sustainability
Article Effects of Half-Precast Concrete Slab System on Construction Productivity
Kyuman Cho 1, Young-su Shin 2 and Taehoon Kim 1,* 1 School of Architecture, Chosun University, Gwangju 61452, Korea; [email protected] 2 Manager, Kunwon Engineering, Seoul 05855, Korea; [email protected] * Correspondence: [email protected]; Tel.: +82-62-230-7145
Received: 6 July 2017; Accepted: 17 July 2017; Published: 19 July 2017
Abstract: A half-precast concrete slab system (HPCSS) is reported to exhibit excellent structural performance when compared with traditional slab systems. However, there is a lack of extant research examining the construction issues of an HPCSS. Thus, in this study, we analyze the construction process and productivity of applying an HPCSS by using a simulation method with the data collected from an actual construction case. The results indicate that (i) the construction productivity of HPCSS is 1.7 times that of a traditional slab system, (ii) the cost per productivity unit of HPCSS exceeds that of a traditional slab system, and (iii) critical resources affecting the HPCSS productivity include form crew and rebar crew. The results of this study suggest that it is possible to develop an optimal construction plan of a construction site in which an HPCSS is installed, and that the HPCSS can be actively applied in the future.
Keywords: half-precast concrete slab system; construction productivity; construction simulation
1. Introduction The construction industry is a highly labor-intensive industry facing several issues, including low productivity and construction quality. In order to overcome such problems, several researchers and practitioners have attempted to develop various methods to facilitate mechanical or manufactured procurements for a part of a facility, and this has subsequently led to the proliferation of automation technology in construction. That is, automation construction technologies are used in the construction of facilities, and the use of construction machines instead of construction laborers has led to high effectiveness and quality in assembling several parts of a facility. In this context, precast concrete (PC) slab systems have been proposed by various researchers because of their advantages in terms of quality, convenience, and construction period. Recently, a half-PC slab (or composite slab) was developed to replace existing construction methods, and to improve the performance of a PC slab system. In general, a half-PC slab system (HPCSS) is defined as a slab system that is pre-stressed and used with slab topping concrete. The structural performance of an HPCSS is known to be higher than that of normal concrete in terms of crack and deflection control because of the manufacturing process employed in controlled environments in a factory [1]. Although several researchers have examined the structural performance of HPCSSs, there is a paucity of research investigating issues concerning construction engineering and management. That is, it is necessary to identify (i) the manner in which relevant work activities are influenced by the application of HPCSS, (ii) the type of work activities comprising the HPCSS that has the maximal impact on determining project success, and (iii) the type of resources required to carry out the aforementioned activities that should be carefully considered to achieve effective construction work. In this context, the aim of the present study involves analyzing the differences between the construction productivity of an HPCSS and that of a traditional slab system. In addition, the study focuses on detailing issues related to an HPCSS based on the results of construction productivity analysis.
Sustainability 2017, 9, 1268; doi:10.3390/su9071268 www.mdpi.com/journal/sustainability Sustainability 2017, 9, 1268 2 of 15
Essentially, in the study, the construction productivity of an HPCSS is analyzed to compare an HPCSS and a traditional slab system (i.e., a cast-in-place slab system or CIPSS). This involves selecting and analyzing an actual construction that is built by using both slab systems experimentally to gather the data necessary to compare the construction process and productivity of the HPCSS with the corresponding parameters of a CIPSS. A discrete event simulation technique based on the collected data is used to measure the performance of each slab system in terms of construction productivity, including installation time, resource utilization, and cost effectiveness.
2. State of the Art Several studies have introduced methods to enhance the structural performance of concrete members. Recent studies have proposed cement-based bonded overlay techniques (i.e., HPCSS) to enhance the structural performance of a PC slab system by topping a layer of cast in-situ reinforced concrete with various materials, including steel fibers and polyvinyl alcohol fibers [2–4]. The purpose of these studies involved adding materials to improve the load-carrying capacity and stiffness of the HPCSS, and their results revealed that the structural performance of the HPCSS was highly dependent on the bonding between the topped layers and the substrate [3]. Most previous studies related to composite slabs have focused on evaluating their structural performance. However, to the best of the authors’ knowledge, very few studies have explored the effect of applying an HPCSS from a construction engineering and management (CEM) viewpoint. A careful review of previous studies that focus on the CEM aspects of precast technology, including HPCSS, indicates that the research objective and scope of the extant studies can be divided into the three following categories: (i) production management of precast members [5–8], (ii) benefit analysis of precast technology in terms of waste management, environment, time, and cost [9–11], and (iii) effective installation of precast members [12–14]. With respect to the first category, Chen et al. [5] examined the issue of improving the current production process of the precast elements based on expert opinions. Ko and Wang [6] and Li et al. [7] proposed a decision support system using genetic algorithms to aid project managers in arranging precast member production plans. Yin et al. [8] developed a precast production management system using radio-frequency identification (RFID) to facilitate the production of precast members by considering production quantity, material quantity, and inspection and inventory information. With respect to research related to benefit analysis in conjunction with the application of a precast technique, Ahmed and Avetisyan [9] analyzed the benefits of applying precast normal weight wall panels in terms of the construction time and costs. Dong et al. [10] measured carbon emissions from the application of a precast method with high-rise building construction work. Shen et al. [11] analyzed the benefits of the precast method in terms of reducing waste. With respect to the effective installation of precast members, Li et al. [12] suggested a new system to train precast installation workers to be productive while ensuring awareness of the risks of precast installation works. Nath et al. [13] proposed a method to generate shop drawings of precast members by using building information modeling (BIM) technique. Pan et al. [14] proposed a new technique termed the “Full-span precast launching method” to develop bridge construction technology based on the results of high-speed rail project case studies. As mentioned previously, there is a lack of studies examining the precast method from the CEM viewpoint, while very few extant studies have focused on improving the production efficiency and delivery issues of precast elements. In addition, although HPCSS was developed to compensate for the several problems of a precast slab system, to the best of the authors’ knowledge, very few studies have explored the construction aspects of HPCSS. Hence, the present study focuses on the manner in which an HPCSS application affects related construction works and construction productivity when compared with those of a conventional CIPSS. Sustainability 2017, 9, 1268 3 of 15
3. Case Study of Half-Precast Slab System Construction Work As mentioned previously, the construction productivity of an HPCSS is based on the comparison results between an HPCSS and a CIPSS. Thus, it is necessary that a case study should be conducted based on an actual project that is constructed using both slab systems (i.e., HPCSS and CIPSS).
3.1. Case Introduction Table1 lists the profile of our selected construction project case. As can be inferred from the table, the building in question was located in Gwangju Metropolitan City, comprising six floors (five floors and one underground floor). With respect to the structure system, (i) the main structure system design was based on the reinforced concrete system, (ii) HPCSS was applied to the slab work at the 5th floor, and (iii) the other floors (i.e., 2nd to 4th floors) were constructed using CIPSS.
Table 1. Details of the case considered in the study.
Items Major Features Project name K Building construction project Location Gwangju Metropolitan City, South Korea Type of building Office building Type of structure Reinforced Concrete (RC) system Construction area 2138.56 m2 Gross floor area 6610.98 m2 Number of Floors 6 floors (five floors and one underground floor) Floor plan HPCSS installed 5th floor CIPSS installed 2nd to 4th floors Floor area installed by HPCSS 564.2 m2
Figure1 shows the floor construction plan with the use of each slab system (i.e., HPCSS and CIPSS). As shown in the figure, each floor has a similar space plan involving the design of two separated spaces (i.e., service area and office area), and HPCSS and CIPSS were applied to construct the office area. Figure1a shows the plan of the 5th floor that was designed such that it was constructed using 16 HPCSS units, while the 2nd to 4th floors were constructed using the traditional slab system (i.e., CIPSS), as shown in Figure1b. The construction productivity of each slab system was deduced based on the data including resource and duration information (Table2) collected during the installation work of each system on the same area, and thus, the construction productivity of both slab systems could be considered reliable. Sustainability 2017, 9, 1268 4 of 15 Sustainability 2017, 9, 1268 4 of 15
1 3
2 4
5
6
7 1 8
10 9
12 11
14 13
16 15
(a) (b)
FigureFigure 1. Floor1. Floor plans plans for for half-precast half-precast concrete concreteslab slab systemsystem (HPCSS) and and a a cast-in-place cast-in-place slab slab system system (CIPSS) for the case project: (a) 5th floor plan; (b) 2nd–4th floor plan. (CIPSS) for the case project: (a) 5th floor plan; (b) 2nd–4th floor plan.
3.2. Installation Process of Each Slab System 3.2. Installation Process of Each Slab System With respect to buildings that adopt a reinforced structure system, the structure system typicallyWith respect comprises to buildings four basic that elements adopt a reinforcedincluding column, structure beam system, and the girder, structure wall, system and slab. typically In comprisesaddition, four a case basic showed elements that there including was no column, difference beam in andterms girder, of installation wall, and work slab. of Inthe addition, column, a casebeam, showed girder, that and there wall, was irrespective no difference of the in type terms of of slab installation works (i.e., work HPCSS of the and column, CIPSS). beam, That is, girder, in andadvance wall, irrespective of slab installation, of the type it is necessary of slab works to complete (i.e., HPCSS a common and process CIPSS). (CP) That of is, the in three advance following of slab installation,work activities: it is necessary (i) preparation, to complete (ii) column a common and beam process installation, (CP) of and the three(iii) wall following installation. work activities: (i) preparation,As shown (ii) in column Figure and2, (i) beampreparation installation, includes and four (iii) tasks wall including installation. marking (CP 1), horizontal standAs showninstallation in Figure (CP 22),, (i) rebar preparation delivery includes (CP 3), and four form tasks and including support marking delivery (CP (CP 1), 4). horizontal This is standfollowed installation by the (CP three 2), rebarfollowing delivery work (CP tasks 3), and to co formmplete and column support and delivery beam (CP installation 4). This is activity: followed bycolumn the three rebar following installation work (CP tasks 5), column to complete form columninstallation and (CP beam 6), and installation beam form activity: installation column (CP rebar 7). installationWith respect (CP to 5), the column final common form installation activity, wall (CP in 6),stallation and beam work form requires installation three common (CP 7). Withwork respecttasks to theincluding finalcommon wall form activity, installation wall (one installation side) (CP work 8), wall requires rebar three installation common (CP work 9), and tasks wall including form wallcompletion form installation (CP 10). With (one respect side) (CP to common 8), wall work rebar ta installationsks (CPs 1 to (CP 10), 9), form and labor, wall steel form labor, completion and a (CPtower 10). Withcrane respect are continuously to common input work to implement tasks (CPs the 1 to work 10), formtasks.labor, steel labor, and a tower crane are continuously input to implement the work tasks. Sustainability 2017, 9, 1268 5 of 15 Sustainability 2017, 9, 1268 5 of 15
Preparation Column and Beam installation Wall installation
CP 1 CP 2 CP 3 CP 4 CP 5 CP 6 CP 7 CP 8 CP 9 CP 10
Work Start
Marking Horizontal stand Rebar Form & Support Column rebar Column form install Beam form Wall form Wall rebar installation Wall form completion installation delivery delivery installation installation Installation(half)
Form installation Rebar installation Concrete work Form removal
CIP 1 CIP 2 CIP 3 CIP 4 CIP 5 CIP 6 CIP 7 CIP 8 CIP 9
Work End
Form & Support Slab form installation Rebar Beam rebar Rebar Slab rebar installation Concrete placing and Form removal (Beam) Form removal(Slab) delivery delivery installation delivery Curing Slab work Concrete work Form removal process PC Slab placing and rebar installation
Figure 2. 2. WorkWork process process of of HPCSS HPCSS and and CIPSS. CIPSS.
After completing the common process, different slab work processes are initiated based on the typeAfter of slab completing system (i.e., the HPCSS common and process,CIPSS), as different shown slabin Figure work 2. processes If a conventional are initiated slab system basedon (i.e., the typeCIPSS) of is slab applied, system then (i.e., the HPCSS four following and CIPSS), work as acti shownvities are in Figurerequired:2. If(i) a form conventional installation, slab (ii) system rebar (i.e.,installation, CIPSS) is(iii) applied, concrete then work, the and four (iv) following form removal. work activities As shown are in required: the figure, (i) form form installation installation, (ii)consists rebar of installation, two work tasks (iii) concreteincluding work, form and and support (iv) form delivery removal. (CIP As 1) shownand slab in form the figure,installation form installation(CIP 2). Rebar consists installation of two requires work tasks two works including and formtwo deliveries, and support namely, delivery beam (CIP rebar 1) delivery and slab (CIP form installation3), beam rebar (CIP installation 2). Rebar installation(CIP 4), slab requires rebar deliv twoery works (CIP and 5), and two slab deliveries, rebar installation namely, beam (CIP rebar 5). deliveryFollowing (CIP the 3), rebar beam installation rebar installation work, concrete (CIP 4), placin slab rebarg and delivery curing (CIP(CIP 5),7) is and conducted, slab rebar and installation this is (CIPfollowed 5). Following by form removal the rebar works installation for the beam work, and concrete slab (CIPs placing 8 and and 9). curing With respect (CIP 7) to is the conducted, CIPSS andwork this process, is followed existing by formresources removal such works as form for theand beam rebar and labor slab and (CIPs a tower 8 and 9).crane With are respect constantly to the CIPSSinput, workand the process, concrete existing labor and resources pump such car are as formfreshly and input rebar to laborperform and the a towerconcrete crane placement are constantly task. input,The and three the concretefollowing labor work and activities pump carare arerequired freshly to input apply to an perform HPCSS: the (i) concreteslab placing placement and rebar task. installationThe three (HPCs following 1 to 4), work(ii) concrete activities work are (HPC required 5), and to apply(iii) form an removal HPCSS: (HPC (i) slab 6). placing The differences and rebar installationbetween HPCSS (HPCs and 1 to CIPSS 4), (ii) are concrete identified work from (HPC the 5),process and (iii) of slab form placing removal and (HPC form 6). removal The differences works. betweenThat is, the HPCSS application and CIPSS of HPCSS are identified allows for from the thesimplification process of and slab removal placing andof two form work removal tasks when works. Thatcompared is, the with application that of the of HPCSSCIPSS process. allows forFirst, the the simplification form installation and removaland slab ofrebar two installation work tasks tasks when comparedare eliminated with thatand ofsimplified, the CIPSS and process. following First, concrete the form curing, installation there and is no slab need rebar for installation the slab form tasks areremoval eliminated task in and the simplified, HPCSS process. and following concrete curing, there is no need for the slab form removal task in the HPCSS process. 4. Simulation Modeling and Implementation 4. Simulation Modeling and Implementation The measurement of the construction productivity of HPCSS and CIPSS was conducted by usingThe the measurement cyclic operation of the network construction (CYCLONE) productivity method of developed HPCSS and by CIPSS Halpin was and conducted Riggs [15]. by This using themethod cyclic is operation widely networkused in (CYCLONE)related research method fields. developed Furthermore, by Halpin CYCLONE and Riggs is [ 15a ].discrete-event This method is widelysimulation used method in related that research focusesfields. on construction Furthermore, work CYCLONE tasks, and is thus, a discrete-event this method simulationis widely applied method thatto model focuses repetitive on construction construction work work. tasks, In and addition thus, this, CYCLONE method isis widelyutilized applied as a management to model repetitive tool to constructionanalyze construction work. In productivity addition, CYCLONE based on isthe utilized logical as connections a management between tool towork analyze tasks, construction duration, productivityand resources, based and onthus, the CYCLONE logical connections can be used between to determine work tasks, the influence duration, of and specific resources, work tasks and thus,on CYCLONEthe overall canconstruction be used to productivity determine the ininfluence conjunction of specific with variations work tasks in on duration the overall and construction resources productivityassigned to each in conjunction work task with [16,17]. variations More ininformation duration and on resourcesCYCLONE assigned including to each modeling work taskelements [16,17 ]. Morecan be information found in the on study CYCLONE by Halpin including and Riggs modeling [15]. elements can be found in the study by Halpin and Riggs [15]. Sustainability 2017, 9, 1268 6 of 15 Sustainability 2017, 9, 1268 6 of 15
4.1. Simulation Modeling 4.1.Using Simulation CYCLONE Modeling and information with respect to the case study including the work processes (i.e., FigureUsing2 )CYCLONE and their precedenceand information relationships, with respect we to developedthe case study CYCLONE including models the work of processes CIPSS and HPCSS,(i.e., Figure as shown 2) and in Figurestheir precedence3 and4, respectively. relationships, As we shown developed in the figures,CYCLONE the twomodels simulation of CIPSS models and consistHPCSS, of theas shown two following in Figures parts: 3 and (i) 4, CP respectively (i.e., elements. As denotedshown inby the the figures, green the area two in Figuresimulation3) and CIPSSmodels (i.e., consist elements of the denoted two following by the parts: red area (i) CP in (i.e Figure., elements3) parts denoted in the by model the green for the area traditional in Figure 3) slab systemand CIPSS installation (i.e., elements process anddenoted (ii) CP by (i.e.,the red elements area in denoted Figure 3) by parts the green in the area model in Figurefor the4 )traditional and HPCSS (i.e.,slab elements system installation denoted by pr theocess blue and area (ii) CP in Figure(i.e., elements4) parts denote in thed model by the forgreen the area targeted in Figure slab 4) system and installationHPCSS (i.e., process. elements In bothdenoted figures, by the (1) blue common area in work Figure activities 4) parts (depicted in the model as CP1 for tothe CP10 targeted in Figure slab 2) aresystem represented installation by Nodes process. 1 toIn 17both in figures, Figures (1)3 and common4, and work (2) indigenous activities (depicted work activities as CP1 to (explained CP10 in basedFigure on 2) CIP are 1 represented to 9 and HPC by 1Nodes to 6 in 1 Figureto 17 in2) Figu are representedres 3 and 4, byand (i) (2) Nodes indigenous 18 to 30work in Figure activities3 for (explained based on CIP 1 to 9 and HPC 1 to 6 in Figure 2) are represented by (i) Nodes 18 to 30 in CIPSS and (ii) Nodes 18 to 27 in Figure4 for HPCSS. Moreover, it is assumed that construction for Figure 3 for CIPSS and (ii) Nodes 18 to 27 in Figure 4 for HPCSS. Moreover, it is assumed that a floor is completed after the completion of concrete curing and form removal tasks, which follow construction for a floor is completed after the completion of concrete curing and form removal tasks, tasks of concrete placing work. However, both simulation models did not include two tasks after which follow tasks of concrete placing work. However, both simulation models did not include two concrete placement, namely, concrete curing and form removal works, because it is not necessary to tasks after concrete placement, namely, concrete curing and form removal works, because it is not inputnecessary specific to input resources specific for resources the concrete for the curing concrete work, curing and work, this otherwise and this otherwise creates noise creates in noise analyzing in otheranalyzing labor crewother productivitieslabor crew productivities and idleness. and In idleness. addition, In form addition, removal form work removal cannot work be cannot initiated be for a longinitiated time for (i.e., a long typically time 4(i.e., to 13 typically working 4 days),to 13 working until concrete days),curing until concrete is finished, curing and is this finished, subsequently and influencesthis subsequently crew productivity influences measurement.crew productivity measurement.
CP(common process) Form Removal R1 (Slab) Rebar Horizontal Horizontal Marking Delivery Delivery Marking Stand Stand Start Ready Installation Ready Ready 2 Ready Installation Form Removal 1 3 5 (C*/W*) 4 6 (Column, Beam) x16 Next Floor R2 Form Curing Dummy Crew 7 33 C1 31 Wall Form Rebar Installation Installation Ready C3 (2/2) (W) 17 14 F1 F3 C4 Form Form Installation Delivery Crane Concrete Concrete Ready Crew Placement (C/B/W) (C/B*/W) 34 C5 C1 11 8 36 30 Form Wall Form Column/Beam Installation Wall Rebar Installation Form Ready Installation R4 C2 (1/2) Installation (W) 15 12 16 13 R5 Concrete R6 P2 P3 Column Rebar Rebar Installation Placement Installation Ready Ready P1 F1 F2 F3 10 9 29
Slab Slab Slab R3 Installation Form/Support Dummy Form/Support Ready Installation 20 Fix 18 19 21 C2 CON # C3 28 C5 C4
Slab Beam Slab Rebar Slab Rebar Rebar Beam Rebar Beam Rebar Rebar Installation Delivery Installation Installation Delivery Installation 27 26 Ready 24 23 Ready 25 22
P4 Available Rebar of Slab Crew Upper Site CIPSS 37 35 P1 (Traditional slab system) R2 R1 P3
CP(common process) R1
Rebar Horizontal Horizontal Marking Delivery Delivery Marking Stand Stand Start Ready Installation Ready Ready 2 Ready Installation Form Removal 1 3 5 (C*/W*) 4 6 (Column, Beam) x16 Next Floor R2 Form Curing Dummy Crew 7 30 C1 28 Wall Form Rebar Installation Installation Ready C3 (2/2) (W) 17 14 F1 F2 C4 Form Form Installation Delivery Crane Concrete Concrete Ready Crew Placement (C/B/W) (C/B*/W) 31 C1 11 8 33 27 Form Wall Form Column/Beam Installation Wall Rebar Installation Form Ready Installation R4 C2 (1/2) Installation (W) 15 12 16 13
Column Rebar Concrete Rebar Installation Placement Installation Ready Ready C2 C3 F2 10 9 26 Rebar Slab Half-PC Half-PC Installation R3 Installation Slab Ready Ready Slab Lifting Installation (B/S*) 18 19 20 21
CON # F1 25 C4
Beam/Slab Slab Rebar Beam Rebar Rebar Installation Installation Delivery 24 23 22
HPCSS Rebar Crew (Half-PC slab process) 32 R2
Table 2. Resource and duration data for each work task.
Resource Duration (hours) Remark Node Work Tasks Crew Equipment Minimum Most Likely Maximum 2 Marking Form - 7 8 9 4 Horizontal stand install Form - 7 8 9 6 Rebar delivery (C/W) Rebar Crane 0.75 1 1.25 8 Form delivery (C/W/B) Form Crane 2.5 3 3.5 CP 10 Column rebar installation Rebar - 15 16 17 12 Column/beam form installation Form Crane 26 28 30 13 Wall form installation (1/2) Form - 3 4 5 15 Wall rebar installation Rebar - 7 8 9 17 Wall form installation (2/2) Form - 3 4 5 19 Slab form/support delivery Form Crane 3 4 5 21 Slab form installation Form - 52 56 60 23 Beam rebar delivery Rebar Crane 2.5 3 3.5 CIPSS 24 Beam rebar installation Rebar - 22 24 26 26 Slab rebar delivery Rebar Crane 2.5 3 3.5 27 Slab rebar installation Rebar - 22 24 26 30 Concrete placement Concrete Pump Car - 8 - 19 Half-PC slab lifting Form Crane 15 16 17 20 Half-PC slab installation Form - 7 8 9 22 Beam/Slab rebar delivery Rebar Crane 2.5 3 3.5 HPCSS 23 Beam rebar installation Rebar - 22 24 26 24 Slab rebar installation Rebar - 7 8 9 27 Concrete placement Concrete Pump Car - 8 -
The simulation was implemented with the simulation models, and input data represented by Figures3 and4 and Table2 to analyze the construction productivity for types of work tasks and resources. The simulation results show that (i) first, the required cycle time for constructing each floor is calculated as 174.6 h and 103.3 h for CIPSS and HPCSS, respectively, (ii) construction productivity corresponds to 0.0057 (cycle/h) and 0.0097 (cycle/h) for CIPSS and HPCSS, respectively, and (iii) finally, these results can be interpreted as the delivery of higher productivity by HPCSS. A detailed explanation of these results is described in the “Findings and discussion” section. In order to conduct a simulation study of the effects of HPCSS on construction productivity, it is necessary to verify if the developed simulation model can adequately reflect actual construction data [20]. In the study, this verification was conducted based on comparing two types of data, namely, “collected data” from the actual case and “simulated data” from each model. That is, the study explores the following: (i) the extent to which the actual and simulated durations are identical for each work task and (ii) the manner in which events during the simulation chronologically occurred when compared with the actual construction process. Table3 lists the percentage difference between the simulated and actual durations for each work task. For example, with respect to Node 2 (i.e., “marking” in Table2), the simulated and actual durations correspond to 7.9 h and 8.0 h, respectively, and subsequently, the percentage difference of sum is estimated as 1.935% (i.e., |0.1019 − 0.1000|/0.1000 × 100). A similar method is used to determine that after calculating the percentage difference of the sub-totals for all tasks (i.e., Nodes 2 to 30 for CIPSS and Nodes 2 to 27 for HPCSS), the lowest value corresponds to 0.443% for Node 27 for CIPSS, while the highest value corresponds to 23.871% for Node 6 for CP. Furthermore, (i) Nodes in the CP process (i.e., Nodes 2 to 17) exhibit an average difference of 85.723%, (ii) Nodes in CIPSS display an average difference of 3.096%, and (iii) Nodes in HPCSS exhibit an average difference of 12.710%. The results indicate that the developed models could be interpreted as being reliable in terms of the accuracy of construction duration. Sustainability 2017, 9, 1268 9 of 15
Table 3. Simulated and actual durations for each work task.
Durations From Simulation Duration from Case Study Percentage Difference (%) Remark Node Rate of (a) Rate of (b) Measured (a) Measured (b) (=|aa − bb|/ bb × 100) on Sum (aa) on Sum (bb) 2 7.9 0.1019 8.0 0.1000 1.935 4 7.8 0.1006 8.0 0.1000 0.645 6 1.2 0.0155 1.0 0.0125 23.871 CP 8 2.8 0.0361 3.0 0.0375 3.656 10 14.9 0.1923 16.0 0.2000 3.871 12 27.9 0.3600 28.0 0.3500 2.857 13–17 15 0.1935 16.0 0.2000 3.226 sum 77.5 1.0000 80.0 1.0000 Average 5.723 19 3.9 0.0324 4.0 0.0328 1.286 21 55.4 0.4598 56.0 0.4590 0.160 23 2.5 0.0207 3.0 0.0246 15.629 CIPSS 24 24.1 0.2000 24.0 0.1967 1.667 26 3 0.0249 3.0 0.0246 1.245 27 23.6 0.1959 24.0 0.1967 0.443 30 8 0.0664 8.0 0.0656 1.245 Sum 120.5 1.0000 122.0 1.0000 Average 3.096 19–20 18.6 0.3131 24.0 0.3582 12.584 22 3 0.0505 3.0 0.0448 12.795 23 23.7 0.3990 24.0 0.3582 11.385 HPCSS 24 6.1 0.1027 8.0 0.1194 13.994 27 8 0.1347 8.0 0.1194 12.795 Sum 59.4 1.0000 67.0 1.0000 Average 12.710
Figure5 compares the simulation results and actual case records, which enables us to examine as to whether the operation of the developed simulation model is identical to the actual work process. That is, the figure lists the HPCSS events that (i) are chronologically completed during the implementation of simulation (i.e., the top panel of the figure) and (ii) chronologically reported from actual construction records (i.e., bottom panel of the figure). In addition, based on COMBI (Nodes 19, 22, and 27) and NORMAL (Nodes 20, 23, and 24) elements with defined durations, the figure captures the simulated events from the initial task of half-PC installation (i.e., Node 19 in Figure4) assuming that the initiation time of node 19 is converted to zero. The principal results of comparison are as follows: As shown in the figure, the installation of the first HPC slab unit is performed in conjunction with the following five tasks: HPC slab lifting (chronological list 1), HPC slab installation (chronological list 2), rebar delivery (chronological list 3), beam rebar installation (chronological list 5), and slab rebar installation (chronological list 7). Under this condition, the simulation time for the aforementioned tasks corresponds to 3.6 h while actual construction time for the first HPC slab unit from the record corresponds to 4.0 h, as denoted by “A” in the figure. Similarly, the installation work for the second HPC slab unit is completed in 6.6 h as per the simulation result and 6.0 h as per the actual record (Refer to “B” in Figure5). This result suggests that the time to complete the first slab as measured by the simulation is less than the time indicated by the actual record (i.e., 0.6 h), while the time to complete the second slab unit in the actual record is less than that in the simulation by a maximum Sustainability 2017, 9, 1268 10 of 15 of 0.6 h. In addition, the time to complete the installation of the last slab (i.e., 16th slab) is 41.2 h as per the simulation and 48 h per by the actual record. According to Hong et al. [19], a simulation model developed using the actual data can yield (i) productivity rates that are closer to that in an ideal situation and (ii) lower uncertainty. Subsequently, the results of the simulation are superior in consistency when compared with those obtained from the actual data. From this viewpoint, the actual record reveals a buffer between the two works, as indicated by “C” in Figure5, although this buffer doesSustainability not exist in2017 the, 9, 1268 simulation result. Consequently, this indicates that the simulated completion10 of 15 time of the final unit is less than that in the actual record. Moreover,Moreover, the simulationthe simulation result result indicates indicates that that the th worke work tasks tasks for for the the first first and and secondsecond unitsunits of slabs are simultaneouslyslabs are simultaneously ongoing, ongoing, and this isand also this observed is also observed in the operations in the operations from the from actual the construction actual construction record (Refer to “D” in Figure 5). Thus, the aforementioned results indicate that the record (Refer to “D” in Figure5). Thus, the aforementioned results indicate that the developed developed simulation models are sufficiently accurate to be of value in further analysis. simulation models are sufficiently accurate to be of value in further analysis.
Chronological list
14 Node 24
Node 13 20 :TasksforHPCSunit#4
12 : Tasks for HPCS unit # 3 Node 23
:TasksforHPCSunit#2 HPCSS Unit #3 Node 19 10, 11 Initiated Node :TasksforHPCSunit#1 20 Node HPCSS Unit #4 8, 9 22 Initiated Node 19
7 HPCSS Unit #2 Node Initiated 24 6 Node 20
5 Node 23 Simulation results Simulation 4 HPCSS Unit #1 Node 19 Initiated Node 22 C 1,2,3 Node 20 D Node 19 A B
Simulation time 1.0h1.6h 2.7h 3.1h 3.6h 4.0h 5.0h 6.0h 6.6h 7.0h 1.5h
Form Node Node Node Crew 20 20 20 Record Node 19 Node 19 Node 19 Node 19
Rebar Rebar Setting Nodes 23 and 24 Nodes 23 and 24 Crew Node 22 Record Node 22
Actual time 1.5h 2.0h 4.0h 6.0h Actual record
Figure 5. Chronological list of simulation results and actual records. Figure 5. Chronological list of simulation results and actual records. 5. Findings and Discussion 5. Findings and Discussion The work productivities of each set of crew and equipment are explored based on the simulationThe work productivitiesstatistics, to identify of each the setadvantages of crew andand equipmentdisadvantages are of explored HPCSS over based those on theof CIPSS. simulation statistics,The results to identify indicate the that advantages the most idle and resources disadvantages in the two of HPCSSslab methods over correspond those of CIPSS. to “concrete The results indicatecrew” that (95.42% the most idle for idle CIPSS resources and 92.26% in the idle two for slab HPCSS methods in Table correspond 4) followed to by “concrete “crane” (70.97% crew” for (95.42% idle forCIPSS CIPSS and 41.71% and 92.26% for HPCSS), idle for “rebar HPCSS crew” in (50.79% Table4 )for followed CIPSS and by 34.98% “crane” for (70.97%HPCSS), forand CIPSS“form and 41.71%crew” for (0.03% HPCSS), for “rebarCIPSS crew”and 0.22% (50.79% for HPCSS for CIPSS in Ta andble 4). 34.98% In summary, for HPCSS), the types and of “form resources crew” for (0.03% installing HPCSS exhibit relatively less idle states, and this suggests that each crew and equipment for CIPSS and 0.22% for HPCSS in Table4). In summary, the types of resources for installing HPCSS for HPCSS work in a smoother manner with less interruption when compared with the case of exhibit relatively less idle states, and this suggests that each crew and equipment for HPCSS work CIPSS. Furthermore, the relatively low idle state also indicates that it is necessary to consider in a smootheradditional work manner crew with or equipment less interruption in terms of when improvements compared in withwork theproductivity. case of CIPSS. Furthermore, the relativelyIn addition low idle to the state basic also analysis indicates shown that above, it is necessarywe conduct to a considersensitivity additional analysis to workexamine crew or equipmentchanges in in terms productivity of improvements due to the changes in work in productivity. input resources. The sensitivity analysis determines the optimal combination of resource inputs and identifies resources that have a significant influence on the work productivity of HPCSS and CIPSS. Conversely, a cost data survey of the input resources is used to analyze work productivity with respect to the input cost. Sustainability 2017, 9, 1268 11 of 15
In addition to the basic analysis shown above, we conduct a sensitivity analysis to examine changes in productivity due to the changes in input resources. The sensitivity analysis determines the optimal combination of resource inputs and identifies resources that have a significant influence on the work productivity of HPCSS and CIPSS. Conversely, a cost data survey of the input resources is used to analyze work productivity with respect to the input cost.
Sustainability 2017, 9, 1268 Table 4. Simulation results in terms11 of of 15 percent of idleness of a resource.
Division Node Resource Average Units Idle Times not Empty Average Wait Time % Idle Table 4. Simulation results in terms of percent33 of idleness Form Crew of a resource. 0 0 0 0.03 34 Crane 0.8 124 1.3 70.97 Division Node Resource Average UnitsCIPSS Idle Times not Empty Average Wait Time % Idle 33 Form Crew 0 350 Rebar Crew0 0.50.03 88.7 1.1 50.79 34 Crane 0.8 36124 Conc. Crew1.3 170.97 166.6 83.3 95.42 CIPSS 35 Rebar Crew 0.5 3088.7 Form Crew1.1 050.79 0.2 0 0.22 36 Conc. Crew 1 31166.6 Crane83.3 0.595.42 43.1 0.5 41.71 30 Form Crew 0 HPCSS 0.2 0 0.22 32 Rebar Crew 0.4 36.1 0.6 34.98 31 Crane 0.5 43.1 0.5 41.71 HPCSS 33 Conc. Crew 0.9 95.3 47.6 92.26 32 Rebar Crew 0.4 36.1 0.6 34.98 33 Conc. Crew 0.9 95.3 47.6 92.26 The change in the work crew for the sensitivity analysis is determined by analyzing the The change in the work crew for the sensitivity analysis is determined by analyzing the construction record. That is, based on theconstruction actual working record. daily report, That is, the based form crew on the is input actual from working at daily report, the form crew is input from least one team, up to a maximum of threeat least teams one, such team, thatup the tochange a maximum in the form of crew three amount teams, is such that the change in the form crew amount determined from 1 to 3. The same methodis determined is applied to determine from 1 to the 3. change The same in the method crane from is applied1 to 2, to determine the change in the crane from 1 the rebar crew from 1 to 3, and the concreteto 2, the crew rebar from crew 1 to from2. This 1 process to 3, and generated the concrete 36 scenarios crew from 1 to 2. This process generated 36 scenarios based on the resource combination (Tablebased 5). on the resource combination (Table5).
Table 5. Sensitivity analysis results based on resource combination scenarios. Table 5. Sensitivity analysis results based on resource combination scenarios. Cost Productivity Construction Productivity Install Time Resource Information Construction(US$/Simulation Productivity Install Time Cost Productivity (Cycle/SimulationResource Time) (a) Information (h/cycle) (b) Scenario (Cycle/SimulationTime) (c) Time) (a) (h/cycle) (b) (US$/Simulation Time) (c) Form Rebar Conc. Scenario Crane HPCSS FormCIPSS RebarHPCSS Conc.CIPSS HPCSS CIPSS Crew Crew Crew Crane HPCSS CIPSS HPCSS CIPSS HPCSS CIPSS Crew Crew Crew 1 1 1 1 1 0.0097 0.0057 103.09 175.44 3.2303 2.8323 1 1 1 1 1 0.0097 0.0057 103.09 175.44 3.2303 2.8323 2 1 1 1 2 0.0096 0.0057 104.17 175.44 3.4046 3.0213 2 1 1 1 2 0.0096 0.0057 104.17 175.44 3.4046 3.0213 3 1 1 2 1 0.0108 0.0066 92.59 151.52 5.3180 4.8846 3 1 1 2 1 0.0108 0.0066 92.59 151.52 5.3180 4.8846 4 1 1 2 2 0.01124 10.0068 1 89.29 2 147.06 2 5.7779 0.0112 5.2969 0.0068 89.29 147.06 5.7779 5.2969 5 1 1 3 1 0.01075 10.0069 1 93.46 3 144.93 1 6.9914 0.0107 6.8161 0.0069 93.46 144.93 6.9914 6.8161 6 1 1 3 2 0.01076 10.0070 1 93.46 3 142.86 2 7.2896 0.0107 7.1034 0.0070 93.46 142.86 7.2896 7.1034 7 1 2 1 1 0.01007 10.0056 2 100.00 1 178.57 1 4.6733 0.0100 3.9409 0.0056 100.00 178.57 4.6733 3.9409 ⁞ ⁞ ⁞ ⁞ ⁞ ⁞ ⁞ ⁞ ⁞ ⁞ ⁞ 13 2 1 1 1 0.010213 20.0062 1 98.0 14 161.29 1 3.4625 0.0102 3.1654 0.0062 98.04 161.29 3.4625 3.1654 14 2 1 1 2 0.010214 20.0062 1 98.04 1 161.29 2 3.7154 0.0102 3.3955 0.0062 98.04 161.29 3.7154 3.3955 15 2 1 2 1 0.012515 20.0075 1 80.00 2 133.33 1 6.2629 0.0125 5.6630 0.0075 80.00 133.33 6.2629 5.6630 16 2 1 2 2 0.012316 20.0074 1 81.30 2 135.14 2 6.4674 0.0123 5.8446 0.0074 81.30 135.14 6.4674 5.8446 17 2 1 3 1 0.013117 20.0079 1 76.34 3 126.58 1 8.6763 0.0131 7.8726 0.0079 76.34 126.58 8.6763 7.8726 18 2 1 3 2 0.0131 0.0079 76.34 126.58 9.0204 8.1598 18 2 1 3 2 0.0131 0.0079 76.34 126.58 9.0204 8.1598 19 2 2 1 1 0.0130 0.0067 76.92 149.25 6.2096 4.8077 19 2 2 1 1 0.0130 0.0067 76.92 149.25 6.2096 4.8077 20 2 2 1 2 0.0130 0.0067 76.92 149.25 6.5034 5.0314 20 2 2 1 2 0.013021 20.0067 2 76.92 2 149.25 1 6.5034 0.0181 5.0314 0.0082 55.25 121.95 5.7748 7.8539 21 2 2 2 1 0.018122 20.0082 2 55.25 2 121.95 2 5.7748 0.0184 7.8539 0.0083 54.35 120.48 6.1043 8.2234 22 2 2 2 2 0.018423 20.0083 2 54.35 3 120.48 1 6.1043 0.0198 8.2234 0.0087 50.51 114.94 7.9178 6.9925 23 2 2 3 1 0.019824 20.0087 2 50.51 3 114.94 2 7.9178 0.0197 6.9925 0.0087 50.76 114.94 8.1189 7.1771 24 2 2 3 2 0.019725 30.0087 1 50.76 1 114.94 1 8.1189 0.0105 7.1771 0.0063 95.24 158.73 3.6477 3.2936 25 3 1 1 1 0.010526 30.0063 1 95.24 1 158.73 2 3.6477 0.0104 3.2936 0.0063 96.15 158.73 3.8688 3.4920 26 3 1 1 2 0.010427 30.0063 1 96.15 2 158.73 1 3.8688 0.0127 3.4920 0.0075 78.74 133.33 6.4744 5.7538 27 3 1 2 1 0.012728 30.0075 1 78.74 2 133.33 2 6.4744 0.0128 5.7538 0.0076 78.13 131.58 6.8355 6.0794 28 3 1 2 2 0.0128 0.0076 78.13 131.58 6.8355 6.0794 34 3 2 2 2 0.0199 0.0087 50.25 114.94 6.6799 5.8298 ⁞ ⁞ ⁞ ⁞ ⁞ ⁞ ⁞ ⁞ ⁞ ⁞ ⁞ 35 3 2 3 1 0.0223 0.0094 44.84 106.38 9.0139 7.5675 34 3 2 2 2 0.0199 0.0087 50.25 114.94 6.6799 5.8298 36 3 2 3 2 0.0217 0.0093 46.08 107.53 9.0530 7.7583 35 3 2 3 1 0.0223 0.0094 44.84 106.38 9.0139 7.5675 36 3 2 3 2 0.0217 0.0093 46.08 107.53 9.0530 7.7583
Table 5 lists the results of the sensitivity analysis. As can be observed from the table, the simulation results for each scenario are categorized into the three following aspects: "construction Sustainability 2017, 9, 1268 12 of 15
Sustainability 2017, 9, 1268 12 of 15 Table5 lists the results of the sensitivity analysis. As can be observed from the table, the simulation resultsproductivity” for each (column scenario (a)), are categorized“installation into time” the (c threeolumn following (b)), and aspects: “cost productivity” “construction productivity”(column (c)). (columnWe note (a)),that “installationthe construction time” productivity (column (b)), of HPCSS and “cost is generally productivity” higher (column than that (c)). of We CIPSS. note In that other the constructionwords, the HPCSS productivity productivity of HPCSS rang is generallyes from 0.0223 higher (cycle/simulation than that of CIPSS. time, In other scenario words, 35) the to HPCSS0.0096 productivity(cycle/simulation ranges time, from scenario 0.0223 (cycle/simulation2), and the CIPSS time,productivity scenario ranges 35) to 0.0096from 0.0094 (cycle/simulation (cycle/simulation time, scenariotime, scenario 2), and 35) the to CIPSS0.0057 productivity(cycle/simulation ranges time, from scenarios 0.0094 (cycle/simulation1 and 2). Corresponding time, scenario to column 35) (a) to 0.0057in Table (cycle/simulation 5, Figure 6 shows time, the productivity scenarios 1 andchart 2). fo Correspondingr each slab system to columnfor each (a)scenario. in Table As5, shown Figure 6in showsthe figure, the productivity (i) HPCSS chartproductivity for each increases slab system with for eachincrease scenario. in the As resource shownin input, the figure, and (ii) (i) HPCSSCIPSS productivity exhibits increases a relatively with increase moderate in the increase resource despite input, additional and (ii) CIPSS resource productivity input. Moreover, exhibits the a relativelyinstallation moderate time based increase on despitethe scenario additional exhibits resource a similar input.Moreover, tendency therelative installation to construction time based onproductivity. the scenario exhibits a similar tendency relative to construction productivity. The cost data of each crew and equipment are examinedexamined to analyze the cost per unit time based on thethe scenarios.scenarios. TheThe estimationestimation of of the the unit unit cost cost for for each each crew crew involved involved the the following: following: (i) analyzing(i) analyzing the detailedthe detailed construction construction labor oflabor each of crew each via analysiscrew via of analysis the construction of the records,construction and (ii)records, considering and the(ii) acquisitionconsidering of the daily acquisition labor costs of fromdaily Korea labor price costs information from Korea (KPI) price [21 information]. Based on this(KPI) method, [21]. Based the unit on costthis ofmethod, each crew the is unit calculated cost of as each follows: crew (i) is unit calculated cost of form as follows: crew =3.99 (i) unit (US$/m cost2 ×of hour),form crew (ii) unit = cost3.99 of(US$/m rebar2 crew× hour), = 80.86 (ii) (US$/tonunit cost of× rebarhour), crew and (iii)= 80.86 unit (U costS$/ton of concrete × hour),crew and =(iii) 12.15 unit (US$/m cost of3 concrete× hour). Thecrew rental = 12.15 cost (US$/m of the tower3 × hour). crane The (25 rental Ton) is cost calculated of the astower 68.75 crane (US$/hour) (25 Ton) based is calculated on KPI (KPI as 2016).68.75 The(US$/hour) cost productivity based on basedKPI (KPI on each2016). resource The cost combination productivity is calculatedbased on each based resource on the abovecombination cost data. is Ascalculated listed in based Table 5on, the the highest above cost data. performance As listed of in HPCSS Table 5, is observedthe highest to cost be 5.7748 performance (US$/simulation of HPCSS time)is observed for scenario to be 21,5.7748 while (US$/simulation the cost productivity time) for of CIPSS scenario corresponds 21, while tothe 2.8323 cost (US$/simulationproductivity of CIPSS time) forcorresponds scenario 1. to 2.8323 (US$/simulation time) for scenario 1.
0.025
0.023 0.0223
0.021
0.019 Construction productivity 0.017
0.015
0.013
0.011 0.0096 0.0094 0.009
0.007 0.0057 0.005 123456789101112131415161718192021222324252627282930313233343536 HPCSS CIPSS Scenario number
Figure 6. Construction productivityproductivity for each scenario.
Figure7 7shows shows the the “cost “cost productivity” productivity” (i.e., (i.e., column colu (c)mn values/column (c) values/column (a) values (a) values in Table in5 Table) based 5) onbased the on above the above simulation simulation results. resu Aslts. shown As shown in the in figure, the figure, scenario scen 21ario of 21 HPCSS of HPCSS corresponds corresponds to the to highestthe highest cost cost productivity productivity (i.e., 319.35(i.e., 319.35 US$/cycle), US$/cycl ande), theand highest the highest value value of cost of productivity cost productivity for CIPSS for correspondsCIPSS corresponds to 497.75 to (US$/cycle)497.75 (US$/cycle) for scenario for scenar 1. Overall,io 1. Overall, the cost productivitythe cost productivity value of HPCSSvalue of is superiorHPCSS is to superior that of CIPSSto that while of CIPSS HPCSS while and HPCSS CIPSS and tend CIPSS to differ tend in to scenarios differ in 20 scenarios to 23. That 20 to is, 23. the That cost productivityis, the cost productivity value of CIPSS value deteriorated of CIPSS deteriorated under conditions under inconditions which the inrebar which crew the wasrebar added crew andwas concreteadded and crew concrete was reduced crew was by one reduced crew setby (i.e.,one conditionscrew set (i.e., from conditions scenario 20from to scenarioscenario 21). 20 to In scenario contrast, the21). costIn contrast, productivity the cost is optimized productivity for is HPCSS. optimized for HPCSS. Sustainability 2017, 9, 1268 13 of 15 Sustainability 2017, 9, 1268 13 of 15
1300.00
1200.00 productivity 1100.00
Cost per per Cost 1000.00
900.00
800.00
700.00
600.00
500.00 497.25 400.00 319.35 300.00 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 Scenario number HPCSS CIPSS
Figure 7. Cost productivity of each scenario.scenario.
From the above above results, results, we we note note that that the the productivit productivitiesies of ofHPCSS HPCSS and and CIPSS CIPSS are areaffected affected by the by thetypes types of resources. of resources. Therefore, Therefore, multivari multivariateate analysis analysis of variance of variance (MANOVA) (MANOVA) method method is applied is applied to tofurther further analyze analyze the the manner manner in in which which the the four four resources resources analyzed analyzed in in the the study study affect affect the work productivityproductivity of HPCSS and CIPSS. In particular,particular, MANOVA isis usefuluseful whenwhen appliedapplied inin conjunctionconjunction withwith experimentalexperimental designs, that is, research designs in which a researcher directly controls one or more independent independent variables variables to determine to determine the effect the on effect the dependent on the dependent variables [22 variables]. Four independent [22]. Four variablesindependent are defined variables to are apply defined MANOVA to apply (form MANOVA crew, crane, (form rebar crew, crew, crane, and rebar conc. crew, crew), and and conc. two dependentcrew), and variables two dependent are defined variables as HPCSS are and defined CIPSS as work HPC productivitySS and CIPSS (i.e., work column productivity (a) of Table (i.e.,5). Thecolumn MANOVA (a) of Table testwas 5). The implemented MANOVA by test using was SPSS implemented Ver. 22 software by using in ourSPSS study. Ver. 22 software in our studyTable. 6 lists the key results of the MANOVA test. From the table, we note that the resources affectingTable the 6 lists HPCSS the workkey results productivity of the MANOVA are form crew test. ( FFrom= 6.775, the Sig.table, = we 0.003 note (p Acknowledgments: This study was supported by research funds from Chosun University, 2017. Author Contributions: Kyuman Cho and Taehoon Kim conceptualized and designed the work; Kyuman Cho carried out the experiments; Young-su Shin helped in collecting and analyzing the data; Kyuman Cho, Young-su Shin, and Taehoon Kim visualized the results; Kyuman Cho wrote the paper; and Taehoon Kim proofread the paper. Conflicts of Interest: The authors declare no conflict of interest. References 1. Lee, J.; Yoon, J.; Kang, H. Combined half precast concrete slab and post-tensioned slab topping system for basement parking structures. J. Struct. Integr. Maint. 2016, 1, 1–9. [CrossRef] 2. Cho, C.; Kappos, A.; Moon, H.; Lim, H. Experiments and failure analysis of SHCC and reinforced concrete composite slabs. Eng. Fail. Anal. 2015, 56, 320–331. [CrossRef] 3. Mansour, F.; Bakar, S.; Ibrahim, I.; Marsono, A.; Marabi, B. Flexural performance of a precast concrete slab with steel fiber concrete topping. Constr. Build. Mater. 2015, 75, 112–120. [CrossRef] 4. Said, S.; Razak, H.; Othman, I. 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