A Comparative Study on the Seismic Behavior of RCC Framed Building and Composite Framed Building

Since different types of RCC and steel Concrete Composite structures with various floor systems are used for multistory buildings, there is a great prospective for increasing the volume of steel in construction industry, especially in Nepal. As the population in cities is increasing rapidly and the land is limited, there is a need of vertical growth of buildings in cities. So, for the fulfilment of this purpose a large number of mediums to high rise buildings are being constructed on a large scale

For medium to high rise buildings, the conventional RCC structures is not excellent choice as there is in-creased dead load along with the span restrictions and consuming more time to construct. This study gives a brief description of various components of steel-concrete composite structure. A comparative analysis of composite and RCC framed structure was carried out by using ETABS software. The total cost comparison of composite framed structure is more economical in case of high-rise buildings than RCC framed structure and the construction time of Composite framed structure requires much less duration than RCC structure [1]. In composite framed structure the dead weight, lateral Displacement, twisting moment and shear force are observed to be decreased whereas the stiffness is found to be increased than RCC framed structure [2]. Literature review study summarizes that the composite sections using steel encased and concrete in filled are economical option if de-sign well and time effective solution in major civil structures such as bridges, warehouses and high-rise buildings.

LITERATURE REVIEW:

(Aniket & Yogesh, 2013): The work on this paper is focused on RCC and Composite framed buildings of (G+9), (G+12), (G+15) and (G+18) storey using ES analysis method in STAAD-Pro 2007 software pro-gram. On this research paper, it is concluded that although the overall cost of Composite framed structure is found to be more than RCC framed system, the reduction in percentage of the direct cost due to the rapid erection of the components in Composite framed structure will lead to the fast finishing touch of the structure. Moreover, the reduction in the dimension of structural members makes it more stable towards lateral loads.  (Wagh & Waghe, 2014): In this research paper a comparative study of RCC and Composite framed structure of four specific multistoried buildings i.e. (G+12, G+16, G+20 and G+24) are taken into consideration using Equivalent Static Analysis method in STAAD pro software. After analyzing, it's observed that in a Composite structural system, the values of beam end forces and the moments are found to be much less as compared to RCC structural system and the overall cost is found to be (10-14) % much less than RCC framed structure which concludes that composite structural system is found to be more cost effective in case of high-rise buildings than RCC system. (Mahesh Suresh Kumawat and L G kalurkar, 2014): On this studies paper, RCC and Composite framed structure are considered for comparative study of (G+9) storey commercial building using ES Analysis method in SAP 2000 software program. After analysis, it is observed that the dead weight of Composite framed system is found to be (15-20) % much less than RCC framed structure resulting the seismic forces to be reduced by (15-20) % than RCC framed structure. The axial forces in Composite systems are found to be (20-30) % much less than RCC framed systems.

(Nitish et al., 2015): This research work concentrates on the study of Composite framed and RCC framed structure of (B + G + 11) storey building located in EQ region III having wind velocity of 39 m/s as per IS 875 part III. Equivalent Static method is used and modelled in ETABS software program. The outcomes thus received are compared for various parameters. After analysis, it is observed that the reduction within the self-weight of the Composite framed structure is decreased by 9.40 % as com-pared to RCC framed structure. The axial forces in column of Composite framed structure are observed to be decreased by 9.0% than RCC framed structure.

(Zaveri et al., 2016): This research paper studies a comparison among steel, RCC and composite framed structure considering various parameters like seismic performance, deformations, forces, moments, cost and weight of building structure. On this research paper, it is concluded that the overall response of composite structure is found to be better than RCC structure. The composite framed system produces less displacement and resists more lateral forces than RCC structure.

(Damam 2016): This research paper focus on comparative study of RCC and steel-Concrete Composite framed structure of (G+15) storey commercial building using ES analysis method in STAAD pro soft-ware program. The building is located in earth-quake zone IV having wind speed 50m/s as per IS 875 part III. After analysis it is observed that the deflection & storey drift of composite structure is observed to be almost double than that of RCC structure however the deflection is within the permissible restriction.

STATEMENTS OF PROBLEM:

Several research studies have concluded that for high rise buildings, steel concrete composite structures are observed to be the best choice among RCC and steel structure either economically or lateral load resistant capability. Unfortunately, in all the studies we get that the researches have been done in the same type of building models i.e. simple and symmetrical using the same type of analysis techniques i.e. either by ESA or RSA method. So the research is not enough to come to the conclusion that composite structures are better than RCC structure. This means there is need to explore it further. Hence this research study tries to identify a comparative analysis on the performance and seismic behavior of RCC and composite building structures using both RSA and PA method of analysis considering various parameters to find out better alternative solution between RCC and Composite structural system.

OBJECTIVES OF STUDY:

The aim of this research is to study a comparison on the Seismic Behavior of RCC Framed Building and Composite Framed Building.

Dimensions and Models:

In this research, two buildings are modelled in ETABS. These models are of (G+33) storey with RCC and composite framed buildings with the identical floor plan, floor height, slab thickness, floor finishers, wall load, wind load, live load and seismic load all are being the same throughout the analysis. The analysis is carried out using Response Spectrum and Pushover Analysis Method. In the present work (G+33) storey with RCC and composite framed buildings are considered for the study. For the both type of buildings, the following data is used including the loadings as per relevant IS code.

Table 1. Collection of Data for Analysis of (G+33)

Figure 1: ETABS Plan View and 3D Model of (G+33) storey Building

Figure 2: Response Spectrum Curve Generated as per IS 1893 part (I): 2016

RESEARCH METHODOLOGY:

To obtain the stated objective, the methodological procedure applied is as following:

1.                                      Study of various literature reviews related to the work.

2.                                       Identify of the problem and set the research question.

3.                                   Selection of samples and modelling of building in ETABS.

4.                  Analysis of the models using Response spectrum and Pushover Analysis Methods

5. Optimization of the structure for RCC and COMP models with the study of static pushover curve and hinge formation of buildings.

Figure 3: Flowchart of Methodological Framework

In this research, two buildings are modelled in ETABS. These models are of (G+33) storey with RCC and composite framed buildings with the identical floor plan, floor height, slab thickness, floor finishers, wall load, wind load, live load and seismic load all are being the same throughout the analysis. The analysis is carried out using Response Spectrum and Pushover Analysis Method. In the present work (G+33) storey with RCC and composite framed buildings are considered for the study. For the both type of buildings, the following data is used including the loadings as per relevant IS code.

1.                            The buildings are situated in seismic zone (V) in Kathmandu, Nepal.

2.                                  The buildings have special moment resisting frame (SMRF).

3. The plan area of both buildings is (20 X 20) m.

4.                                  It consists of 4 bays of 5 m each in both directions X and Y.

5.                      Height of each typical storey is 3 m. and total height of the building is 99 m.

6. Both external and internal wall thickness is 230 mm, waist slab thickness is 200 mm, Slab thickness is 200 mm and Parapet height is 1 m.

7. Grade of concrete used are M25 and M30.

8.                                        Grade of reinforcing steel used are HYSD 415, 500.

9.                   Unit weight of Concrete is 25KN/m3 and Unit weight of brick wall is 18KN/m3.

10.                            Seismic zone factor is 0.36 and soil condition is soft soil type (III).

11.                               Live load on floor is 3KN/m2 and floor finishes is 1.5KN/m2.

RESULTS:

For this study, the seismic behavior of RCC framed building and Composite framed building of (G+33) storey models are analyzed in ETABS using Response Spectrum and Pushover Analysis methods. Then the results are compared in terms of Storey Displacement, Storey Drift, Performance Point and Plastic Hinge Formation. (RCC 1, COMP 1) Type models are analyzed by RSA method and (RCC 2, COMP 2) Type models are analyzed by PA Method.

Storey Displacement:

Storey displacement results obtained by RSA and PA Method in X and Y-direction due to RS-x, PA-x, RS-y and PA-y for the RCC and Composite Structure is shown in (Figure 4).

Figure 4: Variation of Storey Displacement along X and Y Direction due to RSA and PA method.

(Figure 4) shows the variation of Storey Displacement values observed to be the maximum in RCC 2 model followed by COMP 2 and RCC 1 model but the least in COMP 1 model along both directions. Hence the Storey Displacement results of COMP type models are found to be reduced by 22.5% to 26.8% than RCC type models.

Storey Drift:

Storey drift results obtained by RSA and PA Method in X and Y-direction due to RS-x, PA-x, RS-y and PA-y for the RCC and Composite Structure is shown in (Figure 5).

Figure 5: Variation of Storey Drift along X and Y Direction due to RSA and PA method.

(Figure 5) shows the variation of the Storey Drift values are observed to be the maximum in RCC 2 model followed by COMP 2 and RCC 1 model but the least in COMP 1 model along both directions. Hence the Storey Drift results of COMP type models are found to be reduced by 15.2% to 20.7% than RCC models.

Performance Point:

After Pushover analysis in RCC model, Performance Points are observed which provides the Target Displacement of the building. As per (Figure 6), the Target Disp. for RS Curve ‘0.2g’ along X and Y-Directions are 47.43 mm and 48.01 mm respectively, as per (Figure 7), for RS Curve ‘0.4g’ along X and Y-Directions are 52.95 mm and 53.69 mm respectively, as per (Figure 8), for RS Curve ‘0.6g’ along X and Y-Directions are 58.45 mm and 59.50 mm respectively, as per (Figure 9), for RS Curve ‘0.8g’ along X and Y-Directions are 61.63 mm and 63.02 mm respectively, as per (Figure 10), for RS Curve ‘1g’ along X and Y-Directions are 66.64 mm and 59.50 mm respectively and as per (Figure 11), for RS Curve ‘1.2g’ along X and Y-Directions are 68.56 mm and 63.02 mm respectively.

In COMP model, as per (Figure 6), the Target Disp. for RS Curve ‘0.2g’ along X and Y-Directions are 25.48 mm and 25.51 mm respectively, as per (Figure 7) for RS Curve ‘0.4g’ along X and Y-Directions are 31.65 mm and 31.92 mm respectively, as per (Figure 8) for RS Curve ‘0.6g’ along X and Y-Directions are 39.58 mm and 40.17 mm respectively, as per (Figure 9) for RS Curve ‘0.8g’ along X and Y-Directions are 46.63 mm and 47.51 mm respectively, as per (Figure 10) for RS Curve ‘1g’ along X and Y-Directions are 50.66 mm and 40.17 mm respectively and as per (Figure 11) for RS Curve ‘1.2g’ along X and Y-Directions are 53.75 mm and 47.51 mm respectively.

Figure 6: Sa-Sd Curve of RCC 2 and COMP 2 model for RS Curve 0.2g along X-Axis

Figure 7: Sa-Sd Curve of RCC 2 and COMP 2 model for RS Curve 0.4g along X-Axis

Figure 8: Sa-Sd Curve of RCC 2 and COMP 2 model for RS Curve 0.6g along X-Axis

Figure 9: Sa-Sd Curve of RCC 2 and COMP 2 model for RS Curve 0.8g along X-Axis

Figure 10: Sa-Sd Curve of RCC 2 and COMP 2 model for RS Curve 1g along X-Axis

Figure 11: Sa-Sd Curve of RCC 2 and COMP 2 model for RS Curve 1.2g along X-Axis

Plastic Hinge Formation:

The plastic hinges are assigned in the models (RCC 2 and COMP 2) for observing structural behavior of sequential loss of strength in different performance level of structure. After assigning Plastic Hinges in RCC 2 model, as per (Table 2) and (Figure 12), about 82.4% A-B State of hinges followed by 17.3% B-C state of hinges, 0.062% C-D State of hinge, 0.0038% D-E State of hinge and 0% >E State of hinge are observed whereas in COMP 2 model, as per (Table 3) and (Figure 13), about 88.1% A-B State of hinges followed by 11.8% B-C state of hinges, 0% C-D State of hinge, 0% D-E State of hinge and 0% >E State of hinge are observed. As per (Figure 12) and (Figure 13), Since A-B State of hinge represents yielding limit i.e. no deformation occurs up to this state of hinge, B-C State of hinge represents the ultimate capacity/Limit for Pushover Analysis, C-D State of hinge represents the structure initialize collapsing and D-E State of hinge represents total failure of the structure i.e. after this point hinges break down. Here in COMP 2 model all the hinges developed are A-B and B-C state of hinges. This indicates, the structure is safe up to this state of hinge against future EQ effect whereas in RCC 2 model, all the hinges developed are A-B and B-C state of hinges along with C-D and D-E state of plastic hinges in some particular point of frames. This indicates there is still need to improve or reinforced to that particular frame with C-D and D-E state of plastic hinges.

Table 2. Hinge States in each step of (G+33) storey RCC building by Pushover Analysis

Figure 12: Hinge states in the RCC 2 model at (a) step 1, (b) step 2, (c) step 3 and (d) step 4 during Pushover analysis, with different color codes of hinge state

Figure 13: Hinge states in the COMP 2 model at (a) step 1, (b) step 2, (c) step 3 and (d) step 4 during Pushover analysis, with different color codes of hinge state