COMPOSITE BEAM COMPOSED OF STEEL AND PRECAST CONCRETE (MODULARIZED HYBRID SYSTEM). PART III: APPLICATION FOR A 19-STOREY BUILDING

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1 THE STRUCTURAL DESIGN OF TALL AND SPECIAL BUILDINGS Struct. Design Tall Spec. Build. (2009) Published online in Wiley Interscience ( COMPOSITE BEAM COMPOSED OF STEEL AND PRECAST CONCRETE (MODULARIZED HYBRID SYSTEM). PART III: APPLICATION FOR A 19-STOREY BUILDING WON-KEE HONG, SEON-CHEE PARK*, HO-CHAN LEE, JIN-MIN KIM, SEUNG-IL KIM, SEUNG-GEUN LEE AND KI-JOON YOON Department of Architectural Engineering, Kyung Hee University, Kyungki-do, , Korea SUMMARY The authors present an experimental and analytical investigation of the modularized hybrid system (MHS) that utilizes the composite structure described in previous studies, that of a wide steel flange and precast concrete. The objective of this paper was to introduce the application of the MHS structural system to a high-rise building in which one additional floor was added while the overall building height was maintained. The 68-m-tall, 18- storey steel building was redesigned to a 19-storey building using the composite beams, which combine the merits of ductile steel and concrete components to withstand external loading while reducing floor height. The bottom flange of the steel beam is reinforced with concrete at a manufacturing plant, eliminating the use of temporary pour forms. The erection process of the composite beams is identical to that of traditional steel construction. This paper also describes more than 30 potential applications of high-rise composite construction using the MHS frames. The advantages of the MHS are presented in terms of reduced structural steel tonnage and shortened construction schedules. Copyright 2009 John Wiley & Sons, Ltd. 1. INTRODUCTION Many researchers have promoted the use of composite materials to build high-rise structures. Carpinteri et al. (2004) analysed the flexural behaviour of a composite beam (e.g., a reinforced concrete beam) equipped with multiple reinforcements. They cyclically loaded the beam according to a fracture mechanics-based theoretical model that considers a cracked beam subject to an external bending moment and the crack bridging reactions due to the reinforcements. Hong and Kim (2004b) formulated complex frequency response functions and excitation response relations for stationary random processes in order to estimate the responses of multi-storey superstructures isolated with the resilientfriction base isolation system. Both experimental and analytical investigations of axial behaviour of large-scale circular and square concrete columns confined by carbon composite tubes were presented by Hong and Kim (2004a). Hong et al. (2004) also studied full-scale circular and square concrete-filled carbon composite tubes (CFCTs) with various winding angles with respect to the longitudinal axes of the tubes. These tubes were subjected to lateral loads under a constant axial load. Hong et al. (2005) described the construction technique utilized with the composite tubes and discussed the many advantages of the tubes over temporary propping systems. Benjaoran and Dawood (2006) suggested products that are prefabricated off-site, offering a unique opportunity for innovation and cost savings for construction projects. Mirghaderi and Renani (2008) proposed a connection in which two beams pass next * Correspondence to: Seon-Chee Park, Department of Architectural Engineering, Kyung Hee University, Kyungki-do, , Korea. pscgogo@khu.ac.kr Copyright 2009 John Wiley & Sons, Ltd.

2 W.-K. HONG ET AL. to the column faces without interruption and are connected to the column flanges by vertical plates. Pirmoz et al. (2008) presented bolted top and seat angle connections mainly designed to sustain gravitational loads of simply supported steel beams. However, the inherent flexural resistance of topseat angle connections cannot be ignored when an accurate analysis of semi-rigid steel frames is desired. Wakisaka et al. (2000) developed an all-weather automated construction system to reduce the total construction cost of high-rise reinforced concrete buildings. It was applied for the first time in 1995 to the construction of a 26-storey reinforced concrete condominium project located in the Tokyo Metropolitan area. Hong et al. (in press, a) stated that the strength degradation of the composite beams is directly related to the post-yield behaviour of the composite structure, as the ductility is explicitly related to the stiffness degradation. Hong et al. (in press, b) also tested four full-scale composite beams composed of wide steel flanges, with the bottom flange encased in precast concrete, in order to determine the load- carrying capabilities of the beams at both the yield load and the maximum load limit state. Based on these studies, an 18-storey building that was restricted to a height of 68 m by city regulations was redesigned to a 19-storey building using the composite beams. These beams are designed such that the slabs are constructed on top of the edges of the U-shaped precast concrete instead of on top of the steel flanges, reducing the depth of the slab and beam construct by 220 mm per floor. In addition to achieving successful implementation of the modularized hybrid system (MHS) frames, there was a significant decrease in the steel tonnage required in construction. The economy and reliability of the application were also demonstrated. 2. INTERACTION BETWEEN THE STEEL AND CONCRETE Wide flange steel beams with the bottom flange encased in precast concrete are shown in Figure 1. The effective interaction between the two materials could reduce the size of the steel beams. The Cast-in-place concreteast Steel Reinforcement (exposed) Dowel bar Angle Steel Stirrup Reinforcement (embedded) Concrete Reinforcement Shear connector Pre-cast concretere (a) (b) Figure 1. Composition of the MHS composite beam. (a) Section of the MHS composite beam; (b) prefabricated MHS composite beam

3 MHS FOR A HIGH-RISE BUILDING manufacturer of the composite beams maintained a quality control programme with specifications for material properties, steam and natural concrete curing, transport, storing and erections. The quality control programme was strictly emphasized and followed when the composite members were manufactured. The bottom steel reinforcement and concrete were pre-integrated with the bottom flange of the steel beam at the manufacturing plant. The concrete covering the top steel reinforcement and flange was cast at the construction site. 3. THE MHS COMBINATIONS The 54 different combinations of the MHS are based on the column and beam selection shown in Figure 2. The nine types of columns and three types of beams are defined to identify the optimal frame combination, providing the best choice for the construction schedule and cost. Figure 2 shows columns made of conventional steel and reinforced concrete, steel composite encased by concrete and precast concrete with a steel section inserted down the middle to enable connection to an MHS composite girder. The basic combination of columns and beams results in 54 different MHS frames, the length of which is fully or partially consisting of precast concrete. The MHS beams whose full length is encased by precast concrete do not require form work at the ends for concrete pouring of a column beam connection. The MHS beams partially manufactured of precast concrete do require pour forms at the ends for column beam connections. The selection of the MHS frames depends on the construction conditions, including the construction budget, allowed construction schedule and cost for labour and materials. When the construction schedule is more critical than the financial restrictions, path 1 of Figure 2 could be selected. With this selection, the field work is minimized since most of the work is done off-site. When the operating plant cost is too high and the construction schedule is not constrained, the selection oppo- Figure 2. Diagram of the combinations available in the modularized system

4 W.-K. HONG ET AL. site path 2 can be made. This option utilizes partially manufactured precast concrete. In this selection, more field work is required while off-site manufacturing of precast MHS beams and columns is minimized. This option may require labour for end pour forms for beam column connections. It should be noted that there are no special connections required for the MHS frames. The only connection type used for the MHS frames is the conventional steel connection. 4. CONNECTION OF MHS BEAM TO MHS GIRDER Figure 3 describes design details that were used to connect beams to girders with pour forms of limited length. In this building, pin connections were designed as shown in sections A-A and B-B of Figure 4. Figure 3. Details of the connection between the girder and beam (a) (b) Figure 4. Details of the bolted pin connection. (a) A-A section; (b) B-B section

5 MHS FOR A HIGH-RISE BUILDING The moment connections are made possible by full penetration welding between the flanges of the girders and the beams. 5. MOMENT CONNECTIONS BETWEEN MHS COMPOSITE BEAMS AND STEEL COLUMNS The beam column connection used in this building was designed for fixed conditions that enable moments to be transferred through the joints. The typical connection between a steel column and an MHS composite girder is shown in Figure 5, where the web of the beam was connected to the column using high-strength bolts. The flange was welded to the column. A complete penetration weld was employed through the width of both the top and bottom flanges of the MHS composite beams when stresses were required to be transferred for moment connections. This weld was made by welding from one side to a backing bar. When backing bars were not employed, it was required by the specifications that weld roots were chipped or gouged to separate metal for full penetration groove welds. Specific instruction for the type, size, length and location of welds for the assembled pieces is provided in Figure 5. This figure indicates shop details and erection plans for welded construction. (a) (b) Figure 5. Details of the welded moment connection: (a) elevation; (b) plan

6 W.-K. HONG ET AL. 6. CONNECTION OF SLAB TO MHS BEAM Figure 6 demonstrates how the metal deck plates forming a slab were assembled on top of the precast concrete of the MHS composite beams, indicating the rebar detailing for the top and bottom reinforcements and splicing. The detail of Figure 7 was employed to accommodate two different levels of adjacent floors intended to provide the building with diverse architectural flexibilities. Steel sections of T-type supports were welded on top of the MHS beams to successfully support two neighbouring slabs of different levels. 7. EXPERIMENTAL STUDY Four full-scale tests designed to be representative of the effective interaction between the steel and concrete were performed. Figures 8 and 9 show the test set-up with the reaction frame. The experimental investigation examined the hysteretic behaviour, moment capacity and energy dissipation capacity of the specimens under cyclic loading. Figure 10 illustrates the load displacement relationship of the test. A 1 6-m specimen was manufactured and tested in order to observe the resulting type of failure mode. The loading that caused the failure of the specimen was symmetrically distributed on the edges of the precast concrete. The result is shown in Figure 11. Figure 12 shows the test set-up and the reaction frame. When concrete is cast on the metal deck plate located on the edges of the precast concrete, the weight of the concrete slabs and other construction loads must be supported by the contacts between the steel and the precast concrete. This interface must not exhibit bearing failures, shear failures and failures caused by torque due to the loading of the precast concrete, which is shown Figure 6. Details of the connection between the MHS composite beam and metal deck plate

7 MHS FOR A HIGH-RISE BUILDING Figure 7. Details of the connection between two different levels Figure 8. Full-scale test of the MHS composite beam with a slab

8 W.-K. HONG ET AL. Figure 9. Behaviour of the MHS composite beam with a slab Load-displacement curve Load (kn) mm, kn mm, kn mm, kn mm, kn mm, kn mm, kn mm, kn Midspan displacement (mm) Figure 10. Load displacement relationship of the MHS composite beam with a slab in Figures When the contact area between the concrete and the bottom flange of the steel beam is small, bearing failure of the concrete is likely and must be prevented. Three types of concreteencasing steel sections were verified to safely resist vertical loads. The three typical failure modes are shown in Figures At the ultimate load, bearing failure of the concrete on the bottom flanges was observed at kn, as shown in Figure 13. Longitudinal cracks in the bottom surface

9 MHS FOR A HIGH-RISE BUILDING Figure 11. U-shaped MHS specimen and reaction frame Figure 12. The test set-up and reaction frame of the precast concrete led to the bearing failure, as shown in Figure 15. These cracks were caused by the torque initiated by the symmetrically distributed loads on the edges of the precast concrete. The precast concrete demonstrated strength 4 7 times and 3 1 times greater than the requirement for supporting concrete slab thicknesses of 150 and 250 mm for the U-shaped MHS beam, respectively. Figure 16 shows the load displacement relationship at the mid-point of the specimen.

10 W.-K. HONG ET AL. Figure 13. Shear failure Figure 14. Shear failure

11 MHS FOR A HIGH-RISE BUILDING Figure 15. Bearing failure at the bottom of the beam Figure 16. Load displacement relationship of the U-shaped MHS specimen

12 W.-K. HONG ET AL. 8. THE CONSTRUCTION OF A HIGH-RISE BUILDING WITH MHS FRAMES 8.1 Floor height in the MHS structure Table 1 shows the dead and live loads used in the design of the building. The compressive concrete strength was 24 MPa. The yield strength of the reinforcing steel and structural steel was 400 and 330 MPa, respectively. The reduction of the floor thickness obtained from employing MHS beams was verified by the comparison of the MHS beams with a steel beam section, calculated using the same design code and specification. Computer modelling of the building designed with 19 floors is demonstrated in Figure 17. Figure 18 compares both structural plans. Design equations proposed by Hong et al. (Composite Beam Composed of Steel and Precast Concrete. (MHS) Part II: Analytical Investigation), were used to design the MHS beams and the steel beam sections. The MHS composite beams designed for the 19-storey building are shown in Figure 19. The top 150 mm of this figure accounts for the thickness of the concrete slabs. Table 1. Dead and live loadings Floors Dead load (kn/m 2 ) Live load (kn/m 2 ) Public facility (2nd 3rd floor) Business facility (4th 6th floor) PIT Residential facility (7th 19th floor) Roof Figure 17. Computer modelling of the 19-storey building

13 MHS FOR A HIGH-RISE BUILDING (a) (b) Figure 18. Typical floor plan: (a) first sixth floor, PIT; (b) 7th 19th floor, roof (a) (b) Figure 19. Section of the MHS composite beam: (a) second sixth floor, PIT; (b) 7th 19th floor, roof

14 W.-K. HONG ET AL. Table 2 summarizes the size of the MHS structural members including steel sections, reinforcing steel and precast concrete. Floor thicknesses of these members are also listed in the table. Table 3 compares the design flexural moment strength and the factored moment demand of the MHS beams. 8.2 Floor thickness of the steel structure The steel beams for the original 18-storey building were planned for and designed as shown in Table 4, which summarizes the size and floor thickness of the steel sections. Table 5 compares the design flexural moment strength and the factored moment demand of the steel beams. Member Width (B) (mm) Table 2. MHS composite beam sections by floor Depth (D) (mm) Steel Compressive reinforcement Tensile reinforcement SB1 (2nd 3rd floor) H D25 2-D25 SB1 (4th 6th floor) H D25 2-D25 SB1 (PIT) H D25 2-D25 SB1 (7th 19th floor) H D25 4-D25 SB1 (roof) H D25 4-D25 Table 3. Comparison of the design flexural moment strength to the moment demand for the MHS composite beams Member Design flexural moment strength (kn m) Moment demand (kn m) Accepted SB1 (2nd 3rd floor) OK SB1 (4th 6th floor) OK SB1 (PIT) OK SB1 (7th 19th floor) OK SB1 (roof) OK Table 4. Steel beam sections by floor Member Depth (D) (mm) Steel SB1 (2nd 4th floor) 506 H SB1 (5th floor) 506 H SB1 (PIT) 596 H SB1 (6th 18th floor) 596 H SB1 (roof) 344 H Table 5. Comparison of the design flexural moment strength to the moment demand for the steel beams Member Design flexural moment strength (kn m) Moment demand (kn m) Accepted SB1 (2nd 4th floor) OK SB1 (5th floor) OK SB1 (PIT) OK SB1 (6th 18th floor) OK SB1 (roof) OK

15 MHS FOR A HIGH-RISE BUILDING 8.3 Reduction in fl oor height The total thickness of the steel beam consists of the fire spray coating, beam and slab: 786 mm for the residential floors (6th floor 18th floor). In Figure 20, the thickness of the MHS beams was 500 mm, reduced by 286 mm from that of the steel beams. Table 6 presents the total reduction in the height of the building obtained from using MHS beams. Both the total building height and the floor height of the 19-storey building were reduced. The height (66 40 m) of the building redesigned with 19 stories decreased by 1 24 m from that of the 18-storey building (67 64 m). It is also recognized in this table that the total floor thickness of m was reduced, enabling the addition of one more floor. The average reduction of floor thickness per floor was 220 mm. The height from slab to ceiling was not changed. Table 7 describes the building in which the MHS frames were applied. The gross area of the building is m 2. The building consists of both residential and office space. Although originally designed as an 18-storey steel structure building, the design was changed to the 19-storey MHS frame building in order to meet the project budget. 8.4 The selection of the MHS frame For the building shown in Figure 21, it was required to meet both the project budget and construction schedule. Hence, the MHS frame module was selected based on both path 3 of Figure 2 and partially manufactured precast concrete. Pour forms were prepared at both ends of the MHS beam for connections to columns. Pour forms were also necessary to make composite columns. The combination of the low-cost pour forms and the partial length precast concrete manufactured off-site provided affordable MHS frames that enabled the construction to continue as scheduled. Even though the MHS frames of this selected module did not offer a faster construction schedule than steel erection, it did provide a significantly faster schedule than conventional concrete construction practices. The manufacturing plant and the transport of the manufactured MHS products are shown in Figures 22 and 23. Figure 24 demonstrates one of the beam column connections after the pour forms were removed. Figure 20. Comparison of the floor depth achieved with an MHS composite beam and steel beam (residential facility 7th 19th floor)

16 Storey Floors W.-K. HONG ET AL. Table 6. Comparison of floor height between the two designs Steel beam (18 stories) Depth (mm) Floor height (m) Floors MHS composite beam (19 stories) Depth (mm) Floor height (m) Floor height reduction (m) 1st Public facility 5 65 Public facility nd rd th Business facility th Business facility th Residential facility PIT PIT PIT th Residential facility Residential facility th th th th th th th th th th th th Roof Sum m Sum 66 4 m m Table 7. General information regarding the MHS frame building Site Seoul, Korea District Commercial district, district plan zone, central aesthetic zone Site area m 2 Building type Residential housing, public facility, business facility Stories 6 below ground, 19 superstructure Structural system Steel and concrete composite structure Building area m 2 Gross area m 2 Building coverage 59 65% Bulk rate to building lot % 8.5 Construction sequence Table 8 shows the construction schedule for the erections of the MHS beams and composite columns. For the first 5 days of the first week, four-storey steel columns were lifted as shown in Figure 25. The erection of the MHS beams followed as shown in Figures While the metal deck plates were prepared for concrete casting to form slabs for the first four floors (as shown in Figures 29 and 30), the steel columns of the next four floors continued to be erected, as shown in Figure 31. This process was repeated until the completion of the building frame. Figure 32 illustrates the completion of both the columns and MHS girders on the 12th 15th floors. Figure 33 shows the steel

17 MHS FOR A HIGH-RISE BUILDING Figure 21. Building with MHS frames Figure 22. The manufacturing plant

18 W.-K. HONG ET AL. Figure 23. Transport of manufactured MHS products Figure 24. Completed beam column joint

19 MHS FOR A HIGH-RISE BUILDING Table 8. Construction schedule 1st week 2nd week 3rd week 4th week 5th week Field work Steel work Erection of steel column first unit column (1F 4F) second unit column (5F 8F) third unit column (9F 12F) fourth unit column (13F 16F) Installation of MHS composite beam 1F 2F 3F 4F 5F 6F 7F 8F 9F 10F 11F RC work Installation of metal deck plate 1F 2F 3F 4F 5F Installation of pour form 1F 2F 3F 4F Pouring & curing of concrete 1F 2F 3F 4F fifth unit column (17F 19F)

20 W.-K. HONG ET AL. Figure 25. Erection of columns for the first four-storey unit Figure 26. Erection of the MHS composite beam

21 MHS FOR A HIGH-RISE BUILDING Figure 27. Connections with high-strength bolts Figure 28. Installation of the composite beam for the first four-storey unit

22 W.-K. HONG ET AL. Figure 29. Installation of metal deck plates Figure 30. Concrete being cast to form slabs

23 MHS FOR A HIGH-RISE BUILDING Figure 31. Erection of columns for the second four-storey unit Figure 32. Completion of columns and MHS girders (12th 15th floor)

24 W.-K. HONG ET AL. Figure 33. Completion of steel columns (16th 19th floors) columns of the 16th 19th floors being completed while the installation of MHS girders on the lower floors was in progress. The MHS girders for the 16th 19th floors were completed in Figure 34. A total of 35 days was required to finish the structural frame of the first four floors. The concrete cured for 7 days in the summer and 10 days with heating in the winter. The use of the precast concrete with steel beams significantly reduced the use of supports and temporary pour forms, contributing to systematic construction that cannot be achieved using conventional concrete construction practices. If all the concrete had been cast in the field, the construction schedule would have been significantly delayed. In addition to the shortened construction schedule, it was found that the quality assurance programme for the precast concrete could be executed more effectively than the practice of casting the concrete in the field. Figure 35 presents a list of selected buildings in which the MHS technique was used to reduce floor height and save structural tonnage. As shown in this figure, different MHS frame combinations were provided, offering the best construction solutions in terms of construction costs and schedule. This combination reflected the individual project conditions, including limitations, restrictions and favorites as well. Some of these buildings are under construction or in the design stage. Figure 36 presents the MHS combined module for the completed buildings.

25 MHS FOR A HIGH-RISE BUILDING Figure 34. Completion of both the MHS columns and girders (16th 19th floors) 9. CONCLUSIONS The composite construction of high-rise buildings utilizing the MHS frame was presented. The MHS construction technique resulted in both reduced floor height and a shortened construction schedule as compared with conventional construction practices. The successful application of the MHS to an 18- storey building added one additional floor. In this application, the MHS frame module selected consisted of partially manufactured precast concrete and pour forms prepared at both ends of the MHS beam column joint. This successful construction outcome was possible due to the slabs being constructed on top of the edges of the U-shaped precast concrete instead of on top of the steel flanges, reducing the thickness of the slab and beam by 220 mm per floor. This paper also presented the connections between beam and girder, beam and column and slab and beam employed in the construction of the 19-storey building. The construction of two different levels of adjacent floors demonstrates the diverse architectural flexibilities achieved in the design of this building. The use of the precast concrete with steel beams contributed to meeting a construction schedule similar to that of steel structures, but shorter than that of reinforced concrete structures. The quality assurance programme of the MHS construction helped improve construction quality and save cost involved with corrections. Multiple applications using MHS frames were reported in this study, including four cases of completed structures. It is noted that the MHS modules selected for the buildings in this study

26 W.-K. HONG ET AL. Figure 35. List of selected buildings were not identical to each other. The MHS modules are chosen based on the unique conditions of the individual project, including the construction budget and schedule. The structural steel tonnage was also reduced by 40 50%. The contribution of the moment strength produced by the reinforced concrete resulted in both economic advantages with reduced structural steel tonnage and environmental advantages. Further implementations of this type of construction technology and design are expected.

27 MHS FOR A HIGH-RISE BUILDING Figure 36. The MHS combination for selected buildings

28 W.-K. HONG ET AL. ACKNOWLEDGEMENTS The authors would like to thank GS Engineering & Construction for financial support. The photos of the construction site were provided by Daewoo Shipbuilding Marine & Engineering Construction Co., LTD., which brought the idea to reality. The authors would also like to extend their gratitude to Mr. Lim, Sun-Jae of Kumho Engineering and Construction and Mr. Sim, Nam-Ju of Sampyo Engineering and Construction LTD. for their useful recommendations. This work was supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korea government (MEST) (No. R ). This research was supported by Kyung Hee University Research Fund in 2008 (KHU ). We would also like to thank Kyung Hee University for the generous sharing of information and facilities relevant to this research. REFERENCES Benjaoran V, Dawood N Intelligence approach to production planning system for bespoke precast concrete products. Automation in Construction 15(6): Carpinteri A, Spagnoli A, Vantadori S A fracture mechanics model for a composite beam with multiple reinforcements under cyclic bending. International Journal of Solids and Structures 41(20): Hong WK, Kim HC. 2004a. Behavior of concrete columns confined by carbon composite tubes. Canadian Journal of Civil Engineering 31(2): Hong WK, Kim HC. 2004b. Performance of a multi-story structure with a resilient-friction base isolation system. Computer & Structures 82: Hong WK, Kim HC, Yoon SH Lateral behavior of full-scale concrete-filled carbon composite columns. Canadian Journal of Civil Engineering 31(2): Hong WK, Kim SD, Kim SK Up up construction takes off in Korea. Proceedings of the Institution of Civil Engineers. Civil Engineering 158: Hong WK, Kim JM, Park SC, Kim SI, Lee SG, Lee HC, Yoon KJ. Composite beam composed of steel and precast concrete. (Modularized hybrid system, MHS) Part II: analytical investigation. Structural Design of Tall and Special Buildings (in press, a). doi: /tal.484. Hong WK, Park SC, Kim JM, Lee SG, Kim SI, Yoon KJ, Lee HC. Composite beam composed of steel and precast concrete. (Modularized hybrid system, MHS) Part I: experimental investigation. Structural Design of Tall and Special Buildings (in press, b). doi: /tal.485. Mirghaderi SR, Renani MD The rigid seismic connection of continuous beams to column. Journal of Constructional Steel Research 64(12): Pirmoz A, Khoei AS, Mohammadrezapour E, Daryan AS Moment rotation behavior of bolted top-seat angle connections. Journal of Constructional Steel Research 65(4): Wakisaka T, Furuya N, Inoue Y, Shiokawa T Automated construction system for high-rise reinforced concrete buildings. Automation in Construction 9(3):