Evaluation of OSB Webbed Laminated Bamboo Lumber Box-Shaped Joists with a Circular Web Hole

Journal of Building Engineering 29 (2020) 101129

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Journal of Building Engineering

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Evaluation of OSB webbed laminated bamboo lumber box-shaped joists with a circular web hole

Guo Chen *, Jing Wu , Hao Jiang , Tong Zhou , Xiang Li , Yunfei Yu

College of Civil Engineering, Nanjing Forestry University, Nanjing, 210037, China

ARTICLE INFO ABSTRACT

Keywords: Openings are frequently required in the web of oriented strand board (OSB) webbed laminated bamboo lumber Laminated bamboo lumber (LBL) (LBL) box-shaped joists for passage of service ducts, plumbing, and wiring. A total of 105 joists with a circular Oriented strand board (OSB) web hole were tested and compared with 7 joists without a web opening (control joists). It was found that for Web opening smaller circular holes (D/hw � 30%), the effect of the hole was negligible and did not cause strength and stiffness Box-joist reductions. The unreinforced joists with larger web holes (D/h >30%) failed in a brittle and sudden shear mode, Reinforcement w resulting in a reduction in strength. Reinforcing of joists with an opening to stop or prevent crack formation or propagation could be accomplished by using one of three methods including collar shaped oriented strand board patches (C-OSB), two “U” shaped oriented strand board patches (TU-OSB), or collar shaped steel patches (C-SP). Results showed that the C-OSB worked most effectively and returned 2 of 5 series of joists to a strength and stiffness equivalent to the “no hole” condition. The mechanical performance and deformation properties of joists with a web opening could be improved by C-SP, but the improvement was only a small percentage of the total load-carrying capacity. TU-OSB worked effectively for a limited opening diameter (D/hw � 50%), and was easier to install without removing the service pipes and less expensive than the C-OSB or C-SP options. Good correlation was obtained between experimental results and numerical simulations.

1. Introduction sustainable green building material, increasing attention has been paid on the application of laminated bamboo lumber (LBL) in civil engi Wood I joist is an engineered product, which was successfully neering, which is made from bamboo [10–15]. Obviously, the effective introduced into the fieldsof civil engineering in the 1970s as a substitute utilization of engineered bamboo as a substitute to wood will help to for timber beam with rectangular section [1]. The reasons for the mitigate the pressures on the ever-shrinking forests resources and thus, popularity for the wood I joists include light weight, ease of installation, facilitate the conservation of the global environment [16]. a variety of lengths and design options, the possibility of drilling holes Holes in the web of wood joists, usually circular or square shaped, through their web, and better environmental impact [2]. Usually, the are often introduced to allow passage of services (such as ventilation and flangescan be made of laminated veneer lumber or solid wood and the plumbing), because of the headroom clearance limitation in wood web is typically made from wafer board, plywood or oriented strand structure [17]. The flangesand webs of wood I-joists are often designed board (OSB). There is abundant evidence that OSB is thought to be the to carry moment and shear forces, respectively, and the stresses between most cost-effective web materials [3]. With the environment of the the flanges and web are transmitted through the flange-web glue line world deteriorating and the forest coverage being dropped rapidly [4], and nails. Therefore, introducing opening in the web of wood joist large scale deforestation is severely restricted. Therefore, many coun makes the stress distribution more complicated around the opening and tries are facing the difficultyof wood shortages due to over-exploitation changes the failure modes of the joist, resulting to drastic reduction in of their wood resources over the last few decades, particularly in China. capacity for the case of opening located close to the supports and may Bamboo is regarded as one of fast-growing plants, widespread in Africa, cause joists to fail in premature sudden and brittle shear failure. South America and Southeast Asia, and thus to provide adequate raw In the past decades, a series of experimental researches on structural materials for the development of bamboo structure [5–9]. As a performance of wood I-joists with opening in the web has been carried

* Corresponding author. E-mail addresses: [email protected] (G. Chen), [email protected] (J. Wu), [email protected] (H. Jiang), [email protected] (T. Zhou), [email protected] (X. Li), [email protected] (Y. Yu). https://doi.org/10.1016/j.jobe.2019.101129 Received 10 August 2019; Received in revised form 4 December 2019; Accepted 13 December 2019 Available online 14 December 2019 2352-7102/© 2019 Elsevier Ltd. All rights reserved. G. Chen et al. Journal of Building Engineering 29 (2020) 101129

out. Extensive previous research evaluated the failure modes and ca hole in the middle. The yield strength and MOE of C-SP is 220 MPa and pacity reduction of wood I-joists with opening in the web [18–21]. It was 205 GPa, which was provided by the manufacture. demonstrated that joists with web openings exhibited a loss of stiffness The smooth shank nails used in this test are cold-formed from a steel as openings located in shear dominant regions, but little effect on the wire. The average bending yield strength of nails obtained by 5% off-set bending strength of moment critical I-joists. Pirzada et al. [19] studied method is 705.2 Mpa. the influence of the web hole on the performance of wood I-joists and found the typical failure mode was that the OSB fractured from tension 2.2. Unreinforced joists with/without web opening zones around the opening. The joist eventually collapsed after the cracks reached the flanges, which is not conducive to protect personnel and Prefabricated OSB webbed LBL composite joists with a box-shaped property, thus further study and solution are needed urgently. cross-section were introduced [33], which consisted of LBL flanges Previous studies showed that the presence of holes in the web had and OSB webs, as shown in Fig. 1. And the dimensions of the flanges adverse effect on the stress state of joist, therefore could cause a decrease were 2440 mm long by 30 mm wide by 35 mm thick, with a modulus of of strengthen drastically. To change this unfavorable situation, several elasticity (MOE) of 10.24 GPa. Two 240 mm � 9.5 mm webs were reinforcement techniques were developed, such as attaching steel plates, attached to flanges with phenol formaldehyde resin (Yijiayi New Ma plywood plates and FRP sheets by adhesive or nails. Morrissey et al. [20] terial Technology Co., Ltd., Jiangsu Province) and smooth-shank nails tested the performance of wood I joists with and without openings in the (2.1 mm diameter � 38 mm long) spaced at 150 mm on center. Due to webs and found the steel angles retrofits were an effective way to the LBL flanges is relative weak perpendicular to grain, the shear plug enhance the strength and stiffness of joists. Hindman et al. [22] found generated by the nails was likely to cause cracking [34]. So, the webs that the I-joists with the web hole and the double-sided cold formed steel were connected to the flangeswith nails at spacing of 100 mm along the reinforcers retained the I-joist strength and 95.1% of the stiffness of the web edges and the edge distance of nails was 10 mm. Install bearing original I-joist. Ardalany et al. [23] used plywood and thin steel plate for stiffeners tight against the bottom flangeof the joists [35], leaving 5 mm reinforcement of laminated veneer lumber beams with holes and gap at the top (Fig. 1(a)). But the load stiffeners had the opposite concluded that plywood worked more effectively for reinforcing installation (Fig. 1 (b)). The dimension of bearing stiffeners was iden laminated-veneer lumber (LVL) beams. Polocoser et al. [24] has chosen tical to load stiffeners, and the width, thickness and length of stiffeners other reinforcement methods, such as OSB collar, U-shaped OSB and was 30 mm, 35 mm and 165 mm, respectively. For maximum adhesive side laminated-strand lumber (LSL). Results showed that the OSB collar bond strength, the liquid adhesive must “wet” the coating surface, flow reinforcement technique was more effective in returning strength than over and permeate into the surface of OSB webs and LBL flanges. Ac the side LSL technique. cording to the suggestion of manufactures, the consumption of adhesive The flange material of wood I-joist is typically laminated veneer between each other was 250 g/m2. During the gluing process, a pressure lumber or solid sawn lumber, which is made of slow-growing wood [1]. was applied with the aid of nails. Finally, the finished specimens were � Replacing wood by laminated bamboo lumber (LBL) plays an important kept in laboratory room at (20 � 2) C and (65 � 5) % relative humidity, role in mitigating a contradiction of timber supply and demands, natural before being tested after two weeks. forest preservation and improvement of ecological environment. Due to Openings are often made for the passage of ventilation, service ducts higher strength to weight ratio, lower cost and locally available, OSB and wiring, most of which are circular. Previous study showed that up to webbed LBL box-shaped joist is introduced, which had potential to 25 percent of web removal had less influence on the capacity and stiff replace wood I-joist as roof and floorsystems. Cutting web destroys the ness of wood I-joists [18,30]. Therefore, larger opening sizes were integrity of the joists, which is very dangerous and may result in cata considered in this study. To fully understand the mechanical behavior strophic failure. To address these issues, the joists reinforced by collar and failure mode of joists with web opening, the varying ratio of circular shaped oriented strand board patches (C-OSB), two “U” shaped oriented hole diameter to web height (D/hw ¼ 30%, 50% and 75%) and at strand board patches (TU-OSB) and collar shaped steel patches (C-SP) different locations (250 mm, 500 mm, 750 mm and 850 mm from the left around the web opening were tested, respectively. The failure modes, support) were chosen. For D/hw ¼ 30%, 50% and 75%, the nominal strength and stiffness of joists with/without holes were investigated to diameter of circular opening was 51 mm, 85 mm and 127.5 mm, evaluate the reinforcement effectiveness of different methods. respectively.

2. Materials and methods 2.3. Reinforcement joists with web opening

2.1. Materials The specimens were divided into three different series (“A”, “B” and “C”). Among which, control joists (series “A1”) had no opening in the Laminated bamboo lumber (LBL) is an engineered bamboo product web. Series “B” was cut circular hole in the webs, which was common made by peeling bamboo culms usually to 4 mm thickness and 5–8 mm practice in joists to accommodate service pipes. Series “C” was retro width strips and bonding them together with urea formaldehyde adhe fitted by double-sided C-OSB, TU-OSB or C-SP, which had a same size sive [25–27]. During the production process of LBL, the natural flaws circular hole in the webs. Therefore, the joists with same section sizes as such as nodes, cracks, irregular shape and thin-walled hollow existing in Series “B” were retrofittedby double-sided C-OSB (9.5 mm in thickness), raw bamboo are spread at random over the strips, causing its strength to TU-OSB (9.5 mm in thickness) or C-SP sheets to evaluate the impact of be uniform [28–30]. Typically, LBL exhibits less of a tendency to expand the reinforcement on capacity, stiffness and failure modes. And some or contract under the influenceof heat or cold respectively, which means structural measures of reinforcement were adopted as suggested [24, excellent dimensional stability in response to shifting climate conditions 30]. The minimum length of the reinforcement (Lr) on either side of the [31]. opening was twice as much as hole diameter (D) and the height of the The oriented strand board (OSB), 9.5 mm in thickness, is a multi- reinforcement (Hr) was equal to the joist height, as shown in Fig. 2. For layer material made from fast growing Poplar [32]. Both of the C-OSB, the TU-OSB reinforcement technique, the minimum gap between the left TU-OSB and web were manufactured by OSB panels. The tensile and right piece was 2~3 mm. If not, the two pieces were forced between strength, compressive strength, modulus of elasticity (MOE), shear the flanges; it was possible to cause additional stress on the properties of OSB was 12.1 MPa, 13.6 MPa, 3253 MPa and 1420 N/mm2, web-to-flange connection, resulting in delamination. A couple of re respectively. The internal bond strength, moisture content, and density inforcements located on either side of the webs were attached to the joist of OSB was 0.43 MPa, 6.6%, and 580 kg/m3, respectively. The C-SP, 1 by adhesive and the consumption of adhesive between each other was mm in thickness, was made of galvanized steel sheet by cutting a circular 250 g/m2. Then the reinforcements were connected to OSB webs with

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Fig. 1. Test setup (dimensions in mm).

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Fig. 2. Details of web reinforcer.

Table 1 Details of box-shaped joists.

Joist Series Opening location l1 (mm) Reinforcement D/hw Diameter D (mm) Lr � Hr (mm � mm) Quantity of specimens

Control joist A1 – – – – – 7 Unreinforced Joists with opening B1 250 – 30% 51 – 5 B2 250 – 50% 85 – 5 B3 250 – 75% 127.5 5 B4 500 – 50% 85 – 5 B5 850 – 50% 85 – 5 B6 500 – 75% 127.5 – 5 Reinforced joists C1 250 C-OSB 50% 85 170 � 240 5 C2 250 TU-OSB 50% 85 170 � 240 5 C3 250 C-SP 50% 85 170 � 240 5 C4 250 C-OSB 75% 127.5 255 � 240 5 C5 250 TU-OSB 75% 127.5 255 � 240 5 C6 250 C-SP 75% 127.5 255 � 240 5 C7 500 C-OSB 50% 85 170 � 240 5 C8 500 TU-OSB 50% 85 170 � 240 5 C9 500 C-SP 50% 85 170 � 240 5 C10 850 C-OSB 50% 85 255 � 240 5 C11 850 TU-OSB 50% 85 255 � 240 5 C12 850 C-SP 50% 85 255 � 240 5 C13 500 C-OSB 75% 127.5 255 � 240 5 C14 500 TU-OSB 75% 127.5 255 � 240 5 C15 500 C-SP 75% 127.5 255 � 240 5

50 mm common nails along the panel edges, which provided uniform Circular holes are frequently required in the web of joists for the passage pressure for the cure of adhesive. The reinforced joists were allowed to of water supply and drainage pipes. All joists measured 2000 mm be � cure for two weeks at a temperature (20 � 2) C and a relative humidity tween supports (L ¼ 2000 mm) and 240 mm in height (H ¼ 240 mm). � (60 � 5) prior to testing. The C-OSB, TU-OSB and C-SP patches were designed to reinforce the Details about the testing matrix and the different joist configurations joists with web opening. Sometimes the web of joist may be drilled are given in Table 1. In this testing program, a total of 112 joists with through by the sub-contractor without permission, then the service pipes five or seven replicates were tested. For example, the specimens of A1 are installed in place. A common practice is to remove the joists and series had 7 replicas, which are designated as A1-1, A1-2, A1-3, A1-4, replaced by a new one, leading to rising costs of remove and installation. A1-5, A1-6 A1-7, respectively. Among which, 105 joists were fabricated So this may not be a cost-effective solution [17]. Obviously, C-OSB and with openings through the web whilst the others had a solid web. The C-SP were no longer appropriate for this case, so TU-OSB patches were OSB patches used for the subsequent retrofitwas the same as the webs. designed to retrofit the joists without removing service pipes. Joists with a length of 2.4 m are often used in the kitchen and toilet floor.

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Fig. 3. Average load-displacement curves.

2.4. Methods formal loading of specimens was implemented with a displacement control method, according to ASTM D5055-13 [36] requirements with a The three-point bending experiments were conducted to investigate time of 6–10 min for each joist until failure. The maximum load, stiff the mechanical performance and failure modes of simply supported ness, load at a mid-span deflection of L/360 (5.56 mm) and L/180 joists using a 100 kN hydraulic actuator (Fig. 1(d)). Lateral restraints (11.11 mm) were chosen to evaluate the joists reinforcement were applied at the ends of specimens by two pairs of steel supports to techniques. prevent rollover. Three Laser Displacement Sensors (LDS) with an ac � curacy of 0.1 mm were used for continuously monitoring the vertical 3. Experimental observations and results deformations at mid-span and supports of specimens. All the experi mental data was fed to a data acquisition system at a frequency of 10 Hz. All the joists show similar failure behavior and load-displacement To ensure apparatus operating well, pre-loading is necessary before responses, therefore, only the average load-displacement curves are formal testing. Then the specimens should be horizontally and vertically presented in Fig. 3. In case of control joists (series A1), the load- leveled again. The actuator load cell, strain gauges and displacement displacement curves of 7 replicates at load-ascending stage are aver transducer readings were reset to zero, representing the initial state. The aged. However, it is hard to calculate the average curve when the load

Fig. 4. Typical failure modes of control joists without opening.

5 G. Chen et al. Journal of Building Engineering 29 (2020) 101129 drop is occurring. For simplicity, one of the measured curves of speci specimens with smaller opening (D/hw � 30%) was similar to those mens at descending stage is selected as the average descending curve of joists without opening. The failure was initiated mostly due to the web series A1. The load-displacement curves of joists are linear up to shear failure at mid-span, as shown in Fig. 5 (a). Some of specimens approximately 90% of the ultimate load carrying capacity. Subse failed in de-bonding and nail withdrawal, which was investigated in the quently, the load-displacement curves displays non-linear characteris web-flangeinterface (Fig. 5 (b)). Nonetheless, failures in which the nails tics until reach the ultimate load carrying capacity, followed by an pulled through the OSB webs occurred, but were seldom observed, as abrupt and rapid decrease in capacity. Then the observed failure modes shown in Fig. 5 (c). As the tests progressed, failures in the form of nail in control joists, unreinforced joists with web opening, and reinforced heads embedding into and pulling out from the OSB webs were also joists with web opening, were detailed which were all different observed (Fig. 5 (d)). depending on the opening size, opening location and reinforcement Introducing a larger opening (D/hw � 50%) in the web brought a scheme. significantreduction in shear capacity and consequently the flangeshear capacity became important. The rest of the web below and above the hole was not enough to resist shear induced by external load. The 31. Control joists (solid web) presence of large opening markedly affected the flow of stresses in the webs and the stress field at the opening edge varied from tension to Series A1 represents the control joists without web opening. The compression. Due to the removal of material from the web, the reduction load-displacement of curves of seven control joists without hole in the in shear capacity was relatively large. The cracks firstlyappeared almost web are plotted in Fig. 3 (a). As expected, seven control joists without simultaneously at the two tension corners of opening and developed holes behave almost elastically until reaching the ultimate load carrying capacity, followed by abruptly shear failure in the mid-span of the web. As shown in Fig. 4 (a), the failure of these specimens started from shear buckling of the web adjacent to the load point (mid-span), however, the ultimate failure was attributed to a mixture of shear buckling of the webs and separation of OSB in flanges. The ultimate failure condition is definedas the load at 80% of peak load on the descending portion of the load-displacement curve. Surprisingly, no whole fracture of flangeswas observed, which was helpful for protecting personnel from injury or damage. However, this failure phenomenon was very common in the tests of wood I joists [19,20] and bamboo beams [37]. It was observed that only one joist failed at a low load compared to the other control joists, due to the de-bonding of the web-flange joint (Fig. 4 (b)).

3.2. Joists with web opening and without reinforcement

A total of thirty joists with opening were tested with different hole configurations. The presence of web opening has detrimental effect on the mechanical performance of joists, and thereby changes the capacity, stiffness and failure modes of joists. Different failure modes occurred for Fig. 6. Load-strain curves around the circular opening in specimen B3-2. varying hole sizes and location. The mechanical performance of

Fig. 5. Typical failure modes of unreinforced joists with opening.

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Fig. 7. Typical failure modes of reinforced joists.

diagonally towards the flanges, accompanied with noises. Immediately were different depending on the reinforcement scheme. The joists after the cracks reached the flanges, the web above and below the reinforced by OSB plates behaved similarly. The fracture line at mid- opening could not enough to resist the shear stress then the shear was span, as shown in Fig. 7 (a), was caused by critical tensile stress after transmitted to adjacent sections of the webs and flanges. A sudden in buckling. However, some of specimens failed in de-bonding and nail crease of combination stress in flanges and webs usually caused the withdrawal, which was investigated in the web-flange interface, as secondary failures of de-bonding between them and nails pulled out of shown in Fig. 7 (b). For joists with opening reinforced by C-SP, tests the OSB webs, as shown in Fig. 5 (e). Surprisingly, no visible damage in showed that the C-SP yielded and then OSB cracks formed in the tension flanges was observed when the failure of joists has happened. concentration zones around the opening. The application of C-SP The presence of holes reduced cross-section of the web, resulting in a patches to the web opening could improve the tensile strength signifi bad shear load transfer. During the testing, the specimens with large cantly, but the improvement in the compressive strength was relatively holes had similar failure characteristic. With the increase of load, the small. A few nails used to connect the web and reinforcers were pulled circular holes gradually became elliptical. Cracking noise was firstly out, but the adhesive layers between the webs and reinforcers remained heard at 10.47 kN in specimen “B3-2”. Fig. 6 shows the strain readings intact, which could be considered to have successfully transferred from the strain gauge 1 to 4, diagonal parts are going into tension (lower stresses and acted as one piece with the web around the boundary of the left corner and upper right corner) and compression (upper left corner opening. Immediately after the web above and below the hole failed due and lower right corner), which is coincide with the experimental phe to shearing, the load was transmitted to adjacent sections of the web. nomena (Fig. 5 (f)). Cracks formed around the holes with continuous The sudden increase in shear stress along the adjacent sections of the noise and gradually propagated towards the flanges, indicating peak web often caused secondary failures of web pullout or nails shear load is reaching soon. fracture. The U-OSB either prevented the shear cracks initiation or stopped the 3.3. Reinforced joists web shear cracks around the opening from propagating, and thus the effect of opening on the mechanical performance of the joists was Three different reinforcement schemes were considered, including negligible. Most of the joists still failed in shear diagonally, which was TU-OSB, C-OSB and C-SP. Observed failure modes in reinforced joists followed by nail pull through or withdrawal. In the case of C-OSB and

Table 2 Test results of joists.

Joist Pu (kN) COV (%) PL/360 (kN) COV (%) PL/180 (kN) COV (%) Pcr (kN) COV (%) Ke (kN/mm) COV (%)

A1 28.03 11.0 6.16 9.6 13.85 10.5 25.03 10.4 1.37 10.9 B1 27.30 10.9 5.75 11.2 12.98 9.9 23.95 10.1 1.32 11.0 B2 21.17 8.6 5.51 7.8 12.62 10.6 15.22 9.9 1.22 10.0 B3 18.68 10.2 4.72 10.4 11.12 11.4 11.17 11.1 1.07 10.8 B4 22.89 8.9 5.25 8.3 12.89 8.6 15.43 8.7 1.23 8.7 B5 19.35 12.1 4.69 11.0 11.91 10.2 12.90 10.9 1.16 13.7 B6 18.89 10.5 4.22 9.6 9.75 11.3 12.35 11.4 0.93 12.3 C1 28.63 11.9 6.51 8.9 13.90 12.4 18.49 9.8 1.32 13.3 C2 25.91 8.4 6.31 7.9 13.21 9.5 17.25 10.4 1.31 10.4 C3 25.19 8.1 5.77 8.0 12.83 9.3 16.19 10.1 1.27 10.3 C4 22.38 9.6 6.35 10.5 13.71 10.6 18.16 9.8 1.30 12.2 C5 20.41 7.4 5.71 8.7 12.92 8.3 16.14 9.6 1.25 9.4 C6 19.98 10.2 5.82 12.4 12.65 11.3 14.09 11.5 1.20 12.9 C7 28.82 11.3 6.59 10.5 14.75 10.1 19.92 10.8 1.45 14.2 C8 27.43 9.4 5.95 10.0 13.01 8.7 17.53 9.8 1.34 11.7 C9 24.79 11.4 5.58 10.5 13.29 12.5 12.68 10.1 1.31 13.1 C10 25.90 9.9 6.13 8.6 13.75 9.8 16.05 10.9 1.36 12.1 C11 23.83 8.7 5.87 9.1 12.34 10.1 14.93 9.6 1.27 10.4 C12 22.89 10.8 5.98 10.2 12.92 11.2 13.13 10.4 1.23 12.7 C13 23.70 9.9 6.08 8.3 13.23 9.7 15.10 10.2 1.28 9.8 C14 21.51 9.6 4.89 10.6 11.52 10.7 13.20 11.0 1.17 10.8 C15 19.99 10.1 4.48 9.2 10.89 9.5 11.40 9.5 1.12 11.1

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with opening to the control joist (series A1).

4.1. Diameter of the hole

The control joists (Series A1) without web opening had a peak load of 28.03 kN and Series B1, B2 and B3 with varying hole size (D/hw ¼ 30%, 50% and 75%) had a capacity of 27.30 kN, 21.17 kN and 18.68 kN, indicating a decrease of load carrying capacity by 3%, 24% and 33%, respectively compared to the control joists (Fig. 9). With regards to the size of openings, 30 percent of the web height is the demarcation line for the terms “small” and “large”. For smaller opening (D/hw � 30%), the impact of web opening was negligible and did not cause a reduction in load carrying capacity, and so no reinforcement was required. There 00 Fig. 8. Definition of initial stiffness. fore, the opening limit “D/hw � 0.3 for 240 mm high OSB webbed LBL box-shaped joists was 42.5 mm. Similar results were also reported that the limit of 50 mm diameter opening for LVL beams with no obvious strength reduction [23]. Introducing a larger opening (D/hw � 50%) in TU-OSB on both sides, crack propagation was prevented. In the tests, the the web could cause a significantreduction in capacity and consequently changed the failure mechanism to crack initiation and propagation failures of specimens (D/hw ¼ 50%) with web opening reinforced by C- OSB were mainly governed by mid-span failures in the high moment around opening. The load at the ultimate limit states of joists with area of the specimens. Also, the opening locations to the supports from opening (Series B3) even decreased up to 67% in comparison with the 250 mm to 850 mm were considered and it was found that no noticeable control joists (Series A1). Cracking around the opening is a sign of ul failure modes changed for specimens. The specimens (B2 and B4) failed timate failure of joists about to happen and the average ratio of Pcr/Pu is in shear failure at the opening location and the rest of the specimens (B5 59.8%~89.3%. The cracking load decreases with the increasing of the > and B6) failed in combined flexureand shear. The phenomenon of crack diameter of circular web hole, especially for bigger hole (D/hw 30%). initiation and propagation in reinforced joists was similar to the unre As shown in Table 2, the hole diameter in the web has little effect on the stiffness of joists. The average stiffness of Series A1, B1, B2 and B3 inforced joists with larger web opening (D/hw ¼ 75%). was 1.37 kN/mm, 1.32 kN/mm, 1.22 kN/mm and 1.07 kN/mm, 4. Discussion respectively. Even a web removal of up to 75% of web height, the reduction of stiffness was about 22% for Series B3 (D/hw ¼ 75%) in comparison to Series A1. The average and coefficient of variation (COV) of peak load Pu, cracking load Pcr, stiffness Ke, and load at serviceability conditions (PL/ 180 and PL/360) are presented in Table 2. Prior to failure, no cracking was 4.2. Location of the hole visible but noises were heard. It is believed that there must have been micro-cracks that developed in the joists before the macro ones seen at Based on the test results above, a circular hole in the web reduces the failure [38]. The load associated with this stage is defined as the load carrying capacity of a joist, which is depended on the hole size and “cracking load”, and represented by Pcr. As illustrated in Fig. 8, Ke is location. Fig. 10 shows the relationship between load and location of the defined as the slope the secant between 10-40 percent of the peak load hole in the box-shaped joists. Series B2, B4 and B5 had a web opening [39]. The serviceability limit states concerned the deformation property with the same dimension (D/hw ¼ 50%) at a different distance from the of the floor/roof systems, which is closely related to the comfort of mid-span, and the peak load was 21.17 kN, 22.89 kN and 19.35 kN, personnel. PL/180 is load at D ¼ L/180 is the serviceability condition for respectively. Usually, the stiffness criterion is a predominant controlling flooring & roofingsystem [40]subjected to total load (dead load þ live factor in the design and use of longer span wood/bamboo beams, rather load þ snow load), PL/360 is load at D ¼ L/360 is the serviceability than the load carrying capacity [42–46]. In Fig. 11, circular hole were of condition for flooring & roofing system based on live load [41]. The the same size, i.e. half of the web height (D/hw ¼ 50%). The joists effective of three methods of reinforcement (C-OSB, TU-OSB and C-SP) investigated were under constant shear and circular hole at different are considered, in order to restore the full capacity and stiffness of a joist locations were subject to different values of moment but the same shear. Therefore, the hole location has little effect on the stiffness of joists, regardless of the opening size and position along the length of joist if the

Fig. 9. Load versus diameter of circular hole (l1 ¼ 250 mm). Fig. 10. Load versus opening location (D/hw ¼ 50%).

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strength, TU-OSB was the middle and the C-SP was the worst. The average load improvement of Series C13, Series C14 and Series C15 was 36%, 18% and 12% for roof & flooringsystem subjected to total load (Δ ¼ L/180) and 44%, 16% and 6% for roof & flooring system subjected to live load (Δ ¼ L/360), respectively compared to those of the load at serviceability conditions of unreinforced Series B6. The experi mental results indicated that the load at serviceability conditions of joists with web opening could be improved by three different rein forcement techniques, among which, the C-OSB was most effective, TU- OSB less and C-SP least.

4.4. Prediction of load carrying capacity

Many models have been suggested to predict the load carrying ca pacity of wood I-joists with web opening [30,38]. Shahnewaz et al. [30] studied the effect of size and location of web openings on wood I-joists ¼ Fig. 11. Stiffness versus opening location (D/hw 50%). and proposed empirical formulas to calculate the capacity of I-Joists with openings. Zhu et al. [38] conducts a study on OSB webbed timber I-beams with circular and square opening, whilst the location of opening has little effect on the reduction of capacity and developed empirical opening was located at least 250 mm away from the supports and formulas to predict the capacity of joists with web openings. Based on concentrated load. There was very little difference in the stiffness of the experimental results, a regression analysis was performed to develop joists reinforced by C-OSB, TU-OSB and C-SP. As expected, the design of models to estimate the capacity of unreinforced and reinforced OSB webbed LBL box joists is determined by the stiffness, rather than the box-shaped joists with a circular web hole. As mentioned above, for load carrying capacity. small circular web hole (D/hw � 30%), the effect of the hole was negligible and did not cause strength reductions. The reduced capacity due to the presence of circular opening in the web can be determined as 4.3. Retrofit type follows: For unreinforced joists with web opening (D/hw>30%): A couple of C-OSB attached to the joists could effectively restrained � � shear cracks around the circular hole from propagating towards the D Fur ¼ 33:05 À 19:16 (1) flanges, thus helping to prevent shear failure and improve the capacity hw of joists. Compared to unreinforced joists with opening, the biggest For reinforced joists: improvement of load carrying capacity of joists reinforced by C-OSB was � � 35% (Fig. 12). Among the three retrofit methods, the C-OSB reinforce D Fr ¼ 32:9 À 15:3 (2) ment worked most effectively for opening diameter up to 75% of the hw web depth and returned 2 of 5 series of joists to a capacity equivalent to the “no hole” condition. However, the TU-OSB and C-SP could effec Where, Fe is the capacity of unreinforced joists with opening (D/hw � tively improve the capacity of joists with opening diameter less than 30%), Fur and Fr is the capacity of unreinforced and reinforced joists, 50% of the web depth. For joists with web opening (D/hw ¼ 75%), the respectively. average capacity improvement of joists reinforced by C-OSB, TU-OSB The predictions using these models are compared against the test and C-SP were 25%, 14% and 6%, respectively compared to that of results in Fig. 13. In case of reinforced joists, the Zhu’s model signifi the Series B6. It was demonstrated that the C-OSB worked most effec cantly over-predicts the capacity of joists with small web opening (D/hw tively, the C-OSB was shown to be the most effective to return the � 30%), but appropriate for joists with larger opening (D/hw>30%). In

Fig. 13. Comparison of test results and theoretical results.

9 G. Chen et al. Journal of Building Engineering 29 (2020) 101129

Fig. 12. Comparison of load at ultimate limit state (negative sign means capacity decrease in % compared to control joists without web opening, and positive sign means improvement after reinforcement).

case of reinforced joists, Zhu’s model under-estimates the capacity and with opening size, whilst location of opening has little effect on the the deviations between experimental and theoretical model results in reduction of capacity. No significant change was found in stiffness, crease with increasing ratio of diameter of web height (D/hw). The regardless of the opening size and position along the length of unrein Shahnewaz’s model remarkably over-predicts the capacity of unrein forced joist if the opening was located at least 250 mm away from the forced and reinforced joists. The proposed approach (equations (1) and supports and concentrated load. C-OSB worked most effectively for (2)) are quite suitable with the experimental results. retrofittingjoists with web holes to a strength and stiffness equivalent to the “no hole” condition, as it could effectively prevent the cracks 5. Conclusions developing prematurely. The mechanical performance and deformation properties of joists with a circular hole could be improved by C-SP In this paper, the test results of OSB webbed laminated bamboo reinforcer, but the improvement was only a small percentage of the total lumber box-shaped joists in the presence of a circular web hole are load-carrying capacity. TU-OSB worked effective for the limited opening presented. The observed failure modes are reported, and the reinforce diameter (D/hw � 50%), but was easier to install without removing the ment effect on the joists are evaluated. service pipes and less expensive than the C-OSB and C-SP. The proposed With regards to the size of openings, 30 percent of the web height is formulation is proved to be a good method for predict the capacity of the demarcation line for the terms “small” and “large”. For smaller holes box-shaped joists with varying configurations. Further study on more (D/hw � 30%), the detrimental impact on performance of joists was joists with other geometrical and loading conditions is needed to provide negligible and did not cause strength reductions. The unreinforced joists more information for engineering applications of box-shaped joists. with larger opening in the web (D/hw>30%) failed in a brittle and sudden shear mode, resulting to the reduction in strength. The me Declaration of competing interest chanical behavior of reinforced joists could be improved remarkably and failed in web buckling, de-bonding of web-flange joint and nail with The authors declare that they have no conflict of interest. drawal. No catastrophic collapse of box-shaped joists was observed, while this phenomenon is common during the tests of wood joists and bamboo beams. The load carrying capacity of joists decreases linearly

10 G. Chen et al. Journal of Building Engineering 29 (2020) 101129

CRediT authorship contribution statement [21] A.M. Harte, G. Baylor, Structural evaluation of castellated timber I-joists, Eng. Struct. 33 (12) (2011) 3748–3754, https://doi.org/10.1016/j. engstruct.2011.08.011. Guo Chen: Supervision, Writing - original draft, Writing - review & [22] D.P. Hindman, J.R. Loferski, Cold-formed steel reinforcement for improperly cut editing. Jing Wu: Data curation. Hao Jiang: Investigation. Tong Zhou: wood composite I-joists, Pract. Period. Struct. Des. Constr. 13 (4) (2008) 198–203, Investigation. Xiang Li: Investigation. Yunfei Yu: Software, Validation. https://doi.org/10.1061/(ASCE)1084-0680(2008)13:4(198). [23] M. Ardalany, M. Fragiacomo, P.J. Moss, B.L. Deam, An analytical model for design of reinforcement around holes in Laminated Veneer Lumber (LVL) beams, Mater. Acknowledgments Struct. 46 (11) (2013) 1811–1831, https://doi.org/10.1617/s11527-013-0019-3. [24] T. Polocoser, T.H. Miller, R. Gupta, Evaluation of remediation techniques for circular holes in the webs of wood I-joists, J. Mater. Civ. Eng. 25 (12) (2013) The authors gratefully acknowledge the financial support from the 1898–1909, https://doi.org/10.1061/(ASCE)MT.1943-5533.0000737. National Natural Science Foundation of China (Grant No. 51408312), [25] M. Mahdavi, P.L. Clouston, S.R. Arwade, Development of laminated bamboo the Natural Science Foundation of Jiangsu Province (Grant No. lumber: review of processing, performance, and economical considerations, – & – J. Mater. Civ. Eng. 23 (7) (2011) 1036 1042, https://doi.org/10.1061/(ASCE) BK20130982), and R D Project of Ministry of Housing and Urban Rural MT.1943-5533.0000253. Development of People’s Republic of China (Grant No. 2018-K5-003). [26] F. Ramirez, J.F. Correal, L.E. Yamin, J.C. Atoche, C.M. Piscal, Dowel-bearing strength behavior of glued laminated Guadua bamboo, J. Mater. Civ. Eng. 24 (11) – References (2012) 1378 1387, https://doi.org/10.1061/(ASCE)MT.1943-5533.0000515. [27] C.S. Verma, V.M. Chariar, Development of layered laminate bamboo composite and their mechanical properties, Compos. B Eng. 43 (3) (2012) 1063–1069, https://doi. [1] R.J. Leichti, R.H. Falk, T.L. Laufenberg, Prefabricated wood I-joists: an industry org/10.1016/j.compositesb.2011.11.065. overview, For. Prod. J. 40 (3) (1990) 15–20. [28] D. Mitch, K.A. Harries, B. Sharma, Characterization of splitting behavior of bamboo [2] R.D. Bergman, S. Alanya-rosenbaum, Cradle-to-gate life-cycle assessment of culms, J. Mater. Civ. Eng. 22 (11) (2010) 1195–1199, https://doi.org/10.1061/ composite i-joist production in the United States, For. Prod. J. 67 (5/6) (2017) (ASCE)MT.1943-5533.0000120. 355–367, https://doi.org/10.13073/FPJ-D-16-00047. [29] M. Shahnewaz, I.M. Shahidul, A. Moein, T. Thomas, A.M. Shahria, Reinforced [3] S. Malek, N. Zobeiry, C. Dai, R. Vaziri, Strain-softening response and failure wood I-joists with web openings, J. Struct. Eng. 143 (6) (2017), 04017022, https:// prediction in notched oriented strand board, J. Mater. Civ. Eng. 31 (6) (2019), doi.org/10.1061/(ASCE)ST.1943-541X.0001747. 04019094, https://doi.org/10.1061/(ASCE)MT.1943-5533.0002737. [30] H. Li, G. Wu, Q. Zhang, A.J. Deeks, J. Su, Ultimate bending capacity evaluation of [4] C.A. Murad, J. Pearse, Landsat study of deforestation in the Amazon region of laminated bamboo lumber beams, Constr. Build. Mater. 160 (2018) 365–375, � Colombia: departments of Caqueta and Putumayo, Remote Sens. Appl.: Soc. https://doi.org/10.1016/j.conbuildmat.2017.11.058. Environ. 11 (2018) 161–171, https://doi.org/10.1016/j.rsase.2018.07.003. [31] I. Sumardi, S. Suzuki, Dimensional stability and mechanical properties of [5] J. Gottron, K.A. Harries, Q. Xu, Creep behaviour of bamboo, Constr. Build. Mater. strandboard made from bamboo, BioRes 9 (1) (2014) 1159–1167, https://doi.org/ 66 (1) (2014) 79–88, https://doi.org/10.1016/j.conbuildmat.2014.05.024. 10.15376/biores.9.1.1159-1167. [6] G. Quaranta, C. Demartino, Y. Xiao, Experimental dynamic characterization of a [32] G. Chen, B. He, Stress-strain constitutive relation of OSB under axial loading: an new composite glubam-steel truss structure, J. Build. Eng. 25 (2019) 100773, experimental investigation, Bioresources 12 (3) (2017) 6142–6156, https://doi. https://doi.org/10.1016/j.jobe.2019.100773. org/10.15376/biores.12.3.6142-6156. [7] A. Hector, K. Sebastian, T. David, Z.E. Edwin, K.A. Harries, Bamboo reinforced [33] C. Liu, G. Chen, L.Y. Li, Y. Qin, J.Y. Wang, M.H. Xu, Experimental investigation on concrete: a critical review, Mater. Struct. 51 (4) (2018) 102, https://doi.org/ OSB webbed laminated bamboo lumber box shaped joists, in: International 10.1617/s11527-018-1228-6. Conference on Advances in Civil Engineering and Materials and 1st World [8] Q.F. Xu, Y.B. Leng, X. Chen, K.A. Harries, L.Z. Chen, Z.L. Wang, Experimental study Symposium on Sustainable Bio-Composite Materials and Structures, Nanjing, on flexural performance of glued-laminated-timber-bamboo beams, Mater. Struct. China, 2019. 51 (1) (2018) 9, https://doi.org/10.1617/s11527-017-1135-2. [34] T. Reynolds, B. Sharma, K.A. Harries, M. Ramage, Dowelled structural connections [9] M. Xu, Z. Cui, Z. Chen, J. Xiang, Experimental study on compressive and tensile in laminated bamboo and timber, Compos. B Eng. 90 (2016) 232–240, https://doi. properties of a bamboo scrimber at elevated temperatures, Constr. Build. Mater. org/10.1016/j.compositesb.2015.11.045. 151 (2017) 732–741, https://doi.org/10.1016/j.conbuildmat.2017.06.128. [35] Y.H. Sun, Z.H. Jiang, H.R. Liu, Z.J. Sun, C.H. Fang, The bending properties of [10] R. Tomasi, M.A. Parisi, M. Piazza, Ductile design of glued-laminated timber beams, bamboo strand board I-beams, J. Wood Sci. 65 (2019) 50, https://doi.org/ Pract. Period. Struct. Des. Constr. 14 (3) (2009) 113–122, https://doi.org/ 10.1186/s10086-019-1828-y. 10.1061/(ASCE)1084-0680(2009)14:3(113). [36] ASTM D5055-13, Standard Specification for Establishing and Monitoring [11] A. Sinha, D. Way, S. Mlasko, Structural performance of glued laminated bamboo Structural Capacities of Prefabricated Wood I-Joists, American Society for Testing beams, J. Struct. Eng. 140 (1) (2014), https://doi.org/10.1061/(ASCE)ST.1943- and Materials, Philadelphia, PA, 2013. 541X.0000807, 04013021. [37] Y. Xiao, Q. Zhou, B. Shan, Design and construction of modern bamboo bridges, [12] H. Li, G. Wu, Z. Xiong, I. Corbi, O. Corbi, X. Xiong, H. Zhang, Z. Qiu, Length and J. Bridge Eng. 15 (5) (2010) 533–541, https://doi.org/10.1061/(ASCE)BE.1943- orientation direction effect on static bending properties of laminated Moso 5592.0000089. bamboo, Eur. J. Wood Wood Prod. 77 (4) (2019) 547–557, https://doi.org/ [38] E.C. Zhu, Z.W. Guan, P.D. Rodd, D.J. Pope, Finite element modelling of OSB 10.1007/s00107-019-01419-6. webbed timber I-beams with openings, Adv. Eng. Software 36 (11) (2005) [13] Y. Yu, R. Liu, Y. Huang, F. Meng, W. Yu, Preparation, physical, mechanical, and 797–805, https://doi.org/10.1016/j.advengsoft.2005.03.027. interfacial morphological properties of engineered bamboo scrimber, Constr. Build. [39] W. Zheng, W.D. Lu, W.Q. Liu, L. Wang, Z.B. Ling, Experimental investigation of Mater. 157 (2017) 1032–1039, https://doi.org/10.1016/j. laterally loaded double-shear-nail connections used in midply wood shear walls, conbuildmat.2017.09.185. Constr. Build. Mater. 101 (2015) 761–771, https://doi.org/10.1016/j. [14] R.A.S. Ribeiro, M.G.S. Ribeiro, I.P.A. Miranda, Bending strength and conbuildmat.2015.10.100. nondestructive evaluation of structural bamboo, Constr. Build. Mater. 146 (2017) [40] Canadian-Standard-Association, CSA O86 – Engineering Design in Wood, 2010. 38–42, https://doi.org/10.1016/j.conbuildmat.2017.04.074. [41] NBCC, National Building Code of Canada; Part 9 – Specific Provisions, 2010. [15] H.T. Li, R. Liu, R. Lorenzo, G. Wu, L.B. Wang, Eccentric compression properties of [42] G. Chen, H.T. Li, T. Zhou, C.L. Li, Y.Q. Song, R. Xu, Experimental evaluation on laminated bamboo lumber columns with different slenderness ratios, Proc. Inst. mechanical performance of OSB webbed parallel strand bamboo I-joist with holes Civ. Eng. Struct. Build. 172 (5) (2019) 315–326, https://doi.org/10.1680/ in the web, Constr. Build. Mater. 101 (2015) 91–98, https://doi.org/10.1016/j. jstbu.18.00007. conbuildmat.2015.10.041. [16] Y. Xiao, R.Z. Yang, B. Shan, Production, environmental impact and mechanical [43] S.R. Acharya, K.S. Sivakumaran, B. Young, Reinforcement schemes for cold-formed properties of glubam, Constr. Build. Mater. 44 (2013) 765–773, https://doi.org/ steel joists with a large web opening in shear zone-an experimental investigation, 10.1016/j.conbuildmat.2013.03.087. Thin-Walled Struct. 72 (10) (2013) 28–36, https://doi.org/10.1016/j. [17] J.C. Bouldin, J.R. Loferski, D.P. Hindman, Inspection of I-joists in residential tws.2013.06.011. construction, Pract. Period. Struct. Des. Constr. 9 (4) (2014), https://doi.org/ [44] E.C. Zhu, Z.W. Guan, P.D. Rodd, D.J. Pope, Buckling of oriented strand board 10.1061/(ASCE)SC.1943-5576.0000208, 04014016. webbed wood I-joists, J. Struct. Eng. 131 (10) (2005) 1629–1636, https://doi.org/ [18] M.T. Afzal, S. Lai, Y.H. Chui, G. Pirzada, Experimental evaluation of wood I-joists 10.1061/(ASCE)0733-9445(2005)131:10(1629). with web holes, For. Prod. J. 56 (10) (2006) 26–30. [45] Y. Wei, X. Ji, M. Duan, G. Li, Flexural performance of bamboo scrimber beams [19] G.B. Pirzada, Y.H. Chui, S. Lai, Predicting strength of wood I-joist with a circular strengthened with fiber-reinforced polymer, Constr. Build. Mater. 142 (2017) web hole, J. Struct. Eng. 134 (7) (2008) 1229–1234, https://doi.org/10.1061/ 66–82, https://doi.org/10.1016/j.conbuildmat.2017.03.054. (ASCE)0733-9445(2008)134:7(1229). [46] Y. Wei, M.Q. Zhou, D.J. Chen, Flexural behaviour of glulam bamboo beams [20] G.C. Morrissey, D.W. Dinehart, W.G. Dunn, Wood I-joists with excessive web reinforced with near-surface mounted steel bars, Mater. Res. Innov. 19 (2015) openings: an experimental and analytical investigation, J. Struct. Eng. 135 (6) 98–103, https://doi.org/10.1179/1432891715Z.0000000001377. (2009) 655–665, https://doi.org/10.1061/(ASCE)ST.1943-541X.0000013.