sustainability Case Report
The Accelerated Window Work Method Using Vertical Formwork for Tall Residential Building Construction Taehoon Kim 1 , Hyunsu Lim 2, *, Chang-Won Kim 2 , Dongmin Lee 1 , Hunhee Cho 1 and Kyung-In Kang 1 1
2
*
School of Civil, Environmental and Architectural Engineering, Korea University, Anam-Dong, Seongbuk-Gu, Seoul 02841, Korea;
[email protected] (T.K.);
[email protected] (D.L.);
[email protected] (H.C.);
[email protected] (K.-I.K.) BK21 Innovative Leaders for Creating Future Value in Civil Engineering, Korea University, Anam-Dong, Seongbuk-Gu, Seoul 02841, Korea;
[email protected] Correspondence:
[email protected]; Tel.: +82-2-921-5920
Received: 29 January 2018; Accepted: 7 February 2018; Published: 9 February 2018
Abstract: In tall residential building construction, there is a process gap between the window work and the structural work. This process gap extends the total period of the project and increases its cost. In addition, as this process gap increases external exposure to noise and dust, it negatively affects the environment of a site and often causes civil complaints. This paper introduces a new window work process called the accelerated window work (AWW) method, which minimizes the process gap and can reduce construction cost and duration and the number of civil complaints. We provide technical details and management elements of the AWW method with a case study that demonstrates the reductions in construction costs and duration compared with the conventional method. This work contributes to the body of knowledge in window work in tall buildings by introducing and validating a new window work method and process. The proposed method will be useful for practitioners who are under short-term constraints. Keywords: accelerated window work method; vertical formwork; tall residential building construction; window work
1. Introduction In tall residential building construction, there is a process gap between the window work and the structural work [1,2]. For tall building structural work, large formwork with several working platforms is generally installed outside the building [3]. These platforms limit the operation height of the construction hoists that lift window components. In addition, because a residential building has many walls and small windows compared with office buildings, there is a relatively large difference in productivity between the structural work and window work, which increases the process gap between these types of work. Because of these spatial constraints and productivity differences, window construction begins after several floors of structural work. This process gap extends the duration of the project and increases the cost of the entire construction [4]. As the window work is on the critical path of the process, the entire duration of construction is delayed if window work is delayed. In addition, because the construction section between the structural work and the window work is open externally, safety facilities such as safety rails and nets must be installed in this section. These additional safety facilities increase material and labor costs by repetitive installation during the construction. A larger gap between the two processes increases the effect on the duration and cost of construction. In addition, this process gap negatively
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affects the environment of a site and often causes civil complaints because it increases external exposure to noise and dust. In xparticular, dust caused by construction-related activities is a major source of Sustainability 2018, 10, FOR PEER REVIEW 2 of 10 particulate matter (PM) in the urban atmosphere [5], which has been associated with higher rates of affectsand themortality environment of a site and[6,7]. often causes civil complaints because it increases external morbidity in urban areas exposure noise and dust. In particular, dusthave caused by construction-related activities is a major To solve to this problem, various attempts been made to reduce this process gap [2,8]. source of particulate matter (PM) in the urban atmosphere [5], which has been associated with One method is to raise the maximum floor of hoist operation by modifying the platform of the higher rates of morbidity and mortality in urban areas [6,7]. vertical formwork above where the hoist is installed. With this method, window construction can To solve this problem, various attempts have been made to reduce this process gap [2,8]. One start one or two floors earlier. Another method is to reduce the unit of construction for window work. method is to raise the maximum floor of hoist operation by modifying the platform of the vertical This method can reduce thethe gap from the structural work by performing window installation formwork above where hoist is installed. With this method, window construction can start onemore frequently. However, these methods cannot fundamentally eliminate the gaps. or two floors earlier. Another method is to reduce the unit of construction for window work. This Previous studies on the window works focused on by preventing delays to the period ofmore window method can reduce gap from thehave structural work performing window installation However, these methods cannot fundamentally eliminate theconstruction gaps. work frequently. by management methods, or increasing efficiency by automated [9–13]. However, Previous on window have focused on preventing to thethe period of window these studies havestudies not solved the works process gaps. Kang et al. [14] delays proposed concept of using work by management methods, or increasing efficiency by automated construction [9–13]. However, an auto climbing system independently to perform external insulation and finishing work. However, these studies have not solved the process gaps. Kang et al. [14] proposed the concept of using an this method was costly because of the additional system, which must operate five or more floors auto climbing system independently to perform external insulation and finishing work. However, below the formwork floor. Lim et al. [15] proposed a window proximity-tracking method to reduce this method was costly because of the additional system, which must operate five or more floors the process gap. However, they proposed only the concept and did not perform economic analysis below the formwork floor. Lim et al. [15] proposed a window proximity-tracking method to reduce basedthe onprocess an actual application in a proposed construction gap. However, they onlysite. the concept and did not perform economic analysis This study the accelerated window work (AWW) method using vertical forms for tall based on anintroduces actual application in a construction site. residentialThis building construction, which can window reduce the vertical between structural study introduces the accelerated work (AWW)constraint method using vertical forms forwork tall residential building construction, which can reduce the vertical constraint between structural and window work. We describe the advantages of the AWW method compared with conventional work and window describe the advantages of the the costs AWWthrough methoda compared construction methods in work. terms We of the construction period and case studywith of a tall conventional construction methods in terms of the construction period and the costs through a case residential building. The proposed method will help construction managers to ensure cost-effective study of a tall residential building. The proposed method will help construction managers to ensure alternatives in tall building constructions with limited duration. cost-effective alternatives in tall building constructions with limited duration.
2. The Conventional Window Work Method for Tall Residential Building Construction 2. The Conventional Window Work Method for Tall Residential Building Construction
Figure 1 shows the conventional process of window work and structural work in tall residential Figure 1 shows the conventional process of window work and structural work in tall residential building construction. building construction.
Figure 1. Schematic diagram of conventional processes for the structural work and window work.
Figure 1. Schematic diagram of conventional processes for the structural work and window work.
From the N-th floor, which is the structural work floor, to the (N − 2)-th floor, curing is
From the N-th which the structural to the (NThe − 2)-th floor, curing is system performed, performed, andfloor, supports areis dismantled on work the (Nfloor, − 3)-th floor. automatic climbing and supports dismantled onN-th the (N − to 3)-th The automatic installed (ACS) is are installed from the floor the floor. (N − 2)-th floor. Fromclimbing the (N − system 4)-th to (ACS) the (N is − 6)-th from the N-th floor to the (N − 2)-th floor. From the (N − 4)-th to the (N − 6)-th floor, where windows floor, where windows cannot be lifted into place and installed, temporary safety facilities, such as cannot be lifted intoguardrails, place andare installed, facilities, such as safety nets and guardrails, safety nets and installedtemporary to prevent safety accidents involving falling workers and dropping are installed to prevent accidents involving falling workers and dropping objects, while dust filter nets
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or similar resources are installed to prevent air pollution around the site via dust scattering. Windows can beobjects, lifted and onnets the or (Nsimilar − 7)-thresources floor. are installed to prevent air pollution around the whileinstalled dust filter The work in tall residential building constructions generally with an interval site window via dust scattering. Windows can be lifted and installed on is the (N − 7)-thperformed floor. of five or more floors. Because of window work is higher than that of structural work, The window work in the tall productivity residential building constructions is generally performed with an interval five or more floors. Because of window work is work higheravailable. than that of window workofteams only work when there the is aproductivity sufficient quantity of window structural work, window work work when there is a sufficient quantity of window work is After structural work on all teams floorsonly is completed, the caulking work for external windows available. performed outside by using a suspended working platform or gondola with a wire rope that is secured work on all floors is completed, the caulking work for external windows is to the topAfter of thestructural building. This work method potentially involves falls by workers because of the performed outside by using a suspended working platform or gondola with a wire rope that is unstable working environment. secured to the top of the building. This work method potentially involves falls by workers because of As a result, the conventional window work method has a vertical constructability constraint of six the unstable working environment. or more floors work and window work. This increases total construction duration As a between result, thestructural conventional window work method has a vertical constructability constraint of because of the late start time of the window work and increases costs directly due to the safety facilities six or more floors between structural work and window work. This increases total construction required as well as indirectly due to the construction period. duration because of the late start timeextended of the window work and increases costs directly due to the safety facilities required as well as indirectly due to the extended construction period.
3. The AWW Method Using a Vertical Formwork for Tall Residential Building Construction 3. The AWW Method Using a Vertical Formwork for Tall Residential Building Construction
In the AWW method, window work is carried out on the lower work plates of the ACS while the AWW method,on window workwork is carried out and on the lower work of the ACS structural In work is performed the upper plates, window workplates is conducted inwhile the same structural work is performed on the upper work plates, and window work is conducted in the same work cycle as structural work (Figure 2). This method removes the vertical constructability constraint work cycle as structural work (Figure 2). This method removes the vertical constructability between the two processes. It allows for an earlier start of finishing work and reduces the total period constraint between the two processes. It allows for an earlier start of finishing work and reduces the of construction by an amount equal to the decrease of the process gap between structure work and total period of construction by an amount equal to the decrease of the process gap between structure window work. In this method, an additional level of work is added the ACS, and window work and window work. In this method, an additional levelplate of work plate is to added to the ACS, and work window is performed on this level. As in the traditional method, the structural work is performed work is performed on this level. As in the traditional method, the structural work isfrom the N-th to the (N − the 2)-th floor, and support is dismantled the (N − 3)-th Windows performed from N-th to the (Nthe − 2)-th floor, and the support on is dismantled on thefloor. (N − 3)-th floor. are lifted floor to theby (N construction − 2)-th floor byhoists construction hoists to complete window work (N and lifted Windows to the (N are − 2)-th to complete window work on the (Non−the 2)-th − 2)-th and (N − 3)-th floors. To apply the AWW method, the following core technologies and (N − 3)-th floors. To apply the AWW method, the following core technologies and management efforts management are required: (1) ACS, a vertically extended ACS, (2) construction operation, andwork are required: (1) aefforts vertically extended (2) construction hoist operation, hoist and (3) window (3) window work cycle management. cycle management.
Figure 2. Schematic diagram of the AWW method.
Figure 2. Schematic diagram of the AWW method.
3.1. Vertically Extended ACS
3.1. Vertically Extended ACS
To perform window work in the ACS, the additional work plate should be installed on the
To perform window work requires in the ACS, thesimple additional work plate should be installed on theACS bottom bottom of the ACS, which some modifications. First, the vertically extended of the ACS, which requires some simple modifications. First, the vertically extended ACS requires structural strengthening because of the increase in self-weight and workloads. Second, the height of
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the work plate between the (N − 2)-th and (N − 3)-th floors is adjusted to allow workers to perform window work outside. Finally, pollution prevention plates are installed on the work plate below the structure work floor, which prevents windows from being polluted by concrete paste from the upper floor. 3.2. Construction Hoist Operation To lift window materials to the (N − 2)-th floor, some of the construction hoists should be able to access this floor. Some modifications of the construction hoist operation method are required. First, the extension cycle of the hoistway is shortened. In the conventional method, the hoistway is extended at intervals of three floors considering the finishing work cycle. However, in the AWW method, the hoistway should be extended at intervals of one floor to lift windows to each floor. Second, a gangform that has no work plates should be installed above the construction hoist to avoid spatial interference with the construction hoist. The formwork system is lifted by a tower crane. This enables the construction hoist to access the (N − 2)-th floor for window work. 3.3. Window Work Cycle Management In the AWW method, the window work and the structural work are performed on the same ACS that climbs with the cycle of structural work, typically 4–7 days per floor. The window work on a floor should therefore be completed within the cycle of structural work. The window work crew would work with a lower work quantity but a shorter cycle. In the conventional method, a window work crew comes on site when windows are required for five or more floors; in the AWW method, they must install windows on one floor within the cycle of structural work. This requires some changes in window work cycle management. First, it is important to ensure the minimum quantity of work for the window work crew. This can be achieved by appropriately zoning the workspace. Second, the construction manager should ensure an optimal stock of windows on each floor so as not to delay the window work. If they are not hoisted in advance and the window work is delayed, the structural work in the critical path would be delayed, which extends the total construction period. As noted, the AWW method solves the vertical constructability constraint of the conventional method. In the AWW method, the window work is performed on the (N − 3)-th floor, while structural work proceeds on the N-th floor, which allows finishing work to start four or more floors earlier than the conventional method. Moreover, there are no openings that have the potential for fall accidents because the windows are installed in the ACS on every floor. A workspace enclosed by windows improves work safety and prevents noise and dust from being released outside. Furthermore, additional safety facilities and temporary facilities for openings are no longer required, thereby decreasing costs. 4. Case Study 4.1. Case Description The AWW method was applied to two mixed-use residential buildings: a 36-story building (Building A) and a 33-story building (Building B) located in Gongneung-dong, Seoul, South Korea. The construction period was about three years and one month. Figure 3 shows the layout plan and cross-section of this project. Commercial facilities are located from the first floor to the third floor, and residential facilities from the fourth floor to the top floor. Fire escape floors are located on the 31st and 28th floors. The ACS used for external wall formwork was installed on the outside of the buildings, and aluminum forms were used for the internal formwork. Plastic window frames were used, and there were 34 windows per floor for Building A, taking up an area of 110 m2 . For lifting materials, one construction hoist in each building and one tower crane for the site were installed.
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In the scheduling management of this project, the start time of finishing work was a critical factor In the management of this project, the focus start time finishing work waswork a critical because the totalscheduling construction period was short, and the wasof placed on finishing because factor because the total construction period was short, and the focus was placed on finishing work of the characteristics of tall residential buildings. In addition, the start of structural work was delayed because of the characteristics of tall residential buildings. In addition, the start of structural work by about a month compared with the planned schedule. For this reason, the construction managers was delayed by about a month compared with the planned schedule. For this reason, the decided to applymanagers the AWW method from the time the ACS from was installed. construction decided to apply the AWW method the time the ACS was installed.
Figure 3. Case project: layoutplan plan of of equipment; equipment; (b) section of the casecase project. Figure 3. Case project: (a)(a)layout (b)cross cross section of the project.
4.2. AWW Method Application
4.2. AWW Method Application
Figure 4 shows Building A, subject to the AWW method. The method was used for 20 units of
Figure showsthe Building A,was subject to the The method was used for 20 units of the ACS4where walk plate extended toAWW the (N method. − 3)-th floor. The added work plate was made the ACS where the walk plate wasand extended to the (N − prevention 3)-th floor.plates The added work plate of aluminum bars, walk plates, a handrail. Pollution were installed on thewas (N −made 1)-th and bars, (N − 2)-th to and prevent installed Pollution windows from being polluted by concrete paste of aluminum walkfloors plates, a handrail. prevention plates were installed on the (Figure 4d). (N − 1)-th and (N − 2)-th floors to prevent installed windows from being polluted by concrete paste Two units of the ACS located above the construction hoist were installed with only gangform (Figure 4d). without work plates (Figure 4c).above The gangforms were raised the installed tower crane. cycle of Two units of the ACS located the construction hoistby were withThe only gangform extending the hoistway was the same as that for raising the ACS at an interval of one floor. Wall ties without work plates (Figure 4c). The gangforms were raised by the tower crane. The cycle of extending fixing the hoistway to the wall were installed at intervals of two floors. the hoistway was the same as that for raising the ACS at an interval of one floor. Wall ties fixing the Figure 5 shows the process of the AWW method. Structural work for each floor was performed hoistway to the wall days. were Formwork, installed atrebar intervals two floors.placement were conducted on the N-th over six working work,of and concrete Figure 5 shows the process of the AWW method. work for50% each was performed floor while curing took place on the (N − 1)-th floor. OnStructural the (N − 2)-th floor, of floor the supports and over forms six working days. Formwork, rebar work, and concrete placement were conducted onlifted the N-th were dismantled. On the (N − 3)-th floor, the remaining supports were dismantled and the N-th floor. Structural work out in On the same way as thefloor, conventional method, and and floor to while curing took place on the was (N −carried 1)-th floor. the (N − 2)-th 50% of the supports forms were removed on (N the− (N3)-th − 2)-th floorthe in advance forsupports window work. formsonly were dismantled. On the floor, remaining were dismantled and lifted to The window work for each wasout alsoinconducted six working days asand the only the N-th floor. Structural work was floor carried the same within way asthe thesame conventional method, structural work. This work consisted of installing, filling, and caulking window frames and forms were removed on the (N − 2)-th floor in advance for window work. installing glass. First, window frames were lifted and installed on the (N − 2)-th floor (Figure 4a). The window work for each floor was also conducted within the same six working days as the Then, filling, caulking, and glass installation were performed on the (N − 3)-th floor (Figure 4b). A structural work. This work consisted of installing, filling, and caulking window frames and installing window crew performed the installing, filling, and caulking of the window frames and installed the glass.glass. First,To window frames were lifted andperformed installed on the (N − 2)-th 4a). Then, filling, ensure work continuity, a crew four processes for 4floor days(Figure in the building, and caulking, and glass installation were performed on the (N − 3)-th floor (Figure 4b). A window after the crew finished window work on Building A, they immediately began working on Building crew performed the installing, filling, and caulking of thebecause window and installed glass.byTothe ensure B. No safety facilities for openings were installed theframes entire workspace was the enclosed and theawindows. workACS continuity, crew performed four processes for 4 days in the building, and after the crew finished window work on Building A, they immediately began working on Building B. No safety facilities for openings were installed because the entire workspace was enclosed by the ACS and the windows.
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Figure 4. The AWW method in the case project. Figure 4. The AWW method in the case project.
Figure 4. The AWW method in the case project.
Figure 5. Construction process of the AWW method. Figure Construction process process of method. Figure 5.5.Construction ofthe theAWW AWW method.
4.3. Results 4.3. Results 4.3. Results Figure 6 compares the conventional window work method and the AWW method in terms of Figure 6 of compares the conventional window work method anddays the AWW method in with termsthe of the duration construction. In total, there were 24 more working of window work Figure 6 compares the conventional window work method anddays the AWW method inwith terms of the the duration of construction. In total, there were 24 more working of window work the AWW method than with the conventional method. This was because window work using the AWW duration of construction. In the total, there were 24 more working dayswindow of window work with the AWW AWW than with conventional This was because the AWW methodmethod has a shorter cycle than that of the method. conventional method. However, thework start using time of window method than with the conventional method. This was because window work using the AWW method method has a shorter cycle than that of the conventional method. However, the start time of window work began earlier using the AWW method compared with the conventional method because has awork shorter cycle than that of the conventional method. However, the start time of window began theasAWW method compared with the conventional becausework window workearlier beganusing as soon the ACS was installed, while window work using method the conventional as soon as the compared ACS was installed, window work using the conventional beganwindow earlier work usingbegan the AWW method with thewhile conventional method because window work
began as soon as the ACS was installed, while window work using the conventional method does not start until structural work reaches the 8th floor. Moreover, window work using the AWW method
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method does not start until structural work reaches the 8th floor. Moreover, window work using the
was completed 48 days than48itdays is using the conventional method because the delay caused AWW method was earlier completed earlier than it is using the conventional method because the by delay caused by after dismantling the ACS curing of theistop floor structure is eliminated. dismantling the ACS the curing of theafter top the floor structure eliminated. Furthermore, internal Furthermore, internalcuring, finishing works requiringand curing, such as masonry and plasterwork, werewith finishing works requiring such as masonry plasterwork, were completed earlier than completed earlier than with the conventional method because of the speeding-up of curing by the the conventional method because of the speeding-up of curing by the windows, which were installed windows, which were installed in advance and therefore blocked the outside cold air in the winter. in advance and therefore blocked the outside cold air in the winter. Accordingly, the duration of Accordingly, the duration of internal finishing works was shorter by 4 days compared with the internal finishing works was shorter by 4 days compared with the conventional method. Consequently, conventional method. Consequently, finishing works were conducted earlier by reducing the finishing works were conducted earlier by reducing the duration of curing and performing window duration of curing and performing window work in advance, thereby decreasing the entire period of work in advance, thereby decreasing the entire period of construction by 52 days. construction by 52 days.
Figure 6. Comparison of project schedules:(a) (a)conventional conventional method; AWW method. Figure 6. Comparison of project schedules: method;(b) (b) AWW method.
1 shows cost variations by applying themethod AWW compared method compared with the Table Table 1 shows the costthe variations by applying the AWW with the conventional conventional method. in Costs increased in three One was the increase in for labor cost for work. windowFirst, method. Costs increased three way. One wasway. the increase in labor cost window work. First, the quantity of window work per floor in the project was approximately 60% the the quantity of window work per floor in the project was approximately 60% of the quantity ofofwindow quantity of window work that could be performed by a crew in a day. This increased the total work that could be performed by a crew in a day. This increased the total number of working days number of working days for window work by 24 days because of the decreased productivity of for window work by 24 days because of the decreased productivity of window work. The increase in window work. The increase in cost was $25,455. Second, the cost of construction hoist operation cost was $25,455. Second, cost of of required construction hoistofoperation increased. the number increased. Because thethe number extensions the hoistway and wallBecause ties increased by 1.5 of required extensions of the hoistway and wall ties increased by 1.5 times, the labor cost and the times, the labor cost and the material cost increased by $1364 and $455, respectively. Finally,material the cost increased byrental $1364cost and respectively. Finally, equipment rental The costACS for adding a level of equipment for$455, adding a level of work platethe to the ACS increased. was extended vertically byACS a total of 18 units, increasing theextended cost by $24,545. work plate to the increased. The ACS was vertically by a total of 18 units, increasing the However, other costs were reduced. First, the equipment rental cost for the suspended working cost by $24,545. platform used external caulking work wasthe eliminated because the cost caulking work was performed However, otherforcosts were reduced. First, equipment rental for the suspended working on the ACS. The cost of renting the suspended working platforms for 14 days was reduced by $4073. platform used for external caulking work was eliminated because the caulking work was performed Second, the material costs of safety facilities decreased because openings were closed by windows. on the ACS. The cost of renting the suspended working platforms for 14 days was reduced by $4073. Safety nets and guardrails to prevent accidents involving falling workers and dropping objects were Second, the material costs of safety facilities decreased because openings were closed by windows. not required; neither were dust filter nets to prevent air pollution around the site by dust scattering. SafetyCosts nets and guardrails to prevent accidents falling workers droppinghoists objects therefore decreased by $99,179. Finally,involving the equipment rental cost forand construction waswere not required; neither were dust filter nets to prevent air pollution around the site by dust scattering. Costs therefore decreased by $99,179. Finally, the equipment rental cost for construction hoists was reduced by the decrease in the overall duration of construction. The cost of renting construction hoists decreased by $31,491 because the construction period was reduced by 52 days.
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In sum, the reduction in costs of $134,743 was greater than the increase of $51,819; overall costs were therefore reduced by $82,924. Table 1. Estimated cost savings by applying the AWW method compared with the conventional method. Cost Change ($)
Items Window work
Installation labor Construction hoist
Structural work
ACS
Cost increases
Subtotal (b)
Cost reductions
Window work
Suspended platform
Safety work
Safety nets Safety handrails Safety screens
Finishing work
Tower crane Construction hoist
Labor
Materials
25,455 1364
455
26,819
25,000
26,771 16,426 29,229
23,184 3230 339
Equipment
Total +25,455 +1819
24,545
+24,545 – 4073
+51,819
−4073 −49,955 −19,656 −29,568
28,364 3127
−28,364 −3127
Subtotal (a)
72,426
26,753
35,564
−134,743
Total Reduction (a–b)
45,607
1753
35,564
−82,924
5. Discussion The AWW method reduced duration and cost by eliminating process gaps between structural and window processes. The main reduction was achieved by continuously installing windows directly after structural work. The AWW method also provided a stable environment that was closed with windows for finishing work, thereby reducing the risk of delays by rework. The cost of window work increased, but overall costs of construction were reduced by eliminating additional safety facilities. Because the cost of safety facilities increases as the numbers of gaps and floors increase, the AWW method used in large buildings is expected to offer greater overall cost savings. The application of the AWW method also contributed to improved work safety and fewer civil complaints. In the case project, no dropping or falling accidents occurred during the construction period, even though no external safety facilities were installed. In addition, even though the case project was performed in an urban setting, the number of civil complaints about dust and noise because of the structural work decreased by approximately 70% compared with the sites of other buildings of about the same size as that of this case study. This prevention of dust diffusion to the outside reduces air pollution in the vicinity of the construction site. This is because windows installed earlier eliminated unintentional falling and dropping, and effectively prevented dust and noise from being released to the outside. Furthermore, the stable work environment using the ACS reduced the number of window caulking flaws, thereby improving the quality of the window work. Despite these advantages, several factors should be considered to ensure that the AWW method is applied successfully. First, sufficient windows for one cycle of window work are required to minimize productivity loss. If the quantity of windows for one floor is too small, window work at an interval of two floors or zoning the workspace should be considered. Second, structural work can be delayed if any problem occurs during window work, given that both are conducted at the same time. Thus, efforts should be made to reduce the risk of delaying construction by regularly maintaining the stocks of windows and adjusting the relevant processes through weekly meetings. 6. Conclusions This study introduces a new window work method for tall building construction called the accelerated window work (AWW) method, which employs vertical formwork for tall residential building construction. We described the method with technical details and management elements and show that this method can reduce the duration of construction by starting and finishing window work earlier. The results of the case study showed that (1), by decreasing the process gap between structural
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and window work, the proposed method can reduce the construction duration and (2), by eliminating the need for safety facilities for openings, the AWW method can significantly reduce costs. Moreover, the case study verified the effectiveness of the AWW method in constructing tall buildings in urban areas by increasing safety performance and reducing the noise and released dust, which helped reduce civil complaints. This work contributes to the body of knowledge about window work in tall buildings by introducing and validating a new window work method. It is expected that this new method will be useful for practitioners under schedule pressures and for those specializing in building construction in urban areas where many civil complaints and claims are expected. In future work, we plan to investigate the zoning method to minimize the loss of productivity in the AWW method. Also required is further research on curtain wall work, which is on the critical path for initiating internal finishing works including window work. Acknowledgments: This research was supported by a grant (18AUDPB106327-04) from the Architecture & Urban Development Research Program funded by the Ministry of Land, Infrastructure and Transport of the Korean Government. Author Contributions: Taehoon Kim and Hyunsu Lim developed the research ideas and completed the writing; Chang-Won Kim and Dongmin Lee collected and analyzed data; Hunhee Cho and Kyung-In Kang designed and organized the overall research flow. Conflicts of Interest: The authors declare no conflict of interest.
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