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CO2 emission reduction effects of an innovative composite precast concrete structure applied to heavy loaded and long span buildings
Energy and Buildings 126 (2016) 36–43
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CO2 emission reduction effects of an innovative composite precast concrete structure applied to heavy loaded and long span buildings Donghoon Lee, Chaeyeon Lim, Sunkuk Kim ∗ Department of Architectural Engineering, Kyung Hee University, Yongin 446-701, Republic of Korea
a r t i c l e
i n f o
Article history: Received 27 January 2016 Received in revised form 8 April 2016 Accepted 9 May 2016 Available online 10 May 2016 Keywords: CO2 emission Reduction effect SMART frame Composite precast concrete
a b s t r a c t A structural frame built using innovative composite precast concrete (CPC) developed using a new concept called the SMART frame was demonstrated to require less steel materials, concrete, and forms than reinforced concrete (RC) due to its higher structural efficiency. This not only resulted in a reduction of costs, but also less CO2 emissions. In this study, we analyzed the CO2 emission reduction effect of an innovative composite precast concrete structure applied to heavy loaded buildings with more than a 10 m long span. A case study was conducted with CPC and RC members designed under the same conditions. The carbon dioxide emissions of the RC-structured building and SMART frame building were 435.5 kg-CO2 /m2 and 414.1 kg-CO2 /m2 , respectively. Thus, a CO2 emission reduction of 21.4 kg-CO2 /m2 was achieved. This corresponds to a 5.5% CO2 reduction effect when the SMART frame was applied instead of RC, as the CO2 emissions based on the input of resources was analyzed, which is equivalent to around 3.7% of the total CO2 emissions of the case building. In addition, the total CO2 emissions were estimated by also considering the oil and electricity power use. A CO2 reduction effect of around 4.9% was achieved. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Green buildings all over the world are resulting in reductions of green-house gases generated from buildings [1,2]. In addition, many studies are actively being conducted to reduce emissions. Yet, most studies tend to be centered on the operation and maintenance phases, instead of the construction phase [3–7]. The construction phase of a building accounts for a significant part of the construction industry and it is when energy and materials are consumed the most [8–11]. The carbon dioxide (CO2 ) generated in the construction phase is emitted during the production, transportation, manufacturing, and installation of resources used for the construction of new buildings and remodeling existing buildings [12]. It is possible to reduce the CO2 emitted in the process by approximately 10% [13]. One of the representative methods for CO2 emission reduction at the construction phase is composite precast concrete members (CPC), in which the reinforced concrete structure is improved [14]. CPC members reduce CO2 emissions by reducing the amount of resources inputted into the structure and they ensure structural stability as well [14–17]. Hong et al. proposed the concept of a Green Frame, which is an improved variation of the
∗ Corresponding author at: Department of Architectural Engineering, Kyung Hee University, Yongin, Gyeonggi-do, 446-701, Republic of Korea. E-mail addresses: [email protected], [email protected] (S. Kim). http://dx.doi.org/10.1016/j.enbuild.2016.05.022 0378-7788/© 2016 Elsevier B.V. All rights reserved.
original CPC, and confirmed a CO2 reduction effect of around 18–23% when compared to conventional construction methods. Lee et al. improved the columns and beams of the Green Frame proposed by Hong et al., additionally reducing CO2 emissions by around 2.8% [18]. Thus, a structural frame built using innovative composite precast concrete (CPC), which is developed with the new concept called a SMART frame, has been proven to require less steel materials, concrete, and forms than RC (reinforced concrete) due to its higher structural efficiency. This not only results in reduced costs, but also decreased CO2 emissions. Previous studies were performed on residential buildings that have a relatively shorter span when applied with CPC. However, taking into consideration the characteristics of CPC, heavy loaded buildings with more than a 10 m long span, such as warehouses and car park buildings, require more steel to be installed in the member along with a different section shape. Since the increased steel materials imply higher CO2 emissions, it should be proven that CPC is valid in reducing CO2 emissions on heavy loaded and long span buildings when compared to RC. Therefore, in this study, we analyzed the CO2 emission reduction effect of an innovative composite precast concrete structure applied to heavy loaded buildings with more than a 10 m long span. Here, ‘Innovative Composite Precast Concrete Structure’ uses an improved technique and provides heavy and long-span building materials, referred to as an ‘SMART frame’ (abbreviation) to distinguish it from ‘CPC’.
D. Lee et al. / Energy and Buildings 126 (2016) 36–43
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Fig. 1. PC column and beam of GF [19].
In this study, an SMART frame was applied to a car park building where large, heavy members are used, and the results were compared to the existing design. Also, to verify the reduction of CO2 emissions, the quantity of materials was estimated and converted to CO2 emissions based on the input resources. Then, the CO2 emitted at the construction phase was additionally taken into consideration based on the oil and power consumption.
underground, it reduces the amount of excavation. Furthermore, such beams can be applied to steel-reinforced concrete and steelreinforced concrete columns, as well as general columns [16]. As used in the study of Lee et al. [16], T-shape steel is embedded in the beam end. In this study, the length of the T-shaped steel is 1/8 of the beam length, whereas it was 1/3 of the beam length in the previous study.
2. Survey of green frame characteristics
3. Concept of the SMART frame
As shown in Fig. 1, the Green Frame (GF) is a composite PC column-beam structure composed of PC columns in one section consisting of three stories and composite PC beams installed at each story. The PC columns and beams have the characteristics of postand-lintel construction owing to the joint steel. As a result, they can be quickly and accurately installed. Along with the slab, concrete is poured into them to secure the structural integrity. GF can improve constructability and reduce construction duration when applied with the hybrid joint method [19]. When CPC is applied to apartment housing units, the flexibility of Rahmen structures and the floor height, which is the same as that of the conventional wall structure system, can be maintained [19]. For in situ production of PC members, the in situ developed form is used. The produced composite PC members are lifted using a crane and then installed. When the columns and beams are installed, a deck plate is installed for slab pouring and the developed joint form is used for the areas where the columns and beams intersect. When the joint form and deck plate are completely installed, the top bar of the slab is arranged and concrete is poured to integrate the structure. In the lifting and installation of the columns, beams and deck plates are more important for the frame work of CPC than wet construction, and the core part that mainly accounts for the wet construction is applied in the construction of residential parts. Therefore, it is possible to shorten the construction duration compared to the conventional method of on-site concrete pouring for a wall-type structure [20]. Based on a preliminary study, the top or bottom flange, which contributes less to the bending moment, is removed from the section shape steel inserted in the CPC beams to reduce the quantity of steel frames and ensure efficiency of the members [14]. CPC beams are excellent for reducing the quantity of materials, cutting down the construction cost and reducing CO2 emissions [13,14]. When applied on the ground, it reduces the floor height, and when applied
The SMART frame was developed based on the existing CPC structure. As described above, the original CPC improved the structural efficiency and reduced the amounts of steel, concrete, and forms used. In addition, its constructability was enhanced, reducing the construction duration. However, CPC structures analyzed in previous studies were designed to be applied to buildings with a relatively shorter span, such as residential buildings or offices, and it was impossible to apply them to long-span buildings. In particular, new reviews and designs are needed for beams since the amount of rebar is reduced when compared to that applied to an existing RC structure, and the steel to reinforce this reduction is applied to the long-span building. In addition, it requires a new joint design that can bear the weight of increased beams as well as ensure structural reinforcement. The SMART frame is an improved CPC that can be applied to long-span buildings. As shown in Fig. 2, the SMART frame is combined with the steel structure and rebar. The steel applied to the end of a SMART frame structurally reinforces the rebar and improves its constructability as it is connected to columns with bolts. Thus, the SMART frame is integrated with the structural advantages of the reinforced
Fig. 2. Concept of the column-beam joint of SMART frame.
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concrete structure and steel structure. In addition, just like the CPC structure, the SMART frame can be produced on-site, reducing the transportation cost of members. The SMART frame is composed of beams and columns. As they are installed in steel connections, they have the characteristics of post-and-lintel construction and can be quickly and accurately installed. Also, the steel bracket applied to beams is removed with the steel that contributes less to the bending moment, which resulted in less steel being used and reduced self-load of the structure. It is expected that the reduced amount of resource input will lead to reduced CO2 emissions. As illustrated in Fig. 2, the steel bracket at the beam end of the SMART frame is connected to the column bracket with reinforcement plates and bolts. The reinforced concrete columns of the section are connected as steel members of the CPC structure. Precast columns with the composite joint of steel-reinforced concrete have the composite joint part embedded with steel between the precast concrete columns, which solves the problem of the joint between the reinforced concrete column and composite beam. Thus, it is possible to reduce the amount of materials for the section size of columns/beams. Moreover, it demonstrates excellent constructability for the reinforced concrete structure, which can be easily connected like a steel structure. For quick and safe column-beam connections, sliding and setting are performed with reinforcement plates. The sectional shape steel is embedded in the beam end using the same method suggested in the study of Lee et al., but H-shaped steel or T-shaped steel is applied, depending on the length and load of the beams [18]. Thus, the section differs from that of CPC, which uses only Tshaped steel. The structural stability of beams that are more than 10 m long was reviewed and it was found that the length of section shape steel is 1/8 of the beam length. This is because when 1/8 of the beam length is applied based on the structural stability review, the moment distribution and reduced floor height can be maintained although there is a slight increase of rebar. Also, as shown in Fig. 3, the rebar of the beam is anchored to the column with dead anchors. Since the dead anchors are shorter than general anchors, they will reduce the amount of steel materials used. In addition, the project develops a prefabricated form, as shown in Fig. 4, to increase the efficiency ratio of the form. The existing joint form has a complicated shape which is frequently damaged when removed, making it difficult to be reused. To supplement this, it is designed to not be damaged when the form is removed after grouting. Fig. 4(a) illustrates the beam assembled with the column and Fig. 4(b) shows the system form to be applied. It is applied with turn buckles and clamps so that it can be easily removed after grouting. When the efficiency ratio of forms is increased, reductions of the wastes and CO2 emissions are anticipated.
Fig. 3. Cross-sectional drawing of the column-beam joint of SMART frame.
4. Analysis of energy and CO2 emissions (case study) 4.1. Summary of the case The case project is a car park building located in Gyeonggi-do. Its site area is 3445 m2 and the total floor area is 21,199 m2 . It is an eight-story building with basement floor. It was originally designed to have a reinforced concrete structure, but CPC was applied to improve the structural efficiency and reduce CO2 emissions. The CPC structures analyzed in previous studies were applied to residential buildings with a relatively short span and therefore, a new design is required for buildings with a long span of more than 10 m. Furthermore, when CPC is applied to long-span structures, the CO2 reduction effects need to be verified. Therefore, in this study, we applied both a Rahmen structure and SMART frame (SF) to the case project whose span is more than 10 m under the same conditions, as shown in Fig. 5. Upon the contractor’s request, the project was fully redesigned to an SMART frame from the original Rahmen structure with the purpose of improving the seismic performance and reducing CO2 emissions. As described in Table 1, the concrete strength was 24 MPa and the rebar strength was 400 MPa for D16 (Diameter: 16 mm) or below and 500 MPa for D19 (Diameter: 19 mm) or above. In addition, 2 types of steel materials were used. The main material was SHN490 (fy = 325 MPa) and the sub-material was SS400 (fy = 235 MPa). High-tension bolts (900 MPa) were used.
Fig. 4. Concept of joint form.
D. Lee et al. / Energy and Buildings 126 (2016) 36–43 Table 1 The Strength of Materials applied to the Structure Design.
Table 3 The efficiency ratio of SMART frame among all members of the project.
Material
Strength
Concrete Rebar
fck = 24 MPa fy = 400 MPa fy = 500 MPa fy = 325 MPa fy = 235 MPa fy = 900 MPa fy = 235 MPa
D16 or below D19 or above SHN490 SS400 High-Tension Bolt Typical Bolt
Steel Bolts
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Table 2 Design strength of the project. Load
Floor
1F 2F 3F 4F 5F 6F 7F 8F Rooftop Total
Total Members
RC frame → SF
Column
Girder & Beam
Column
Girder & Beam
Ratio(%)
31 31 33 37 36 36 36 36
77 80 88 89 89 89 89 107 24 732
21 22 24 28 27 27 27 27
52 64 72 74 74 74 74 75 24 583
67.6% 77.5% 79.3% 81.0% 80.8% 80.8% 80.8% 71.3% 100.0% 78.0%
276
203
Strength
Basic Wind Velocity Seismic Load Design Load (Parking Lot) 1.2 × Dead load + 1.6 × Live load
Effective Ground Acceleration 1–2nd floor 3rd floor 4th floor 5–8th floor
30 m/sec S = 0.176 18.8 kN/m2 14.5 kN/m2 12.1 kN/m2 9.5 kN/m2
As described in Table 2, the basic wind velocity of this project is 30 m/sec, the seismic load is S = 0.176, and the design load is 9.5–18.8 kN/m2 . For the structural design programs, Midas Gen was used for the frame analyses, Midas SDS for the plate analyses, and BeST for the member analyses. When the RC structure was applied to the project, the main beam section was designed with a thickness of 600–700 mm and a width of 500–600 mm, as shown in Fig. 6. For its structural stability, the top bar was arranged with up to 3 rows. The columns were designed with a composite CPC structure combined with steel frames and RC, considering the structural stability and space efficiency. When the SMART frame was applied to the case project with the same floor plan and design load, steel was installed and the amount of rebar was reduced. Fig. 7 shows the case of applying the SMART frame to the main beam section, where the amount and thickness of main rebar are reduced. However, as more steel materials were added, its structural strength increased. For columns, the same section as the case designed with the RC structure was applied. As listed in Table 3, the number of members originally designed was 276 columns, 511 girders, and 221 beams, for a total of 1008 members. Among these, 203 main columns and 583 beams (78%), excluding the lamps and cores, were applied to SMART frame. The remaining members (22%), excluding the main columns, girders, and beams, were designed based on the original plan. However, it is expected that there will be sufficient CO2 reduction effects since the main members were changed.
Fig. 5. Typical floor plan of the case project (2nd Floor).
Table 4 The quantity of concrete and forms for each floor. Floor
Area (m2 )
B1 1 2 3 4 5 6 7 8 RF Total
628 2571 2476 2498 2607 2607 2607 2607 2607 2593 23,801
Concrete (m3 )
Form (m2 )
RC
SF
RC
SF
2066 1056 684 654 724 642 614 612 620 863 8535
1359 974 623 672 620 591 587 591 571 652 7240
1173 4550 2549 2152 3003 2412 2066 2050 2118 3842 25,915
1496 1761 1676 1709 1764 1677 1677 1698 1675 298 15,431
Table 5 The quantity of rebar and steel frames for each floor. Floor
B1 1 2 3 4 5 6 7 8 RF Total
Area (m2 )
628 2571 2476 2498 2607 2607 2607 2607 2607 2593 23,801
Rebar (ton)
Steel Frame (ton)
RC
SF
RC
SF
201.5 122.8 93.2 69.3 77.9 74.6 69.2 69.0 69.4 104.2 951.1
93.7 65.9 50.0 56.2 51.7 55.8 55.7 56.2 58.4 65.1 608.7
11.1 43.2 34.2 30.4 28.5 22.9 19.6 19.5 20.1 16.4 245.9
12.9 32.9 56.2 61.7 57.1 54.7 58.0 58.8 58.9 42.2 493.3
4.2. Estimation of the frame quantity The frame quantity of the RC structure, which is the original design of the case project, is estimated in Table 4. The weight of rebar was estimated per rebar diameter and the forms were estimated for each part to apply the efficiency ratio. For the material quantity estimation of the case project, parts of the PC work and the RC parts were estimated separately and then added up. Case 1 (RC application) requires 8539 m3 of concrete and Case 2 (SMART frame application) requires 7245 m3 of concrete, resulting in a difference of around 1300 m3 . The efficiency ratio of the forms in Case 2 is 15,435 m2 , which is drastically decreased from that of Case 1 (25,919 m2 ). This is the result of the efficiency ratio of PC members produced on the floor compared to the RC forms. Rebar and steel frames have complementary characteristics for reinforcement. Thus, when an SMART frame is reinforced with steel frames, the amount of rebar can be reduced compared to the RC. The quantities of rebar and steel frames used in the 2 different structures are shown in Table 5. The RC structure used 951.1 t of rebar, which is more than the SMART frame structure, which used 608.7 t
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D. Lee et al. / Energy and Buildings 126 (2016) 36–43
Fig. 6. RC Beam section design (main members).
of rebar. On the other hand, the SMART frame used 493.3 t of steel frames, whereas RC used 245.9 t. 4.3. Estimation of the CO2 emissions The CO2 emissions of an entire building can be estimated using the basic unit of CO2 emissions per material quantity obtained from the case application. Hong et al. [13,14] and Lee et al. [16] conducted studies in this way to estimate the CO2 emissions at the construction phase of a building. In reference to the Inter-Industry Relations Table of the Korea Institute of Civil Engineering and Building Technology, the CO2 emissions per construction material based on the energy consumption of all stages from the collection of raw materials to processing and production was defined. This estimation is the
most logical way of converting the CO2 emissions of materials and we applied this data in this study. Table 6 shows the CO2 emissions per unit quantity of the major construction materials. In this study, we verified that the CO2 emissions were reduced based on the material quantity using the CO2 emission per unit quantity data. As shown in Table 6, steel materials emit the most CO2 per unit quantity. In the case of rebar, the CO2 emissions are 3500 kg/t and in the case of steel sections, the emissions are 4166 kg/t. These values are much more than the case of concrete, which emits 140 kg/t. Thus, the amount of steel is likely to impact the overall CO2 emissions. The basic unit of high strength reinforcing steel was applied to the rebar and the basic unit of the steel section was applied to the steel. The basic unit for the formwork was applied to the forms using mostly wooden materials and the basic unit of the steel plate
Fig. 7. Beam section design of SMART frame (main members).
D. Lee et al. / Energy and Buildings 126 (2016) 36–43
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Table 6 The basic units of CO2 emission per key material used in CPC [14,21]. Item
Concrete Rebar Steel Outer form of ext. wall Form for int. wall Form for slab Joint form High-tensile bolt
Applied basic unit of CO2 emission Item
Basic unit
ready-mixed-concrete High strength reinforcing steel Steel section Formwork
140.43 3,500.00 4,166.00 3.83
kg-CO2 /m3 kg-CO2 /t kg-CO2 /t kgCO2 /m2
Bolt and nut
0.0005
kg-CO2 /EA
can be applied to steel forms [14]. The basic unit of bolts and nuts was converted into quantity to be applied to high-tensile bolts [14]. The CO2 emissions of the resources used for the construction of a building in the case project were estimated by applying the basic units of CO2 emissions, shown in Table 7, to the material quantities given in Tables 4 and 5, which were estimated based on the design drawings, as shown in Table 7. The CO2 emitted from concrete of the RC structure is 1199 t and that of the SMART frame (SF) structure is 1017 t, which is about a 10% reduction. The CO2 emitted from reinforcement of the RC structure is 3329 t, which is more than that of the SMART frame structure (2131 t). However, the CO2 emitted from the steel of the RC structure is 1024 t, which is 50% less than that of the SMART frame (2055 t). It was found that the RS structure generates 5% more CO2 emissions for the reinforcements in total than the SMART frame structure. The CO2 emissions from forms are relatively smaller than those from reinforcements. The emissions are 98 t in the RC structure and 59 t in the SMART frame structure. The total CO2 emissions of the 2 structures compared based on the amount of materials used are 10,003 t (RC) and 9447 t (SMART frame). Therefore, the SMART frame emits only 94.5% of the emissions of the RC structure. Besides the CO2 emissions from materials, oil and power (electricity) may be consumed to use equipment and devices during the construction of a building, and such energy use generates CO2 as well [21]. Kim et al. analyzed 28 apartment building construction projects with LCA and proposed a regression equation of CO2 emissions at the construction phase [21]. Since the total floor area is the variable of the regression equation, it is easy to estimate the CO2 emissions based on oil and power consumption. The energy consumption of construction work according to the oil consumption at the construction phase is calculated using Eq. (1) and the CO2 emissions are calculated using Eq. (2) [21]. The total floor area of the case project was estimated to be 21,199 m2 and the energy consumption (Eco ) is 73.5 TOE. When the consumed energy is converted into CO2 , the CO2 emissions are 225.03 T-CO2 . Eco = 0.0017 × Af + 37.5
(1)
QCO2 o = Eco × 3.06
(2)
Eco : Oil energy consumption at the construction phase [TOE].
Fig. 8. Tower crane arrangement plan.
Af : Total floor area [m2 ]. QCO2o : CO2 emissions according to the oil use at the construction phase [T-CO2 ]. The energy consumption according to the power consumption at the construction phase can be estimated using Eq. (3) and the CO2 emissions can be calculated using Eq. (4) [21]. Ece was estimated to be 64.6 TOE. When Ece was calculated using Eq. (4), QCO2e was 106 T-CO2 . Ece = 0.0247 × Af 0.79
(3)
QCO2 a = Eca × 1.64
(4)
Ece : Power consumption (electricity use) at the construction phase [TOE]. QCO2e : CO2 emissions according to the power consumption at the construction phase [T-CO2 ]. To apply the SMART frame to the case project, the plan to operate tower cranes needs to be changed. As illustrated in Fig. 8, Case
Table 7 Comparison of CO2 emission by material use. Classification
Work Concrete Reinforcement
Form PC installation Total
Item Rebar Steel Total (rebar + steel) High-tensile bolt
Total CO2 emission (T-CO2 )
CO2 emission per unit area (kg-CO2 /m2 )
Ratio of emission (%)
RC
SF
RC
SF
SF/RC
1199 3329 1024 4353 98 0.026 10,003
1017 2131 2055 4186 59 0.012 9447
50.4 139.8 43 182.8 4.1 0.0011 420
42.74 89.5 86.3 175.8 2.5 0.0005 397
84.8 64.0 200.7 96.2 61.0 45.5 94.5
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D. Lee et al. / Energy and Buildings 126 (2016) 36–43
Table 8 Comparison of total CO2 emission. Item
Material use Oil use Electricity use Total CO2 emission
CO2 emission (T-CO2 )
CO2 emission per unit area (kg-CO2 /m2 )
Ratio of emission (%)
RC
SMART Frame
RC
SMART Frame
SF/RC
10,003 225 143 10,371
9447 225 180 9852
420 9.5 6 435.5
397 9.5 7.6 414.1
94.5 100 127 95.1
1 (RC structure applied), which originally required 1 tower crane, was changed to have 2 tower cranes when the SMART frame was applied. This is because the lifting weight increased and the project schedule changed. The power consumption of the selected model was 149 kVA and can be converted into approximately 880 kwh assuming that it has 8 h of operation. When the duration of operating the tower cranes for the case project (5 months) was applied, the total power consumption was estimated to be 88,000 kwh. When the CO2 conversion factor of 0.424 kg-CO2 /kwh [22,23] was applied, the CO2 emissions of each tower crane were 37.3 t-CO2 . For reference, using one more tower crane will definitely increase the cost and CO2 emissions. However, in case of a modular construction such as the SMART frame, using a small crane supportively will reduce the required construction time per floor and the rental time of the cranes. Furthermore, as the construction duration is shortened, there will be increased income from earlier operation of the parking lot. In conclusion, using an additional small crane has an effect of reducing the construction project cost. 880 kwh × 20 days × 5months = 88, 000 kwh(5) 88, 000 kwh × 0.424 kg-CO2 /kwh = 37.3 t-CO2 (6) Table 8 shows the total CO2 emissions based on the input resources and energy use. The CO2 emissions per unit area applied with the RC structure were 435.5 kg-CO2 /m2 and those applied with the SMART frame were 414.1 kg-CO2 /m2 . Thus, a reduction of 21.4 kg-CO2 /m2 was realized. 5.5% of the CO2 reduction effect is due to the resource input when the SMART frame was applied instead of the RC structure. In addition, the total CO2 emissions were estimated considering the oil and electricity power use, where around 4.9% of the CO2 reduction effect is obtained. 5. Conclusion CPC (Composite Precast Concrete) members require less steel materials, concrete, and forms than RC (Reinforced Concrete) members due to structural efficiency. In addition, there is a CO2 reduction effect. This study applied an SMART frame (CPC frame) to a car park building that requires large and heavy members, and the results were compared to the existing design. In addition, the quantity of material was estimated and converted into CO2 reduction based on the input resources to verify its reduction effect. Then, based on the oil and electricity power consumption at the construction phase, the CO2 emitted during the construction phase was additionally considered. The case project was originally designed to have a reinforced concrete structure, but CPC was applied to improve the structural efficiency and reduce CO2 emissions. Among the CPC structures that improve structural efficiency and lower CO2 emissions, GF was applied to residential buildings with a relatively shorter span. As a result, a new design was applied to the building with a span greater than 10 m, just like the case project. The basic units of CO2 emissions were applied to the material quantity estimates based on the design drawings to calculate the CO2 emissions of the resource input for the construction of this case
project. As a result, the CO2 emitted for the concrete of the RC structure was 1199 t and that of the SMART frame structure was 1017 t, which is about a 10% reduction. The CO2 emitted from reinforcement of the RC structure was 3329 t, which was more than that of the SMART frame structure (2131 t). However, the CO2 emitted from the steel of the RC structure was 1024 t, which is 50% less than that of SMART frame (2055 t). It was found that the RC structure generated 5% more CO2 emissions due to reinforcements in total than the SMART frame structure. The CO2 emissions from the forms were relatively smaller than those from reinforcements, where 98 t were generated from the RC structure and 59 t were emitted from the SMART frame structure. The total CO2 emissions of the 2 structures based on the amount of materials used were 10,003 t (RC) and 9447 t (SMART frame). The emissions from the SMART frame were 94.5% of the emissions from the RC structure. Furthermore, the CO2 emissions per unit area for the RC structure and SMART frame were 435.5 kg-CO2 /m2 and 414.1 kg-CO2 /m2 , respectively. Thus, a reduction of 21.4 kg-CO2 /m2 was achieved. As the SMART frame was applied instead of the RC structure, 5.5% of the CO2 reduction effect was due to the CO2 emissions according to the resource input, which is equivalent to around 3.7% of the total CO2 emissions of the case building. In addition, the total CO2 emissions were estimated considering the oil and electricity power use. A CO2 reduction effect of around 4.9% was achieved. The study examined the amount of materials required and CO2 emissions of an SMART frame redesigned with the existing GF to be applied to long-span buildings. The study proved that an Innovative Composite Precast Concrete Structure can be applied to large buildings with a long span in order to improve the RC structure in terms of greenhouse gas emissions. It is believed that this approach will be helpful in reducing the tremendous amount of CO2 emitted during the construction phase of a building.
Acknowledgements This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2013R1A2A2A01068297)
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Contents lists available at ScienceDirect
Energy and Buildings journal homepage: www.elsevier.com/locate/enbuild
CO2 emission reduction effects of an innovative composite precast concrete structure applied to heavy loaded and long span buildings Donghoon Lee, Chaeyeon Lim, Sunkuk Kim ∗ Department of Architectural Engineering, Kyung Hee University, Yongin 446-701, Republic of Korea
a r t i c l e
i n f o
Article history: Received 27 January 2016 Received in revised form 8 April 2016 Accepted 9 May 2016 Available online 10 May 2016 Keywords: CO2 emission Reduction effect SMART frame Composite precast concrete
a b s t r a c t A structural frame built using innovative composite precast concrete (CPC) developed using a new concept called the SMART frame was demonstrated to require less steel materials, concrete, and forms than reinforced concrete (RC) due to its higher structural efficiency. This not only resulted in a reduction of costs, but also less CO2 emissions. In this study, we analyzed the CO2 emission reduction effect of an innovative composite precast concrete structure applied to heavy loaded buildings with more than a 10 m long span. A case study was conducted with CPC and RC members designed under the same conditions. The carbon dioxide emissions of the RC-structured building and SMART frame building were 435.5 kg-CO2 /m2 and 414.1 kg-CO2 /m2 , respectively. Thus, a CO2 emission reduction of 21.4 kg-CO2 /m2 was achieved. This corresponds to a 5.5% CO2 reduction effect when the SMART frame was applied instead of RC, as the CO2 emissions based on the input of resources was analyzed, which is equivalent to around 3.7% of the total CO2 emissions of the case building. In addition, the total CO2 emissions were estimated by also considering the oil and electricity power use. A CO2 reduction effect of around 4.9% was achieved. © 2016 Elsevier B.V. All rights reserved.
1. Introduction Green buildings all over the world are resulting in reductions of green-house gases generated from buildings [1,2]. In addition, many studies are actively being conducted to reduce emissions. Yet, most studies tend to be centered on the operation and maintenance phases, instead of the construction phase [3–7]. The construction phase of a building accounts for a significant part of the construction industry and it is when energy and materials are consumed the most [8–11]. The carbon dioxide (CO2 ) generated in the construction phase is emitted during the production, transportation, manufacturing, and installation of resources used for the construction of new buildings and remodeling existing buildings [12]. It is possible to reduce the CO2 emitted in the process by approximately 10% [13]. One of the representative methods for CO2 emission reduction at the construction phase is composite precast concrete members (CPC), in which the reinforced concrete structure is improved [14]. CPC members reduce CO2 emissions by reducing the amount of resources inputted into the structure and they ensure structural stability as well [14–17]. Hong et al. proposed the concept of a Green Frame, which is an improved variation of the
∗ Corresponding author at: Department of Architectural Engineering, Kyung Hee University, Yongin, Gyeonggi-do, 446-701, Republic of Korea. E-mail addresses: [email protected], [email protected] (S. Kim). http://dx.doi.org/10.1016/j.enbuild.2016.05.022 0378-7788/© 2016 Elsevier B.V. All rights reserved.
original CPC, and confirmed a CO2 reduction effect of around 18–23% when compared to conventional construction methods. Lee et al. improved the columns and beams of the Green Frame proposed by Hong et al., additionally reducing CO2 emissions by around 2.8% [18]. Thus, a structural frame built using innovative composite precast concrete (CPC), which is developed with the new concept called a SMART frame, has been proven to require less steel materials, concrete, and forms than RC (reinforced concrete) due to its higher structural efficiency. This not only results in reduced costs, but also decreased CO2 emissions. Previous studies were performed on residential buildings that have a relatively shorter span when applied with CPC. However, taking into consideration the characteristics of CPC, heavy loaded buildings with more than a 10 m long span, such as warehouses and car park buildings, require more steel to be installed in the member along with a different section shape. Since the increased steel materials imply higher CO2 emissions, it should be proven that CPC is valid in reducing CO2 emissions on heavy loaded and long span buildings when compared to RC. Therefore, in this study, we analyzed the CO2 emission reduction effect of an innovative composite precast concrete structure applied to heavy loaded buildings with more than a 10 m long span. Here, ‘Innovative Composite Precast Concrete Structure’ uses an improved technique and provides heavy and long-span building materials, referred to as an ‘SMART frame’ (abbreviation) to distinguish it from ‘CPC’.
D. Lee et al. / Energy and Buildings 126 (2016) 36–43
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Fig. 1. PC column and beam of GF [19].
In this study, an SMART frame was applied to a car park building where large, heavy members are used, and the results were compared to the existing design. Also, to verify the reduction of CO2 emissions, the quantity of materials was estimated and converted to CO2 emissions based on the input resources. Then, the CO2 emitted at the construction phase was additionally taken into consideration based on the oil and power consumption.
underground, it reduces the amount of excavation. Furthermore, such beams can be applied to steel-reinforced concrete and steelreinforced concrete columns, as well as general columns [16]. As used in the study of Lee et al. [16], T-shape steel is embedded in the beam end. In this study, the length of the T-shaped steel is 1/8 of the beam length, whereas it was 1/3 of the beam length in the previous study.
2. Survey of green frame characteristics
3. Concept of the SMART frame
As shown in Fig. 1, the Green Frame (GF) is a composite PC column-beam structure composed of PC columns in one section consisting of three stories and composite PC beams installed at each story. The PC columns and beams have the characteristics of postand-lintel construction owing to the joint steel. As a result, they can be quickly and accurately installed. Along with the slab, concrete is poured into them to secure the structural integrity. GF can improve constructability and reduce construction duration when applied with the hybrid joint method [19]. When CPC is applied to apartment housing units, the flexibility of Rahmen structures and the floor height, which is the same as that of the conventional wall structure system, can be maintained [19]. For in situ production of PC members, the in situ developed form is used. The produced composite PC members are lifted using a crane and then installed. When the columns and beams are installed, a deck plate is installed for slab pouring and the developed joint form is used for the areas where the columns and beams intersect. When the joint form and deck plate are completely installed, the top bar of the slab is arranged and concrete is poured to integrate the structure. In the lifting and installation of the columns, beams and deck plates are more important for the frame work of CPC than wet construction, and the core part that mainly accounts for the wet construction is applied in the construction of residential parts. Therefore, it is possible to shorten the construction duration compared to the conventional method of on-site concrete pouring for a wall-type structure [20]. Based on a preliminary study, the top or bottom flange, which contributes less to the bending moment, is removed from the section shape steel inserted in the CPC beams to reduce the quantity of steel frames and ensure efficiency of the members [14]. CPC beams are excellent for reducing the quantity of materials, cutting down the construction cost and reducing CO2 emissions [13,14]. When applied on the ground, it reduces the floor height, and when applied
The SMART frame was developed based on the existing CPC structure. As described above, the original CPC improved the structural efficiency and reduced the amounts of steel, concrete, and forms used. In addition, its constructability was enhanced, reducing the construction duration. However, CPC structures analyzed in previous studies were designed to be applied to buildings with a relatively shorter span, such as residential buildings or offices, and it was impossible to apply them to long-span buildings. In particular, new reviews and designs are needed for beams since the amount of rebar is reduced when compared to that applied to an existing RC structure, and the steel to reinforce this reduction is applied to the long-span building. In addition, it requires a new joint design that can bear the weight of increased beams as well as ensure structural reinforcement. The SMART frame is an improved CPC that can be applied to long-span buildings. As shown in Fig. 2, the SMART frame is combined with the steel structure and rebar. The steel applied to the end of a SMART frame structurally reinforces the rebar and improves its constructability as it is connected to columns with bolts. Thus, the SMART frame is integrated with the structural advantages of the reinforced
Fig. 2. Concept of the column-beam joint of SMART frame.
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D. Lee et al. / Energy and Buildings 126 (2016) 36–43
concrete structure and steel structure. In addition, just like the CPC structure, the SMART frame can be produced on-site, reducing the transportation cost of members. The SMART frame is composed of beams and columns. As they are installed in steel connections, they have the characteristics of post-and-lintel construction and can be quickly and accurately installed. Also, the steel bracket applied to beams is removed with the steel that contributes less to the bending moment, which resulted in less steel being used and reduced self-load of the structure. It is expected that the reduced amount of resource input will lead to reduced CO2 emissions. As illustrated in Fig. 2, the steel bracket at the beam end of the SMART frame is connected to the column bracket with reinforcement plates and bolts. The reinforced concrete columns of the section are connected as steel members of the CPC structure. Precast columns with the composite joint of steel-reinforced concrete have the composite joint part embedded with steel between the precast concrete columns, which solves the problem of the joint between the reinforced concrete column and composite beam. Thus, it is possible to reduce the amount of materials for the section size of columns/beams. Moreover, it demonstrates excellent constructability for the reinforced concrete structure, which can be easily connected like a steel structure. For quick and safe column-beam connections, sliding and setting are performed with reinforcement plates. The sectional shape steel is embedded in the beam end using the same method suggested in the study of Lee et al., but H-shaped steel or T-shaped steel is applied, depending on the length and load of the beams [18]. Thus, the section differs from that of CPC, which uses only Tshaped steel. The structural stability of beams that are more than 10 m long was reviewed and it was found that the length of section shape steel is 1/8 of the beam length. This is because when 1/8 of the beam length is applied based on the structural stability review, the moment distribution and reduced floor height can be maintained although there is a slight increase of rebar. Also, as shown in Fig. 3, the rebar of the beam is anchored to the column with dead anchors. Since the dead anchors are shorter than general anchors, they will reduce the amount of steel materials used. In addition, the project develops a prefabricated form, as shown in Fig. 4, to increase the efficiency ratio of the form. The existing joint form has a complicated shape which is frequently damaged when removed, making it difficult to be reused. To supplement this, it is designed to not be damaged when the form is removed after grouting. Fig. 4(a) illustrates the beam assembled with the column and Fig. 4(b) shows the system form to be applied. It is applied with turn buckles and clamps so that it can be easily removed after grouting. When the efficiency ratio of forms is increased, reductions of the wastes and CO2 emissions are anticipated.
Fig. 3. Cross-sectional drawing of the column-beam joint of SMART frame.
4. Analysis of energy and CO2 emissions (case study) 4.1. Summary of the case The case project is a car park building located in Gyeonggi-do. Its site area is 3445 m2 and the total floor area is 21,199 m2 . It is an eight-story building with basement floor. It was originally designed to have a reinforced concrete structure, but CPC was applied to improve the structural efficiency and reduce CO2 emissions. The CPC structures analyzed in previous studies were applied to residential buildings with a relatively short span and therefore, a new design is required for buildings with a long span of more than 10 m. Furthermore, when CPC is applied to long-span structures, the CO2 reduction effects need to be verified. Therefore, in this study, we applied both a Rahmen structure and SMART frame (SF) to the case project whose span is more than 10 m under the same conditions, as shown in Fig. 5. Upon the contractor’s request, the project was fully redesigned to an SMART frame from the original Rahmen structure with the purpose of improving the seismic performance and reducing CO2 emissions. As described in Table 1, the concrete strength was 24 MPa and the rebar strength was 400 MPa for D16 (Diameter: 16 mm) or below and 500 MPa for D19 (Diameter: 19 mm) or above. In addition, 2 types of steel materials were used. The main material was SHN490 (fy = 325 MPa) and the sub-material was SS400 (fy = 235 MPa). High-tension bolts (900 MPa) were used.
Fig. 4. Concept of joint form.
D. Lee et al. / Energy and Buildings 126 (2016) 36–43 Table 1 The Strength of Materials applied to the Structure Design.
Table 3 The efficiency ratio of SMART frame among all members of the project.
Material
Strength
Concrete Rebar
fck = 24 MPa fy = 400 MPa fy = 500 MPa fy = 325 MPa fy = 235 MPa fy = 900 MPa fy = 235 MPa
D16 or below D19 or above SHN490 SS400 High-Tension Bolt Typical Bolt
Steel Bolts
39
Table 2 Design strength of the project. Load
Floor
1F 2F 3F 4F 5F 6F 7F 8F Rooftop Total
Total Members
RC frame → SF
Column
Girder & Beam
Column
Girder & Beam
Ratio(%)
31 31 33 37 36 36 36 36
77 80 88 89 89 89 89 107 24 732
21 22 24 28 27 27 27 27
52 64 72 74 74 74 74 75 24 583
67.6% 77.5% 79.3% 81.0% 80.8% 80.8% 80.8% 71.3% 100.0% 78.0%
276
203
Strength
Basic Wind Velocity Seismic Load Design Load (Parking Lot) 1.2 × Dead load + 1.6 × Live load
Effective Ground Acceleration 1–2nd floor 3rd floor 4th floor 5–8th floor
30 m/sec S = 0.176 18.8 kN/m2 14.5 kN/m2 12.1 kN/m2 9.5 kN/m2
As described in Table 2, the basic wind velocity of this project is 30 m/sec, the seismic load is S = 0.176, and the design load is 9.5–18.8 kN/m2 . For the structural design programs, Midas Gen was used for the frame analyses, Midas SDS for the plate analyses, and BeST for the member analyses. When the RC structure was applied to the project, the main beam section was designed with a thickness of 600–700 mm and a width of 500–600 mm, as shown in Fig. 6. For its structural stability, the top bar was arranged with up to 3 rows. The columns were designed with a composite CPC structure combined with steel frames and RC, considering the structural stability and space efficiency. When the SMART frame was applied to the case project with the same floor plan and design load, steel was installed and the amount of rebar was reduced. Fig. 7 shows the case of applying the SMART frame to the main beam section, where the amount and thickness of main rebar are reduced. However, as more steel materials were added, its structural strength increased. For columns, the same section as the case designed with the RC structure was applied. As listed in Table 3, the number of members originally designed was 276 columns, 511 girders, and 221 beams, for a total of 1008 members. Among these, 203 main columns and 583 beams (78%), excluding the lamps and cores, were applied to SMART frame. The remaining members (22%), excluding the main columns, girders, and beams, were designed based on the original plan. However, it is expected that there will be sufficient CO2 reduction effects since the main members were changed.
Fig. 5. Typical floor plan of the case project (2nd Floor).
Table 4 The quantity of concrete and forms for each floor. Floor
Area (m2 )
B1 1 2 3 4 5 6 7 8 RF Total
628 2571 2476 2498 2607 2607 2607 2607 2607 2593 23,801
Concrete (m3 )
Form (m2 )
RC
SF
RC
SF
2066 1056 684 654 724 642 614 612 620 863 8535
1359 974 623 672 620 591 587 591 571 652 7240
1173 4550 2549 2152 3003 2412 2066 2050 2118 3842 25,915
1496 1761 1676 1709 1764 1677 1677 1698 1675 298 15,431
Table 5 The quantity of rebar and steel frames for each floor. Floor
B1 1 2 3 4 5 6 7 8 RF Total
Area (m2 )
628 2571 2476 2498 2607 2607 2607 2607 2607 2593 23,801
Rebar (ton)
Steel Frame (ton)
RC
SF
RC
SF
201.5 122.8 93.2 69.3 77.9 74.6 69.2 69.0 69.4 104.2 951.1
93.7 65.9 50.0 56.2 51.7 55.8 55.7 56.2 58.4 65.1 608.7
11.1 43.2 34.2 30.4 28.5 22.9 19.6 19.5 20.1 16.4 245.9
12.9 32.9 56.2 61.7 57.1 54.7 58.0 58.8 58.9 42.2 493.3
4.2. Estimation of the frame quantity The frame quantity of the RC structure, which is the original design of the case project, is estimated in Table 4. The weight of rebar was estimated per rebar diameter and the forms were estimated for each part to apply the efficiency ratio. For the material quantity estimation of the case project, parts of the PC work and the RC parts were estimated separately and then added up. Case 1 (RC application) requires 8539 m3 of concrete and Case 2 (SMART frame application) requires 7245 m3 of concrete, resulting in a difference of around 1300 m3 . The efficiency ratio of the forms in Case 2 is 15,435 m2 , which is drastically decreased from that of Case 1 (25,919 m2 ). This is the result of the efficiency ratio of PC members produced on the floor compared to the RC forms. Rebar and steel frames have complementary characteristics for reinforcement. Thus, when an SMART frame is reinforced with steel frames, the amount of rebar can be reduced compared to the RC. The quantities of rebar and steel frames used in the 2 different structures are shown in Table 5. The RC structure used 951.1 t of rebar, which is more than the SMART frame structure, which used 608.7 t
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D. Lee et al. / Energy and Buildings 126 (2016) 36–43
Fig. 6. RC Beam section design (main members).
of rebar. On the other hand, the SMART frame used 493.3 t of steel frames, whereas RC used 245.9 t. 4.3. Estimation of the CO2 emissions The CO2 emissions of an entire building can be estimated using the basic unit of CO2 emissions per material quantity obtained from the case application. Hong et al. [13,14] and Lee et al. [16] conducted studies in this way to estimate the CO2 emissions at the construction phase of a building. In reference to the Inter-Industry Relations Table of the Korea Institute of Civil Engineering and Building Technology, the CO2 emissions per construction material based on the energy consumption of all stages from the collection of raw materials to processing and production was defined. This estimation is the
most logical way of converting the CO2 emissions of materials and we applied this data in this study. Table 6 shows the CO2 emissions per unit quantity of the major construction materials. In this study, we verified that the CO2 emissions were reduced based on the material quantity using the CO2 emission per unit quantity data. As shown in Table 6, steel materials emit the most CO2 per unit quantity. In the case of rebar, the CO2 emissions are 3500 kg/t and in the case of steel sections, the emissions are 4166 kg/t. These values are much more than the case of concrete, which emits 140 kg/t. Thus, the amount of steel is likely to impact the overall CO2 emissions. The basic unit of high strength reinforcing steel was applied to the rebar and the basic unit of the steel section was applied to the steel. The basic unit for the formwork was applied to the forms using mostly wooden materials and the basic unit of the steel plate
Fig. 7. Beam section design of SMART frame (main members).
D. Lee et al. / Energy and Buildings 126 (2016) 36–43
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Table 6 The basic units of CO2 emission per key material used in CPC [14,21]. Item
Concrete Rebar Steel Outer form of ext. wall Form for int. wall Form for slab Joint form High-tensile bolt
Applied basic unit of CO2 emission Item
Basic unit
ready-mixed-concrete High strength reinforcing steel Steel section Formwork
140.43 3,500.00 4,166.00 3.83
kg-CO2 /m3 kg-CO2 /t kg-CO2 /t kgCO2 /m2
Bolt and nut
0.0005
kg-CO2 /EA
can be applied to steel forms [14]. The basic unit of bolts and nuts was converted into quantity to be applied to high-tensile bolts [14]. The CO2 emissions of the resources used for the construction of a building in the case project were estimated by applying the basic units of CO2 emissions, shown in Table 7, to the material quantities given in Tables 4 and 5, which were estimated based on the design drawings, as shown in Table 7. The CO2 emitted from concrete of the RC structure is 1199 t and that of the SMART frame (SF) structure is 1017 t, which is about a 10% reduction. The CO2 emitted from reinforcement of the RC structure is 3329 t, which is more than that of the SMART frame structure (2131 t). However, the CO2 emitted from the steel of the RC structure is 1024 t, which is 50% less than that of the SMART frame (2055 t). It was found that the RS structure generates 5% more CO2 emissions for the reinforcements in total than the SMART frame structure. The CO2 emissions from forms are relatively smaller than those from reinforcements. The emissions are 98 t in the RC structure and 59 t in the SMART frame structure. The total CO2 emissions of the 2 structures compared based on the amount of materials used are 10,003 t (RC) and 9447 t (SMART frame). Therefore, the SMART frame emits only 94.5% of the emissions of the RC structure. Besides the CO2 emissions from materials, oil and power (electricity) may be consumed to use equipment and devices during the construction of a building, and such energy use generates CO2 as well [21]. Kim et al. analyzed 28 apartment building construction projects with LCA and proposed a regression equation of CO2 emissions at the construction phase [21]. Since the total floor area is the variable of the regression equation, it is easy to estimate the CO2 emissions based on oil and power consumption. The energy consumption of construction work according to the oil consumption at the construction phase is calculated using Eq. (1) and the CO2 emissions are calculated using Eq. (2) [21]. The total floor area of the case project was estimated to be 21,199 m2 and the energy consumption (Eco ) is 73.5 TOE. When the consumed energy is converted into CO2 , the CO2 emissions are 225.03 T-CO2 . Eco = 0.0017 × Af + 37.5
(1)
QCO2 o = Eco × 3.06
(2)
Eco : Oil energy consumption at the construction phase [TOE].
Fig. 8. Tower crane arrangement plan.
Af : Total floor area [m2 ]. QCO2o : CO2 emissions according to the oil use at the construction phase [T-CO2 ]. The energy consumption according to the power consumption at the construction phase can be estimated using Eq. (3) and the CO2 emissions can be calculated using Eq. (4) [21]. Ece was estimated to be 64.6 TOE. When Ece was calculated using Eq. (4), QCO2e was 106 T-CO2 . Ece = 0.0247 × Af 0.79
(3)
QCO2 a = Eca × 1.64
(4)
Ece : Power consumption (electricity use) at the construction phase [TOE]. QCO2e : CO2 emissions according to the power consumption at the construction phase [T-CO2 ]. To apply the SMART frame to the case project, the plan to operate tower cranes needs to be changed. As illustrated in Fig. 8, Case
Table 7 Comparison of CO2 emission by material use. Classification
Work Concrete Reinforcement
Form PC installation Total
Item Rebar Steel Total (rebar + steel) High-tensile bolt
Total CO2 emission (T-CO2 )
CO2 emission per unit area (kg-CO2 /m2 )
Ratio of emission (%)
RC
SF
RC
SF
SF/RC
1199 3329 1024 4353 98 0.026 10,003
1017 2131 2055 4186 59 0.012 9447
50.4 139.8 43 182.8 4.1 0.0011 420
42.74 89.5 86.3 175.8 2.5 0.0005 397
84.8 64.0 200.7 96.2 61.0 45.5 94.5
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D. Lee et al. / Energy and Buildings 126 (2016) 36–43
Table 8 Comparison of total CO2 emission. Item
Material use Oil use Electricity use Total CO2 emission
CO2 emission (T-CO2 )
CO2 emission per unit area (kg-CO2 /m2 )
Ratio of emission (%)
RC
SMART Frame
RC
SMART Frame
SF/RC
10,003 225 143 10,371
9447 225 180 9852
420 9.5 6 435.5
397 9.5 7.6 414.1
94.5 100 127 95.1
1 (RC structure applied), which originally required 1 tower crane, was changed to have 2 tower cranes when the SMART frame was applied. This is because the lifting weight increased and the project schedule changed. The power consumption of the selected model was 149 kVA and can be converted into approximately 880 kwh assuming that it has 8 h of operation. When the duration of operating the tower cranes for the case project (5 months) was applied, the total power consumption was estimated to be 88,000 kwh. When the CO2 conversion factor of 0.424 kg-CO2 /kwh [22,23] was applied, the CO2 emissions of each tower crane were 37.3 t-CO2 . For reference, using one more tower crane will definitely increase the cost and CO2 emissions. However, in case of a modular construction such as the SMART frame, using a small crane supportively will reduce the required construction time per floor and the rental time of the cranes. Furthermore, as the construction duration is shortened, there will be increased income from earlier operation of the parking lot. In conclusion, using an additional small crane has an effect of reducing the construction project cost. 880 kwh × 20 days × 5months = 88, 000 kwh(5) 88, 000 kwh × 0.424 kg-CO2 /kwh = 37.3 t-CO2 (6) Table 8 shows the total CO2 emissions based on the input resources and energy use. The CO2 emissions per unit area applied with the RC structure were 435.5 kg-CO2 /m2 and those applied with the SMART frame were 414.1 kg-CO2 /m2 . Thus, a reduction of 21.4 kg-CO2 /m2 was realized. 5.5% of the CO2 reduction effect is due to the resource input when the SMART frame was applied instead of the RC structure. In addition, the total CO2 emissions were estimated considering the oil and electricity power use, where around 4.9% of the CO2 reduction effect is obtained. 5. Conclusion CPC (Composite Precast Concrete) members require less steel materials, concrete, and forms than RC (Reinforced Concrete) members due to structural efficiency. In addition, there is a CO2 reduction effect. This study applied an SMART frame (CPC frame) to a car park building that requires large and heavy members, and the results were compared to the existing design. In addition, the quantity of material was estimated and converted into CO2 reduction based on the input resources to verify its reduction effect. Then, based on the oil and electricity power consumption at the construction phase, the CO2 emitted during the construction phase was additionally considered. The case project was originally designed to have a reinforced concrete structure, but CPC was applied to improve the structural efficiency and reduce CO2 emissions. Among the CPC structures that improve structural efficiency and lower CO2 emissions, GF was applied to residential buildings with a relatively shorter span. As a result, a new design was applied to the building with a span greater than 10 m, just like the case project. The basic units of CO2 emissions were applied to the material quantity estimates based on the design drawings to calculate the CO2 emissions of the resource input for the construction of this case
project. As a result, the CO2 emitted for the concrete of the RC structure was 1199 t and that of the SMART frame structure was 1017 t, which is about a 10% reduction. The CO2 emitted from reinforcement of the RC structure was 3329 t, which was more than that of the SMART frame structure (2131 t). However, the CO2 emitted from the steel of the RC structure was 1024 t, which is 50% less than that of SMART frame (2055 t). It was found that the RC structure generated 5% more CO2 emissions due to reinforcements in total than the SMART frame structure. The CO2 emissions from the forms were relatively smaller than those from reinforcements, where 98 t were generated from the RC structure and 59 t were emitted from the SMART frame structure. The total CO2 emissions of the 2 structures based on the amount of materials used were 10,003 t (RC) and 9447 t (SMART frame). The emissions from the SMART frame were 94.5% of the emissions from the RC structure. Furthermore, the CO2 emissions per unit area for the RC structure and SMART frame were 435.5 kg-CO2 /m2 and 414.1 kg-CO2 /m2 , respectively. Thus, a reduction of 21.4 kg-CO2 /m2 was achieved. As the SMART frame was applied instead of the RC structure, 5.5% of the CO2 reduction effect was due to the CO2 emissions according to the resource input, which is equivalent to around 3.7% of the total CO2 emissions of the case building. In addition, the total CO2 emissions were estimated considering the oil and electricity power use. A CO2 reduction effect of around 4.9% was achieved. The study examined the amount of materials required and CO2 emissions of an SMART frame redesigned with the existing GF to be applied to long-span buildings. The study proved that an Innovative Composite Precast Concrete Structure can be applied to large buildings with a long span in order to improve the RC structure in terms of greenhouse gas emissions. It is believed that this approach will be helpful in reducing the tremendous amount of CO2 emitted during the construction phase of a building.
Acknowledgements This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2013R1A2A2A01068297)
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