A Study on Seismic Performance of Open Ground Storey RCC Frames Analyzed by Response Spectrum Method

Abstract

In the present study, seismic performance of Open Ground Storey (OGS) RCC frames is investigated using ETABS software. Bare frame, OGS frames and frames with RCC walls at ground storey are considered and infill walls are modelled as equivalent diagonal strut as per IS 1893–Part 1 (2016) codal provisions and equation given by Paulay and Priestley (1992). Seismic parameters viz. storey displacement, drift ratio, stiffness, shear and overturning moments for the developed RCC models are obtained by response spectrum analysis as per IS 1893–Part 1 (2016) in seismic zone III.

Introduction

I. INTRODUCTION

Earthquake is one of the most devastating of all the natural hazards and is considered to be the most powerful disaster which is unavoidable. IS 1893–Part 1 (2016) stipulates the criteria for earthquake resistant design of structures. Due to rapid urbanization and increase in population, need of space is becoming very important. To fulfil the need of parking spaces, open ground storey (OGS) buildings are constructed, which are having no infill walls in ground storey, but having infill wall in all the upper stories. In OGS buildings, base shear is resisted by the columns of the ground storey, will induce increase in the curvatures and bending moments, causing larger drifts at first storey. Upper stories are undamaged and behave like a rigid body. Damage occurs in the ground storey columns which is known as “soft–storey collapse”. To avoid soft storey collapse and to facilitate parking of vehicles, most bays of ground storey can be provided with masonry walls.

II. BUILDING DESCRIPTION

Table 1 Shows the parameters of the developed bare frame and OGS RCC Models. 

Table 1 : Parameters of the developed bare frame and OGS RCC models

Table 2 shows the identity for the developed RCC frame models.

Table 2 : Identity for the developed RCC frame models

III. SEISMIC ANALYSIS OF RCC MODELS

Using ETABS 2016 software, the developed bare frame and OGS RCC models are subjected to response spectrum analysis as per IS 1893–Part 1 (2016). Seismic parameters viz. storey displacement, drift ratio, stiffness, shear and overturning moments are obtained from the analysis for all the developed models in seismic zone III.

IV. RESULTS AND DISCUSSION

Figures 10 to 19 show the variation of storey displacement, drift ratio, stiffness, shear and overturning moment over the number of stories in both X and Y directions obtained for all the RCC models by response spectrum analysis.

From Figs. 10 and 11 for the seismic zone III, it is observed that all the models exhibit similar kind of variation in storey displacement. However, Storey displacement in Y–direction is found to be more than that of X–direction.

From Figs. 12 and 13 for the seismic zone III, it is observed that all the models exhibit similar kind of variation in storey drift ratio. However, Storey drift ratio in X–direction is found to be more than that of Y–direction.

From Figs. 14 and 15 for the seismic zone III, it is observed that all the models exhibit similar kind of variation in stiffness. However, Storey stiffness in Y–direction is found to be more than that of X–direction.

From Figs. 16 and 17 for the seismic zone III, it is observed that all the models exhibit similar kind of variation in storey shear. However, Storey shear in Y–direction is found to be relatively more than that of X–direction.

From Figs. 18 and 19 for the seismic zone III, it is observed that all the models exhibit similar kind of variation with respect to overturning moment. However, overturning moment in Y–direction is found to be less than that of X–direction.

Figures 20 to 29 show the variation of maximum storey displacement, drift ratio, stiffness, shear and overturning moment for all the RCC frame models by response spectrum analysis.

From Figs. 20 and 21, in both X and Y directions, maximum storey displacement is observed in model M 1 (i.e. bare frame). OGS models viz. M 2, M 4 and M 6 which are modelled with infill walls show reduced maximum displacement as compared to Model M 1.  However least value of maximum displacement is observed in models M 3, M 5 and M 7 which are provided with RCC walls at ground storey and modelled with infill walls at higher storey.

From Figs. 22 and 23, in both X and Y directions, maximum storey drift ratio value in all the models is within the allowable limit specified in Cl. 7.11.1 of IS 1893–Part 1 (2016). However least value of maximum storey drift ratio is observed in models M 3, M 5 and M 7 which are provided with RCC walls at ground storey and modelled with infill walls at higher storey.

From Figs. 24 and 25, in both X and Y directions, minimum storey stiffness is observed in model M 1 (i.e. bare frame). OGS models viz. M 2, M 4 and M 6 which are modelled with infill walls show high storey stiffness as compared to Model M 1.  However highest value of storey stiffness is observed in models M 3, M 5 and M 7 which are provided with RCC walls at ground storey and modelled with infill walls at higher storey. Further, effect of 20% opening in the infill wall was found not to influence the maximum storey stiffness in OGS models and models provided with RCC walls at ground storey.

From Fig. 26, in X direction, as compared to bare frame model (i.e M 1), OGS models viz. M 2, M 4 and M 6 are subjected to high base shear. However highest values of base shear is observed in models M 3, M 5 and M 7 which are provided with RCC walls at ground storey and modelled with infill walls at higher storey. From Fig. 27, in Y direction, as compared to bare frame model (i.e M 1), models M 3, M 5 and M 7 are subjected to high base shear. However highest values of base shear is observed in OGS models viz. M 2, M 4 and M 6.  Further, effect of 20% opening in the infill wall was found to reduce the base shear in OGS models and models provided with RCC walls at ground storey. From Fig. 28, in X direction, as compared to bare frame model (i.e M 1), models M 3, M 5 and M 7 are subjected to high over turning moment at the base. However highest values of overturning moment is observed in OGS models viz. M 2, M 4 and M 6. From Fig. 29, in Y direction, as compared to bare frame model (i.e M 1), OGS models viz. M 2, M 4 and M 6 are subjected to overturning moment at the base. However highest values of overturning moment is observed in models M 3, M 5 and M 7 which are provided with RCC walls at ground storey and modelled with infill walls at higher storey. Further, effect of 20% opening in the infill wall was found to reduce the overturning moment in OGS models and models provided with RCC walls at ground storey.

Conclusion

In the present study, seismic performance of Open Ground Storey (OGS) RCC frames is investigated using ETABS software. Bare frame, OGS frame and frames with RCC walls at ground storey are considered and infill walls are modelled as equivalent diagonal strut as per IS 1893–Part 1 (2016) codal provisions and equation given by Paulay and Priestley (1992). Seismic parameters viz. storey displacement, drift ratio, stiffness, shear and overturning moments for the developed RCC models are obtained by response spectrum analysis as per IS 1893–Part 1 (2016) in seismic zone III. The important conclusions drawn from the present study are as follows. 1) Similar variation of storey displacement, drift ratio, stiffness, shear and overturning moments is observed in both X and Y directions for all the models. 2) In both X and Y directions, maximum storey drift ratio value in all the models is within the allowable limit specified in Cl. 7.11.1 of IS 1893–Part 1 (2016). However least value of maximum storey drift ratio is observed in models M 3, M 5 and M 7 which are provided with RCC walls at ground storey and modelled with infill walls at higher storey. 3) In both X and Y directions, maximum storey displacement is observed in model M 1 (i.e. bare frame). OGS models viz. M 2, M 4 and M 6 which are modelled with infill walls show reduced maximum displacement as compared to Model M 1. However least value of maximum displacement is observed in models M 3, M 5 and M 7 which are provided with RCC walls at ground storey and modelled with infill walls at higher storey. 4) In both X and Y directions, minimum storey stiffness is observed in model M 1 (i.e. bare frame). OGS models viz. M 2, M 4 and M 6 which are modelled with infill walls show high storey stiffness as compared to Model M 1. However highest value of storey stiffness is observed in models M 3, M 5 and M 7 which are provided with RCC walls at ground storey and modelled with infill walls at higher storey. Further, effect of 20% opening in the infill wall was found not to influence the maximum storey stiffness in OGS models and models provided with RCC walls at ground storey. 5) In X direction, as compared to bare frame model (i.e M 1), OGS models viz. M 2, M 4 and M 6 are subjected to high base shear. However highest values of base shear is observed in models M 3, M 5 and M 7 which are provided with RCC walls at ground storey and modelled with infill walls at higher storey. Whereas in Y direction, as compared to bare frame model (i.e M 1), models M 3, M 5 and M 7 are subjected to high base shear. However highest values of base shear is observed in OGS models viz. M 2, M 4 and M 6. Further, effect of 20% opening in the infill wall was found to reduce the base shear in OGS models and models provided with RCC walls at ground storey. 6) In X direction, as compared to bare frame model (i.e M 1), models M 3, M 5 and M 7 are subjected to high over turning moment at the base. However highest values of overturning moment is observed in OGS models viz. M 2, M 4 and M 6. Where as in Y direction, as compared to bare frame model (i.e M 1), OGS models viz. M 2, M 4 and M 6 are subjected to overturning moment at the base. However highest values of overturning moment is observed in models M 3, M 5 and M 7 which are provided with RCC walls at ground storey and modelled with infill walls at higher storey. Further, effect of 20% opening in the infill wall was found to reduce the overturning moment in OGS models and models provided with RCC walls at ground storey.

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Copyright

Copyright © 2022 Ramesh M, Dr. Chidananda G. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.