes under the work platform ...... 33

Fig. 2-19 Load cases for Option 3.2 near the center of scaffolding ...... 34

Fig. 2-20 Moment diagram for two types of bamboo failure ...... 35

Fig. 2-21 Configuration and dimensions of the scaffolding ...... 36

Fig. 2-22 Load positions for anchorage test ...... 37

Fig. 2-23 Setup of static point load test ...... 38

Fig. 2-24 Static point load test for various test cases ...... 39

Fig. 2-25 Bamboo post and standard labelling for Table 2-13 (a)-(f) ...... 39

Fig. 2-26 Setup of drop load test ...... 40

v Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Fig. 2-27 Drop load test and typical drop force-time curves ...... 43

Fig. 2-28 Multiple anchorages for Option 2 regional reinforcement ...... 44

Fig. 3-1 A safer bamboo scaffolding erection process ...... 69

Fig. 3-2 Illustration of various options to facilitate the new erection process ...... 70

Fig. 3-3 Bamboo scaffoldings above roof level ...... 71

Fig. 3-4 Configuration of a HLL system with different anchorage options [14] ...... 71

Fig. 3-5 Miller SkyGrip Wire Rope Lifeline and anchorage [15] ...... 71

Fig. 4-1 Normal steel tube (left) and anti-sliding steel tube (right) ...... 93

Fig. 4-2 Test setup for normal steel tube-bamboo connection ...... 94

Fig. 4-3 Slippage tests for normal steel tube (post)-bamboo (ledger) connection ...... 95

Fig. 4-4 Rotational tests for normal steel tube (post)-bamboo (ledger) connection .... 96

Fig. 4-5 Modeling of normal steel tube-bamboo connection ...... 97

Fig. 4-6 Test setup for connection involving anti-sliding steel tube ...... 97

Fig. 4-7 Five different orientation angles for the anti-sliding steel tube ...... 98

Fig. 4-8 Splitting of plastic stripes for 0°, 45° and 90° orientation ...... 98

Fig. 4-9 Load-displacement curves for anti-sliding steel tube-bamboo connection .... 99

Fig. 4-10 Failure mode for 180° orientation of anti-sliding steel tube-bamboo connection ...... 100

Fig. 4-11 Failure mode for 180° orientation of anti-sliding steel tube-normal steel tube connection ...... 101

Fig. 4-12 Illustration of anti-sliding steel tube orientation with transom ...... 102

Fig. 4-13 Right-angle coupler (left) and swivel coupler (right) ...... 102

Fig. 4-14 Typical configuration of a double-layered bamboo scaffolding (DLBS) ... 102

Fig. 4-15 Three different types of mixed scaffolding ...... 104

Fig. 4-16 A one-bay unboarded lift of scaffolding ...... 104

Fig. 4-17 Two types of platform commonly used in scaffolding ...... 105

Fig. 4-18 Modeling of scaffolding platforms ...... 105

Fig. 4-19 Dimension and modeling of metal bracket ...... 106

vi Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Fig. 4-20 The full-scale mixed scaffolding used for test ...... 107

Fig. 4-21 Test arrangement for UDL test on platform ...... 108

Fig. 4-22 Test arrangement for static point load test on connection ...... 109

Fig. 4-23 Setup of UDL test for platform ...... 109

Fig. 4-24 UDL test on platform ...... 110

Fig. 4-25 Labeling of metal post and bamboo standard...... 111

Fig. 4-26 Setup of static point load test on connection ...... 112

Fig. 4-27 Load-displacement curves for Connections (1) and (3) (see Fig. 4-22)..... 113

Fig. 4-28 Failure of Connections (1) and (4) under static point load ...... 113

Fig. 4-29 Comparison of load-displacement curves between test and analysis ...... 114

Fig. 5-1 Three working platform Types ...... 140

Fig. 5-2 Thin and thick wooden boards made out of plywood ...... 140

Fig. 5-3 Dimension of pre-fabricated iron plank ...... 141

Fig. 5-4 Three-point loading test on wooden board and iron plank ...... 141

Fig. 5-5 A typical load-deflection curve for an iron plank ...... 141

Fig. 5-6 Dimensions and position of the partial area ...... 142

Fig. 5-7 Setup of static point load test on the middle span of platform ...... 143

Fig. 5-8 Typical load-deflection curves of three platform types ...... 144

Fig. 5-9 Comparison of load-deflection curves between test and analysis ...... 144

Fig. A-1 Setup of splice test ...... 157

Fig. A-2 Test setup of splice with contact length 1.3 m and different number of ties157

Fig. A-3 Test setup of actual connection with six ties ...... 158

Fig. A-4 Typical configuration of “打戒指” ...... 158

Fig. A-5 Failure mode and typical load-displacement curve of “打戒指” ...... 159

Fig. B-1 Three sizes of steel tube available in Hong Kong ...... 166

Fig. B-2 Setup for the tensile test...... 167

Fig. B-3 Load-displacement curve for specimen D2 under tensile test ...... 168

vii Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Lists of tables

Table 2-1 Test configurations for bamboo connection ...... 45

Table 2-2 Resistance of bamboo connection with node ...... 45

Table 2-3 Resistance of bamboo connection without node ...... 46

Table 2-4 Rotation stiffness for beam-column connection ...... 46

Table 2-5 Load-carrying capacity of ledger after reinforcement ...... 47

Table 2-6 Load-carrying capacity for Option 2 near the center of scaffolding ...... 47

Table 2-7 Load-carrying capacity for Option 2 near the edge of scaffolding ...... 48

Table 2-8 Effect of tube thickness on load-carrying capacity for Option 2 load case (1)

...... 48

Table 2-9 Load-carrying capacity for various options under load case (1) ...... 49

Table 2-10 Load-carrying capacity for Option 3.2 near the center of scaffold ...... 49

Table 2-11 Summary of load-carrying capacity for Option 2 ...... 50

Table 2-12 Load-carrying capacity for Option 3.2 with a tube length of 1.2 m ...... 50

Table 2-13 Results of static point load test for test cases (1) to (6) ...... 51

Table 2-14 Comparison of computer analysis with static point load test ...... 54

Table 2-15 Summary for the static point load test ...... 57

Table 2-16 Results of drop load test ...... 57

Table 2-17 Anchorages for DLBS with 3 standards and a span of 0.6 m ...... 59

Table 2-18 Reinforced anchorages for different bamboo scaffoldings ...... 60

Table 2-19 Load-carrying capacity (in kN) of one anchor point for Option 2 with more steel struts...... 62

Table 2-20 Load-carrying capacity for Option 2 under two users ...... 64

Table 4-1 Resistance for normal steel tube-bamboo connection ...... 115

Table 4-2 Rotational stiffness for normal steel tube-bamboo connection ...... 115

Table 4-3 Test results for anti-sliding steel tube-bamboo/normal steel tube connection

...... 115

viii Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Table 4-4 Connection resistance for 0°, case 45° and case 90° orientation ...... 116

Table 4-5 Total displacement for 0°, case 45° and case 90° orientation ...... 116

Table 4-6 Properties for various types of couplers ...... 116

Table 4-7 Material required for a one-bay unboarded lift ...... 117

Table 4-8 Material cost for scaffoldings ...... 117

Table 4-9 Equivalent density for scaffoldings ...... 117

Table 4-10 Self-weight and weight distribution of a one-bay unboarded lift ...... 118

Table 4-11 Allowable loads for scaffolding platforms ...... 118

Table 4-12 Maximum deflections for scaffolding platforms ...... 118

Table 4-13 Allowable buckling loads for metal and bamboo posts ...... 119

Table 4-14 Allowable heights of scaffoldings ...... 119

Table 4-15 Test data for Fook Shing anchor bolts [2, 3] ...... 120

Table 4-16 Safety of anchor bolt and bracket for scaffolding with allowable height 120

Table 4-17 Comparison of three mixed scaffoldings and bamboo scaffolding ...... 121

Table 4-18 Results for UDL test on platform...... 122

Table 4-19 Comparison of UDL test results with computer analysis ...... 126

Table 4-20 Summary of UDL test and analysis ...... 129

Table 4-21 Displacement of connection under 2 kN static point load ...... 129

Table 4-22 Results for static point load test (2 kN) on connection ...... 130

Table 4-23 Load-carrying capacity of connections ...... 131

Table 4-24 Comparison of connection displacement between test and analysis ...... 132

Table 4-25 Comparison of load-carrying capacity of connection ...... 132

Table 4-26 Comparison of axial forces under 2.0 kN load ...... 132

Table 4-27 Summary of connection test and analysis ...... 134

Table 5-1 Mechanical properties for wooden boards ...... 145

Table 5-2 Mechanical properties for iron planks ...... 145

Table 5-3 Deflection at the midpoint of inner layer ...... 146

Table 5-4 Results for static point load (3 kN) on working platform ...... 146

ix Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Table 5-5 Comparison of deflection between test and analysis ...... 147

Table 5-6 Comparison of axial forces under 3 kN load ...... 148

Table 5-7 Summary for platform test and analysis ...... 149

Table A-1 Effects of presence of nodes and number of round turns on resistance .... 160

Table A-2 Experiments to study the effect of number of ties and contact length ...... 160

Table A-3 Tested resistance of actual splices ...... 160

Table A-4 Resistance of “打戒指” beam-column connection ...... 161

Table B-1 Summary of physical and mechanical properties of Kao Jue and Mao Jue

...... 168

Table B-2 Results of tensile test for three different sizes of steel tube ...... 169

Table C-1 Buckling design example of Kao Jue with effective length 2 m ...... 175

Table D-1 Allowable compressive load for steel column with 퐿퐸 = 1.0 퐻 ...... 177

x Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Chapter 1 Introduction

1.1 Background

The safety and reliability of bamboo scaffoldings have been investigated previously in three separate studies funded by the Occupational Safety and Health Council [1-3]. Recommendations have been made and published to ensure safe usage of these temporary structures. Recent feedbacks from the industry however reveal that some additional issues have surfaced and might hinder the safety of bamboo scaffoldings. First, it was recommended in [1] that the intersections of the bamboo scaffoldings cannot be used to anchor safety belts. This restriction unfortunately has created a rather unfavorable condition for the workers to anchor the independent lifeline and the safety harness to a reliable anchorage during erection, alteration or dismantling of bamboo scaffolding, especially for bamboo scaffolding above the roof level. Also, there appear some scaffoldings constructed using a mixture of both bamboo and metal tubes. These mixed scaffoldings have created a series of new technical challenges that need to be addressed. Furthermore, there is a concern that needs to be addressed about using different materials for the working platform on the scaffoldings. This proposed study is intended to investigate these three issues and to provide solutions and practical guidebooks to the industry for the safe erection, usage as well as dismantling of bamboo and mixed scaffoldings.

1.2 Research plan and methodology

This research aims at conducting a systematic study on the three issues listed above using both computer analyses and laboratory tests. The computer analyses are conducted using the finite element analysis program SAP 2000 and the laboratory tests

1 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings are conducted in the Structural Laboratory of the Hong Kong University of Science and Technology. Details of the proposed study are discussed in the following.

(1) Anchorages for safety harness For bamboo scaffolding under roof level, some regions of scaffolding are reinforced by using either stronger bamboo components or other non-bamboo components such as metal tubes. For bamboo scaffolding above the roof level, the possibility of using extra external support or anchorage to improve the safety of bamboo scaffolding is considered and investigated.

(2) Issues relating to the use of mixed scaffolding The load-carrying capacity and safe usage of typical mixed scaffolding are investigated via numerical analyses first. A mixed scaffolding will then be constructed and tested in the laboratory to verify the results obtained from the numerical analyses.

(3) Use of different materials for the working platform Recently, there are some discussions about whether different materials such as prefabricated bamboo panels, wooden boards or metal plate can be used for the working platform on the scaffoldings. This issue is investigated numerically as well as experimentally in this study.

2 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Chapter 2 Anchorage for Bamboo Scaffolding: Regional Reinforcement

Anchorage can be defined as an element or series of elements or components which incorporates an anchor point or anchor points. An anchor point is an element to which personal protective equipment can be attached after installation of anchor device. Some basic requirements for fall arrest systems or personal protective equipment are available in various standards [4-7] and are summarized in the following.

(1) Anchorages selected for fall arrest systems shall have sufficient strength capable of sustaining static load applied in the directions permitted by system of at least two times the maximum arrest force (MAF) for certified anchorages [4, 5]. When more than one fall arrest system is attached to an anchorage, the strength shall be multiplied by the number of systems attached to the anchorage.

(2) According to the ANSI Z359.6 [6] and CSA Z259.16 [7], MAF imposed on a user’s body shall not exceed 8 kN. Note that the 8 kN limitation aims at worker’s body mass of at least 91 kg. A smaller MAF shall be applied to worker whose weight is less than 91 kg. In 2002, the Technical Committee on Fall Protection has actually voted to move toward a standardized MAF of 6 kN in all standards, thus protecting workers down to body mass of 67 kg, see Appendix A.6 of ANSI Z359.6 and Annex A.6 of CSA Z259.16. The static strength test of 12kN required in BS EN 795 [8] is also based on MAF of 6 kN and a safety factor of 2.

These two main requirements ensure the safety of workers and prevent their injuries when fall happens. This chapter is focused on exploring possible anchorages for the workers when they perform their jobs on bamboo scaffoldings. Several regional reinforcement options are investigated through numerical analysis to explore whether

3 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings any part of scaffolding after reinforcement could have adequate strength to serve as safe anchorages. To improve the accuracy of numerical analysis, systematic tests and statistical analysis have been done to investigate the connection properties firstly. For those options meeting the requirements, they will then be tested for deformation, static and dynamic strength and integrity in the laboratory.

2.1 Mechanical properties of connection in bamboo scaffolding

Connection plays a very important part in the load transfer mechanism for bamboo scaffolding. External loads acting on a scaffolding will first be carried by its horizontal transoms and ledgers and then transferred to its vertical posts via connections. The connections of two bamboo members are fastened manually using plastic stripes. As not much research has been done about the behavior of this type of connection in the past, it is necessary to perform a study on the bamboo scaffolding connection in order to model the scaffolding more accurately. This section presents an experimental investigation on the resistance and the stiffness of bamboo scaffolding connection. Through systematic tests and statistical analysis, the characteristic resistance and stiffness of beam-column connection are proposed for further analysis. For other types of connection, such as the column or beam splice and “打戒指”, their properties were also investigated and concluded in Appendix A1 and A2 for practical design. The tests were carried out in the Structural Engineering Laboratory of HKUST using the MTS 810 Universal Testing Machine. Also, a fixture was made as loading equipment to simulate the actual load or moment condition. The dimensions of the test fixture are presented in Appendix A3.

Fig. 2-1 shows a typical setup of beam-column connection test. A total of 75 tests were conducted to obtain the following parameters:

4 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

(1) Connection resistance with and without the presence of nodes; (2) Slipping stiffness of connection without the presence of nodes; (3) Rotational stiffness of connection.

Possible configurations of bamboo connection are summarized in Table 2-1. It is noted that the external diameter is fairly uniform over the length of Kao Jue but not so for that of Mao Jue (noticeably reduces from bottom to top). Some connections involving Mao Jue can only be fastened with 4 round turns (instead of 5 used for the other conditions) using one plastic strip due to larger diameter of Mao Jue. This effect on resistance and stiffness behavior is considered in the experiment.

2.1.1 Connection resistance with and without nodes

Table 2-2 summaries the resistance of bamboo connection with the presence of nodes. It is seen that the mean connection resistance ranges between 1.89 and 2.21 kN with the standard deviation (Std) ranges between 0.35 and 0.81 kN. Table 2-3 presents the experimental results of connection resistance without the presence of nodes. It is seen that the mean connection resistance ranges between 0.62 and 0.98 kN with the standard deviation (Std) ranges between 0.06 and 0.22 kN. As a conservative measure, the connection resistance without nodes was taken as the minimum slipping force during the initial 30 mm displacement. Results show that the connection resistance is larger when bamboo nodes are present around the connection.

Fig. 2-2 shows two failure modes for the connection with nodes: (a) rupture of plastic strip and (b) slippage over the node. Note that these two failure modes could occur at the same time. Fig. 2-3 shows a typical load-displacement curve for connection with nodes under loading. It is seen that small initial slippage occurred which caused small reduction of UTM force as UTM displacement increased. The plastic strip resettled

5 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings after the initial slippage and provided a bit more resistant force until the final failure.

For connection without the presence of nodes, the connection resistance depends primarily on the number of turns of plastic stripes and the workmanship of the scaffolding practitioners. The failure mode for all connection tests without the presence of nodes is slippage between bamboo members (see Fig. 2-4).

2.1.2 Slipping stiffness of connection without nodes

As a conservative measure, the slipping stiffness of connection between two Kao Jue is used as a representative value for all connections between bamboo members. Five tests have been conducted in the laboratory and their load-displacement curves are shown in Fig. 2-5 (a). It is seen that the force-displacement shows an approximately linear trend up to about 20 mm. After that slippage occurred, the forces decreased slightly as the slippage continued. Based on these five test results, the average minimum slipping force within the initial 30 mm displacement is found to be 0.9 kN, which is used as the slipping resistance in the further numerical analyses. A linear relation was used to model the initial slippage through the least square method as shown in Fig. 2-5 (b). The average slipping stiffness before reaching the maximum slipping resistance is 56.2 kN/m. In SAP 2000, the multi-linear element and panel zone are used to model the slipping stiffness of the bamboo connection (see Fig. 2-6).

2.1.3 Rotational stiffness of connection

The rotational stiffness of a bamboo connection is non-symmetrical. It would be zero if the two components rotate toward the direction perpendicular to the direction of the fastening tie. To obtain the rotational stiffness when the two components rotate toward the direction of fastening tie, the MTS 810 Universal Testing Machine was again used. Fig. 2-7 shows the setup for obtaining this rotational stiffness. Load was applied on one side of horizontal member at a distance of 125 mm from the center of vertical member. 6 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

The load-displacement relationship was recorded and transformed to moment-rotational angle plot. The M − θ curve can be obtained through the following two equations.

푉 θ = arctan( ) 퐻 푀 = 퐹 × 퐻 where 퐹: applied load; 푉: vertical displacement of loading point; 퐻: horizontal distance between loading point and central line of vertical bamboo; 휃: rotational angle (rad); and

푀: rotational moment (kN·m).

Fig. 2-8 shows three vertical load-displacement curves of the intersection between two Kao Jue and the corresponding M − θ curves, respectively. It can be found that the stiffness against rotation approximately follows linear relationship and the rotational resistance is quite small. The rotational stiffness was obtained as the slope of straight line though a linear curve fit.

A total of 21 tests were conducted with different configuration of beam-column connections. Table 2-4 presents the experimental results of rotational behavior of bamboo connection. It can be found that the rotational stiffness is about the same for different configuration of connection. The effect of round turns of plastic stripes on rotational stiffness is not significant. The overall mean value of all tests is 0.113 kN·m/rad and was selected as rotational stiffness against the direction of the fastening tie in further analysis. In SAP 2000, the multi-linear element and panel zone are also used to model the bilinear stiffness behavior against rotation, see Fig. 2-9.

7 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

2.2 Modeling of bamboo scaffolding

This section presents some important points about the modeling of bamboo scaffolding in SAP 2000. Modeling and analysis of scaffolding have been reported in some previous studies [2, 9, 10]. Some useful information were extracted and applied in the current modeling. The experimental results of connection obtained in the previous section, including both the slipping stiffness and the rotational stiffness of connection, were adopted to obtain more realistic behavior of scaffolding.

2.2.1 Description of bamboo scaffolding

Bamboo scaffoldings are classified by their applications [11], such as single-layered scaffolding, double-layered scaffolding, truss-out scaffolding and signage scaffolding. In this report, the attention was focused on double-layered bamboo scaffolding

(DLBS).

DLBS consists of two layers: an outer layer scaffolding and an inner layer of posts and ledgers. For the outer layer, Mao Jue is used for both posts and base ledgers, and Kao Jue is used for the other ledgers, standards, transoms and diagonal bracings. For the inner layer, all posts and ledgers are Kao Jue and there are no standards, bracings and secondary ledgers. Transoms are used to connect the inner and the outer layers. These transoms are also used to support the working platform. Lateral restraints (putlogs) are provided at regular or staggered interval to prevent inward and outward leaning of the scaffold. The inner layer is at about 200 – 250 mm from the building face and the outer layer is at about 600 mm from the inner layer [12].

With the above basic requirements of DLBS, there are several different configurations and dimensions due to scaffolders’ own experience. Fig. 2-10 shows two typical arrangements and configuration of DLBS in accordance with [9, 12].

8 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

2.2.2 Finite element modeling of bamboo scaffolding

Even differences exist in the configuration and dimension of DLBS, the modeling of scaffolding remains very much the same. Some details and key issues for the modeling are summarized as follows:

(1) Bamboo members, Kao Jue and Mao Jue, were modeled as prismatic elements with a circular hollow section using averaged external and internal diameters. Also, their material properties under natural moisture content were used. The dimensions and mechanical properties of bamboo were summarized in Appendix B1. (2) The vertical, horizontal and rotational stiffness of the joint between bamboo members were modeled in SAP 2000 using multi-linear elements and panels. For simplicity, the out-of-plane displacement between bamboo members at connection was not considered. (3) It should be noted that in each main ledger-post/standard fastening, there was always a transom-post/standard fastening connected at the same location. Thus, the total connection resistance, vertical stiffness and horizontal stiffness should be doubled. The rotational stiffness was not doubled because the post/standard, main ledger and transom were orthogonal to each other. (4) The support condition of transoms linking up the ledgers of inner layer and outer layer were simulated as a pinned connection. (5) The putlog was comprised of a short bamboo strut and a metal tie (minimum at 6 mm∅) acting as a prop and a tie respectively to prevent inward and outward leaning of the scaffold, which was modeled with only inward and outward restraints. (6) All main posts were assumed to be pinned at the bottom. The braces were only connected to main posts of outer layer as a conservative consideration. (7) Nonlinear analysis with P-Delta effect was adopted in the SAP 2000 software. The P-Delta effect referred specifically to the nonlinear geometric effect under a large

9 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

tensile or compressive direct stress upon transverse bending and shear behavior. A compressive stress tends to make a structural member more flexible in transverse bending and shear, whereas a tensile stress tends to stiffen the member against transverse deformation [13]. Note that the P-Delta effect was not significant in our numerical analysis.

We first focused on the alternative arrangement of DLBS as shown in Fig. 2-10 (b), which actually gave a more conservative results than the configuration of DLBS in Fig. 2-10 (a). More detailed analysis was considered to ensure the designed anchorage can be applied on scaffolding with different arrangement and configuration. Fig. 2-11 shows the finite element model in accordance with the alternative arrangement of DLBS.

2.3 Regional reinforcement of bamboo scaffolding

To anchor personal protective equipment on bamboo scaffolding, the potential anchorage location must be reinforced to provide a load-carrying capacity of at least 12 kN. Numerical analysis of a full-scale bamboo scaffolding showed that the commonly used ledger component, Kao Jue (BP), could only sustain a concentrated load of about 1.9 kN (see Table 2-5). The following possible reinforcement options for the anchorage were investigated through numerical analysis. The analysis was conducted on the full-scale model. For simplicity, the force was acted at the middle of reinforced region to determine the load-bearing capacity of anchorage. For those options meeting the requirement, more detailed study and experiment were conducted.

2.3.1 Option 1 - Ledger reinforcement

The first option is to reinforce ledger using multiple bamboo members and/or steel tubes. Note that the dimensions and mechanical properties of steel tubes were

10 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings experimentally tested and summarized in Appendix B2. Fig. 2-12 shows a partially enlarged model after reinforcement. The contact surface between reinforced ledgers was modeled by gap elements with no opening and stiffness of 3 MN/m. To decrease the relative displacement between ledger and post (standard) at the connection, the ledger was tied to every standard and post. The mechanical properties of connection between bamboo and steel tube were also modeled using the multi-linear element and panel zone according to testing results from Section 4.1. The concentrated load acting on the anchorage was increased until the stress in ledger reaching its characteristic strength. The characteristic strength (95% probability) for Kao Jue (BP) and Mao Jue (PP) are 58.5 N/mm²and 53.4 N/mm² respectively, and the characteristic yield strength for steel tube is 350 N/mm² (see Appendix B). Table 2-5 presents the load-carrying capacity of anchorage for ledgers with different composition of BP, PP and steel tube. It was found that there was no reinforcement cases that could meet the load requirement.

2.3.2 Option 2 - Reinforcing two adjacent ledgers

The analysis above showed that the ledger consisting of three BP or two steel tubes could not offer enough strength for an anchorage. Considering the load-carrying capacity of ledger consisting of one steel tube and one BP could reach 6.9 kN, the option of strengthening two adjacent ledgers using steel tubes was investigated. The steel tubes were tied to bamboo standards/posts through plastic stripes and the two ledgers were combined together though a linked steel tube. Two types of connection between steel ledgers were considered: Type 1: an anti-sliding steel tube was used as the linked strut connecting the two steel ledgers through 5-round plastic stripes; and Type 2: a normal steel tube was used as the linked strut connecting the two steel ledgers through metal couplers (swivel coupler). Fig. 2-13 shows the configuration of this reinforcement option. The load-carrying capacity for Type 1 and Type 2 was found to be 12.2 kN and 7.9 kN, respectively. Their corresponding moment

11 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings distribution diagrams in the ledgers are shown in Fig. 2-14. It should be noted that the contact surface was modeled by gap elements with no opening and stiffness of 3000 kN/m in Fig. 2-14 (a). In Fig. 2-14 (b), due to the use of couplers, the contact surface at coupler position (width of coupler 50mm) was modeled by gap elements with no opening and stiffness of 3000 kN/m and the gap elements at other position have an opening of 10 mm (thickness of coupler) and stiffness of 3000 kN/m (see Fig. 2-15).

It seems that metal coupler can ensure the applied force could be shared equally by the connected ledgers which helps to obtain a larger load-carrying capacity. Further analysis on this type of reinforcement was performed and three load cases near the center as shown in Fig. 2-16 (a) were analyzed. For each load case, the load-carrying capacities of reinforcement with different steel tube length at each side were studied. Results obtained were summarized in Table 2-6. It is seen that the length of steel tube at each side of reinforcement should be at least 0.6 m and the load case (3) seems to offer the lowest load-carrying capacity of 12.1 kN under steel tubes failure. It should be noted that the thickness of tube in Table 2-6 and Table 2-7 is 4 mm and the size effect of tube will be investigated in the following.

Next, the load-carrying capacities of this reinforcement near the edge of scaffolding were analyzed. Fig. 2-16 (b) shows the three load positions near the edge of scaffolding with steel tube length of 0.6 m (1’, 2’, 3’) and 1.2 m (1’’, 2’’, 3’’), respectively. Table 2-7 summarizes their load-carrying capacities. It is seen that the length of steel tube at each side of anchor point should be at least 2.4 m and the load case (3) seems to offer the lowest load-carrying capacity of 12.35 kN under steel tubes failure. The load case (1) offers the highest load-carrying capacity among the three load cases and the required length of steel tube at each side of anchor point is 0.6 m. Note that the load case (2) with steel tube length 0.6m at the position most close to the edge (marked as ‘2’ in Fig. 2-16 (b)) will generate a very large displacement when reaching the load-carrying capacity, which is not allowed and is

12 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings not considered in this report (see Fig. 2-17). Considering all three load cases near the edge of scaffolding, at least 4.8 m long of steel tube (a total mass about 21 kg) should be used to provide a safe anchorage, which is not practical.

Based on the analysis results and considering practical feasibility, the connection between bamboo post (Mao Jue) and ledger corresponding to load case (1) could be recommended as an anchor location for the personal protective equipment. It should be noted that such an anchorage shall be used with at least 0.6 m long of steel tube at each side of the anchor point.

It was noted that there were three steel tubes available in the market that have the same outside diameter of 48.3 mm but different thickness of 2.3 mm, 3.2 mm and 4 mm respectively. As the anchorages near the edge of scaffolding have smaller load-carrying capacity than those in the middle region, the load-carrying capacities of anchorages under load case (1) near the edge with different tube length and different tube thickness were analyzed and summarized in Table 2-8. Results suggest that the thickness of tube shall be at least 3.2 mm to provide a safe anchorage for this reinforcement option.

2.3.3 Option 3 - Platform reinforcement

The principle behind Option 2 is to transform the external point load into uniformly distributed load which can be shared by a long span of bamboo ledger with a smaller stress. Following the same principle, a steel tube was added underneath the work platform as shown in Fig. 2-18. The steel tube was fastened to transoms using plastic stripes. This steel tube has a potential to be used to anchor safety harness for the worker at the platform below and for the whole range of platform.

As stated above, the safety factors for the steel tube and the bamboo member were

13 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings assumed to be 2. Hence the load-carrying capacity of the whole reinforced region shall be at least 12 kN considering a MAF of 6 kN. In addition to installing one steel tube underneath the platform, additional options were also investigated through numerical analysis: Option 3.1: adding an additional transom to each existing one; Option 3.2: using Option 3.1 plus adding one more steel tube (a total of two steel tubes) underneath the platform.

The analysis was first conducted on a full-scale scaffolding with the anchorage assumed to be around the middle of platform. For simplicity, the load-carry capacity was calculated by imposing a static force at the connection between steel tube and the transom which was connected to two posts (see load case (1) in Fig. 2-19). For those options meeting the load requirement, more specific load cases covering the whole platform were then conducted. Table 2-9 summaries the results obtained for the two options (Option 3.1 and Option 3.2). The load-carrying capacity of the original design with just one steel tube underneath the platform was also provided for comparison (denoted as “Option 3” in Table 2-9). Results show that only Option 3.2 can offer a load-carrying capacity larger than 12 kN (MAF of 6 kN and a safety factor of 2.0). Hence this option was chosen for further analysis to determine whether this option can offer sufficient load-carrying capacity under different loading conditions.

For Options 3.2 (adding two steel tubes underneath the platform and an additional transom to each existing one), five load cases near the center as shown in Fig. 2-19 were analyzed. For each load case, the load-carrying capacities of anchorage with different length of steel tube at two sides were analyzed. It should be noted that the maximum stress in the outer layer ledger is always smaller than that of the inner layer ledger due to additional standards at the outer layer. Results obtained are summarized and shown again in Table 2-10. It is seen that only load case (1) with full tube length of 6 m offers the load-carrying capacity larger than 12 kN. So this option cannot provide safe anchorages along the whole length of platform.

14 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

2.3.4 Personal energy absorber (PEA) lanyard and self-retracting lifeline (SRL)

When anchoring safety harness to a location, a connecting subsystem need be used to link the safety harness to the anchor point. Lots of connecting subsystems found in market incorporate some forms of energy absorbing device, such as personal energy absorber (PEA) lanyard and self-retracting lifeline (SRL). They are designed to comply with requirements in various standards such as ANSI Z359 and CSA Z259 standards. These energy absorbing subsystems can limit the MAF to 4 kN for workers below 141 kg [14, 15]. That is to say, the anchorage could be reinforced to have a load-carrying capacity of 8 kN instead of 12 kN (assumed MAF = 4 kN and a safety factor of 2) when these energy absorbing device are used.

From above analysis, these two options can both meet the load requirements and have better performance than other choice: (a) Option 2: reinforcing two adjacent ledgers with steel tubes and linking them through a steel strut; (b) Option 3.2: reinforcing platform with two steel tubes and adding an additional transom to each existing one.

For Option 2, when the steel tube length is 0.6 m at each side of anchor point, the load-carrying capacity is mostly determined by failure of bamboo ledger. Failure could happen at the loading location or at the end of steel tube depending on load cases and steel tube thickness. When the tube length is more than 1.2 m at two sides of anchor point, the load-carrying capacity would be larger with longer tube and is determined by the failure of tube or bamboo ledger at loading position. Also, anchorages at more central region of scaffolding will have larger load-carrying capacity. The load-carrying capacity of three load cases for Option 2 near the edge with two critical tube length (0.6 m and 1.2 m) and three different tube size (thickness = 2.3 mm, 3.2 mm and 4 mm) are summarized in Table 2-11. It is found that the load-carrying capacities for all cases could be all larger than 8 kN. 15 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

For Option 3.2, the length of steel tube (thickness = 4 mm) at two sides of anchor point shall be at least 1.2 m to provide safe anchorages with load-carrying capacity larger than 8 kN as seen in Table 2-10. Also, the load-carrying capacity of anchorage would increase as the tube length increases. The results near the edge of scaffolding are summarized in Table 2-12. It is found that all cases with different tube size and with tube length of at least 1.2 m can withstand a load larger than 8 kN.

2.3.5 Critical cases for experimental test

A series of tests are devised to validate the reinforcement options determined above. The tests are divided into two groups depending on whether the connecting subsystem incorporating an energy absorbing device. These two groups are indicated by their target load-carrying capacity of “12 kN” and “8 kN” respectively. These critical test cases are described as follows.

12 kN anchorage tests: The load case (1) for Option 2 (thickness of tube at least 3.2 mm and tube length at least 0.6 m at each side of anchor point) was designed to provide safe anchorages with 12 kN load-carrying capacity in Section 2.3.2. From Table 2-8, all load-carrying capacities with tube thickness of at least 3.2 mm were under bamboo failure. There are two types of bamboo failure: (a) when tube length at each side of anchor point is 0.6 m, the bamboo failure occurred at the tube end; (b) when tube length at each side of anchor point is at least 1.2 m, the bamboo failure occurred at the loading position (see Fig. 2-20). These two types of bamboo failure with lowest load-carrying capacity will be considered.

8 kN anchorage tests: For load cases (2) and (3) of Option 2 from Table 2-11, only when the tube length was

16 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

0.6 m with tube thickness at least 3.2 mm, the load-carrying capacity was determined by bamboo failure and happened at the tube end. The failure mode of load cases (2) and (3) for other situations were tube failure at loading position. So, these two failure modes (bamboo failure at tube end and tube failure at loading point) with lowest load-carrying capacity will be considered.

From Table 2-12 for Option 3.2, there were two failure modes when reaching their load-carrying capacities, one was bamboo failure of main inner ledger for load case (2) and the other one was steel tube failure for all other situations. These two failure modes with lowest load-carrying capacity will be considered.

In summary, the following six critical cases will be investigated in the experimental study: (1) The load case (1) for Option 2 with 0.6 m tube length (tube size: 48.3 mm × 4 mm) at both sides of anchor point. (2) The load case (1) for Option 2 with 1.2 m tube length (tube size: 48.3 mm × 3.2 mm) at both sides of anchor point. (3) The load case (3) for Option 2 with 0.6 m tube length (tube size: 48.3 mm × 4 mm) at both sides of anchor point. (4) The load case (3) for Option 2 with 1.2 m tube length (tube size: 48.3 mm × 2.3 mm) at both sides of anchor point. (5) The load case (2) for Option 3.2 with 1.2m tube length (tube size: 48.3 mm × 3.2 mm) at both sides of anchor point. (6) The load case (5) for Option 3.2 with 1.2m tube length (tube size: 48.3 mm × 2.3 mm) at both sides of anchor point.

2.4 Full-scale bamboo scaffolding test

The objective of the full-scale scaffolding tests is to experimentally validate the safety 17 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings of anchorages. Both static load test and drop load test will be performed for the six critical loading cases mentioned above. The description of full-scale scaffolding, test setup and test results are presented in the following.

2.4.1 Description of the scaffolding

The scaffolding used for the test was a double-layer bamboo scaffolding (DLBS) with dimensions of 4.8 m × 5.6 m × 0.6 m (length × height × width). Fig. 2-21 shows configuration and dimension of scaffolding. Details of this scaffolding are described below.

(1) Outer layer: Mao Jue was used as the main posts and base ledger of the outer layer. Three Kao Jue were then erected in between two Mao Jue as standards which were overhung from the ledgers but not resting on the ground. Kao Jue was used as secondary and the other main ledgers as well as the diagonal members. (2) Inner layer: Kao Jue was used throughout the inner layer. There was no bracing for the inner layer. (3) Platform: There were two platforms and their heights were 2.3 m and 3.95 m respectively. The inner and outer ledgers were connected by transoms.

2.4.2 Test arrangement

12kN anchorage test cases: The two critical cases (1) and (2) for 12 kN anchorage were tested at the center of scaffolding with a static point load of 12 kN and a drop load (free fall of a 100 kg dead weight achieving at least a drop force of 9 kN [8]). Fig. 2-22 (a) shows the location of the load position for the two cases.

8kN anchorage test cases: The four critical cases (3) to (6) for 8 kN anchorage were tested at the edge of 18 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings scaffolding with a point load of 8 kN and a drop load (free fall of a 100 kg dead weight achieving at least a drop force of 8 kN). The testing positions for critical cases are shown in Fig. 2-22 (b) shows the location of the load position for the four cases. It should be noted that the required drop force of 8 kN is to maintain a general safety factor of 2 [4, 5].

2.4.3 Static point load test

The static point load test was performed to check whether the anchor point can hold the load about twice the maximum arrest force statically. Fig. 2-23 depicts details for the test setup. The equipment used in the test included a tensile jack with load cell, data logger and computer and strain gauges. Strain gauges were installed at bottom locations of all the bamboo standards, posts and bracings. For metal tubes, strain gauges were also installed to measure the bending moment in horizontal metal tube and axial force in metal strut. Note that the bending moment in horizontal metal tubes was measured at a distance of 10 or 5 cm from loading point depending on installing convenience. There were a total 20 ports in data logger for strain gauges to connect so that only the force in total ten bamboos or metal tubes could be measured every time. Under this limitation, the main load-bearing components were selected for force measurement. The load cell was mounted on ground through four expansion bolts, which could sustain a pullout load over 20 kN.

The load generated by tensile jack was applied on a reinforced anchor point through steel wire. Load was increased from 0 kN to a specified value (either 12 kN or 8 kN) slowly to avoid dynamic effects. When the load reached the specified value, the load would be maintained for 3 minutes to observe whether failure would occur in the reinforced region. For each test case, three independent tests were conducted. Fig. 2-24 (a)-(c) show the anchor points under the specified loads for test cases (2), (3) and (6), respectively. Axial forces and bending moments in selected components were

19 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings calculated by multiplying the measured strain values with the bamboo cross sectional area and the section of modulus of area, respectively. The mean values and standard deviations of strains and calculated forces for every test case were summarized in Table 2-13 (a)-(f). The numbering of posts and standards are shown in Fig. 2-25. The outside diameter of each selected bamboo component in Table 2-13 was obtained through measurement. The thickness of bamboo was calculated by assuming a linear relationship between thickness and outside diameter as following:

퐶푎푙푐푢푙푎푡푒푑 푡ℎ𝑖푐푘푛푒푠푠 퐴푣푒푟푎푔푒 푣푎푙푢푒 표푓 푡ℎ𝑖푐푘푛푒푠푠 = 푀푒푎푠푢푟푒푑 표푢푡푠𝑖푑푒 푑𝑖푎푚푒푡푒푟 퐴푣푒푟푎푔푒 푣푎푙푢푒 표푓 표푢푡푠𝑖푑푒 푑𝑖푎푚푒푡푒푟

Note that the average value of thickness and outside diameter of Kao Jue and Mao Jue are listed in Appendix B1. Based on the test results, the following observations can be made:

(1) All reinforced anchor points could resist the required load for 3 minutes without causing any damage to the scaffolding. The whole scaffolding remained stable and intact during and after test. (2) The deformation of bamboo ledger and metal tube was rather small. (3) The relative slipping distance between connections at anchor point was negligible. (4) The measured forces in bamboo standards was much smaller than those in bamboo posts. (5) The standard deviations of the measured strain for the same critical case were quite small suggesting that the test results were quite consistent.

In this section, the results obtained from the finite element program SAP 2000 were compared with that obtained from the static point load test. Table 2-14 (a)-(f) show the comparison of axial force and bending moment in selected components between the measured and the analyzed values. Results summarized in Table 2-15 show that the average difference between the numerical analysis and the test results was about 26% 20 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings for the bamboo members and 8% for the metal components.

2.4.4 Drop load test

Drop load test was performed to investigate the performance of reinforced anchor points and the safety of scaffolding under dynamic loads. The procedure of drop load test followed the test methods described in BS EN 795 [8] and BS EN 364 [16]. A sand bag was used to simulate a person falling from a height. The six critical cases mentioned above were all tested under free fall a 100 kg sand bag which generated a required drop force as specified in Section 2.4.2.

The test equipment and setup is shown in Fig. 2-26. A load cell was attached to the anchor point. One end of the lanyard was attached to the load cell and the other end to the sand bag. During the test, the sand bag was raised to a free fall height that could generate a drop force larger than the required drop force and hold at no more than 300 mm horizontally from the anchor point [8]. The sampling rate of the load cell was set at 50 Hz to capture the dynamic load induced by the free fall of sand bag. For simplicity, the strain values in components are not measured in the drop test.

For test cases (1) and (2), the free fall aimed at generating a peak load larger 9 kN at the anchor point. For test cases (3) to (6), the peak load due to free fall should be larger than 8 kN at the anchor point. For each test case, three independent tests were conducted. Fig. 2-27 (a)-(c) show the anchor points before and after drop test for test cases (2), (3) and (6), respectively. Also shown are their corresponding drop force-time curves. Table 2-16 (a)-(f) show the test results with maximum drop force and corresponding free fall for six critical cases respectively. From these results, the following observations can be seen:

(1) The anchor points of all six test cases could withstand the free fall of a100 kg sand

21 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

bag without damaging any part of the scaffolding. All designed anchor points can sustain a drop load larger than its designed load-carrying capacity. (2) A small vibration of the scaffolding was observed which did not seem to affect the stability and the safety of the scaffolding. The deformation of the anchor point after the drop load test was negligible. (3) For test case (3), the reinforced anchor point could withstand a drop load larger than 8 kN which was the intended load-carrying capacity. When the drop load increased to 11.96 kN, it was noted that the bamboo ledge at tube end fractured. This failure mode coincided with the result obtained from the numerical result.

2.5 Scaffoldings with different configuration and dimensions

Note that the above findings and summaries were obtained on the scaffolding with the configuration and dimensions specified in Fig. 2-21 (three standards between posts and span of about 0.6 m between standards), which are concluded in Table 2-17. As the configuration and dimension of scaffoldings vary from site to site, more detailed analysis is needed to provide more general recommendations for these reinforcement options. In this section, finite element numerical analyses were performed on three additional scaffoldings with different configuration and dimensions as follow:

(1) Double layered bamboo scaffolding with three standards between posts of outer layer and a larger span of 0.75 m between standards: results summarized in Table 2-18 (a); (2) Double layered bamboo scaffolding with one standard between two posts of outer layer and different spans of 0.6 m, 0.75 m or 0.9 m between standards respectively: results summarized in Table 2-18 (b); and (3) Single layered bamboo scaffolding (SLBS) with one standard between two posts of outer layer and different spans of 0.6 m, 0.75 m or 0.9 m between standards respectively: results summarized in Table 2-18 (c). 22 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

2.6 Multiple anchorages for Option 2 regional reinforcement

Above analysis for Option 2 only use one steel strut to link the two adjacent ledgers at the anchor points. In this section, we further explore the possibility of accommodate multiple anchorages for Option 2 regional reinforcement by connecting the two adjacent ledgers with additional steel struts as shown in Table 2-19. The load-carrying capacity of the anchor points at the middle of reinforcement as well as additional potential anchor points on the reinforcement were obtained through finite element analysis presented above and are shown in Table 2-19. The load-carrying capacities of the original Option 2 regional reinforcement (Table 2-11) are also listed for comparison. It is seen that the additional steel struts do not seem to affect the load-carrying capacity of the two anchor points at the middle of reinforcement. Furthermore, the load-carrying capacity of those additional potential anchor points produced due to the additional vertical steel struts can be larger than 8 kN as long as these points are not located at the edges of the reinforcement.

Next, the load-carrying capacities for Option 2 regional reinforcement with different length and additional steel struts under two users simultaneously were obtained and are shown in Table 2-20. It is seen that Option 2 regional reinforcement with additional steel struts can offer a load-carrying capacity larger than 8 kN for both users simultaneously as long as the spacing between the two users is equal or larger than two spans. This conclusion is now summarized in Fig. 2-28. The analysis results show that it is possible to generate an anchorage region using Option 2 regional reinforcement with additional steel struts. This anchorage region can accommodate multiple users simultaneously as long as the spacing between the users is equal or larger than two spans. The anchor points inside the reinforcement region can provide a load-carrying capacity larger than 8 kN. It is recommended that energy absorbing devices with a MAF of 4 kN be used on these anchor points so that these anchor points can protect the users with a safety factor of two. 23 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Fig. 2-1 Setup of bamboo connection test

(a) Rupture of plastic strip

(b) Slippage over the node

24 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Fig. 2-2 Two failure modes for connection with node

2.5

2 Small initial slippage

1.5 UTM Force (kN) Force UTM

1

0.5

0 0 20 40 60 80 UTM Displacement (mm)

Fig. 2-3 Typical load-displacement curve for conection test with node

Slipping distance

Fig. 2-4 Slippage failure for connection test without node

25 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

1.6 1.4 1.2

1 1 0.8 UTM Force (kN) Force UTM 2 0.6 3 0.4 4 5 0.2 0 0 10 20 30 40 50 60 UTM Displacement (mm)

(a) Load-displacement curves

1.6

1.4 y = 0.066x

1.2 y = 0.059x y = 0.049x y = 0.055x UTM Force (kN) Force UTM 1 y = 0.052x 0.8

0.6

0.4

0.2

0 0 5 10 15 20 25 UTM Displacement (mm)

(b) Initial slippage and linear regression Fig. 2-5 Vertical testing curves of BP-BP connection

26 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

1 16, 0.9 0.8 0.6

Force (kN) Force 0.4 0.2 0 -60 -40 -20 0 20 40 60 -0.2 -0.4 -0.6 -16, -0.9 -0.8 -1 Relative displacement (mm)

Fig. 2-6 Modeling of slippage stiffness for bamboo connection

Fig. 2-7 Setup of rotational stiffness test

27 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

0.6

0.5

0.4

0.3 1

2 UTM Force (kN) Force UTM 0.2 3 0.1

0 0 10 20 30 40 50 60 70 UTM Displacement (mm)

(a) UTM load-displacement curve

0.07 0.06 y = 0.121x 0.05 y = 0.112x M (kN·m) M 0.04 y = 0.103x 0.03 0.02 0.01 0 0 0.1 0.2 0.3 0.4 0.5 θ (rad)

(b) Corresponding M − θ curves Fig. 2-8 Rotational test curves of BP-BP connection

0.4 M=0.113× θ 0.35 0.3

0.25 M (kN·m) M 0.2 0.15 0.1 0.05 M= 0 θ (rad) 0 -4 -3 -2 -1 0 1 2 3 4

28 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Fig. 2-9 Modeling of rotational stiffness for bamboo connection

Bracing (outer layer): Kao Jue

Ledger: Kao Jue Post (inner layer): Kao Jue

Transom: Kao Jue Post (outer layer): Mao Jue

Ledger on the first 1.3 m Standard (outer lift: Mao Jue layer): Kao Jue

(a) Configuration of DLBS according to code [12]

Bracing (outer layer): Kao Jue

Ledger: Kao Jue Post (inner layer): Kao Jue

Transom: Kao Jue Post (outer layer): Mao Jue 2.4 m Ledger on the first lift: Mao Jue Standards (outer layer): Kao Jue

29 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

(b) An alternative arrangement of DLBS according to [9] Fig. 2-10 Two typical arrangements and configuration of DLBS

Fig. 2-11 Modeling of bamboo scaffolding

Typical length of bamboo/steel tube = 6 m

30 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Fig. 2-12 Deformation of scaffolding after reinforcement

F

v

Steel tube Bamboo member Connection between tubes (plastic stripes or coupler) v Fig. 2-13 Reinforcement option: combining two adjacent ledgers with steel tubes

F=7.90 kN

5-round plastic stripes Anti-sliding tube

(a) Using anti-sliding tube as linked strut

31 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

F=12.20 kN

Metal couplers Normal steel tube

(b) Using normal steel tube as linked strut Fig. 2-14 Load-carrying capacities and moment distribution diagrams

50 mm

Fig. 2-15 Modeling of contact surface with couplers

(1) ( 2 ) ( 3 ) Normal steel tube

Coupler

(a) Near the center of scaffolding

32 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

3’ (3’’) 2 ’ (2 ’’ ) 1 ’ (1 ’’ )

2 Edge

(b) Near the edge of scaffolding Fig. 2-16 Load cases for Option 2

10.3 kN

Relative displacement＞ 200 mm

Fig. 2-17 Deformation of load case (2) at the position closest to the edge

Fig. 2-18 Reinforcement option: installing steel tubes under the work platform

33 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Two steel tubes

Two transoms

Fig. 2-19 Load cases for Option 3.2 near the center of scaffolding

Largest moment in bamboo ledger is at one of tube ends

(a) Bamboo failure at the position of tube end (tube length at each side of anchor point is 0.6 m)

Largest moment in bamboo ledger is at loading point

(b) Bamboo failure at the position of loading point (tube length at each side of anchor point is at least 1.2 m)

34 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Fig. 2-20 Moment diagram for two types of bamboo failure

(a) Front view of the scaffolding (b) Side view of the scaffolding

(c) Dimensions of scaffolding (m)

35 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Fig. 2-21 Configuration and dimensions of the scaffolding

Critical cases (1) and (2)

(a) 12 kN anchorage

Critical case (6) Critical case (5)

Critical cases (3) and (4)

(b) 8 kN anchorage 36 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Fig. 2-22 Load positions for anchorage test

(a) Tensile jack and load cell (b) Data logger and computer

(c) Stain gauges attached on bamboo components

Strain gauges on metal tubes

37 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

(d) Strain gauges attached on metal components Fig. 2-23 Setup of static point load test

Small slipping

(a) Test case (2) under static point load ≥ 12 kN

` (b) Test case (3) under static point load ≥ 8 kN

38 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

(c) Test case (6) under static point load ≥ 8 kN Fig. 2-24 Static point load test for various test cases

Brace 1 Brace 2 Post 3

Standard 4 Standard 3 Standard 2 Standard 1 Post 8 Post 4 Post 7

Post 1 Post 6 Post 2 Post 5

Fig. 2-25 Bamboo post and standard labelling for Table 2-13 (a)-(f)

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Anchor point Load cell

Data logger & computer

Fig. 2-26 Setup of drop load test

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3.2 m

Before drop load test After drop load test

Typical drop force-time curve 14 12.80

12 Force (kN) Force 10 8 6 4 2 0 0 2 4 6 8 -2 Time (s)

(a) Test case (2): before and after drop test and typical drop force-time curve

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Before drop load test (free fall: 2.9 m) Before drop load test (free fall: 3.1 m)

Upper ledger Under ledger

Bamboo failure at tube end with free fall 3.1 m (no failure with free fall of 2.9 m)

Corresponding drop force-time curve with bamboo failed at tube end 14 11.96

12 Force (kN) Force 10 8 6 4 2 0 0 1 2 3 4 5 6 7 -2 Time (s)

(b) Test case (3): before and after drop test and typical drop force-time curve

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2.0 m

Before drop load test After drop load test

Typical drop force-time curve 9 8 8.19

7 Force (kN) Force 6 5 4 3 2 1 0 -1 0 2 4 6 8 10 Time (s)

(c) Test case (6): before and after drop test and typical drop force-time curve Fig. 2-27 Drop load test and typical drop force-time curves

43 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

≥ 4 spans ≥ 1 span ≥ 1 span Anchorage region for energy absorbing devices ≥ 1 span ≥ 1 span with MAF ≤ 4 kN Horizontal spacing between two users ≥ 2 spans Fig. 2-28 Multiple anchorages for Option 2 regional reinforcement

44 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Table 2-1 Test configurations for bamboo connection H: Kao Jue V: Kao Jue H: Kao Jue V: Mao Jue

H: Mao Jue V: Kao Jue H: Mao Jue V: Mao Jue

Note: H: horizontal member; V: vertical member.

Table 2-2 Resistance of bamboo connection with node Type of connection No. of Connection resistance (kN) No. of Horizontal Vertical turns for tests Mean Std member member strips BP BP 5 4 2.12 0.35 BP PP 4 or 5 4 2.21 0.81 PP PP 4 or 5 4 2.11 0.63 PP BP 4 or 5 4 1.89 0.46

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Table 2-3 Resistance of bamboo connection without node Type of connection No. of Connection resistance (kN) No. of Horizontal Vertical turns for tests Mean Std member member strips BP BP 5 5 0.90 0.15 5 5 0.98 0.12 BP PP 4 5 0.70 0.09 5 5 0.92 0.08 PP BP 4 5 0.62 0.12 5 5 0.90 0.22 PP PP 4 5 0.66 0.06

Table 2-4 Rotation stiffness for beam-column connection Type of connection Rotational stiffness (kN·m/rad) No. of turns No. of Horizontal Vertical for strips tests Mean Std member member BP BP 5 3 0.112 0.007 5 3 0.118 0.003 BP PP 4 3 0.107 0.007 5 3 0.116 0.019 PP PP 4 3 0.113 0.014 Overall overage 0.113 0.012

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Table 2-5 Load-carrying capacity of ledger after reinforcement Relative displacement Load-carrying Maximum Reinforcement of ledger between ledger and capacity (kN) stress(N/mm²) standard (mm) One BP 1.90 58.4 20.5 Upper BP 58.9 Two BP 3.50 15.1 Under BP 54.8 Upper BP 58.6 Three BP Middle BP 4.45 53.2 11.9 Under BP 50.8 One PP 4.05 53.3 38.2 Upper PP 53.4 Two PP 7.75 22.0 Under PP 50.2 One BP & Upper BP 58.6 4.90 15.4 One PP Under PP 39.4 Steel tube 5.10 349.9 57.4 Steel tube and Steel tube 350.2 6.90 12.6 BP BP 26.6 Two Steel Upper tube 350.5 9.80 36.5 tubes Under tube 312.0 Note: The tested yield strength 350 N/mm² and young’s modulus 200 GPa of steel tube with external diameter 48.3 mm and thickness 4 mm are used in this table.

Table 2-6 Load-carrying capacity for Option 2 near the center of scaffolding load-carrying capacity (kN) and corresponding maximum stress (N/mm²) Length of tube at each side of anchor point 0.6 m (1) 1.2 m (2) 1.8 m (3) 2.4 m (4) 3.0 m (5) (No. of connections) 12.95 13.15 13.20 13.20 13.20 (1) 298.9 58.9 313.2 59.0 312.8 58.9 312.4 58.8 304.9 58.1 12.90 13.10 13.10 13.15 13.20 Load case (2) 303.8 58.5 348.1 58.4 342.1 58.3 333.9 58.5 325.4 58.5 12.80 12.10 12.10 12.40 12.50 (3) 298.0 58.1 350.6 47.0 349.5 47.0 350.8 46.5 349.9 50.1 Note 1: For each case, the upper value is load-carrying capacity and the under left and right values are corresponding maximum stress in metal tube and bamboo ledger, respectively. Note 2: Bold font represents failed component and its maximum stress.

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Table 2-7 Load-carrying capacity for Option 2 near the edge of scaffolding Load-carrying capacity (kN) and corresponding maximum stress (N/mm²) Length of tube at each side of anchor point 0.6 m (1) 1.2 m (2) 1.8 m (3) 2.4 m (4) 3.0 m (5) (No. of connections) 12.80 13.05 13.10 13.10 13.20 (1) 290.6 58.5 306.8 58.1 312.5 58.9 310.2 58.6 305.3 58.2 12.50 13.00 13.00 13.10 13.20 Load case (2) 286.9 59.0 350.5 57.2 349.5 55.8 333.9 58.4 325.8 58.8 10.70 11.50 11.80 12.35 12.45 (3) 257.5 58.9 351.1 46.1 350.6 47.1 350.9 46.4 350.5 47.1 Note 1: For each case, the upper value is load-carrying capacity and the under left and right values are corresponding maximum stress in metal tube and bamboo ledger, respectively. Note 2: Bold font represents failed component and its maximum stress.

Table 2-8 Effect of tube thickness on load-carrying capacity for Option 2 load case (1) Load-carrying capacity (kN) and corresponding maximum stress (N/mm²) Length of tube at each side of anchor point 0.6 m (1) 1.2 m (2) 1.8 m (3) 2.4 m (4) 3.0 m (5) (No. of connections) 12.80 13.05 13.10 13.10 13.20 4.0 mm 290.6 58.5 306.8 58.1 312.5 58.9 310.2 58.6 305.3 58.2 Tube 12.85 12.20 12.30 12.30 12.55 3.2 mm thickness 345.4 58.6 312.9 58.3 315.3 58.7 314.9 58.6 318.8 58.4 11.70 11.20 11.20 11.40 11.60 2.3 mm 350.0 46.3 333.2 58.5 332.8 58.5 335.4 58.7 340.9 58.6 Note 1: For each case, the upper value is load-carrying capacity and the under left and right values are corresponding maximum stress in metal tube and bamboo ledger, respectively. Note 2: Bold font represents failed component and its maximum stress.

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Table 2-9 Load-carrying capacity for various options under load case (1) Maximum Maximum Maximum Maximum Load-carrying Stress in Stress in Reinforcement Stress in Stress in steel capacity ledger of ledger of options transom tube outer layer inner layer kN N/mm² N/mm² N/mm² N/mm² Option 3 4.25 58.2 5.2 17.4 148.3 Option 3.1 8.80 56.3 16.2 39.7 350.1 Option 3.2 12.15 57.6 21.1 50.0 350.4 Note: Bold font represents failed component and its maximum stress.

Table 2-10 Load-carrying capacity for Option 3.2 near the center of scaffold Load-carrying capacity (kN) and corresponding maximum stress (N/mm²) Length of tube at each side of anchor 0.6m (1) 1.2m (2) 1.8m (3) 2.4m (4) 3.0m (5) point (No. of pairs of transoms) 7.00 11.35 11.40 11.65 12.15 (1) 140.1 58.8 44.4 350.7 55.0 56.5 350.5 53.8 56.9 350.6 54.2 56.9 350.4 50.0 57.6 7.80 10.50 10.55 10.70 11.10 (2) 185.2 38.2 58.3 340.8 58.4 43.1 338.7 58.2 45.8 339.1 58.5 45.8 336.2 58.4 46.1 Load 7.00 11.00 11.05 11.25 11.60 (3) case 149.0 58.7 52.0 350.1 44.5 46.1 350.5 44.9 46.1 350.7 45.2 46.1 350.5 44.7 46.4 9.40 10.65 10.90 11.20 11.50 (4) 266.4 58.4 49.7 350.1 58.3 52.9 351.0 53.4 53.6 349.9 56.7 53.9 350.7 57.8 53.9 9.00 10.40 10.60 11.10 11.40 (5) 263.0 58.6 141.5 351.0 52.6 42.8 349.7 52.4 42.5 350.6 52.5 42.8 350.4 52.4 43.1 Note 1: For each case, the upper value is load-carrying capacity and the under left, middle and right values are corresponding maximum stress in metal tube, main ledger of inner layer and transom, respectively. Note 2: Bold font represents failed component and its maximum stress.

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Table 2-11 Summary of load-carrying capacity for Option 2 Load-carrying capacity (kN) and corresponding maximum stress (N/mm²) Tube Size 48.3 × 4.0 mm 48.3 × 3.2 mm 48.3 × 2.3 mm Length of tube at each side of anchor point 0.6m (1) 1.2m (2) 0.6m (1) 1.2m (2) 0.6m (1) 1.2m (2) (No. of connections) 12.80 13.05 12.85 12.20 11.70 11.20 (1) 290.6 58.5 306.8 58.1 345.4 58.6 312.9 58.3 350.0 46.3 333.2 58.5 12.50 13.00 12.50 12.00 11.45 10.45 Load case (2) 286.9 59.0 350.5 57.2 336.2 58.0 349.4 54.5 350.6 41.6 349.2 53.1 10.70 11.50 10.90 10.10 10.20 8.20 (3) 257.5 58.9 351.1 46.1 303.7 58.5 350.9 44.6 349.7 48.9 349.7 42.0 Note 1: For each case, the upper value is load-carrying capacity and the under left and right values are corresponding maximum stress in metal tube and bamboo ledger, respectively. Note 2: Bold font represents failed component and its maximum stress.

Table 2-12 Load-carrying capacity for Option 3.2 with a tube length of 1.2 m Load-carrying capacity (kN) and corresponding maximum stress (N/mm²) Tube size 48.3 × 4.0 mm 48.3 × 3.2 mm 48.3 × 2.3 mm 11.10 10.55 9.30 (1) 349.9 56.2 56.9 349.2 50.6 57.2 350.9 45.6 57.2 9.75 9.60 8.60 (2) 307.3 58.1 43.8 338.4 58.2 44.4 349.5 54.4 44.8 10.90 9.90 9.05 Load case (3) 350.6 50.3 43.8 350.2 45.9 44.8 350.1 44.5 46.1 10.65 9.80 8.70 (4) 350.3 56.7 53.9 350.3 56.1 52.9 351.0 51.3 52.3 10.20 9.40 8.20 (5) 349.5 51.3 42.5 350.4 48.9 42.8 350.1 43.9 41.8 Note 1: For each case, the upper value is load-carrying capacity and the under left, middle and right values are corresponding maximum stress in metal tube, main ledger of inner layer and transom, respectively. Note 2: Bold font represents failed component and its maximum stress.

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Table 2-13 Results of static point load test for test cases (1) to (6) (a) Test case (1) under 12 kN static point load Measured axial Strain Cross section area 퐴 Young's force Component modulus 퐸 Outside Mean Std Thickness 퐴 Mean Std diameter × 10−6휀 kN/mm² mm mm mm² kN Post 1 -37.1 6.1 7.60 112.0 11.6 3659.5 -1.03 0.17 Standard 3 -42.8 6.8 8.55 43.6 5.6 665.8 -0.24 0.04 Axial Post 2 -382.8 41.4 7.60 102.2 10.6 3043.3 -8.85 0.96 force Standard 4 -35.6 7.9 8.55 45.2 5.8 715.3 -0.22 0.05 (front) Post 3 -13.6 3.8 7.60 107.9 11.2 3394.2 -0.35 0.10 Brace 2 -81.6 19.1 8.55 51.9 6.6 942.5 -0.66 0.15 Metal strut -62.5 7.6 200 48.3 3.2 453.4 -5.67 0.69 Measured Strain Section of modulus of area 푍 Young's bending moment Component modulus 퐸 Outside Mean Std Thickness 푍 Mean Std diameter × 10−6휀 kN/mm² mm mm cm³ kN·m Bending Upper tube 1238.5 127.5 200 48.3 4.0 5.7 1.42 0.15 moment Under tube 1107.8 80.7 200 48.3 4.0 5.7 1.27 0.09 (b) Test case (2) under 12 kN static point load Measured axial Strain Cross section area 퐴 Young's force Component modulus 퐸 Outside Mean Std Thickness 퐴 Mean Std diameter × 10−6휀 kN/mm² mm mm mm² kN Post 1 -38.8 7.0 7.60 112.0 11.6 3659.5 -1.08 0.19 Standard 3 -37.1 5.9 8.55 43.6 5.6 665.8 -0.21 0.03 Axial Post 2 -365.9 64.3 7.60 102.2 10.6 3043.3 -8.46 1.49 force Standard 4 -37.9 5.4 8.55 45.2 5.8 715.3 -0.23 0.03 (front) Post 3 -17.7 3.9 7.60 107.9 11.2 3394.2 -0.46 0.10 Brace 2 -77.3 14.2 8.55 51.9 6.6 942.5 -0.62 0.11 Metal strut -63.8 5.3 200 48.3 3.2 453.4 -5.79 0.48 Measured Strain Section of modulus of area 푍 Young's bending moment Component modulus 퐸 Outside Mean Std Thickness 푍 Mean Std diameter × 10−6휀 kN/mm² mm mm cm³ kN·m Bending Upper tube 1461.1 89.1 200 48.3 3.2 4.8 1.40 0.09 moment Under tube 1353.2 102.7 200 48.3 3.2 4.8 1.30 0.10

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(c) Test case (3) under 8 kN static point load Measured axial Strain Cross section area 퐴 Young's force Component modulus 퐸 Outside Mean Std Thickness 퐴 Mean Std diameter × 10−6휀 kN/mm² mm mm mm² kN Post 1 -105.8 9.7 7.60 112.0 11.6 3659.5 -2.94 0.27 Standard 1 -45.8 6.4 8.55 44.9 5.7 705.2 -0.28 0.04 Axial Standard 2 -89.3 12.6 8.55 44.2 5.7 685.4 -0.52 0.07 force Standard 3 -48.0 7.8 8.55 43.6 5.6 665.8 -0.27 0.04 (front) Post 2 -142.5 17.1 7.60 102.2 10.6 3043.3 -3.30 0.40 Metal strut -46.3 4.7 200 48.3 3.2 453.4 -4.19 0.42 Measured Strain Section of modulus of area 푍 Young's bending moment Component modulus 퐸 Outside Mean Std Thickness 푍 Mean Std diameter × 10−6휀 kN/mm² mm mm cm³ kN·m Bending Upper tube 806.0 62.4 200 48.3 4.0 5.7 0.92 0.07 moment Under tube 628.3 72.0 200 48.3 4.0 5.7 0.72 0.08 (d) Test case (4) under 8 kN static point load Measured axial Strain Cross section area 퐴 Young's force Component modulus 퐸 Outside Mean Std Thickness 퐴 Mean Std diameter × 10−6휀 kN/mm² mm mm mm² kN Post 1 -104.6 14.7 7.60 112.0 11.6 3659.5 -2.91 0.41 Standard 1 -33.0 5.0 8.55 44.9 5.7 705.2 -0.20 0.03 Axial Standard 2 -35.0 7.1 8.55 44.2 5.7 685.4 -0.21 0.04 force Standard 3 -31.0 6.5 8.55 43.6 5.6 665.8 -0.18 0.04 (front) Post 2 -164.5 20.2 7.60 102.2 10.6 3043.3 -3.80 0.47 Metal strut -39.6 4.9 200 48.3 3.2 453.4 -3.59 0.45 Measured Strain Section of modulus of area 푍 Young's bending moment Component modulus 퐸 Outside Mean Std Thickness 푍 Mean Std diameter × 10−6휀 kN/mm² mm mm cm³ kN·m Bending Upper tube 1467.7 137.6 200 48.3 2.3 3.6 1.07 0.10 moment Under tube 1339.5 100.3 200 48.3 2.3 3.6 0.98 0.07

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(e) Test case (5) under 8 kN static point load Measured axial Strain Cross section area 퐴 Young's force Component modulus 퐸 Outside Mean Std Thickness 퐴 Mean Std diameter × 10−6휀 kN/mm² mm mm mm² kN Post 1 -33.4 5.2 7.60 112.0 11.6 3659.5 -0.93 0.15 Axial Standard 1 -13.1 2.2 8.55 44.9 5.7 705.2 -0.08 0.01 force Standard 2 -20.0 4.3 8.55 44.2 5.7 685.4 -0.12 0.03 (front) Standard 3 -14.6 3.1 8.55 43.6 5.6 665.8 -0.08 0.02 Post 2 -114.3 15.1 7.60 102.2 10.6 3043.3 -2.64 0.35 Axial Post 4 -34.0 5.9 8.55 49.0 6.3 841.3 -0.24 0.04 force Post 5 -177.5 20.4 8.55 49.3 6.3 852.2 -1.29 0.15 (back) Post 6 -169.0 11.8 8.55 51.6 6.6 930.9 -1.35 0.09 Measured bending Strain Section of modulus of area 푍 Young's moment Component modulus 퐸 Outside Mean Std Thickness 푍 Mean Std diameter × 10−6휀 kN/mm² mm mm cm³ kN·m Bending Outer tube 993.2 112.6 200 48.3 3.2 4.8 0.95 0.11 moment Inner tube 1217.0 88.7 200 48.3 3.2 4.8 1.17 0.09 (f) Test case (6) under 8 kN static point load Measured axial Strain Cross section area 퐴 Young's force Component modulus 퐸 Outside Mean Std Thickness 퐴 Mean Std diameter × 10−6휀 kN/mm² mm mm mm² kN Post 1 -44.0 7.8 7.60 112.0 11.6 3659.5 -1.22 0.22 Axial Standard 1 -16.0 3.3 8.55 44.9 5.7 705.2 -0.10 0.02 force Standard 2 -19.0 4.3 8.55 44.2 5.7 685.4 -0.11 0.03 (front) Standard 3 -17.0 2.9 8.55 43.6 5.6 665.8 -0.10 0.02 Post 2 -106.1 12.1 7.60 102.2 10.6 3043.3 -2.45 0.28 Axial Post 4 -65.6 7.1 8.55 49.0 6.3 841.3 -0.47 0.05 force Post 5 -175.6 30.0 8.55 49.3 6.3 852.2 -1.28 0.22 (back) Post 6 -147.2 12.6 8.55 51.6 6.6 930.9 -1.17 0.10 Measured bending Strain Section of modulus of area 푍 Young's moment Component modulus 퐸 Outside Mean Std Thickness 푍 Mean Std diameter × 10−6휀 kN/mm² mm mm cm³ kN·m Bending Outer tube 1321.0 96.5 200 48.3 2.3 3.6 0.96 0.07 moment Inner tube 1407.0 143.7 200 48.3 2.3 3.6 1.03 0.10

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Table 2-14 Comparison of computer analysis with static point load test (a) Test case (1) under 12 kN static point load Difference Measured mean Component Analyzed value 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% value 푚푒푎푠푢푟푒푑 Post 1 -1.03 -1.29 25% Standard 3 -0.24 -0.37 52% Axial force Post 2 -8.85 -9.68 9% (front) Standard 4 -0.22 -0.33 51% (kN) Post 3 -0.35 -0.37 5% Brace 2 -0.66 -0.82 25% Metal strut -5.67 -6.00 6% Bending Upper tube 1.42 1.26 11% moment (kN·m) Under tube 1.27 1.39 10% (b) Test case (2) under 12 kN static point load Difference

Measured mean 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 Component Analyzed value | | value 푚푒푎푠푢푟푒푑 × 100% Post 1 -1.08 -1.30 20% Standard 3 -0.21 -0.33 56% Axial force Post 2 -8.46 -9.41 11% (front) Standard 4 -0.23 -0.34 47% (kN) Post 3 -0.46 -0.61 34% Brace 2 -0.62 -0.85 37% Metal strut -5.79 -5.99 3% Bending Upper tube 1.40 1.49 6% moment (kN·m) Under tube 1.30 1.37 5%

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(c) Test case (3) under 8 kN static point load Difference Measured mean Component Analyzed value 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% value 푚푒푎푠푢푟푒푑 Post 1 -2.94 -3.74 27% Standard 1 -0.28 -0.34 23% Axial force Standard 2 -0.52 -0.36 31% (front) Standard 3 -0.27 -0.33 21% (kN) Post 2 -3.30 -4.26 29% Metal strut -4.19 -3.98 5% Bending Upper tube 0.92 0.87 6% moment (kN·m) Under tube 0.72 0.77 7% (d) Test case (4) under 8 kN static point load Difference Measured mean Component Analyzed value 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% value 푚푒푎푠푢푟푒푑 Post 1 -2.91 -3.74 29% Standard 1 -0.20 -0.20 1% Axial force Standard 2 -0.21 -0.31 51% (front) Standard 3 -0.18 -0.20 13% (kN) Post 2 -3.80 -4.26 12% Metal strut -3.59 -3.99 11% Bending Upper tube 1.07 1.16 8% moment (kN·m) Under tube 0.98 1.08 11%

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(e) Test case (5) under 8 kN static point load Difference Measured mean Component Analyzed value 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% value 푚푒푎푠푢푟푒푑 Post 1 -0.93 -1.09 17% Axial force Standard 1 -0.08 -0.09 14% (front) Standard 2 -0.12 -0.14 19% (kN) Standard 3 -0.08 -0.12 44% Post 2 -2.64 -2.87 9% Axial force Post 4 -0.24 -0.25 2% (back) Post 5 -1.29 -1.80 39% (kN) Post 6 -1.35 -1.80 34% Bending Outer tube 0.95 0.91 4% moment (kN·m) Inner tube 1.17 0.99 15% (f) Test case (6) under 8 kN static point load Difference Measured mean Component Analyzed value 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% value 푚푒푎푠푢푟푒푑 Post 1 -1.22 -1.40 14% Axial force Standard 1 -0.10 -0.09 7% (front) Standard 2 -0.11 -0.15 35% (kN) Standard 3 -0.10 -0.13 34% Post 2 -2.45 -2.63 7% Axial force Post 4 -0.47 -0.53 12% (back) Post 5 -1.28 -1.80 41% (kN) Post 6 -1.17 -1.75 49% Bending Outer tube 0.96 1.10 14% moment (kN·m) Inner tube 1.03 1.12 9%

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Table 2-15 Summary for the static point load test

푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 퐷𝑖푓푓푒푟푒푛푐푒 = | | × 100% Reinforcement options and Assigned 푚푒푎푠푢푟푒푑 test cases load Bamboo Metal tube Max Mean Std Max Mean Std Test case (1) 52% 28% 18% 11% 9% 2% Option 2 12 kN Test case (2) 56% 34% 15% 6% 5% 1% Test case (3) 31% 26% 4% 7% 6% 1% Option 2 8 kN Test case (4) 51% 21% 17% 11% 10% 1% Test case (5) 44% 22% 14% 15% 10% 6% Option 3.2 8 kN Test case (6) 49% 25% 16% 14% 12% 3% Total 56% 26% 16% 15% 8% 3%

Table 2-16 Results of drop load test (a) Test case (1) Test Test Free Drop Results Test Standards Pass/Fail series mass fall force (kN) 1 12.38 No EN 795 (2012) & ANSI 2 100kg 3.2m 12.35 component Z359.1 (2007) & OSHA Pass 3 12.08 failed 1926.502 (b) Test case (2) Test Test Free Drop Results Test Standards Pass/Fail series mass fall force (kN) 1 12.80 No EN 795 (2012) & ANSI 2 100kg 3.2m 12.94 component Z359.1 (2007) & OSHA Pass 3 12.14 failed 1926.502 (c) Test case (3) Test Test Free Drop force Results Test Standards Pass/Fail series mass fall (kN) 1 2.9m 9.18 No component 2 2.9m 8.87 failed ANSI Z359.1 (2007) 100kg Pass Bamboo ledger & OSHA 1926.502 3 3.1m 11.96 failed at tube end

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(d) Test case (4) Test Test Free Drop Results Test Standards Pass/Fail series mass fall force (kN) 1 2.8m 8.25 No component ANSI Z359.1 (2007) & 2 100kg 2.8m 8.69 Pass failed OSHA 1926.502 3 3.1m 11.86 (e) Test case (5) Test Test Free Drop Results Test Standards Pass/Fail series mass fall force (kN) 1 2.0m 8.35 No component ANSI Z359.1 (2007) & 2 100kg 2.0m 8.58 Pass failed OSHA 1926.502 3 2.0m 8.04 (f) Test case (6) Test Test Free Drop force Results Test Standards Pass/Fail series mass fall (kN) 1 2.0m 8.10 No ANSI Z359.1 (2007) & 2 100kg 2.0m 8.32 component Pass OSHA 1926.502 3 2.0m 8.19 failed

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Table 2-17 Anchorages for DLBS with 3 standards and a span of 0.6 m

Minimum tube Reinforcement Load-carrying Location of Connecting thickness T & Illustration options capacity anchor point devices length L

Only the Anchor T=3.2 mm, intersection No specific 12 kN points L=0.6 m between post requirements Option 2: and ledger adding two steel tubes to

two adjacent bamboo All ledgers intersections T=2.3 mm, Anchor 8 kN between L=0.6 m points post/standard Using energy and ledger absorber

lanyard/ Self-retracting lifeline Anchor region All anchor marked with Option 3.2: T=2.3 mm, points in the MAF ≤ 4 kN platform 8 kN L=1.2 m middle region reinforcement of tube

Note 1: The tube length represents minimum tube length at each side of anchor point; Note 2: The load case (2) with steel tube length 0.6m at the position most close to the edge shouldn’t be used as anchorage, see Section 2.3.2.

59 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Table 2-18 Reinforced anchorages for different bamboo scaffoldings (a) Anchorages for DLBS with 3 standards between posts and span of 0.75 m

Minimum tube Reinforcement Load-carrying Location of Connecting thickness T & Illustration options capacity anchor point devices length L

Only the Anchor T=4.0 mm, intersection No specific points 12 kN L=0.75 m between post requirements Option 2: and ledger adding two steel tubes to

two adjacent bamboo All ledgers intersections Anchor T=4.0 mm, 8 kN between points L=1.5 m post/standard Using energy and ledger absorber

lanyard/ Self-retracting lifeline All anchor marked with Option 3.2: T=3.2 mm, points in the MAF ≤ 4 kN platform 8 kN Anchor L=1.5 m middle region reinforcement region of tube

Note 1: The tube length represents minimum tube length at each side of anchor point; Note 2: The load case (2) with steel tube length 0.6m at the position most close to the edge shouldn’t be used as anchorage, see Section 2.3.2.

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(b) Anchorages for DLBS with 1 standard between posts and span of 0.6, 0.75 or 0.9 m

Minimum tube Load-carrying Location of Connecting Span thickness T & Illustration capacity anchor point devices length L

T=2.3 mm, 0.6 m Using energy L=1.2 m absorber All anchor lanyard/ T=3.2 mm, points in the Anchor 0.75 m 8 kN Self-retracting L=1.5 m middle region region lifeline 0.6/0.75/0.9 m of tube marked with T=4.0 mm, 0.90 m MAF ≤ 4 kN L=1.8 m

Note 1: The tube length represents minimum tube length at each side of anchor point; Note 2: This table only shows analytical results of Option 3.2 and the application of Option 2 for this table is the same as in Table 2-18 (c).

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(c) Anchorages for SLBS with 1 standard between posts and span of 0.6, 0.75 or 0.9 m

Minimum tube Load-carrying Location of Connecting Span thickness T & Illustration capacity anchor point devices length L

Only the Anchor T=3.2 mm, intersection No specific points 12 kN L=0.6 m between post requirements and ledger 0.6 m

0.6 m Using energy All absorber intersections lanyard/ Anchor T=2.3 mm, 8 kN between Self-retracting points L=0.6 m post/standard lifeline marked and ledger with MAF ≤ 4 0.6 m

kN

Only the Anchor T=4.0 mm, intersection No specific 12 kN points L=1.5 m between post requirements and ledger 0.75 m

0.75 m Using energy All absorber Anchor intersections lanyard/ T=2.3 mm, points 8 kN between Self-retracting L=0.75 m post/standard lifeline marked and ledger with MAF ≤ 4 0.75 m kN Using energy All absorber intersections lanyard/ Anchor T=2.3 mm, 0.90 m 8 kN between Self-retracting points L=0.9 m post/standard lifeline marked and ledger with MAF ≤ 4 0.9 m kN Note 1: The tube length represents minimum tube length at each side of anchor point; Note 2: The connection at the position most close to the edge is also not recommended as anchorage. Table 2-19 Load-carrying capacity (in kN) of one anchor point for Option 2 with more 62 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

steel struts Only one Steel strut covering whole steel strut Critical reinforced region Configuration connecting case anchor Anchor point A B points A

(1) 12.8 6.0 - 12.8 Anchor point

A B

(2) 12.5 12.5 5.8 12.2 Anchor

point

A (3) 10.3 5.7 - 10.7 Anchor point

A B (4) 8.0 10.0 6.5 8.2 Anchor point

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Table 2-20 Load-carrying capacity for Option 2 under two users No. of spans Load-carrying Configuration between the capacity for each two users anchor point (kN)

User 1 User 2

1 6.5

User 1 User 2 2 8.7

User 1 User 2

3 10.3

User 1 User 2

4 10.6

Note: The load case (3) near the edge of scaffolding was chosen as the anchorage for “user 1” because it offers the minimum load-carrying capacity among all three load cases for Option 2.

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Chapter 3 Anchorage for Bamboo Scaffolding: Other Options

3.1 A safer scaffolding erection process

It is noted that Clause 5.3.1 (n) of the Code of Practice for Bamboo Scaffolding Safety [17] states that “No shock loading on the platforms should be allowed.” It is believed that such a restriction might have been originated from the consideration that any shock loading acting on the platforms would result in vibration of the platforms and endanger workmen on the platforms. Despite that the reinforcement options presented in the previous chapter have been validated numerically and experimentally. Such a concern remain valid and might hinder the overall acceptance of these reinforcement options. Also Clause 5.3.1 (t) “When a scaffolder or workman has to work in a place where it is impracticable to erect a safe working platform or to provide safe access and egress, the use of safety nets and safety belt attached to a secure anchorage point or an independent lifeline throughout the work is required.” suggests that safety belt attached to a secure anchorage point or an independent lifeline is an alternative option to a safe working platform. Such a safe working platform is usually not available till the last stage of erection due to the reason that it appears to be more time efficient to construct the outer layer as a whole before erecting inner layer and the working platforms [11].

In this section, a safer scaffolding erection process is proposed to address the safety issue during the erection of bamboo scaffolding. This erection process ensures that a safe working platform and necessary guardrails are available during the erection such that the safety of scaffolders and workmen can be better protected without the need of attaching safety belt to a secure anchorage or an independent lifeline. This proposed erection process complies with the erection sequence for metal scaffolding described in [18]. This erection sequence consists of the following steps:

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(1) Fig. 3-1 (a): the standards and posts for the next lift above are installed from a fully planked platform (the existed lift); (2) Fig. 3-1 (b): the main ledgers of both inner and outer layer for the next lift above are installed; (3) Fig. 3-1 (c): the guardrails (intermediate guardrail and top guardrail) and edge protection for the lift above are then installed; (4) Fig. 3-1 (d): the transoms and planks for the lift above are installed to form working platform above; (5) Fig. 3-1 (e): access the new working platform and install toe-boards; and (6) Fig. 3-1 (f): install other components such as putlogs or metal brackets from the new working platform.

Note that when working from a fully planked platform to erect standards/posts (where the standard/post joint is 1 to 1.5 m above the existed platform level) and guardrails for the lift above, several possible options such as a temporary ladder or platform as shown in Fig. 3-2 are possible for the scaffolders to reach the desired height [18]. This proposed erection process complying with the scaffolding requirements has been modeled using a BIM software, Revit and Navisworks, for illustrative purpose.

3.2 Anchorages for bamboo scaffolding above roof level

For some special conditions, regional reinforcement on the scaffolding itself as described in the previous chapter may not be applicable. These conditions include when the scaffolding is erected above any permanent structure. The portion of bamboo scaffoldings is more flexible and not suitable for any regional reinforcement option proposed above. According to Clause 5.3.1 (b): “The height of the bamboo scaffold erected at any side should not be higher than the topmost part of the building/structure by one storey.” These above-the-roof-top scaffolding might be 66 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings several ledges’ height (see Fig. 3-3) and could pose a threat to scaffolders or workmen as a secure anchorage point or an independent lifeline above the height of scaffolders/workmen is almost non-existent.

It could be anticipated that the work above roof level would require mostly horizontal movement. Hence, a horizontal lifeline (HLL) system will be an efficient way to protect workmen from the consequence of falling. This HLL system can be either permanent or temporary. As summarized in various standards including ANSI Z359.6 [6], CSA Z259.16 [7] and CSA Z259.13 [19], a good HLL system should meet the following requirements:

(1) Their components and anchorages are of adequate strength to withstand the maximum arrest load (MAL) or maximum arrest force (MAF). (2) The MAF experienced by the user is within acceptable limits (such as 6 kN as described above) to minimize the possibility of injury. (3) Clearance in the fall path is adequate to prevent the user from hitting the ground or any other obstruction. (4) For a HLL system used to support bamboo scaffolding, the anchorage device should be fixed on a permanent structure. Expansion bolts or rebar can be used to fix the anchorages. (5) A HLL system could be temporary or permanent and should allow at least two workmen attached to it simultaneously. (6) A stanchion can also be considered as a possible option for offering anchorage points above the roof top.

According to the above requirement for selection of a HLL system, Fig. 3-4 shows a typical HLL system produced by DBI-SALA [14]. The system consists of multi-span horizontal lifeline, 2.3 m tall posts, different types of bases and various components which make it more flexible to suit different types of structures.

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3.3 Anchorages for bamboo scaffolding below roof level

When workers perform jobs on platform below roof level, the HLL system is also an effective way to provide anchorages for needed horizontal movement. The stanchion is not necessary and the configuration of the HLL system could be simpler. The requirements (1)-(5) described above should be followed for choosing an applicable system. When the HLL system is fixed on vertical concrete wall, the worker should be able to reach the lifeline easily with his/her arm in order to travel across the scaffolding.

Most commercially available HLL products are single-span and allow a maximum span up to 18 m. If the largest span allowed by manufacturer is not enough for worker to perform their jobs, another single-span HLL system can be used independently. Fig. 3-5 gives an example of this type of system produced by Miller [15]. A Miller SkyGrip Wire Rope Lifeline may be used in conjunction with approved Miller brand anchorage connectors to provide a temporary HLL system that is quick and easy to install.

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(a) Standards and posts (b) Main ledgers

(c) Guardrails and edge protection (d) Transoms and planks

(e) Toe-boards (f) Other components such as putlogs and metal bracket

Fig. 3-1 A safer bamboo scaffolding erection process

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(a) Temporary ladder used for erection

(b) Temporary platform supported on ledgers/guardrails

(c) Proprietary temporary edge protection system Fig. 3-2 Illustration of various options to facilitate the new erection process

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Fig. 3-3 Bamboo scaffoldings above roof level

Fig. 3-4 Configuration of a HLL system with different anchorage options [14]

Fig. 3-5 Miller SkyGrip Wire Rope Lifeline and anchorage [15]

71 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Chapter 4 Use of Mixed Scaffolding

Recently, there are some scaffoldings constructed using a mixture of both bamboo and metal tubes. While there are respective codes of practice for bamboo scaffolding safety [17] and metal scaffolding safety [20], there is no specific guideline governing the safe usage of this hybrid type of scaffoldings. These mixed scaffoldings have created a series of new technical challenges that need to be addressed. In this chapter, issues relating to the safe usage of mixed scaffoldings were investigated numerically and validated experimentally. These issues are reported in the following.

4.1 Mechanical properties of connection

In mixed scaffoldings, steel tube is the primary load-bearing component while bamboo serves as the secondary component. Kao Jue (BP) is commonly used in the mixed scaffolding as it has similar external diameter as that of steel tube. There are generally two types of steel tube used in mixed scaffolding (see Fig. 4-1): steel tube with smooth surface (normal steel tube) and steel tube with anti-sliding bumps on the surface (anti-sliding steel tube). There are a few possible types of connection in mixed scaffoldings: (a) bamboo-bamboo; (b) normal steel tube-bamboo; (c) anti-sliding steel tube-bamboo; (d) anti-sliding steel tube-normal steel tube; and (e) normal steel tube-normal steel tube. Note that except type (e), all the other types of connection are fastened using the same plastic stripes as used in bamboo scaffoldings. Metal couplers are used for type (e) connection. While the mechanical properties for bamboo-bamboo connection have been reported in Section 2.1, the mechanical properties for the other types of connection were obtained experimentally and summarized in the following.

4.1.1 Normal steel tube-bamboo connection

A series of tests were conducted to obtain the slippage stiffness and rotational stiffness 72 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings of connection between normal steel tube and bamboo component (BP). Also, the effect of bamboo node was considered in the tests. Fig. 4-2 shows the test setup for the slippage stiffness and the rotational stiffness. In most normal steel tube-bamboo connections, the bamboo serves as a horizontal member while the steel tube is used as a vertical load-bearing column. A total of five load-displacement curves were obtained and plotted in Fig. 4-3 for the slippage stiffness. The mean slippage stiffness before reaching the maximum slippage resistance is 60.6 kN/m and the average minimum resistive force during slippage and up to 30 mm displacement is 0.76 kN. Three load-displacement curves and the corresponding M − θ curves were obtained and plotted in Fig. 4-4 for the rotational stiffness. The mean rotational stiffness against the direction of the fastening tie is found to be 0.11 kN∙m/rad.

Table 4-1 summaries the resistance for the normal steel tube-bamboo connection. As a conservative measure, the connection resistance without nodes was taken as the minimum slipping force during the initial 30 mm displacement. For connection with the presence of bamboo node, there were two possible failure modes: (a) fracture of plastic stripes and (b) the plastic stripes slipping over the node. For connection without the presence of bamboo nodes, the failure mode was the slipping between two members. Table 4-2 summaries the rotational stiffness for the normal steel-bamboo connection. It is noted that the connection between two normal steel tubes fastened by plastic stripes were also shown in the two tables for comparison. For simplicity, the slippage stiffness of normal steel tube (vertical)-bamboo (horizontal) connection was used as the representative mechanical property for this type of connection in the modeling. In SAP2000, the multi-linear element and panel zone are also used to model the bilinear stiffness behavior against rotation and the multi-linear slippage stiffness behavior of the connection as shown in Fig. 4-5 (a) and (b).

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4.1.2 Anti-sliding steel tube-bamboo/normal steel tube connection

For connection involving anti-sliding steel tube, the anti-slide steel tube is always used as a vertical component such that the anti-sliding bump can take effect to prevent slippage of horizontal component which can be either bamboo (BP) or normal steel tube. Fig. 4-6 shows a typical setup for anti-sliding steel tube-bamboo/normal steel tube connection test. For this type of connection, the orientation of anti-sliding bumps would be an issue affecting its mechanical properties. Hence, tests were conducted with different orientation angles of the bumps with respect to the perpendicular direction of the post-ledger plane. A total of five different angles, 0°，45°, 90°, 135° and 180° were selected to represent different connecting situations. Each angle was tested at least 5 times (see Fig. 4-7).

For connection tests with 0°, 45°, 90°, the failure modes was always splitting and slipping of plastic stripes over the bump as seen in Fig. 4-8. Two typical load-displacement curves with initial slippage and without initial slippage for connection test with 0° are shown in Fig. 4-9. For the 135° orientation, the test results obtained were very similar to those of normal steel tube-bamboo connection shown in the previous section. This was due to the reason that the plastic strip was not in direct contact with the bumps. For 180° orientation of anti-sliding steel tube-bamboo connection, the failure mode was the damage of bamboo surface at the connection between bamboo and the anti-sliding steel tube as shown in Fig. 4-10. For 180° orientation of anti-sliding steel tube-normal steel tube connection, the failure mode was the rotation of horizontal tube as shown in Fig. 4-11.

The slippage resistance and corresponding slippage displacement are summarized in Table 4-3. The average ultimate slippage resistance decreased as the orientation angle increasing from 0° to 135°. Results show that 135° orientation angle has the smallest connection resistance among all cases considered for the anti-sliding steel

74 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings tube-bamboo/normal steel tube connection. Based on these results, it is recommended that the orientation angle of the anti-sliding steel tube for this type of connection should be within [-90°, 90°]. When a transom is also present at the connection, the orientation of the anti-sliding steel tube is recommended to be within [0°, 90°] or [-90°, 0°] depending the configuration as shown in Fig. 4-12.

For the modeling of this type of connection, the average connection resistance and average total displacement of 0°, 45° and 90° orientation were adopted. Linear elements were selected to model the slippage behavior including the average connection resistance and the average total displacement. Table 4-4 and Table 4-5 summarize the connection resistance and the total displacement, respectively. Note that bilinear stiffness behavior against rotation for connection between anti-sliding tube and bamboo or normal steel tube is assumed to be the same as described in Section 4.1.1. In summary, the linear slippage stiffness of the connection was modeled as follows: For anti-sliding tube (vertical)-bamboo (horizontal) connection: Slippage force = 51.21 kN/m × displacement For anti-sliding tube (vertical)-normal steel tube (horizontal) connection: Slippage force = 57.83 kN/m × displacement

4.1.3 Normal steel tube-normal steel tube connection

All connections between two normal steel tubes were fastened by couplers as shown in Fig. 4-13. Various types of couplers are available such as the right angle coupler which is used to join tubes at right angles and the swivel coupler for connecting components at flexible angles. Mechanical properties for different types of couplers are summarized in Table 4-6 based on BS EN 74-1 [21] and BS 12811-1 [22].

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4.1.4 Thermal effect of steel tube on connection

In this section, the thermal expansion effect of steel tube on scaffolding connection due to temperature change was investigated. The change in circumference of steel tube due to temperature change could be approximated as:

푑퐶 = 휋푑1 − 휋푑0 = 휋푑0(푑푡)훼 where 푑퐶 is change in circumference (mm);

푑0 and 푑1 are initial diameter and final diameter (mm), respectively; 푑푡 is temperature change (oC); and 훼 is linear thermal expansion coefficient (10 × 10-6/°C according to Annex E of BS 5975 [23]).

For a steel pipe with outer diameter 푑0 = 48.3 푚푚 and an assumed temperature change of 푑푡 = ±25℃, the final outer diameter 푑1 would be 48.3 ± 0.012 푚푚. According to previous research [1], the dimension of the fastening tie was width = 6 mm and thickness = 1 mm. The Young’s modulus of fastening tie was about 퐸 = 2 푘푁/푚푚² . The force change ∆퐹 in the fastening tie of steel tube-bamboo connection due to temperature changing of 25℃ is about:

∆퐹 = (푑1 − 푑0) × 휋 × 퐸 × 퐴/(푑0 × 휋 × 2) = 1.49 푁

Note that the outer diameter of bamboo is assumed to be the same as steel tube. The force change in the fastening tie of an anti-sliding steel tube and normal steel tube connection due to a temperature change of 25℃ should be doubled (2.98 kN). In previous report [1], it was also found that the mean tensile force in the fastening tie during fixing the joints is about 23 N and the ultimate tensile force of fastening tie is

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1,135 N. In summary, a temperature change of ±25℃ would not affect the property of scaffolding connections very much.

4.2 Design and modeling of mixed scaffolding

4.2.1 Design of mixed scaffolding

The design of mixed scaffolding was based on the structural form of traditional double layered bamboo scaffoldings (DLBS) such as the one shown in Fig. 4-14 [12]. As shown in Fig. 4-15, there are three possible types for the mixed scaffolding:

Type 1: Posts and bracings of a DLBS are replaced by anti-sliding steel tubes. Type 2: Type 1 plus main ledgers replaced by normal steel tubes. Type 3: Posts, main ledgers and bracings of a DLBS are replaced by normal steel tubes and connected using couplers.

In this study, the size of steel tube is 48.3 × 2.3 mm (outer diameter × thickness) and its characteristic yield strength = 235 N/mm² and young’s modulus E = 200 GPa.

4.2.2 Modeling of mixed scaffolding

As the design of mixed scaffolding was based on the traditional DLBS, the finite element modeling of bamboo components was the same as that in Section 2.2.2. Also, nonlinear analysis with P-Delta effect has been considered in the analysis. Details of the modeling are outlined as follow:

(1) The posts, main ledgers, and diagonal bracings substituted by steel tubes were modeled as members with circular hollow cross sections. (2) The vertical, horizontal and rotational stiffness of the joint between bamboo

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members or between bamboo and steel tube members were modeled using multi-linear elements and panel zones. For simplicity, the out-of-plane relative displacement at connection was ignored. (3) It should be noted that in each main ledger-post/standard fastening, there was always a transom-post/standard fastening connected at the same location. Thus, the total connection resistance, vertical stiffness and horizontal stiffness should be doubled. The rotational stiffness was not doubled because the post/standard, main ledger and transom were orthogonal to each other. (4) For Type 3 mixed scaffolding, the joints between steel tubes fastened by right angle couplers were assumed to be rigid connections. Those non-orthogonal connections fastened by swivel couplers were modeled as panel zones with a simple constraint which could not transmit moments. (5) The bamboo transoms linking up the inner layer and outer layer ledgers were simulated as pinned connection. (6) For Type 1 and Type 2 mixed scaffolding, putlogs were anti-sliding steel tubes fastened to scaffolding by plastic stripes and connected to wall by anchor bolts. For Type 3 mixed scaffolding, putlogs were normal steel tubes fastened to scaffolding by metal couplers and connected to wall with specific anchorages. These putlogs were modeled with only inward and outward restraints and were used to prevent inward and outward movement of the scaffoldings. (7) All the main posts were assumed to be pinned at the bottom. The braces were only connected to main posts of the outer layer.

4.3 Comparison among three types of mixed scaffolding

In this section, the three mixed scaffolding types were compared with regard to the following aspects:

(1) Construction cost and time; 78 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

(2) Weight and weight distribution; and (3) Load-carrying capacity.

The analytical result of pure bamboo scaffolding was also provided for comparison. The configuration and dimensions of bamboo scaffolding and mixed scaffoldings were assumed to be the same with a platform height of 2 m and width of 0.6 m as shown respectively in Fig. 4-14 and Fig. 4-15.

4.3.1 Construction cost and time

To compare the cost of these mixed scaffoldings, a one-bay (1.3 m) unboarded lift as shown in Fig. 4-16 was selected for analysis. The work platform board and toe-board were not included as they could all be used on these scaffoldings. Table 4-7 summaries the material required for constructing a one-bay unboarded lift for the bamboo scaffolding and the three mixed scaffoldings. The actual length of a scaffolding component was calculated by multiplying its net length (physical size of the scaffolding) with an overlap factor. The overlap factors were determined according to the requirements in relevant scaffolding codes. To calculate the material consumption, the following assumptions have been made:

(1) Bracings of outer layer was assumed to be 0.5 m/m². (2) Bamboo and tube were assumed to be 6 m/piece [12]. (3) For connection between 2 bamboo members, the length of overlap was assumed to be 2 m [17]. Hence the overlap factor for bamboo (1.5) was based on that only 4 m out of a 6 m bamboo component could contribute to the physical size of scaffolding. (4) For both Type 1 and Type 2, the overlap of connection in continuous anti-sliding tubes was negligible [24]. (5) For Type 2, the overlap of connection in horizontal normal steel tubes was

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assumed to be 1.5 m. The overlap factor (1.1) for steel tube in this type was based on that every 4.5 m increase of horizontal normal steel tube required 1.5 m overlap, and then this increase is averaged to all tube length. (6) For Type 3, the normal steel tubes for continuous diagonal brace were joined by 2 swivel or parallel couplers with an overlap length of 0.3 m [20]. The overlap factor of 1.01 for steel tube was based on that every 5.7 m increase of brace required 0.3 m overlap, and such an overlap is averaged by the total tube length. (7) For Type 3, joints between posts and main ledgers should be made with sleeve couplers or expanding joint pins [20] with no overlap. So, a total of 4.5 couplers (2 right angle couplers for post-ledger connection, 0.5 swivel or parallel couplers for brace overlap, 1 sleeve coupler or expanding joint pin for ledgers and posts, and 1 swivel coupler for connection between steel brace and post) were required for a one-bay lift.

A comparison of the material costs of three different mixed scaffoldings and bamboo scaffolding is summarized in Table 4-8. It is seen that the material costs of Type 1, 2 and 3 mixed scaffoldings are 6, 8.4 and 7.7 times of that of bamboo scaffolding. It should be noted that metal tube and fittings are recyclable which was not reflected in this table. Furthermore, the labor cost of the three mixed scaffolding types and the bamboo scaffolding should be in the following order: bamboo scaffolding ﹤ Type 1 ≈ Type 2 ﹤ Type 3.

There are no specific researches or data about the construction time of three different mixed scaffolding and bamboo scaffolding. Obviously, the erection and dismantling of bamboo scaffolding is faster than that of mixed scaffoldings as bamboo components are much lighter than metal components. Comparing Type 1 and Type 2, moving, installing and dismantling metal main ledgers would not be convenient and easy for a single worker due to their relatively heavy weight (15.6 kg/piece). Hence constructing Type 1 should be faster than Type 2. Furthermore, the using of couplers in Type 3 would need

80 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings more time. In summary, the construction time of the three mixed scaffolding types and the bamboo scaffolding should be in the following order: bamboo scaffolding ﹤ Type 1 ﹤ Type 2 ﹤ Type 3.

4.3.2 Weight and weight distribution

For comparison, the density of bamboo (Kao Jue and Mao Jue) under natural condition was used, which was obtained according to average dry density, moisture content for natural condition and geometric dimensions from Appendix B1. The increased self-weight due to overlap and the using of coupler described in Section 4.3.1 has been considered in an equivalent density by applying corresponding increasing factors, as shown in Table 4-9. The equivalent density (kg/m) of Kao Jue, Mao Jue and steel tube were used to calculate the self-weight of a one-bay unboarded lift for these scaffoldings and are summarized in Table 4-10 for comparison. It is seen that the weight of a mixed scaffolding is about 2 to 3 times that of a bamboo scaffolding.

4.3.3 Load-carrying capacity

This section compared the load-carrying capacity including allowable load (UDL) on platform and allowable height of the three mixed scaffolding types and bamboo scaffolding. Load-carrying capacity of a scaffolding and its components was determined based on the method of permissible stress design for scaffoldings according to BS 5975 [23] and BS EN 12811-1 [22]. In this method, all loads are unfactored loads and all characteristic resistances are reduced to working resistances by dividing them by a single factor: 1.1 (material factor) × 1.5 (load factor) = 1.65 for steel components and 1.5 (material factor [9]) × 1.5 (load factor) = 2.25 for bamboo components. It should be noted that the mechanical properties of bamboo under normal supply condition from Appendix B1 was used in analysis.

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Allowable loads (UDL) on scaffolding platforms: There are two types of platform commonly used in both bamboo scaffolding and mixed scaffolding: Type 1: placing wooden boards or iron planks on transoms; Type 2: fastening longitudinal bamboos to transoms at a closer spacing (≤ 150 mm) to form a platform (see Fig. 4-17). For Type 1 platform, scaffolding boards contribute bending strength to the platform and load is transferred from boards to transoms in the form of uniformly distributed load (UDL). For Type 2 platform, the longitudinal bamboo (Kao Jue) would contribute bending strength to the platform and load is transferred from longitudinal bamboos to transoms through a series of point loads. Loads acting on transoms would be transferred to ledgers and then to posts/standards. The allowable load on platform would be determined considering all components involved in the load transfer based on limit state design.

The deflection of platform under two scaffolding duties (light duty 1.5 kN/m² and special duty 3 kN/m²) was analyzed for the serviceability design. The deflection of platform mainly comes from the relative slippage at the connections and the bending deformation of components. The maximum member deflection across all components supporting platform was recorded as the maximum deflection of platform. Due to different configuration between the inner and outer layer, load on platform may not be shared equally by all transoms and main ledgers. So, the allowable load and deflection of these two types of platform were determined using a full-scale scaffolding model.

For Type 1 platform, wooden boards are fairly popular due to their lower price. For simplicity, wooden boards were chosen as representative for Type 1 platform in this section. In the full-scale model, Type 1 platform was modelled by two thick shell element placing on bamboo transoms through gap elements and each shell element represents one 225 mm (width) × 25 mm (thick) piece of wooden board as seen in Fig. 4-18 (a). The young's modulus and bending strength of wooden boards were obtained from the test to be reported in Chapter 5. For Type 2 platform, usually five

82 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings longitudinal bamboos (Kao Jue) were fastened to transoms using plastic stripes as seen in Fig. 4-18 (b). Based on these assumptions, the allowable loads and the maximum deflections for the two types of platform for the bamboo scaffolding and the three mixed scaffolding types are presented in Table 4-11 and Table 4-12, respectively. It is seen that the allowable loads on the two types of platform are between 3.23 and 4.0 kN/m2 for all types of scaffolding considered. The allowable loads for Type 1 mixed scaffolding are the same as those of bamboo scaffolding, while Types 2 and 3 mixed scaffolding have almost the same but slightly higher allowable loads. Overall speaking, there is no significant difference among the allowable loads for the two types of platform for all scaffoldings considered. As for the maximum deflection, it is seen that, except that Type 3 mixed scaffolding has significantly the smallest deflection, all the other scaffoldings (bamboo and Types 1 and 2 mixed scaffoldings) have about the same maximum deflections.

Allowable height of scaffoldings: Next, the allowable height of a scaffolding was determined based on allowable compressive buckling load of vertical posts. The scaffolding configuration and dimension corresponding to Figs. 4-15 and 4-16 were used, where the platform width was 0.6 m, the lift height h was 2 m and the lift width (length of ledger between two posts) was 1.3 m. Also, assume the vertical distance between lateral restraints was 퐻 = 2ℎ = 4 푚 and the lateral restraints were arranged regularly. The maximum forces in the posts were obtained through nonlinear full-scale model analysis in SAP 2000. The allowable buckling loads of posts were calculated and summarized in Table 4-13 (detailed calculations presented in Appendices C and D). Based on these results, the allowable heights of scaffoldings are summarized and presented in Table 4-14. It is seen that the allowable heights for mixed scaffoldings are considerably larger than that of bamboo scaffolding under light duty condition.

Safety of metal bracket

83 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Metal brackets are used to support posts in tall scaffoldings. Fig. 4-21 shows the dimensions and the modeling of a commonly used metal bracket for bamboo scaffolding [12]. Test data about metal brackets obtained from previous research [2, 3] were used in the modeling. The properties of the metal brackets were assumed to be: young’s modulus E = 210 GPa and yield strength Fy = 350 MPa. These metal brackets were assumed to be anchored using Fook Shing expansion bolts with properties summarized in Table 4-15 [3]. The anchor bolts were modeled by two springs with coefficients of KH and KV. The contact surface between the metal bracket and the concrete panel was modeled by gap elements. The failure of an expansion bolt under combined pull-out and shear forces is determined by the following formula [25]:

푁 1.5 푉 1.5 ( 푆 ) + ( 푆 ) ≤ 1 푁푅푢,푚 푉푅푢,푚 where

푁푅푢,푚 and 푉푅푢,푚 are the pull-out and shear strength (Table 4-15 (b)), respectively;

푁푠 and 푉푠 are the pull-out force and shear force under loading, respectively.

For simplicity and conservative consideration, the concrete was assumed to have a low strength of 25 MPa. The maximum axial forces in posts of inner layer and outer layer under allowable height shown in Table 4-14 were used as external load for a conservative consideration. Table 4-16 shows the analysis results for different types of

1.5 1.5 푁 푉 scaffolding. It is seen that values of ( 푆 ) + ( 푆 ) are all smaller than 0.5 and the 푁푅푢,푚 푉푅푢,푚 maximum stress in steel is smaller than half of the yield strength under the condition that the scaffolding was erected up to its allowable height. These results indicate that the metal bracket has adequate strength to support either light-duty or heavy-duty scaffoldings.

Safety of lateral restraint (putlog) 84 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

The load generated on putlogs is mainly from the wind load. Wind loads shall be calculated by assuming that there is a velocity pressure on a reference area of the working scaffolding, which is in general the projected area perpendicular to the wind direction. According to the Code of Practice on Wind Effects in Hong Kong [26], the total wind force 퐹 acting on a scaffolding is determined by the following equation:

퐹 = 퐶푓 ∑ 푞푧 × 퐴푧

where 퐶푓 is the force coefficient for open framework, 퐶푓 = 1.85 when the solidity ratio φ = 0.15; 푞푧 is the design wind pressure at height 푧, determined in accordance with Table 1 in [26]; and 퐴푧 is the effective projected area of that part of the building corresponding to 푞푧. The solidity ratio φ equaling to the effective projected area 퐴푧 of the open framework building divided by the area 퐴 enclosed by the boundary of the frame normal to the direction of the wind, i.e, 퐴푧 = 휑 × 퐴. In this study, it was assumed that φ = 0.15 according to [27]. Note that a factor of 0.7 may be applied to wind pressures for temporary buildings or structures. To calculate the load on putlogs, area 퐴 should be taken as the area enclosed by the boundary of a quadrangle with four putlogs at four corners. The top portion of scaffolding should be used to determine the maximum pull-out load. As an example, the maximum allowable height 62 m in Table 4-14 was used and the putlogs were arranged every 4 m vertically and 2.6 m horizontally, the pull-out load acting on a putlog was calculated to be 5.35 kN. For a putlog using steel wire of 6 mm diameter, the unfactored stress in the steel wire was 188 MPa which was smaller than the required yield strength of 250 MPa specified in [12].

4.3.4 Summary

The material cost, construction time, self-weight, sensitivity of materials to the environment, typical connection properties and load-carrying capacity of three

85 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings different mixed scaffoldings and bamboo scaffoldings are summarized in Table 4-17. Those of a pure metal scaffolding according to code [20] was also provided for comparison. This pure metal scaffolding was assumed to have platform height of 2 m, width of 0.6 m and bay length of 1.3 m. All components in the metal scaffolding are consisted of normal steel tubes same as those used in the mixed scaffoldings and there is no standard between posts. The transoms are fixed to the inside and outside ledgers with couplers at each pair of posts. The joint between tubes in metal scaffolding are similar to Type 3 mixed scaffolding. From this table, the following findings can be concluded:

(1) All three types of mixed scaffolding can meet the load requirements specified in the bamboo scaffolding code [17] and the metal scaffolding code [20]. The mixed scaffoldings have a better performance than bamboo scaffolding in terms of load-carrying capacity. However, in terms of costs (material cost and labor cost), self-weight and construction time, bamboo scaffolding is still much better than the mixed scaffoldings. Metal scaffolding is the most costly but can offer a more robust performance under different environmental condition. (2) The allowable load (UDL) on platform of bamboo scaffolding and mixed scaffoldings are all larger than 3 kN/m², which is determined by the failure of bamboo transom between posts. Metal scaffolding gives the largest allowable load (UDL) on platform among all scaffoldings, which is determined by the failure of wooden boards. The allowable loads (UDL) on platform of Type 2 and Type 3 are slightly larger than that of Type 1 and bamboo scaffolding. (3) The deflection of platform under designed load is smallest in Type 3 mixed scaffolding, which is slightly smaller than that of metal scaffolding. Bamboo scaffolding and Type 1 and Type 2 mixed scaffoldings show a larger but similar deflection behavior. Also, two different types of platform (wooden board and closely-spaced bamboo members) give a similar load-carrying capacity and deflection for all three mixed scaffoldings and bamboo scaffolding.

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(4) Bamboo scaffolding can only be used as light-duty scaffolding (two working platforms rated at 1.5 kN/m²) and both mixed and metal scaffoldings can serve as heavy-duty scaffolding (two working platforms rated at 2.50 kN/m² plus one working platform rated at 0.75 kN/m²). Considering the allowable height within a single zone (a separate zone between metal brackets), all mixed scaffoldings have a larger erection height (more than twice) than the bamboo scaffolding.

4.4 Full-scale mixed scaffolding test

The objective of the full-scale scaffolding test is to experimentally validate the load-carrying capacity of scaffolding, anchorage issue as well as the accuracy of numerical modeling. From above analysis and comparison, it seems that Type 1 offers a smaller allowable load (UDL) and a larger deflection of platform of all three mixed scaffoldings. Type 1 mixed scaffolding was chosen as the candidate for validation.

4.4.1 Description of the scaffolding

The full-scale mixed scaffolding used for testing is a scaffolding with dimensions of 6.3 m×4.6 m×0.65 m (height×length×width) erected by the Sinoscaff (Hong Kong) Limited. The properties of the anti-sliding tubes provided by this company were: 48.2 mm×2.23 mm (outer diameter×thickness), E = 204 GPa and a yield strength of 220 N/mm²[28]. The outer layer consisted of four anti-sliding steel tube posts and 3 bamboo standards (Kao Jue). The inner layer had four anti-sliding steel tube posts. There were three platforms at the height of 1.1 m, 3.1 m and 5.1m, respectively. The scaffolding was X-braced by two anti-sliding tubes at the outer layer and connected to building façade through five putlogs. The configuration and dimension of mixed scaffolding is shown in Fig. 4-20.

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4.4.2 Test arrangement

On this scaffolding, two types of test were performed: UDL test on platform and static point load test on connection. Details of these tests are provided in the following.

UDL test on platform: Two sets of UDL test were performed to validate the behavior and the load-carrying capacity of scaffolding (see Fig. 4-21):

(1) UDL of 5 kN/m² (equivalent point load of 10 kN) and 7.6 kN/m² (equivalent point load of 15 kN) acting on two spans of platform, respectively. (2) UDL of 5.1 kN/m2 (equivalent point load of 5 kN) and 10.3 kN/m2 (equivalent point load of 10 kN) on the middle span of platform respectively.

Static point load test on connection: The point load test were performed to obtain the behavior and the load-carrying capacity of connection. Two types of connection were tested:

(1) Connection of bamboo ledger and bamboo standard (load position (1) and (2) in Fig. 4-22). (2) Connection of bamboo ledger and anti-sliding steel tube post (load position (3) and (4) in Fig. 4-22).

4.4.3 UDL test on platform

The equipment used in the tests were the same as that reported in Section 2.4. Strain gauges were installed at the bottom of all bamboo standards and steel tube posts. For each test case described in above, loads were conducted on both the upper platform and the bottom platform separately. To create the UDL condition, a loading device

88 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings made by steel tubes and coupler was used to convert the applied point load to UDL as shown in Fig. 4-23. For the UDL test on two spans of both the upper and the bottom platform, a point load up to 10 kN (5.0 kN/m²) and 15 kN (7.6 kN/m²) was applied, respectively. For UDL test on the middle span of both the upper and the bottom platform, a point load up to 5 kN (5.1 kN/m²) and 10 kN (10.3 kN/m²) was applied, respectively. Fig. 4-24 shows two of the loading conditions: middle span of the bottom platform under 10 kN (10.3 kN/m²) load and two spans of the upper platform under 15 kN (7.6 kN/m²) load. For each case, 3 independent tests were conducted. Table 4-18 summarizes the test results according to the post number and standard number labelling as shown in Fig. 4-25. Based on these testing results, the following observations can be made:

(1) There were no notable deformation nor any sign of damage in any part of the scaffolding even under an UDL with a magnitude twice as large as the required value for all cases. The measured axial forces in posts were all much less than their compressive buckling strength. (2) Under UDL, the middle steel posts (posts 4, 6 of back layer and posts 3, 5 of front layer) carried larger axial loads than the other posts. (3) The axial forces in bamboo standards were much smaller than those in steel posts. (4) For the same loading condition, the axial forces in the posts and standards were approximately linearly proportional to the UDL magnitude. (5) The standard deviations of the measured strains were quite small which suggested that the test results were quite consistent and reliable.

To compare the test results obtained above, finite element analysis using SAP 2000 reported in Section 4.2 was performed for all the UDL cases tested above. Table 4-19 presents the comparison between the UDL test and the computer analysis results. Note that strain gauges used in the test had a precision of 1 × 10−6휀, hence comparison of those axial forces obtained from strain values smaller than or around this precision

89 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings was not made. Table 4-20 further summarizes the average differences obtained between the full-scale test and the numerical analysis. It shows that the average difference in the axial forces between the full-scale UDL test and the numerical analysis of Type 1 mixed scaffolding was about 33% for the bamboo members and about 20% for the metal members.

4.4.4 Static point load test on connection

The static point load tests were performed to obtain the deformation behavior and the load-carrying capacity of connection and check whether the connection could be used as an anchorage for safety harness. The setup of static point load test was similar to that of UDL test. The load generated by tensile jack was applied on connection through a steel wire. Two types of point load test were performed to obtain the deformation behavior and the load-carrying capacity of scaffolding connection, respectively. First, the point load applied on connection was slowly increased from 0 kN to 2 kN to obtain the deformation behavior of connection. The deformation at about 10 cm away from the connection was measured by the LVDT as illustrated in Fig. 4-26. Each of four connections as shown in Fig. 4-22 were tested three times. Then, load acting on connection was increased gradually until some sign of connection failure occurred to obtain its load-carrying capacity.

Fig. 4-27 shows the load-displacement curves for Connection (1) and Connection (3). It is seen that the load-displacement relation is rather linear indicating that the scaffolding remains linear elastic up to 2 kN load applied to these locations. Table 4-21 summaries the displacement measured near the four connections under 2 kN static point load. Table 4-22 summarizes the mean values and standard deviations of measured strains and axial forces for vertical posts and standards under 2 kN static point load acting on each of the four connections. It is seen that the load acting on connection was mainly carried by the posts directly underneath. The axial force in a

90 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings post decreases as the distance between the post and the connection increases. The axial forces in the bamboo standards were generally very small comparing to those in the posts.

Fig. 4-28 shows the failure of Connections (1) and (4) under static point load. The ultimate failure loads corresponded to the maximum point loads attained during the loading process. Table 4-23 summarizes the failure loads of these four connections. Results show that the connections can only sustain around 4 kN load before failure. This is not sufficient to be used as an anchorage for safety harness even an energy absorbing connecting device is used (requiring a minimum of 8 kN). This indicates that the connections in Type 1 mixed scaffolding cannot be used as an anchorage for safety harness.

To compare the test results obtained above, finite element analysis using SAP 2000 reported in Section 4.2 was performed for all the static point load cases tested above. Fig. 4-29 shows the comparison of load-displacement curves between test and analysis for Connection (1) and (3). It is seen that the computer analysis results coincided with the first test results very well at both connections, both of which exhibited linear behavior. Tables 4-24 and 4-25 further summarize the comparison of displacement and load-carrying capacity of connections between test and analysis, respectively. It is seen that the displacement difference between test and analysis ranges between 10 to 45 % if the average diameter from Appendix B1 was used in the analysis. The difference becomes smaller (between 1 to 23%) if the diameters of bamboo ledges were measured in-situ and used in the computer model. Similarly, the difference of load-carrying capacity between test and analysis ranges between 15 to 30% if the measured diameters were used in the model. Table 4-26 compares the axial forces in some of the posts and standards between test and analysis under 2 kN point load acting on the four connections. Table 4-27 further summarizes the difference between test and analysis results. It can be concluded that the axial force difference

91 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings between full-scale test and numerical analysis was about 38% for the bamboo members and about 22% for the metal members.

4.5 Anchorages for mixed scaffolding

As revealed experimentally and numerically in Table 4-25, the four connections on a Type 1 mixed scaffolding were found not suitable to anchor safety harness. We have conducted a similar numerical analysis on a Type 2 mixed scaffolding with span 1.3 m and using normal steel tube (size: 48.3 × 2.3 mm; E = 200 GPa; characteristic yield strength = 235 N/mm²) as main ledgers, the load-carrying capacity of main ledger-post connection was found to be around 4.75 kN. This suggests that the connection on Type 2 mixed scaffolding is also not a good anchorage location for safety harness.

For Type 3 mixed scaffolding, the steel ledger (48.3×2.3 mm) has a larger load-carrying capacity due to the use of right angle couplers. Assume that the support condition of the metal ledger are clamped supports with a span of 1.3m, the load-carrying capacity at the midpoint is 5.3 kN under the yield strength of 235 N/mm² (or 7.95 kN under the yield strength 350 N/mm²). It can be briefly concluded that the Type 3 mixed scaffolding also cannot provide safe anchorages to resist the drop force of 4 kN with a safety factor of 2 even when an energy absorber lanyard or SRL/Fall limiter is used.

92 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Fig. 4-1 Normal steel tube (left) and anti-sliding steel tube (right)

93 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

(a) Test for slippage stiffness (b) Test for rotational stiffness Fig. 4-2 Test setup for normal steel tube-bamboo connection

1.2

1

0.8 1

UTM Force (kN) Force UTM 2 0.6 3 4 0.4 5 0.2

0 0 10 20 30 40 50 60 70 UTM Displacement (mm)

(a) Load-displacement curves

94 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

1.2 y = 0.056x

1 y = 0.068x y = 0.063x y = 0.053x y = 0.063x 0.8

UTM Force (kN) Force UTM 1

0.6 2 3

0.4 4 5

0.2

0 0 5 10 15 20 25 UTM Displacement (mm)

(b) Initial slippage Fig. 4-3 Slippage tests for normal steel tube (post)-bamboo (ledger) connection

0.6

0.5

0.4 1 0.3

2 UTM Force (kN) Force UTM 0.2 3 0.1

0 0 10 20 30 40 50 60 70 -0.1 UTM Displacement (mm)

(a) Load-displacement curves

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0.07

0.06 y = 0.124x

M (kN·m) M 0.05 y = 0.109x y = 0.100x 0.04 1 0.03 2 3 0.02

0.01

0 0 0.1 0.2 0.3 0.4 0.5 -0.01 θ (rad)

(b) M − θ curves Fig. 4-4 Rotational tests for normal steel tube (post)-bamboo (ledger) connection

1

12.5, 0.76

0.5 Force (kN) Force 0 -60 -40 -20 0 20 40 60 -0.5 -12.5, -0.76

-1 Relative displacement (mm)

(a) Slippage stiffness

0.35 M=0.11× θ 0.3 0.25

0.2 M (kN·m) M 0.15 0.1 0.05 M=0 θ (rad) 0 -4 -2 0 2 4

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(b) Rotational stiffness Fig. 4-5 Modeling of normal steel tube-bamboo connection

Fig. 4-6 Test setup for connection involving anti-sliding steel tube

(a) 0° orientation (b) 45° orientation (c) 90° orientation

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(d) 135° orientation (e) 180° orientation Fig. 4-7 Five different orientation angles for the anti-sliding steel tube

(a) 0° orientation (b) 45° orientation (c) 90° orientation Fig. 4-8 Splitting of plastic stripes for 0°, 45° and 90° orientation

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Horizontal member: BP & 0° orientation

4 Connection resistance 3.5 Second bump

3 UTM Force (kN) Force UTM 2.5

2 Slipping force 1.5 First bump 1

0.5 Initial slippage 0 0 20 40 60 80 100 120 140 160 UTM Displacement (mm)

(a) With initial slippage

Horizontal member: BP & 0° orientation 4

3.5

3

UTM Force (kN) Force UTM 2.5

2

1.5

1

0.5

0 0 10 20 30 40 50 60 70 80 UTM Displacement (mm)

(b) Without initial slippage Fig. 4-9 Load-displacement curves for anti-sliding steel tube-bamboo connection

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(a) Damage of bamboo for 180° orientation

Horizontal member: BP & 180° orientation 2.5

2

UTM Force (kN) Force UTM 1.5

1

0.5

0 0 10 20 30 40 50 60 UTM Displacement (mm)

(b) Load-displacement curve for 180° orientation Fig. 4-10 Failure mode for 180° orientation of anti-sliding steel tube-bamboo connection

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(a) Rotation failure of horizontal tube for 180° orientation

Horizontal member: normal steel tube & 180° orientation 3

2.5

2 UTM Force (kN) Force UTM 1.5

1

0.5

0 0 10 20 30 40 50 60 UTM Displacement (mm) (b) Load-displacement curve for 180° orientation Fig. 4-11 Failure mode for 180° orientation of anti-sliding steel tube-normal steel tube connection

Inner layer

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Fig. 4-12 Illustration of anti-sliding steel tube orientation with transom

Fig. 4-13 Right-angle coupler (left) and swivel coupler (right)

Bracing (outer layer): Kao Jue

Ledger: Kao Jue Post (inner layer): Kao Jue

Post (outer layer): Mao Jue

1.3 m Ledger on the first Standard (outer lift: Mao Jue layer): Kao Jue

Fig. 4-14 Typical configuration of a double-layered bamboo scaffolding (DLBS)

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Anti-sliding tube

Ledger: Kao Jue

Standard (outer layer): Kao Jue Ledger on the first 1.3 m lift: Mao Jue

(a) Type 1 mixed scaffolding

Tube size: 48.3×2.3 mm. Vertical tube (anti-sliding)

Horizontal tube (normal)

1.3 m

(b) Type 2 mixed scaffolding

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1.3 m

(c) Type 3 mixed scaffolding Fig. 4-15 Three different types of mixed scaffolding

2m

One bay 1.3m

Fig. 4-16 A one-bay unboarded lift of scaffolding

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(a) Type 1 platform: wooden boards or iron planks placed on transoms

(b) Type 2 platform: closely-spaced bamboo members Fig. 4-17 Two types of platform commonly used in scaffolding

(a) Type 1 platform (b) Type 2 platform Fig. 4-18 Modeling of scaffolding platforms

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(a) Dimension of metal bracket

(b) Modeling of metal bracket Fig. 4-19 Dimension and modeling of metal bracket

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(a) Front view of the scaffolding

(b) Dimension of the scaffolding Fig. 4-20 The full-scale mixed scaffolding used for test

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10 kN/15 kN

(a) UDL test on two spans of platform

5 kN/10 kN

(b) UDL test on single span of platform Fig. 4-21 Test arrangement for UDL test on platform

(2)

(4)

(1)

(3)

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Fig. 4-22 Test arrangement for static point load test on connection

(a) Two spans of bottom platform (b) Two spans of upper platform

(c) Middle span of bottom platform (d) Middle span of upper platform Fig. 4-23 Setup of UDL test for platform

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(a) Middle span of the bottom platform under 10 kN (10.3 kN/m²) load

(b) Two spans of the upper platform under 15 kN (7.6 kN/m²) load Fig. 4-24 UDL test on platform

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Post 2 Post 4 Post 6 Post 8 Post 1 Post 3 Post 5 Post 7

Brace 1 Brace 2

Standard 1 Standard 2 Standard 3

Fig. 4-25 Labeling of metal post and bamboo standard

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Fig. 4-26 Setup of static point load test on connection

30

25

20 1st Test

15 2nd Test Diplacement (mm) Diplacement

10 3rd Test

5

0 0 0.5 1 1.5 2 2.5 Point load (kN)

(a) Load-displacement curve for Connection (1)

25

20

15 1st Test

2nd Test Displacement (mm) Displacement 10 3rd Test 5

0 0 0.5 1 1.5 2 2.5 Point load (kN)

(b) Load-displacement curve for Connection (3)

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Fig. 4-27 Load-displacement curves for Connections (1) and (3) (see Fig. 4-22)

3.5 3.23 3

2.5

2 Point (kN) load 1.5

1

0.5

0 0 10 20 30 40 50 60 Displacement (mm)

(a) Failure of Connection (1)

5 4.55 4.5 4 3.5

3 Point (kN) load 2.5 2 1.5 1 0.5 0 0 10 20 30 40 50 Displacement (mm) (b) Failure of Connection (4) Fig. 4-28 Failure of Connections (1) and (4) under static point load

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30

25

20 SAP 2000

Diplacement (mm) Diplacement 1st Test 15 2nd Test 10 3rd Test

5

0 0 0.5 1 1.5 2 2.5 Point load (kN)

(a) Load-displacement curve for Connection (1)

25

20

15 SAP 2000

1st Test Displacement (mm) Displacement 10 2nd Test 3rd Test 5

0 0 0.5 1 1.5 2 2.5 Point load (kN) (b) Load-displacement curve for Connection (3) Fig. 4-29 Comparison of load-displacement curves between test and analysis

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Table 4-1 Resistance for normal steel tube-bamboo connection No. of Connection resistance Test series Presence No. of round (kN) of nodes tests Horizontal member Vertical member turns Mean Std BP Normal steel tube No 5 5 0.76 0.09 Normal steel tube BP No 5 5 0.80 0.14 Normal steel tube Normal steel tube No 5 5 0.74 0.13 Normal steel tube BP Yes 5 4 2.20 0.36

Table 4-2 Rotational stiffness for normal steel tube-bamboo connection No. of Rotational stiffness Test series No. of round (kN·m/rad) tests Horizontal member Vertical member turns Mean Std BP Normal steel tube 5 3 0.111 0.01 Normal steel tube Normal steel tube 5 3 0.109 0.003 Total 0.110 0.007

Table 4-3 Test results for anti-sliding steel tube-bamboo/normal steel tube connection Test series Initial No. of Total slippage Connection Slippage test with No. of distance resistance displacement Horizontal Vertical Angle initial tests (average over (kN) (mm) member member (°) slippage 푁 푁) 푛 mm Mean Std Mean Std 0 5 4 10.92 3.36 0.11 61.33 5.69 Anti- 45 5 3 4.20 2.81 0.24 54.05 6.28 Bamboo sliding 90 5 4 7.95 2.60 0.25 55.68 7.11 steel tube 135 5 / / 0.82 0.10 / / 180 5 1 1.20 1.81 0.45 20.24 9.81 0 5 2 2.95 3.42 0.23 52.08 5.80 Anti- 45 5 3 2.70 2.94 0.28 49.95 6.20 Normal sliding 90 5 4 5.85 2.50 0.43 51.00 4.93 steel tube steel tube 135 5 / / 0.88 0.16 / / 180 5 1 1.80 2.02 0.56 10.16 6.01

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Table 4-4 Connection resistance for 0°, case 45° and case 90° orientation Horizontal Bamboo Normal steel tube member 0° 45° 90° 0° 45° 90° 3.42 2.36 2.39 3.57 2.59 2.80 Connection 3.55 2.75 3.01 2.98 2.78 2.58 resistance 3.24 2.99 2.73 3.65 3.22 3.04 (kN) 3.26 2.96 2.33 3.47 2.79 2.28 3.34 2.97 2.52 3.41 3.33 1.81 Mean (kN) 3.36 2.81 2.60 3.42 2.94 2.50 Std (kN) 0.11 0.24 0.25 0.23 0.28 0.43 Overall (kN) Mean = 2.92 Std = 0.39 Mean = 2.95 Std = 0.49

Table 4-5 Total displacement for 0°, case 45° and case 90° orientation Horizontal Bamboo Normal steel tube member 0° 45° 90° 0° 45° 90° 65.05 64.48 51.04 56.33 46.10 55.52 Total 62.39 44.79 59.56 43.36 44.28 52.96 Displacement 51.88 54.36 47.88 47.53 55.38 56.12 (mm) 58.84 54.16 52.27 54.01 44.67 43.90 68.48 52.45 67.66 59.15 59.33 46.49 Mean (mm) 61.33 54.05 55.68 52.08 49.95 51.00 Std (mm) 5.69 6.28 7.11 5.80 6.20 4.93 Overall (mm) Mean = 57.02 Std = 7.11 Mean = 51.01 Std = 5.73

Table 4-6 Properties for various types of couplers Characteristic Safe load or Coupler type Resistance values moment Class A Class B Class A Class B Right angle coupler Slippage force Fs (kN) 10.0 15.0 6.1 9.1 Swivel coupler Slippage force Fs (kN) 10.0 15.0 6.1 9.1 Parallel coupler Slippage force Fs (kN) 10.0 15.0 6.1 9.1 Slippage force Fs (kN) 6.0 9.0 3.6 5.5 Friction type sleeve Bending moment coupler 2.4 1.5 (kN·m) Internal joint pin Slippage force (kN) Safe load = 0 kN A) (expanding spigot A) coupler) Shear strength (kN) Safe load = 21.0 kN Putlog coupler Slippage force Fs (kN) Safe load = 0.63 kN A) Note 1: These figures are extracted from Annex C of BS EN 12811-1 [22]. Note 2: A) From BS 5975 [23].

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Table 4-7 Material required for a one-bay unboarded lift Mao Jue Kao Jue Steel tube Scaffolding Net Net Net Number of Overlap Overlap Overlap type length length length couplers factor factor factor (m) (m) (m) Bamboo 2 11.7 / / 0 Type 1 / 8.4 5.3 1.0 0 1.5 1.5 Type 2 / 5.8 7.9 1.1 0 Type 3 / 5.8 7.9 1.01 4.5 Note: The consumption of plastic stripes is not included.

Table 4-8 Material cost for scaffoldings Material price of an unboarded lift one bay long (1.3 m) Length of Cost of Ratio to Scaffolding Length of tube or Mao Total price Kao Jue fittings bamboo type Jue (m) (HKD) (m) (HKD) scaffold Bamboo 3 (PP) 17.6 4 39 1.0 5.3 (anti-sliding steel Type 1 12.6 4 235 6.0 tube) 8.7 (normal steel tube Type 2 3.4 m; anti-sliding 8.7 4 331 8.4 steel tube 5.3 m) Type 3 8.0 (normal steel tube) 8.7 47 300 7.7 Note: The price of Kao Jue, Mao Jue, normal tube and anti-sliding tube are HK$1.5/m, HK$3.0/m, HK$30/m and HK$40/m respectively; The price of coupler is HK$10/Unit; The price of plastic stripes is HK$0.83/m² based on quantity analysis by WLS Scaffolding Works Co. Ltd. [29].

Table 4-9 Equivalent density for scaffoldings Density under natural Equivalent density Increasing Material condition factor kN/m³ kg/m (kN/m³) Kao Jue 7.82 1.5 11.7 0.69 Mao Jue 9.35 1.5 14.0 1.95 Type 1 1.0 77.0 2.60 Steel Type 2 77.00 1.1 84.7 2.86 tube Type 3 1.23 94.7 3.20 Note: The mass of coupler is assumed to be 1 kg each.

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Table 4-10 Self-weight and weight distribution of a one-bay unboarded lift Scaffolding type Outer layer (kg) Inner layer (kg) Ratio Total weight (kg) Bamboo 9.28 2.69 3.45 11.97 Type 1 13.07 6.51 2.01 19.58 Type 2 16.74 9.85 1.70 26.59 Type 3 18.31 10.97 1.67 29.28 Note: Ratio = weight of outer layer / weight of inner layer.

Table 4-11 Allowable loads for scaffolding platforms Allowable UDL on Platform type Scaffolding type Failure components platform (kN/m²) Bamboo 3.23 Type 1: Type 1 3.23 wooden boards Type 2 3.75 Type 3 3.75 Bamboo transom Bamboo 3.50 between posts Type 2: Type 1 3.50 closely-spaced Type 2 4.00 bamboo members Type 3 3.95 Note: Considering a single factor of 2.25 for bamboo, the maximum allowable stress against bending for Kao Jue is 26.0 N/mm² under normal supply condition.

Table 4-12 Maximum deflections for scaffolding platforms Maximum member Maximum member Scaffolding deflection under 1.5 kN/m² deflection under 3.0 kN/m² Platform type type Deflection Deflection Member Member (mm) (mm) Bamboo 6.8 13.6 Ledger of inner Ledger of inner Type 1: Type 1 6.8 13.6 layer layer wooden Type 2 6.1 12.3 boards Transom Transom Type 3 1.1 2.2 (midpoint) (midpoint) Bamboo 6.7 13.3 Ledger of inner Ledger of inner Type 1 6.7 13.3 layer layer Type 2: Type 2 6.2 12.3 closely-spaced Middle Middle bamboo longitudinal longitudinal members Type 3 1.1 bamboo or 2.2 bamboo or transom transom (midpoint) (midpoint)

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Table 4-13 Allowable buckling loads for metal and bamboo posts Allowable buckling Buckling strength Material Safety factor load (kN) (kN) Metal post 9.13 1.65 5.53 (48.3×2.3 mm) Bamboo inner post 2.31 2.25 1.54 (Kao Jue) Bamboo outer post 9.33 2.25 6.22 (Mao Jue)

Note: The material factor (푟푚=1.5) of bamboo column was considered in buckling strength.

Table 4-14 Allowable heights of scaffoldings Maximum force in posts for a zone (kN) Scaffolding Allowable Inner layer Outer layer Duty type height (m) Live Live Self-weight Total Self-weight Total load load Bamboo 16 0.22 1.32 1.54 0.72 1.37 2.09 Light Type 1 62 1.98 1.32 3.30 4.31 1.23 5.54 duty Type 2 48 2.33 1.35 3.68 4.29 1.24 5.53 Type 3 52 2.82 1.33 4.15 4.24 1.26 5.50 Bamboo scaffolding cannot be used for heavy-duty purpose Heavy Type 1 44 1.42 2.47 3.89 3.20 2.29 5.49 duty Type 2 36 1.72 2.51 4.23 3.26 2.31 5.57 Type 3 40 2.17 2.47 4.64 3.21 2.34 5.55 Note 1: For simplicity, only the working platforms are boarded in calculation of height and this assumption is acceptable for the purpose of comparison. Note 2: The real erection height of scaffolding can be increased by separating the whole scaffolding into different zones by installing brackets at corresponding levels.

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Table 4-15 Test data for Fook Shing anchor bolts [2, 3] (a) Spring coefficients for Fook Shing anchor bolts Concrete panel Low strength (25 MPa) Standard strength (65 MPa)

퐾퐻 (kN/cm) 15 25 퐾푉 (kN/cm) 30 50 (b) Average pull-out and shear strengths for Fook Shing anchor bolts

Concrete panel Pull-out strength 푁푅푢,푚 (kN) Shear strength 푉푅푢,푚 (kN) Low strength (25 MPa) 11.3 18.7 Standard strength (65 MPa) 18.2 30.1

Table 4-16 Safety of anchor bolt and bracket for scaffolding with allowable height Maximum axial Safety check of anchor bolts and metal bracket Scaffolding force in posts (kN) Force in top anchor bolt Maximum Duty type Inner Outer Pull-out Shear 푁 1.5 푉 1.5 stress in steel ( 푆 ) + ( 푆 ) layer layer force (kN) force (kN) 푁푅푢,푚 푉푅푢,푚 (MPa) Bamboo 1.54 2.09 1.55 1.20 0.07 35.89 Light Type 1 3.3 5.54 3.94 2.93 0.27 81.64 duty Type 2 3.68 5.53 4.02 3.05 0.28 88.16 Type 3 4.15 5.50 4.10 3.20 0.29 96.14 Bamboo scaffolding cannot be used for heavy-duty purpose Heavy Type 1 3.89 5.49 4.04 3.11 0.28 91.61 Duty Type 2 4.23 5.57 4.16 3.25 0.30 97.83 Type 3 4.64 5.55 4.23 3.38 0.31 104.83

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Table 4-17 Comparison of three mixed scaffoldings and bamboo scaffolding Bamboo Mixed scaffolding Pure metal Issue scaffolding Type 1 Type 2 Type 3 scaffolding Material cost for a one-bay unboarded lift 39 235 331 300 405 (HKD) Self-weight for a one-bay unboarded lift 11.97 19.58 26.59 29.28 36.08 (kg) Sensitive to the environment Yes Middle No No No Construction time Fast Middle Middle Slow Slow Allowable load (UDL) on wooden-board 3.23 3.23 3.75 3.75 6.00 platform (kN/m²) Allowable height within Light duty 16 62 48 52 42 a single zone (m) Heavy duty - 44 36 40 32 Max. deflection of wooden-board 13.6 13.6 12.3 2.2 5.5 platform under UDL of 3.0 kN/m² (mm) Resistance (kN) 0.9 2.92 2.95 10.0 10.0 Typical beam-column connection Slippage 56.2 51.2 57.8 - - stiffness (kN/m)

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Table 4-18 Results for UDL test on platform (a) 5 kN (UDL = 5.1 kN/m²) on the middle span of upper platform Measured Strain Young's Cross section area 퐴 axial force modulus Component Outside Mean Std 퐸 Thickness 퐴 Mean Std diameter × 10−6휀 kN/mm² mm mm mm² kN Post 2 -1.1 0.7 204 48.2 2.23 322.1 -0.07 0.04 Post 4 -19.1 0.9 204 48.2 2.23 322.1 -1.26 0.06 Back Post 6 -20.0 1.3 204 48.2 2.23 322.1 -1.31 0.08 Post 8 0.4 0.3 204 48.2 2.23 322.1 0.03 0.02 Post 1 1.4 4.4 204 48.2 2.23 322.1 0.09 0.29 Post 3 -16.1 0.8 204 48.2 2.23 322.1 -1.06 0.05 Post 5 -17.4 2.6 204 48.2 2.23 322.1 -1.14 0.17 Front Post 7 0.6 0.4 204 48.2 2.23 322.1 0.04 0.02 Standard 1 -0.4 0.2 8.55 49.7 6.34 863.3 -0.003 0.001 Standard 2 -8.2 1.4 8.55 43.3 5.53 656.1 -0.05 0.01 (b) 5 kN (UDL = 5.1 kN/m²) on the middle span of bottom platform Measured Strain Young's Cross section area 퐴 axial force modulus Component Outside Mean Std 퐸 Thickness 퐴 Mean Std diameter × 10−6휀 kN/mm² mm mm mm² kN Post 2 -1.00 0.7 204 48.2 2.23 322.1 -0.07 0.05 Post 4 -14.77 0.3 204 48.2 2.23 322.1 -0.97 0.02 Back Post 6 -24.66 1.3 204 48.2 2.23 322.1 -1.62 0.08 Post 8 0.78 0.2 204 48.2 2.23 322.1 0.05 0.01 Post 1 1.62 0.3 204 48.2 2.23 322.1 0.11 0.02 Post 3 -13.42 1.6 204 48.2 2.23 322.1 -0.88 0.10 Post 5 -14.47 0.8 204 48.2 2.23 322.1 -0.95 0.05 Front Post 7 0.57 0.3 204 48.2 2.23 322.1 0.04 0.02 Standard 1 -0.33 0.4 8.55 49.7 6.34 863.3 -0.002 0.003 Standard 2 -9.06 3.2 8.55 43.3 5.53 656.1 -0.05 0.02

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(c) 10 kN (UDL = 10.3 kN/m²) on the middle span of upper platform Measured Strain Young's Cross section area 퐴 axial force modulus Component Outside Mean Std 퐸 Thickness 퐴 Mean Std diameter × 10−6휀 kN/mm² mm mm mm² kN Post 2 -0.9 0.4 204 48.2 2.23 322.1 -0.06 0.03 Post 4 -36.3 0.9 204 48.2 2.23 322.1 -2.38 0.06 Back Post 6 -38.6 0.5 204 48.2 2.23 322.1 -2.54 0.03 Post 8 -1.0 1.2 204 48.2 2.23 322.1 -0.07 0.08 Post 1 2.3 0.6 204 48.2 2.23 322.1 0.15 0.04 Post 3 -34.1 2.1 204 48.2 2.23 322.1 -2.24 0.14 Post 5 -35.5 1.5 204 48.2 2.23 322.1 -2.33 0.10 Front Post 7 1.0 0.8 204 48.2 2.23 322.1 0.066 0.05 Standard 1 -1.1 0.3 8.55 49.7 6.34 863.3 -0.008 0.002 Standard 2 -17.4 4.2 8.55 43.3 5.53 656.1 -0.098 0.02 (d) 10 kN (UDL = 10.3 kN/m²) on the middle span of bottom platform Measured Strain Young's Cross section area 퐴 axial force modulus Component Outside Mean Std 퐸 Thickness 퐴 Mean Std diameter × 10−6휀 kN/mm² mm mm mm² kN Post 2 -1.7 0.7 204 48.2 2.23 322.1 -0.11 0.04 Post 4 -35.2 0.6 204 48.2 2.23 322.1 -2.31 0.04 Back Post 6 -40.0 3.1 204 48.2 2.23 322.1 -2.63 0.20 Post 8 -0.6 0.8 204 48.2 2.23 322.1 -0.04 0.06 Post 1 2.5 0.7 204 48.2 2.23 322.1 0.16 0.05 Post 3 -26.3 0.8 204 48.2 2.23 322.1 -1.73 0.06 Post 5 -33.9 0.4 204 48.2 2.23 322.1 -2.23 0.03 Front Post 7 1.0 0.8 204 48.2 2.23 322.1 0.07 0.05 Standard 1 -0.5 0.7 8.55 49.7 6.34 863.3 -0.004 0.005 Standard 2 -14.8 4.7 8.55 43.3 5.53 656.1 -0.08 0.03

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(e) 10 kN (UDL = 5.0 kN/m²) on the two spans of upper platform Measured Strain Young's Cross section area 퐴 axial force modulus Component Outside Mean Std 퐸 Thickness 퐴 Mean Std diameter × 10−6휀 kN/mm² mm mm mm² kN Post 2 -14.7 1.4 204 48.2 2.23 322.1 -0.96 0.09 Post 4 -34.3 0.5 204 48.2 2.23 322.1 -2.26 0.03 Back Post 6 -13.5 1.2 204 48.2 2.23 322.1 -0.89 0.08 Post 8 1.0 1.2 204 48.2 2.23 322.1 0.07 0.08 Post 1 -12.0 2.8 204 48.2 2.23 322.1 -0.79 0.19 Post 3 -36.3 2.9 204 48.2 2.23 322.1 -2.38 0.19 Post 5 -14.2 1.3 204 48.2 2.23 322.1 -0.93 0.09 Front Post 7 1.8 0.6 204 48.2 2.23 322.1 0.12 0.04 Standard 1 -11.1 2.4 8.55 49.7 6.34 863.3 -0.08 0.02 Standard 2 -10.8 3.1 8.55 43.3 5.53 656.1 -0.06 0.02 (f) 10 kN (UDL = 5.0 kN/m²) on the two spans of bottom platform Measured Strain Young's Cross section area 퐴 axial force modulus Component Outside Mean Std 퐸 Thickness 퐴 Mean Std diameter × 10−6휀 kN/mm² mm mm mm² kN Post 2 -20.8 0.5 204 48.2 2.23 322.1 -1.37 0.03 Post 4 -29.7 0.5 204 48.2 2.23 322.1 -1.95 0.03 Back Post 6 -22.1 0.3 204 48.2 2.23 322.1 -1.45 0.02 Post 8 -1.3 0.7 204 48.2 2.23 322.1 -0.08 0.05 Post 1 -11.4 0.9 204 48.2 2.23 322.1 -0.75 0.06 Post 3 -34.9 5.4 204 48.2 2.23 322.1 -2.29 0.36 Post 5 -22.0 4.6 204 48.2 2.23 322.1 -1.45 0.30 Front Post 7 1.5 0.8 204 48.2 2.23 322.1 0.10 0.05 Standard 1 -13.8 4.0 8.55 49.7 6.34 863.3 -0.10 0.03 Standard 2 -12.6 3.1 8.55 43.3 5.53 656.1 -0.07 0.02

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(g) 15 kN (UDL = 7.6 kN/m²) on the two spans of upper platform Measured Strain Young's Cross section area 퐴 axial force modulus Component Outside Mean Std 퐸 Thickness 퐴 Mean Std diameter × 10−6휀 kN/mm² mm mm mm² kN Post 2 -24.2 1.0 204 48.2 2.23 322.1 -1.59 0.07 Post 4 -52.6 1.0 204 48.2 2.23 322.1 -3.45 0.07 Back Post 6 -22.1 0.8 204 48.2 2.23 322.1 -1.45 0.05 Post 8 0.5 2.9 204 48.2 2.23 322.1 0.03 0.19 Post 1 -20.2 0.6 204 48.2 2.23 322.1 -1.32 0.04 Post 3 -57.3 1.3 204 48.2 2.23 322.1 -3.76 0.09 Post 5 -22.3 1.0 204 48.2 2.23 322.1 -1.46 0.07 Front Post 7 2.0 0.7 204 48.2 2.23 322.1 0.13 0.05 Standard 1 -18.2 4.0 8.55 49.7 6.34 863.3 -0.13 0.03 Standard 2 -15.8 6.1 8.55 43.3 5.53 656.1 -0.09 0.03 (h) 15 kN (UDL = 7.6 kN/m²) on the two spans of bottom platform Measured Strain Young's Cross section area 퐴 axial force modulus Component Outside Mean Std 퐸 Thickness 퐴 Mean Std diameter × 10−6휀 kN/mm² mm mm mm² kN Post 2 -29.0 0.8 204 48.2 2.23 322.1 -1.91 0.05 Post 4 -49.3 1.0 204 48.2 2.23 322.1 -3.24 0.07 Back Post 6 -31.8 0.2 204 48.2 2.23 322.1 -2.09 0.02 Post 8 -1.4 0.3 204 48.2 2.23 322.1 -0.09 0.02 Post 1 -16.2 0.8 204 48.2 2.23 322.1 -1.06 0.06 Post 3 -48.4 8.3 204 48.2 2.23 322.1 -3.18 0.55 Post 5 -35.4 0.5 204 48.2 2.23 322.1 -2.33 0.03 Front Post 7 2.7 0.5 204 48.2 2.23 322.1 0.18 0.03 Standard 1 -11.3 3.5 8.55 49.7 6.34 863.3 -0.08 0.03 Standard 2 -15.5 4.1 8.55 43.3 5.53 656.1 -0.09 0.02

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Table 4-19 Comparison of UDL test results with computer analysis (a) 5 kN (UDL = 5.1 kN/m²) on the middle span of upper platform Difference Measured axial force Analyzed Component 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% (mean value) (kN) value (kN) 푚푒푎푠푢푟푒푑 Post 4 -1.26 -1.1 12% Back Post 6 -1.31 -1.08 18% Post 3 -1.06 -1.29 22% Front Post 5 -1.14 -1.29 13% Standard 2 -0.05 -0.06 31% Note: Axial forces obtained from strain values smaller than or around its precision (1 × 10−6휀) was not considered in comparison. (b) 5 kN (UDL = 5.1 kN/m²) on the middle span of bottom platform Difference Measured axial force Analyzed Component 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% (mean value) (kN) value (kN) 푚푒푎푠푢푟푒푑 Post 4 -0.97 -1.2 24% Back Post 6 -1.62 -1.21 25% Post 1 0.11 0.07 34% Post 3 -0.88 -1.18 34% Front Post 5 -0.95 -1.20 26% Standard 2 -0.05 -0.06 18% Note: Axial forces obtained from strain values smaller than or around its precision (1 × 10−6휀) was not considered in comparison. (c) 10 kN (UDL = 10.3 kN/m²) on the middle span of upper platform Difference Measured axial force Analyzed Component 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% (mean value) (kN) value (kN) 푚푒푎푠푢푟푒푑 Post 4 -2.38 -2.18 9% Back Post 6 -2.54 -2.17 15% Post 1 0.15 0.09 40% Post 3 -2.24 -2.58 15% Front Post 5 -2.33 -2.59 11% Standard 2 -0.098 -0.13 33% Note: Axial forces obtained from strain values smaller than or around its precision (1 × 10−6휀) was not considered in comparison.

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(d) 10 kN (UDL = 10.3 kN/m²) on the middle span of bottom platform Difference Measured axial force Analyzed Component 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% (mean value) (kN) value (kN) 푚푒푎푠푢푟푒푑 Post 2 -0.11 -0.15 34% Back Post 4 -2.31 -2.42 5% Post 6 -2.63 -2.43 8% Post 1 0.16 0.14 15% Post 3 -1.73 -2.35 36% Front Post 5 -2.23 -2.39 7% Standard 2 -0.08 -0.12 45% Note: Axial forces obtained from strain values smaller than or around its precision (1 × 10−6휀) was not considered in comparison. (e) 10 kN (UDL = 5.0 kN/m²) on the two spans of upper platform Difference Measured axial force Analyzed Component 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% (mean value) (kN) value (kN) 푚푒푎푠푢푟푒푑 Post 2 -0.96 -1.11 15% Back Post 4 -2.26 -2.2 2% Post 6 -0.89 -1.15 30% Post 1 -0.79 -1.11 41% Post 3 -2.38 -2.85 20% Post 5 -0.93 -1.25 34% Front Post 7 0.12 0.10 14% Standard 1 -0.08 -0.08 2% Standard 2 -0.06 -0.09 49% Note: Axial forces obtained from strain values smaller than or around its precision (1 × 10−6휀) was not considered in comparison.

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(f) 10 kN (UDL = 5.0 kN/m²) on the two spans of bottom platform Difference Measured axial force Analyzed Component 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% (mean value) (kN) value (kN) 푚푒푎푠푢푟푒푑 Post 2 -1.37 -1.29 6% Back Post 4 -1.95 -2.43 25% Post 6 -1.45 -1.34 8% Post 1 -0.75 -0.92 23% Post 3 -2.29 -2.65 16% Post 5 -1.45 -1.08 25% Front Post 7 0.10 0.12 22% Standard 1 -0.10 -0.07 31% Standard 2 -0.07 -0.09 28% Note: Axial forces obtained from strain values smaller than or around its precision (1 × 10−6휀) was not considered in comparison. (g) 15 kN (UDL = 7.6 kN/m²) on the two spans of upper platform Difference Measured axial force Analyzed Component 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% (mean value) (kN) value (kN) 푚푒푎푠푢푟푒푑 Post 2 -1.59 -1.67 5% Back Post 4 -3.45 -3.31 4% Post 6 -1.45 -1.73 19% Post 1 -1.32 -1.67 26% Post 3 -3.76 -4.27 14% Post 5 -1.46 -1.88 29% Front Post 7 0.13 0.15 14% Standard 1 -0.13 -0.11 18% Standard 2 -0.09 -0.14 58% Note: Axial forces obtained from strain values smaller than or around its precision (1 × 10−6휀) was not considered in comparison.

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(h) 15 kN (UDL = 7.6 kN/m²) on the two spans of bottom platform Difference Measured axial force Analyzed Component 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% (mean value) (kN) value (kN) 푚푒푎푠푢푟푒푑 Post 2 -1.91 -1.95 2% Back Post 4 -3.24 -3.66 13% Post 6 -2.09 -2.01 4% Post 1 -1.06 -1.37 29% Post 3 -3.18 -3.96 24% Post 5 -2.33 -1.62 30% Front Post 7 0.18 0.19 8% Standard 1 -0.08 -0.11 32% Standard 2 -0.09 -0.13 50% Note: Axial forces obtained from strain values smaller than or around its precision (1 × 10−6휀) was not considered in comparison.

Table 4-20 Summary of UDL test and analysis

푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 퐷𝑖푓푓푒푟푒푛푐푒 = | | × 100% Applied 푚푒푎푠푢푟푒푑 UDL test cases UDL Metal tube Bamboo Max Average Std Max Average Std Upper 5 kN 22% 16% 4% 31% / / platform 10 kN 40% 18% 11% 33% / / Middle span Bottom 5 kN 34% 29% 4% 18% / / platform 10 kN 36% 18% 13% 45% / / Upper 10 kN 41% 22% 13% 49% 26% 24% platform 15 kN 29% 16% 9% 58% 38% 20% Two spans Bottom 10 kN 25% 18% 8% 31% 29% 2% platform 15 kN 30% 16% 11% 50% 41% 9% Total 41% 19% 11% 58% 33% 15% Note: “/” means there is only one bamboo member with strain value larger than its precision (1 × 10−6휀), see Table 4-19 (a)-(d).

Table 4-21 Displacement of connection under 2 kN static point load Displacement (mm) Connection 1st test 2nd test 3rd test (1) Bamboo-bamboo 22.81 18.10 17.87 (2) Bamboo-bamboo 25.27 17.17 16.30 (3) Bamboo-anti-sliding steel tube 19.87 14.48 13.59 (4) Bamboo-anti-sliding steel tube 22.63 15.75 15.27 129 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Table 4-22 Results for static point load test (2 kN) on connection (a) Connection (1) Measured Strain Young's Cross section area 퐴 axial force modulus Component Outside Mean Std 퐸 Thickness 퐴 Mean Std diameter × 10−6휀 kN/mm² mm mm mm² kN Post 1 1.4 1.1 204 48.2 2.23 322.1 0.09 0.08 Post 3 -14.1 0.3 204 48.2 2.23 322.1 -0.92 0.02 Post 5 -12.1 1.1 204 48.2 2.23 322.1 -0.80 0.07 Post 7 1.1 0.6 204 48.2 2.23 322.1 0.07 0.04 Front Standard 1 0.9 0.7 8.55 49.7 6.34 863.3 0.007 0.01 Standard 2 -7.2 1.9 8.55 43.3 5.53 656.1 -0.04 0.01 Standard 3 -0.9 0.3 8.55 50.0 6.38 874.4 -0.007 0.00 Brace 1 -3.3 0.6 204 48.2 2.23 322.1 -0.21 0.04 Brace 2 -4.0 0.4 204 48.2 2.23 322.1 -0.26 0.03 (b) Connection (2) Measured Strain Young's Cross section area 퐴 axial force modulus Component Outside Mean Std 퐸 Thickness 퐴 Mean Std diameter × 10−6휀 kN/mm² mm mm mm² kN Post 1 1.7 0.4 204 48.2 2.23 322.1 0.11 0.02 Post 3 -13.7 0.2 204 48.2 2.23 322.1 -0.90 0.01 Post 5 -10.9 1.1 204 48.2 2.23 322.1 -0.72 0.07 Post 7 1.2 0.5 204 48.2 2.23 322.1 0.08 0.03 Front Standard 1 1.1 0.8 8.55 49.7 6.34 863.3 0.008 0.01 Standard 2 -13.7 1.5 8.55 43.3 5.53 656.1 -0.08 0.01 Standard 3 -0.4 0.2 8.55 50.0 6.38 874.4 -0.003 0.001 Brace 1 -2.0 0.4 204 48.2 2.23 322.1 -0.13 0.03 Brace 2 -2.3 0.2 204 48.2 2.23 322.1 -0.15 0.01

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(c) Connection (3) Measured Strain Young's Cross section area 퐴 axial force modulus Component Outside Mean Std 퐸 Thickness 퐴 Mean Std diameter × 10−6휀 kN/mm² mm mm mm² kN Post 1 -2.3 0.4 204 48.2 2.23 322.1 -0.15 0.03 Post 3 -25.6 1.3 204 48.2 2.23 322.1 -1.68 0.08 Post 5 -1.0 1.2 204 48.2 2.23 322.1 -0.06 0.08 Post 7 -1.0 0.9 204 48.2 2.23 322.1 -0.07 0.06 Front Standard 1 -0.7 0.8 8.55 49.7 6.34 863.3 -0.005 0.01 Standard 2 -0.7 1.4 8.55 43.3 5.53 656.1 -0.004 0.01 Standard 3 -0.5 1.2 8.55 50.0 6.38 874.4 -0.004 0.01 Brace 1 -1.5 0.4 204 48.2 2.23 322.1 -0.10 0.02 Brace 2 -1.4 0.3 204 48.2 2.23 322.1 -0.09 0.02 (d) Connection (4) Measured Strain Young's Cross section area 퐴 axial force modulus Component Outside Mean Std 퐸 Thickness 퐴 Mean Std diameter × 10−6휀 kN/mm² mm mm mm² kN Post 1 -1.4 0.5 204 48.2 2.23 322.1 -0.09 0.04 Post 3 -25.7 0.2 204 48.2 2.23 322.1 -1.69 0.01 Post 5 -0.9 0.4 204 48.2 2.23 322.1 -0.06 0.02 Post 7 -1.1 0.5 204 48.2 2.23 322.1 -0.07 0.03 Front Standard 1 -1.0 0.6 8.55 49.7 6.34 863.3 -0.007 0.005 Standard 2 -1.3 0.5 8.55 43.3 5.53 656.1 -0.007 0.003 Standard 3 -0.2 0.5 8.55 50.0 6.38 874.4 -0.002 0.004 Brace 1 -3.0 0.7 204 48.2 2.23 322.1 -0.20 0.05 Brace 2 -2.1 0.3 204 48.2 2.23 322.1 -0.14 0.02

Table 4-23 Load-carrying capacity of connections Connection Tested failure load (kN) (1) Bamboo-bamboo 3.23 (2) Bamboo-bamboo 4.57 (3) Bamboo-anti-sliding steel tube 4.82 (4) Bamboo-anti-sliding steel tube 4.55

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Table 4-24 Comparison of connection displacement between test and analysis SAP 2000 with average SAP 2000 with measured Displacement bamboo ledger diameter bamboo ledger diameter Connection from 1st test Displacement Difference Displacement Difference (mm) (mm) (%) (mm) (%) (1) 22.81 30.2 32.4 19.7 -13.6 (2) 25.27 36.5 44.4 19.4 -23.2 (3) 19.87 25.3 27.3 21.3 7.2 (4) 22.63 25.1 10.9 22.3 -1.5 Note 1: The measured outside diameter and thickness of bamboo ledger is determined by the same procedure as in Section 2.4.3 Note 2: Difference= (Model-Test) / Test.

Table 4-25 Comparison of load-carrying capacity of connection SAP 2000 with average SAP 2000 with measured Testing bamboo ledger diameter bamboo ledger diameter Connection results (kN) Load-carrying Difference Load-carrying Difference capacity (kN) (%) capacity (kN) (%) (1) 3.23 2.05 -36.5 2.75 -14.9 (2) 4.57 2.0 -56.2 3.25 -28.9 (3) 4.82 3.0 -37.8 4.0 -17.0 (4) 4.55 3.0 -34.1 3.75 -17.6 Note: Difference= (Model-Test) / Test.

Table 4-26 Comparison of axial forces under 2.0 kN load (a) Connection (1) Difference Measured axial force Analyzed Component 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% (mean value) (kN) value (kN) 푚푒푎푠푢푟푒푑 Post 1 0.09 0.08 8% Post 3 -0.92 -0.84 9% Post 5 -0.80 -0.96 21% Front Standard 2 -0.04 -0.064 58% Brace 1 -0.21 -0.26 20% Brace 2 -0.26 -0.23 12% Note: Axial forces obtained from strain values smaller than or around its precision (1 × 10−6휀) was not considered in comparison.

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(b) Connection (2) Difference Measured axial force Analyzed Component 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% (mean value) (kN) value (kN) 푚푒푎푠푢푟푒푑 Post 1 0.11 0.10 14% Post 3 -0.90 -1.01 12% Post 5 -0.72 -1.03 43% Front Standard 2 -0.08 -0.063 18% Brace 1 -0.13 -0.10 24% Brace 2 -0.15 -0.09 38% Note: Axial forces obtained from strain values smaller than or around its precision (1 × 10−6휀) was not considered in comparison. (c) Connection (3) Difference Measured axial force Analyzed Component 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% (mean value) (kN) value (kN) 푚푒푎푠푢푟푒푑 Post 1 -0.15 -0.09 -42% Post 3 -1.68 -1.58 -6% Front Brace 1 -0.10 -0.13 31% Brace 2 -0.09 -0.08 -14% Note: Axial forces obtained from strain values smaller than or around its precision (1 × 10−6휀) was not considered in comparison. (d) Connection (4) Difference Measured axial force Analyzed Component 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% (mean value) (kN) value (kN) 푚푒푎푠푢푟푒푑 Post 1 -0.09 -0.08 -15% Post 3 -1.69 -1.61 -5% Front Brace 1 -0.20 -0.13 -36% Brace 2 -0.14 -0.08 -42% Note: Axial forces obtained from strain values smaller than or around its precision (1 × 10−6휀) was not considered in comparison.

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Table 4-27 Summary of connection test and analysis

푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 퐷𝑖푓푓푒푟푒푛푐푒 = | | × 100% Static 푚푒푎푠푢푟푒푑 Connection point load Metal tube Bamboo Max Average Std Max Average Std (1) 21% 14% 5% 58% / / (2) 43% 26% 12% 18% / / 2.0 kN (3) 42% 23% 14% / / / (4) 42% 25% 15% / / / Total 43% 22% 13% 58% 38% 20% Note: “/” means there is only one or no bamboo member with strain value larger than its precision (1 × 10−6휀), see Table 4-26 (a)-(d).

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Chapter 5 Use of Different Materials for the Working Platform

5.1 Types for the working platform

There are two types of working platform commonly used in the industry. First one is formed by placing wooden boards or pre-fabricated iron planks on transoms. The other one is by fastening bamboo members (Kao Jue) on transoms at a closely-spaced distance (≤ 150 mm) to form an integrated bamboo platform, above which thin wooden boards are usually placed for ease of work as well as to prevent debris/objects falling through. In this chapter, the safety of the following three commonly used platform Types were investigated numerically and experimentally:

(1) Type 1: Integrated bamboo members with thin wooden boards, see Fig. 5-1 (a); (2) Type 2: Thick wooden boards, see Fig. 5-1 (b); (3) Type 3: Pre-fabricated iron planks, see Fig. 5-1 (c).

5.2 Mechanical properties of wooden boards and iron planks

The material properties of bamboo (Kao Jue) have been studied in previous investigations. Please see Appendix B1 for a summary. The wooden boards used in this study were purchased from the market and were made of plywood as seen in Fig. 5-2. Both the thick and thin wooden boards have a width of 200 mm and with a thickness of 25 mm and 12 mm, respectively. The iron planks were provided by the Sinoscaff (HK) Ltd. with dimensions shown in Fig. 5-3.

Three-point loading tests were used to evaluate the flexure modulus and the ultimate bending strength of the wooden boards and the iron planks. Specimens were placed in 135 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings the Dartec loading machine with round pin supports at both ends. Load was added at the middle of specimens through a round tube as shown in Fig. 5-4. The distance between two simply supported pins for wooden board test and iron plank test was set as 0.6 m and 1.6 m, respectively. For the thick and thin wooden boards, six tests were performed each. Four tests were performed for the iron planks. Fig. 5-5 shows a typical load-deflection curve for the iron plank. The flexural modulus 퐸 can be obtained through the formula:

푃 48퐸퐼 = ∆ 퐿3 where P is load in the initial load-deflection curve; △ is the corresponding deflection; L is the distance between the two simply supported pins; I is the moment of area.

The ratio of P over △ can be obtained from a linear regression of the initial slope of the load–deflection curve as shown in Fig. 5-5. Table 5-1 summarizes the mechanical properties for the thin and thick wooden boards. It is seen that the ultimate load for the thin wooden board is about 1 kN, while that for the thick wooden board is about four times. Both of them have about the same ultimate bending strength 30-35 MPa and about the same flexural modulus 4.5-4.8 GPa. Table 5-2 summarizes the mechanical properties for the iron planks. It is seen that its ultimate load is about 2 kN, ultimate bending strength is about 376 MPa and flexural modulus is about 167 GPa.

5.3 Full-scale test of working platform

After obtain the properties of wooden boards and iron planks, the structural behavior

136 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings of three types of platform was investigated experimentally and numerically.

5.3.1 Test arrangement

The Type 1 mixed scaffolding tested in Chapter 4 was used for the full-scale test of working platform with three different types: integrated bamboo members with thin wooden boards; thick wooden boards and iron planks. From the UDL test and load-carrying capacity analysis of platform in Chapter 4, the platform boards would not fail under the UDL and the load-carrying capacity is dominated by the failure of bamboo transom. In this section, the safety and deflection behavior of three different types on real support under partial area load or point load would be investigated. According to BS EN 12811-1 [22], the working area for load classes 5 and 6 shall be capable of supporting a uniformly distributed partial area load of 7.5 kN/m² and 10 kN/m², respectively. The partial area for load classes 5 and 6 is obtained by multiplying the area of the bay by the partial area factor 0.4 and 0.5, respectively. The dimensions and position of the partial area shall be chosen to give the most unfavourable codition (maximum moment and deflection), as shown in Fig. 5-6. For simplicity, an equivalent point load was used in test instead of the partial area load, which gives a larger moment and deflection. The equivalent point load for load classes 5 and 6 is 2.93 kN and 4.88 kN when testing in Type 1 mixed scaffolding with bay length 1.5 m and platform width 0.65 m. A loading device made of the steel tube and couplers was used to form a static point load condition (equivalent line UDL). The static point load was applied in the middle working area of platform. The setup of static point load test for the three platform types is shown in Fig. 5-7. The loading device was set to apply a point load up to 3 kN or 5 kN on the middle of working area. Each type was tested four times. The displacement at the midpoint of the inner layer was recorded by LVDT for comparison.

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5.3.2 Test results

Table 5-3 summaries the deflection of the midpoint of the inner layer for the three platform types under 3 kN and 5 kN point load for comparison. Fig. 5-8 shows the load-deflection curves for the three types under a static point load larger than 3 kN. It is seen that all three platform types have about the same linear elastic deflection behavior under loads. This shows that the platform with all three types remained very much intact during the tests. No noticeable damage on the platform and the scaffolding was observed after all the tests. The measured axial force in bamboo standards and steel posts were calculated by multiplying the measured strain values with the calculated cross sectional area of bamboo and steel tube respectively. Table 5-4 summarizes the mean values and standard deviations of strains and axial forces under recorded static point load of 3 kN. The post number and standard number are the same as in Fig. 4-25. It is seen that the point load acting on the platform was mainly carried by the posts directly under the loading position.

To compare the test results obtained above, finite element analysis using SAP 2000 reported in Section 4.2 was performed for all the static point load cases tested above. Fig. 5-9 shows the comparison of load-deflection curves between test and analysis for all three platform types. It is seen that the displacements estimated from the numerical analysis are in general higher than those measured from the test. Both of them show linear elastic behavior. Table 5-5 summarizes the comparison of displacement at the midpoint of inner layer of the bottom platform for the three platform types under 3 and 5 kN load. It is seen that the difference between test and analysis ranges between 30 to 67%. Table 5-6 compares the axial forces in some of the posts and standards between test and analysis under 3 kN point load acting on the platform. Table 5-7 further summarizes the difference between test and analysis results. It can be concluded that the axial force difference between full-scale test and numerical analysis was about 32% for the bamboo members and about 14% for the metal members. In

138 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings summary, both the test and analysis results confirm that all three platform types: integrated bamboo members with thin wooden boards, thick wooden boards, and iron planks, have similar mechanical behavior on real support and seem to be able to be used as a safe platform for the scaffolding.

(a) Type 1: Integrated bamboo members (thin wooden boards are not shown)

(b) Type 2: Thick wooden boards

139 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

(c) Type 3: Prefabricated iron planks Fig. 5-1 Three working platform Types

Fig. 5-2 Thin and thick wooden boards made out of plywood

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Fig. 5-3 Dimension of pre-fabricated iron plank

1.6 m 0.6 m

(a) Test on a wooden board (b) Test on an iron plank Fig. 5-4 Three-point loading test on wooden board and iron plank

2.5

2

Mid load (kN) Midload 1.5

1

P y = 0.0488x + 0.2925 0.5

△ 0 0 20 40 60 80 100 120 140 160 Mid deflection (mm)

Fig. 5-5 A typical load-deflection curve for an iron plank

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Area of the bay

Partial area

Fig. 5-6 Dimensions and position of the partial area

(a) Type 1: Integrated bamboo members with thin wooden boards

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(b) Type 2: Thick wooden boards

(c) Type 3: Iron planks Fig. 5-7 Setup of static point load test on the middle span of platform

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14 Bamboo + 12 thin wooden board

10 Deflection (mm) Deflection 8 Thick wooden 6 board

4

2 Iron plank

0 0 0.5 1 1.5 2 2.5 3 3.5 4 Line UDL (kN)

Fig. 5-8 Typical load-deflection curves of three platform types

18 Bamboo + thin 16 wooden board Model 14 Test

12 Deflection(mm) Thick wooden 10 board Model

8 Test 6

4 Iron plank Model 2 Test 0 0 1 2 3 4 Line UDL (kN)

Fig. 5-9 Comparison of load-deflection curves between test and analysis

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Table 5-1 Mechanical properties for wooden boards Ultimate Initial slope of Ultimate Flexural Flexural Width Thickness bending the load– Specimen test load rigidity modulus (mm) (mm) strength deflection (kN) (N·m²) (GPa) (MPa) curve (kN/mm) Thin wooden board 1 200 11.6 1.22 40.4 0.0285 128.3 4.88 2 199 11.6 0.95 31.7 0.0258 116.1 4.46 3 200 11.6 0.92 30.4 0.0306 137.7 5.24 4 200 11.6 1.02 33.7 0.0275 123.8 4.71 5 200 11.7 1.01 33.3 0.0273 122.9 4.65 6 200 11.7 1.26 41.6 0.0299 134.6 5.11 Average 200 11.6 1.06 35.2 0.0283 127.2 4.84 Thick wooden board 7 200 23.7 4.50 35.9 0.2090 940.5 4.22 8 201 24.2 3.83 29.2 0.2490 1120.5 4.71 9 200 23.4 3.28 26.9 0.2070 931.5 4.36 10 200 23.5 3.16 25.8 0.2030 913.5 4.24 11 200 23.9 4.79 37.7 0.2260 1017.0 4.46 12 200 23.9 3.65 28.7 0.2390 1075.5 4.73 Average 200 23.8 3.86 30.7 0.2222 999.8 4.45

Table 5-2 Mechanical properties for iron planks Ultimate Initial slope of Ultimate Flexural Flexural Width Thickness bending the load– Specimen test load rigidity modulus (mm) (mm) strength deflection (kN) (N·m²) (GPa) (MPa) curve (kN/mm) 1 221 1.20 2.17 414.3 0.0408 3481.6 149.9 2 220 1.21 1.89 360.7 0.0456 3891.2 167.5 3 220 1.18 1.88 358.8 0.0470 4010.7 172.6 4 220 1.22 1.95 372.2 0.0488 4164.3 179.2 Average 220 1.20 1.97 376.5 0.0456 3886.9 167.3 Note: Due to complexity of the section of iron planks, the second moment of area and section modulus based on average measured dimensions are used for all specimens.

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Table 5-3 Deflection at the midpoint of inner layer Under line UDL: 3 kN (mm) Under line UDL: 5 kN (mm) Platform Type 1st 2nd 3rd 4th 3rd 4th Integrated bamboo members with thin wooden 10.74 9.49 10.59 8.94 18.14 16.59 boards Thick wooden boards 10.82 8.14 8.58 8.12 16.21 15.08 Iron planks 10.63 9.45 8.97 9.21 15.57 15.18

Table 5-4 Results for static point load (3 kN) on working platform (a) Type 1: Integrated bamboo members with thin wooden boards Measured Strain Young's Cross section area 퐴 axial force modulus Component Outside Mean Std 퐸 Thickness 퐴 Mean Std diameter × 10−6휀 GPa mm mm mm² kN Post 2 0.4 1.0 204 48.2 2.23 322.1 0.03 0.07 Post 4 -13.7 0.3 204 48.2 2.23 322.1 -0.90 0.58 Back Post 6 -14.5 1.0 204 48.2 2.23 322.1 -0.95 0.52 Post 8 0.7 0.8 204 48.2 2.23 322.1 0.05 0.05 Post 1 1.2 0.7 204 48.2 2.23 322.1 0.08 0.05 Post 3 -9.7 1.9 204 48.2 2.23 322.1 -0.64 0.12 Post 5 -9.0 2.4 204 48.2 2.23 322.1 -0.59 0.16 Front Post 7 1.2 0.8 204 48.2 2.23 322.1 0.08 0.05 Standard 1 0.3 0.6 8.55 49.7 6.34 863.3 0.003 0.004 Standard 2 -8.6 2.7 8.55 43.3 5.53 656.1 -0.05 0.01

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(b) Type 2: Thick wooden boards Measured Strain Young's Cross section area 퐴 axial force modulus Component Outside Mean Std 퐸 Thickness 퐴 Mean Std diameter × 10−6휀 GPa mm mm mm² kN Post 2 0.8 1.5 204 48.2 2.23 322.1 0.05 0.10 Post 4 -13.7 0.3 204 48.2 2.23 322.1 -0.90 0.02 Back Post 6 -11.6 0.8 204 48.2 2.23 322.1 -0.76 0.05 Post 8 1.3 1.1 204 48.2 2.23 322.1 0.08 0.07 Post 1 2.0 0.9 204 48.2 2.23 322.1 0.13 0.06 Post 3 -9.5 0.6 204 48.2 2.23 322.1 -0.63 0.04 Post 5 -10.9 0.7 204 48.2 2.23 322.1 -0.72 0.05 Front Post 7 1.4 0.3 204 48.2 2.23 322.1 0.09 0.02 Standard 1 -0.3 0.3 8.55 49.7 6.34 863.3 -0.002 0.002 Standard 2 -6.7 0.9 8.55 43.3 5.53 656.1 -0.04 0.01 (c) Type 3: Iron planks Measured Strain Young's Cross section area 퐴 axial force modulus Component Outside Mean Std 퐸 Thickness 퐴 Mean Std diameter × 10−6휀 GPa mm mm mm² kN Post 2 0.7 1.3 204 48.2 2.23 322.1 0.04 0.09 Post 4 -11.0 1.5 204 48.2 2.23 322.1 -0.72 0.10 Back Post 6 -15.1 2.1 204 48.2 2.23 322.1 -1.00 0.14 Post 8 1.2 0.9 204 48.2 2.23 322.1 0.08 0.06 Post 1 2.6 1.2 204 48.2 2.23 322.1 0.17 0.08 Post 3 -11.4 3.6 204 48.2 2.23 322.1 -0.75 0.24 Post 5 -10.7 1.8 204 48.2 2.23 322.1 -0.70 0.12 Front Post 7 1.3 0.2 204 48.2 2.23 322.1 0.08 0.01 Standard 1 0.4 0.7 8.55 49.7 6.34 863.3 0.003 0.01 Standard 2 -11.3 4.1 8.55 43.3 5.53 656.1 -0.06 0.02

Table 5-5 Comparison of deflection between test and analysis Under line UDL: 3 kN (mm) Under line UDL: 5 kN (mm) Platform Type Testing Testing SAP model Difference SAP model Difference result result Type 1 10.74 14.1 31.3% 18.14 23.5 29.5% Type 2 10.82 16.2 49.7% 16.21 27.1 67.2% Type 3 10.63 13.8 29.8% 15.57 23.0 47.7%

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Note: Difference= (Model-Test) / Test. Table 5-6 Comparison of axial forces under 3 kN load (a) Type 1: Integrated bamboo members with thin wooden boards Difference Measured axial force Analyzed Component 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% (mean value) (kN) value (kN) 푚푒푎푠푢푟푒푑 Post 4 -0.90 -0.88 2% Back Post 6 -0.95 -0.88 8% Post 3 -0.64 -0.71 12% Front Post 5 -0.59 -0.66 11% Standard 2 -0.05 -0.04 17% Note: Axial forces obtained from strain values smaller than or around its precision (1 × 10−6휀) was not considered in comparison. (b) Type 2: Thick wooden boards Difference Measured axial force Analyzed Component 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% (mean value) (kN) value (kN) 푚푒푎푠푢푟푒푑 Post 4 -0.90 -0.82 9% Back Post 6 -0.76 -0.82 7% Post 1 0.13 0.09 32% Post 3 -0.63 -0.78 24% Front Post 5 -0.72 -0.79 10% Post 7 0.09 0.08 12% Standard 2 -0.04 -0.06 59% Note: Axial forces obtained from strain values smaller than or around its precision (1 × 10−6휀) was not considered in comparison. (c) Type 3: Iron planks Difference Measured axial force Analyzed Component 푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 | | × 100% (mean value) (kN) value (kN) 푚푒푎푠푢푟푒푑 Post 4 -0.72 -0.79 9% Back Post 6 -1.00 -0.80 20% Post 1 0.17 0.11 35% Post 3 -0.75 -0.80 7% Front Post 5 -0.70 -0.79 13% Post 7 0.08 0.08 5% Standard 2 -0.06 -0.05 21% Note: Axial forces obtained from strain values smaller than or around its precision (1 × 10−6휀) was not considered in comparison.

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Table 5-7 Summary for platform test and analysis

푎푛푎푙푦푧푒푑 − 푚푒푎푠푢푟푒푑 퐷𝑖푓푓푒푟푒푛푐푒 = | | × 100% Static point 푚푒푎푠푢푟푒푑 Platform Type load Metal tube Bamboo Max Average Std Max Average Std Type 1 12% 8% 4% 17% / / Type 2 3 kN 32% 16% 9% 59% / / Type 3 35% 15% 10% 21% / / Total 35% 14% 9% 59% 32% 19% Note: “/” means there is only one bamboo member with strain value larger than its precision (1 × 10−6휀), see Table 5-6 (a)-(c).

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Chapter 6 Conclusions and Recommendations

The aim of this study is on the safe usage of bamboo and mixed scaffoldings using combination of laboratory tests and computer analysis. The computer analyses were conducted using the finite element analysis program SAP 2000 and the laboratory tests were conducted in the Structural Laboratory of the Hong Kong University of Science and Technology. Conclusions and recommendations obtained from this study can be summarized as follows.

(1) Anchorages for the safety harness Two regional reinforcement options that can meet the anchorage requirements for safety harness are proposed to serve as safe anchorages: Option 1: Reinforce ledgers of two layers by adding two steel tubes and linking them though a steel strut; and Option 2: Reinforce platform by adding an additional transom and two steel tubes underneath the platform. Both reinforcement options can resist more than 8 kN of static load and 100 kg of drop load without causing any damage to the scaffolding. Furthermore, it is feasible to form a reinforcement region by adding additional vertical steel struts to Option 1. This reinforcement region can accommodate multiple users simultaneously as long as the spacing between the users is equal or larger than two spans. The anchor points inside the reinforcement region can provide a load-carrying capacity larger than 8 kN. It is recommended that energy absorbing devices with a MAF of 4 kN be used on these anchor points so that these anchor points can protect the users with a safety factor of two. A safer erection and dismantling procedure is presented for bamboo scaffolding to ensure that there are guardrails up to the chest of workers at all time and the maximum falling height is limited to less than 2 meters to prevent any serious injury

150 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings to workers in case of accident. This erection and dismantling procedure is animated and illustrated using the building information modeling (BIM) software. Note that this procedure could also be applied to mixed scaffoldings. For those scaffoldings that extend beyond roof top, horizontal lifeline systems (HLLs) with stanchions appear to be a good option for anchoring safety harness. For those platforms below the roof level, HLLs fixed on vertical concrete wall is also an effective way to provide safe anchorage.

(2) Issue relating to the use of mixed scaffoldings Three different types of mixed scaffolding are established: Type 1: Anti-sliding vertical tube with bamboo ledger; Type 2: Anti-sliding vertical tube with steel main ledger; and Type 3: Mixed scaffolding incorporating couplers. Studies show that all three types of mixed scaffolding can meet the load requirements (3 kN/m² for masonry or special duty) specified in the bamboo or metal scaffolding codes. Among the three types of mixed scaffolding, Type 1 is the least expensive and is more suitable for short term usage. Type 3 is the most costly but can offer a more robust performance under different environmental condition.

(3) Use of different materials for the working platform Three commonly used platform types have been investigated and compared numerically and experimentally: Type 1: Bamboo members with thin wooden boards (thickness 12 mm); Type 2: Thick wooden boards (thickness 25 mm); and Type 3: Prefabricated iron planks. All three types of platform exhibit good integrity under full-scale scaffolding tests. None of them show any sign of damage under a static load larger than 5 kN acting at the middle of platform. Results suggest that all three types can function very well as a platform for the scaffolding.

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Appendix

Appendix A Other types of connection and test fixture

A1 Column (or beam/bracing) splice test

The splice in scaffolding is the type of connection used to join or overlap same units together. In this chapter, the experiments and analysis will be focused on four parameters which affect the characteristic resistance of splice for bracings, ledgers and standards used in the erection of bamboo scaffold. Firstly, we will analyze the effect of presence of nodes, the contact length, number of ties and number of round turns on resistance. Then the resistance of actual splice between bamboos according to Hong Kong bamboo scaffolding codes [12, 17] will be investigated. The controlling variable method was used to arrange experiments and analyze their different degrees of influence. The setup of splice test is shown in Fig.A-1. In the test, one bamboo member was hold in position and the load was applied parallel to the other one.

The effect of presence of nodes and number of round turns: Firstly, two same bamboo members (BP) were used in experiments to find the effect of presence of nodes and number of round turns on resistance of splice between bamboos. All of these tests maintain the same contact length and single tie between bamboo members. The contact length between two bamboo members is 0.45 m. Three cases of presence of node were studied: case 1: the tie is far away from nodes; case 2: the tie is close to only one node; case 3: the tie is closely between two nodes. Different number of round turns to fasten splice was analyzed for case 1: (1) splice was fastened with five round turns; (2) splice was fastened with four round turns. Table A-1 shows the arrangement of experiments and the testing results. From experimental data, following observations can be seen:

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(1) The resistance of splice under case 1 with 5 round turns and case 2 is very close. The failure mode of these two cases is always slipping between bamboo members. (2) Comparing case 1 with different round turns to fasten splice, the number of round turns shows a big impact on the resistance. (3) The splice fastened closely between two nodes (case 3) shows a very large resistance, and the failure mode is always splitting of plastic stripes.

The effect of number of ties and contact length: This section focused on the effect of contact length and number of ties on resistance between two bamboo members. Also, two same bamboo members (BP) were used in experiment to eliminate the effect of other factors. During the tests, the situation that ties closely between two nodes was intentionally avoided to prevent the buckling failure of bamboo. Fig. A-2 shows test set up of splice between two BP with same contact length 1.3m and different number of ties. Table A-2 shows the results of the experiments and the following conclusions can be drawn:

(1) The influence of number of ties on resistance is far greater than the contact length between two bamboo members. (2) The resistance of splice shows approximately multiple relationships with the number of ties.

Resistance of actual column (or beam/bracing) splice in bamboo scaffoldings: Resistance of actual splice between bamboo members for bracings, ledgers and standards used in the erection of bamboo scaffolding was studied in this section. The contact length between two bamboo members are 1.8 m and total six ties were arranged at an approximate distance of 30 cm [12, 17] (see Fig. A-3). In experiments, the ties between two close nodes were artificially avoided for conservative consideration. This practice also helps to avoid the buckling destruction of bamboo members in test. Every

153 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings five tests were conducted for splice between two BP and two PP respectively. The bamboo members were selected randomly and two different bamboo members were used for each test. This arrangement can give a more realistic experimental result. Tested resistance data is concluded in Table A-3, and from which, following observations can be seen:

(1) The resistance of splice between two PP is smaller than which between two BP. This is mainly because of the larger diameter of PP so that the number of round turns is less than it in the splice between two BP. (2) During tests, the occurrence of loose of stripes under loading for actual splice is more often than above four-ties splice. This due to the bending effect is more important in long bamboo members and this effect may cause the loose of plastic strips during the deformation of strips under loading. Thus, the resistance of six-ties splice didn’t show a larger resistance compared with four-ties splice. (3) Due to the different shape (cross-section area, initial curvature) and surface property of different bamboo members, a larger variation of resistance is shown compared with previous tests.

A2 A special type of connection called “打戒指”

“打戒指” is a commonly used type of beam-column connection in bamboo scaffolding. Fig. A-4 shows a typical configuration of this type of connection. It is commonly used to avoid slipping between two bamboo members caused by shrink of new bamboos. The slipping stiffness behavior and resistance of this type connection were investigated through experiments. Table A-4 presents the experimental results of this type of connection. It should be noted that the resistance of connection with a slipping of 100 mm was selected and shown in this table.

It can be found that the failure mode of this type of connection is always the large

154 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings deformation of plastic stripes and slipping between bamboo members. The resistance will increase as the slipping between two orthotropic members increased, and a relative displacement larger than 100 mm will always happen without splitting and looseness of plastic stripes. The failure mode of “打戒指” and a corresponding load-displacement curve are shown in Fig. A-5 (a) and (b), respectively. This type of connection has a larger connection resistance and smaller slipping stiffness compared with the connection fastened by 5-round plastic stripes. The connection behavior of “打戒指” has also been considered in design of bamboo scaffolding reinforced anchorages but it couldn’t improve the safety of connection as anchorage due to its small slipping stiffness.

A3 Fixture for beam-column connection test

CAD view of connection test fixture

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Front view and dimensions (mm) of connection test fixture

Top view and dimensions (mm) of connection test fixture

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Fig. A-1 Setup of splice test

0.2 m 0.3 m 0.3 m 0.3 m 0.2 m

0.2 m 0.9 m 0.2 m

Fig. A-2 Test setup of splice with contact length 1.3 m and different number of ties

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(a) Actual connections between two PP

(b) Actual connections between two BP Fig. A-3 Test setup of actual connection with six ties

Fig. A-4 Typical configuration of “打戒指”

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(a) Failure mode of “打戒指” (before and after loading)

3

2.5 y = 0.0239x 2

1.5 UTM Force (kN) Force UTM

1

0.5

0 0 20 40 60 80 100 120

UTM Displacement (mm) (b) Typical load-displacement curve of “打戒指” Fig. A-5 Failure mode and typical load-displacement curve of “打戒指”

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Table A-1 Effects of presence of nodes and number of round turns on resistance No. No. of Test Contact Presence Resistance(kN) Failure of round Illustration series length(m) of nodes Mode tests turns Mean Std

Case 5 0.45 5 None 0.53 0.128 1

Relative slippage Case 5 0.45 4 None 0.37 0.074 between 1 bamboo

members

Case 5 0.45 5 One side 0.52 0.044 2

Splitting Case Two of 5 0.45 5 4.18 0.296 3 sides plastic strips

Table A-2 Experiments to study the effect of number of ties and contact length Contact No. of round Resistance(kN) No. of tests No. of ties length(m) turns Mean Std 5 0.65 5 2 1.02 0.237 5 1.3 5 2 1.38 0.275 5 1.3 5 4 2.20 0.179

Table A-3 Tested resistance of actual splices No. of Contact No. of round Resistance(kN) Test series No. of ties tests length(m) turns Mean Std BP-BP 5 1.8 5 6 2.83 0.53 PP-PP 5 1.8 4 6 2.28 0.65

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Table A-4 Resistance of “打戒指” beam-column connection Test series Resistance (kN) Presence of No. of Horizontal Vertical Mean nodes tests Std member member (Disp. = 100 mm) BP BP None 3 2.30 0.28 BP PP None 3 2.52 0.31 Steel tube BP None 3 2.36 0.19

Appendix B Material properties of bamboo and steel tube

B1 Mechanical properties of bamboo

There were two bamboo species, namely Bambusa Pervariabilis (or Kao Jue) and Phyllostachys Pubecens (or Mao Jue), commonly used in bamboo scaffoldings. Recent scientific investigations on bamboo as construction materials were published by Chung and Yu in 2002 [30]. Compression and bending tests were conducted to establish the characteristic strengths and the Young’s modulus of these bamboo species. Table B-1 summaries the physical and mechanical properties of Kao Jue and Mao Jue under different moisture. The experimental results have been verified with an average model

푀푒푎푠푢푟푒푑 푓표푟푐푒 푎푛푑 푐푎푝푎푐푖푟푦 factor about 2 ( 푚표푑푒푙 푓푎푐푡표푟 = ) when using a proposed 퐷푒푠푖푔푛 푓표푟푐푒 푎푛푑 푐푎푝푎푐푖푡푦 material partial safety factor 1.5 against the characteristic strength (at fifth percentile) to get the design strength of bamboo. So the proposed mechanical properties with the appropriate material partial safety factor were used in analysis for this report.

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B2 Mechanical properties of steel tube

According to material requirements of loose tubes (BS EN 12811-1 [22]), loose tubes connected by couplers (BS EN 74-1 [21]) shall have a minimum nominal yield strength of 235 N/mm², nominal external diameter of 48.3 mm and a minimum nominal wall thickness of 3.2 mm. It should however be noted that the steel tubes with the same external diameter but a thickness of 2.3mm are commonly used in mixed scaffoldings in Hong Kong.

There are three sizes of steel tube commonly available in Hong Kong (see Fig. B-1): (a) 48.3 mm (external diameter) × 4 mm (thickness) complying with BS EN 10255 [31]; (b) 48.3 mm × 3.2 mm complying with [31] and (c) 48.3 mm × 2.3 mm with no specific standards. To determine their mechanical properties, tensile test were carried out in accordance with ASTM E8 [32]. Dimensions of the test specimens are shown in Appendix B3. Due to the curved surface of tube, a pair of testing fixture with the same curved surface shape was made for the test. The dimensions of the fixture are also presented in Appendix B3. The tensile test was carried out in the Structural Engineering Laboratory of HKUST using a MTS Universal Testing Machine with MTS 647 hydraulic wedge grip (see Fig. B-2). Fig. B-3 (a) and (b) show the load-displacement curve and the enlarged initial stress-strain curve of specimen D2 for obtaining the yield strength and the young’s modulus of the specimen, respectively.

Results obtained from the tensile test are shown in Table B-2. It can be see that the characteristic yield strength, which is about 350 MPa for all three sizes of steel tube, is much larger than the minimum yield strength of 235 N/mm² (235 MPa) as specified in [22]. Also, the average Young’s modulus was tested to be about 200 GPa. In this report, the yield strength 350 MPa (characteristic value) and Young’s modulus 200 GPa were adopted in the finite element numerical analysis for steel tubes from Hong

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Kong market. In Table B-2, the original cross-section area 푆0 of a test specimen is calculated according to the formula given in [32]:

푏 퐷2 푏 푏 퐷 − 2푎 2 푏 푆 = ( ) × √퐷2 − 푏2 + ( ) × 푎푟푐푠𝑖푛 ( ) − ( ) × √(퐷 − 2푎)2 − 푏2 − ( ) × 푎푟푐푠𝑖푛 ( ) 0 4 4 퐷 4 2 퐷 − 2푎

where 푎: thickness of the tube wall; 푏: average width of the stripe; and 퐷: external diameter of the tube.

The percentages of elongation after fracture under a fixed gauge length of 50 mm were obtained in test. These elongation values should be converted to those corresponding to a gauge length of 퐿 = 5.65√푆0 using the formula given in BS EN ISO 2566-1 [33]:

−0.4 퐴 √푆0 퐴푟 = ( ) 2 퐿0 where

퐴푟: required elongation on gauge length of 5.65√푆0;

퐴: elongation on gauge length 50 mm;

퐿0: original gauge length; and

푆0: original cross-sectional area of test piece.

B3 Tube specimens and fixture for tensile test

Metal tube specimens for tensile test:

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Dimensions (mm) of tube specimens

Side view of the specimens Front view of the specimens

Tensile test fixture:

CAD view of tensile test fixture

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Top view of the specimens and test fixture

Front view and dimensions (mm) of tensile test fixture

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Top view and dimensions (mm) of tensile test fixture

Fig. B-1 Three sizes of steel tube available in Hong Kong

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Fig. B-2 Setup for the tensile test

25

20

15 UTM force (kN) force UTM

10

5

0 0 5 10 15 20 Displacement (mm) 167 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

(a) Load-displacement curve

0.4 y = 202.29x 0.35

0.3

Stress (GPa) Stress 0.25

0.2

0.15

0.1

0.05

0 0 0.0005 0.001 0.0015 0.002 Strain ε

(b) Initial stress-strain curve Fig. B-3 Load-displacement curve for specimen D2 under tensile test

Table B-1 Summary of physical and mechanical properties of Kao Jue and Mao Jue Avg. Avg. 95% characteristic Avg. Young's external internal strength (N/mm²) modulus (kN/mm²) Bamboo Moisture content diameter diameter Compression Bending Compression Bending (mm) (mm) Dry < 5.0% 79.0 80.0 10.3 22.0 Kao Jue Natural 12.5% 40.7 30.4 57.0 58.5 8.6 19.2 (BP) Wet > 20.0% 35.0 37.0 6.8 16.4 Dry < 5.0% 117.0 51.0 9.4 13.2 Mao Natural 20.0% 68.6 54.5 73.2 53.4 7.6 11.0 Jue (PP) Wet > 30.0% 44.0 55.0 6.4 9.6 Note: Based on a total of 364 compression and 91 bending tests reported in [30].

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Table B-2 Results of tensile test for three different sizes of steel tube Dimensions Testing Properties Percentage Width Cross Lower elongation after External Tensile Young’s Thick of section yield fracture on Specimen diameter strength modulus 푇 strip area strength 50mm 퐷 푅푚 퐸 푏 푆0 푅푒퐿 gauge 5.65√푆0 length (mm) (mm) (mm) (mm²) (MPa) (MPa) (GPa) ( %) 48.3×2.3 mm (no standards) A1 48.3 2.2 12.5 28.3 367 469 199 28% 34% A2 48.3 2.3 12.5 28.6 381 472 188 25% 31% B1 48.4 2.3 12.5 28.8 377 472 182 23% 28% B2 48.4 2.2 12.6 28.7 362 468 243 25% 30% C1 48.3 2.3 12.6 28.8 375 469 215 20% 24% C2 48.3 2.3 12.5 29.1 380 470 201 21% 25% Average 48.3 2.3 12.6 28.7 374 470 205 24% 29% 48.3×3.2 mm (BS EN 10255) D1 48.4 3.3 12.5 41.8 381 473 181 20% 23% D2 48.4 3.2 12.6 41.3 385 473 202 21% 24% E1 48.6 3.3 12.5 41.8 388 477 185 21% 24% E2 48.6 3.3 12.6 41.9 394 472 176 22% 25% F1 48.4 3.2 12.5 40.9 388 476 196 20% 23% F2 48.4 3.2 12.5 40.3 391 481 209 21% 24% Average 48.5 3.3 12.5 41.3 388 475 192 21% 24% 48.3×4.0 mm (BS EN 10255) G1 48.7 3.9 12.5 49.1 358 436 198 25% 27% G2 48.7 3.9 12.6 49.7 347 411 198 26% 29% H1 48.7 3.9 12.5 49.2 351 418 186 26% 28% H2 48.7 3.8 12.6 49.1 365 437 188 26% 28% I1 48.7 4.0 12.6 50.6 353 406 203 20% 22% I2 48.7 4.0 12.5 51.2 360 426 212 20% 22% Average 48.7 3.9 12.5 49.8 356 422 197 24% 26% (1) Yield strength: Average = 372.5 MPa; Std = 14.4 MPa; Characteristic strength Summary (95%) = 348.8 MPa; (2) Young’s modulus: Average = 197.9 GPa; Std = 15.3 MPa.

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Appendix C Column buckling of structural bamboo in bamboo scaffoldings

The buckling of structural bamboo in bamboo scaffoldings is mostly determined by the arrangement of ties and mechanical properties and geometrical dimensions of bamboo members. In previous researches [10, 34, 35], a design method based on Perry-Robertson interaction formula was proposed for column buckling of both Kao Jue and Mao Jue. The predicted the axial buckling resistances of the bamboo columns by this method have been proved through experimental investigation with an averaged model factor of 1.65. It may be used effectively to design against column buckling of structural bamboo in bamboo scaffoldings. The main points of the proposed method are described as follows:

(1) The effective length of structural bamboo in bamboo scaffolding was determined through advanced non-linear finite element analysis using Nonlinear Integrated Design and Analysis software (NIDA). It is shown that the axial buckling resistances of the bamboo columns are affected significantly by the presence or the absence of lateral restraints. It was also found that due to the presence of bracing members and secondary ledgers in the outer layer and larger dimensions of post (Mao Jue) of outer layer, the post of the inner layer (Kao Jue) always fails against buckling firstly. (2) The Robertson constant of Mao Jue and Kao Jue should be selected as 15 and 28 respectively [34], which represent initial imperfection of bamboo members. (3) Also, the non-prismatic effect of bamboo is considered by incorporating a non-prismatic parameter, 훼, to the elastic Euler buckling load of the bamboo member, see Appendix C2.

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C1 Effective length of the post in bamboo scaffoldings [10]

According to previous research [10], it was recommended that the effective length of a structural bamboo may conservatively be taken as follows.

Effective length of post in single layered bamboo scaffoldings (SLBS): In single layered bamboo scaffoldings, the recommended effective length of a post ℎ푒 may be taken as follows:

ℎ푒 = 푘푒 × 퐻 where

푘푒 is the effective length coefficient = 1.0 for SLBS with regular lateral restraints with H = 1.0 h to 3.0 h; = 0.7 for SLBS with staggered lateral restraints with H = 2.0 h to 3.0 h; 퐻 is the system length between lateral restraints; and ℎ is the height of a platform, or the vertical distance between two platforms.

Effective length of post in double layered bamboo scaffoldings(DLBS): In double layered bamboo scaffoldings, the recommended effective length of a post ℎ푒 may be taken as follows:

Inner layer

ℎ푒 = 푘푒 × ℎ where

푘푒 is the effective length coefficient, 푘푒 = 푘푖 × 푘푏;

푘푖 is the secondary effective length coefficient which depends on the restraint

171 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings arrangement provided at the posts of the outer layer as follows:

H/h 1.00 1.50 2.00 2.667 3.00

푘푖 1.00 1.10 1.25 1.50 1.75

푘푏 = 1.0 for DLBS with regular lateral restraints, or 0.7 for DLBS with staggered lateral restraints; 퐻 is the system length between lateral restraints; and ℎ is the height of a platform, or the vertical distance between two platforms.

Modified effective length of post of inner layer If the lateral restraints are provided to the base ledger of bamboo scaffoldings, the column member at the base level will be most critical regardless of distance between lateral restraints according to the experimental and numerical results in [10]. The comparison between test and design results also showed that above design method is fairly conservative for bamboo scaffoldings. Consequently, above proposed method to determine the effective length of the post of inner layer is modified as follows:

ℎ푒 = 푘푒 × ℎ where

푘푒 is the effective length coefficient, = 1.0 for DLBS with 퐻 = 1.0ℎ 푡표 3.0ℎ; ℎ is the height of base column, but not less than height of a platform; and 퐻 is the system length between lateral restraints.

Outer layer

ℎ푒 = 푘푒 × 퐻 where 172 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

푘푒 is the effective length coefficient, 푘푒 = 푘0 × 푘푏;

푘0 =0.7 for DLBS with H = 1.0 h to 2.667 h to allow for the restraint effect provided by both ledgers and standards;

푘푏 =1.0 for DLBS with regular lateral restraints, or 0.7 for DLBS with staggered lateral restraints; 퐻 is the system length between lateral restraints; and ℎ is the height of a platform, or the vertical distance between two platforms.

Based on the predicted structural performance of DLBS from the non-linear analysis, the maximum value of 퐻 should not exceed 2.667 h in practice.

C2 Non-prismatic parameter 휶 [34]

As natural non-homogenous organic materials, large variations of physical properties along the length of bamboo members such as external and internal diameters are shown. Thus, the non-prismatic effect is significant in the buckling analysis of bamboo column. And this may be considered by incorporating a non-prismatic parameter, 훼, to the elastic Euler buckling load of the bamboo member [34]. The non-prismatic parameter 훼 is a function of the change of the second moment of area along member length, and it could be evaluated through the minimum energy method [34].

The elastic critical buckling strength of the bamboo column 푝푐푟 is given by:

2 휋 퐸푏 푝푐푟 = 훼 2 휆1 where the non-prismatic parameter 훼 is the minimum root of the following cubic function,

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3 2 푔(훼) = 푐3훼 + 푐2훼 + 푐1훼 + 푐0 = 0 where

푐3 = −0.2880

푐2 = 2.016(2 + 휌) 2 푐1 = −(14.11 + 14.11휌 + 3.098휌 ) 2 3 푐0 = 10.37 + 15.55휌 + 7.047휌 + 0.932휌 퐼 −퐼 휌 = 2 1 퐼1

If the value of ρ lies between 0 and 3, the value of 훼 may be calculated approximately as follows:

α = 1.005 + 0.4751ρ − 0.011휌2 where α lies between 1.00 and 2.35.

It should be noted that the value of non-prismatic parameter 훼 for Kao Jue is found to range from 1.00–1.28 [10], and thus, the variation of external diameter and thickness along the length of Kao Jue is considered not to be significant. In assessing axial buckling resistances of Kao Jue, the external and the internal diameters are considered to be constant along the length of the bamboo so that non-prismatic parameter is 1.0 for Kao Jue.

C3 Working example: column buckling of bamboo post using Kao Jue

For simplicity, the vertical distance between ties in bamboo scaffolding are assumed to equal to 퐻 = 2ℎ = 4푚, ℎ is the vertical distance between lifts. Assume the lateral restraints are provided to the base ledger of bamboo scaffoldings and this is the

174 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings common practice in real scaffolding construction. The calculations of the allowable compressive load of Kao Jue under natural moisture content are shown in Table C-1. Table C-1 Buckling design example of Kao Jue with effective length 2 m Calculation methods and steps Results or values i) Section properties Characteristic compressive From Table B-1 푝푐,푘 = 57 푁/푚푚² strength (95% prob.) 푝푐,푘 Young's Modulus against From Table B-1 퐸푏 = 19.2 푘푁/푚푚² bending Eb 2 2 2 Cross section area 퐴1 and 퐴2 퐴 = 휋(퐷푒 − 퐷푖 )/4 퐴1 = 퐴2 = 5.75 푐푚 4 4 4 Moment of inertia 퐼1 and 퐼2 퐼 = 휋(퐷푒 − 퐷푖 )/64 퐼1 = 퐼2 = 9.28 푐푚

Radius of gyration 푟1 푟1 = √퐼1/퐴1 푟1 = 12.70 푚푚 ii) Elastic critical buckling strength considering non-prismatic effect Effective length should be determined Effective length 퐿 Assumed 퐿 = 2 푚 퐸 from Appendix C1 퐸

Slenderness ratio 휆1 휆1 = 퐿퐸/푟1 휆1 = 157.48 Non-prismatic parameter 훼 See Appendix C2 휌 = 0; α = 1.0

Elastic critical buckling strength 2 2 푝푐푟 = 훼(휋 퐸푏/휆1) 푝푐푟 = 7.64 푁/푚푚² 푝푐푟 iii) Compressive buckling strength using Perry-Robertson interaction formula

Design compressive strength 푝 푝 = 푐,푘 Where 푟 = 1.5 푐,푑 푟 푚 푝푐,푑 = 38 푁/푚푚² 푝푐,푑 푚 휂 = 0.001푎(휆 − 휆 ) 1 0 푎 = 28 where 푎 is Robertson constant; Perry factor 휂 휆0 = 14.12 퐸푏 휆0 = 0.2휋 is Limiting slenderness 휂 = 4.01 푝푐,푑

푝푐푟 × 푝푐,푑 푝푐푐,푑 = 0.5 2 Design compressive buckling ∅ + (∅ − 푝푐푟 × 푝푐,푑) ∅ = 38.16푁/푚푚²

strength 푝푐푐,푑 푝 +(1+휂)푝 푝푐푐,푑 = 4.016푁/푚푚² where ∅ = 푐,푑 푐푟 2

푝 × 퐴 푃 = 푐푐,푑 1 Permissible axial load 푃 훾푚 푃 = 1.54푘푁

where 훾푚 = 1.5 Note 1: Above design method is based on [9]. Note 2: Subscripts 1 and 2 denote the upper (smaller) cross-section and the lower (larger) cross-section, respectively.

Note 3: 훾푓 = 1.5 is a single partial safety factor for loads and 훾푚 = 1.5 is a single partial safety factor for resistances.

175 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

Appendix D Allowable compressive load on metal post in mixed scaffoldings

In metal scaffolding or mixed scaffolding, the effective length 퐿퐸 of a compression member should be derived from its actual centre-to-centre, between the intersections with supporting members in accordance with the conditions of restraint in the appropriate plane. Effective joint restraint is only likely to exist in riveted or bolted structural connections, or with welded joints combined with reasonable continuity of members [23]. So, an effective length of 1.0 퐻 is selected as conservative value to calculate the permissible stress on the gross section of steel tube for axial compression, 퐻 is the vertical distance between the lateral restraints. According to Annex B of BS 5975 [23] or BS EN 1993-1-1 [36], the characteristic compressive strength 푁 of a tubular strut with an effective length 퐿퐸 is given by:

N = χA푓푦

Where 1 χ = 휙 + (휙2 − 휆̅2)0.5 where

휙 = 0.5[1 + 0.49(휆̅ − 0.2) + 휆̅2] 휆 휆̅ = 휋2퐸 √ 푓푦 퐿 휆 = 퐸 푟 Where χ is the reduction factor for the relevant buckling mode; A is the cross-sectional area of the post; 휆 is the slenderness ratio; 176 Occupational Safety and Health Council Study on Safe Usage of Bamboo and Mixed Scaffoldings

푟 is the radius of gyration; 퐸 is the elastic modulus (= 200 kN/mm²);

푓푦 is the yield stress; and 휆̅ is non-dimensional slenderness.

The allowable compressive load of a steel column may be obtained by applying a single factor: 1.1 (material factor) × 1.5 (load factor) = 1.65:

푁 P = 푐 1.65

Here, assume the vertical distance between lateral restraints 퐻 = 2ℎ and the platform height ℎ is 2 m. The effective length 퐿퐸 of steel column is taken as 1.0 퐻. Note that a distance of 4 m between lateral restraints is actually the maximum vertical distance between ties allowed in bamboo scaffolding code [17]. The allowable compressive load for steel tube column is given in Table D-1.

Table D-1 Allowable compressive load for steel column with 퐿퐸 = 1.0 퐻 Modulus Characteristic Effective Outside Wall Characteristic Permissible of compressive Single length diameter thickness yield strength axial load elasticity strength factor m mm mm N/mm² N/mm² kN kN

퐿퐸 = 2.0 ℎ 48.3 2.3 200000 235 9.13 1.65 5.53 Note: The Characteristic compressive strength 9.13 kN is the same in Table B.2 of BS 5975 [23].

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