Influence of Effective Stiffness on Seismic Response of RC Frame Building with Shear Walls

Purpose This article aims to explore the implication of effective stiffness modifiers of structural elements on the seismic performance of high-rise RC frame buildings with shear walls. Contribution and method Effective stiffness of structural elements i.e., beams, columns, shear walls etc. plays a pivotal role in the seismic evaluation of Reinforced Concrete (RC) shear wall buildings which are predominantly considered through the use of stiffness modifiers in Indian design standards like various national design standards worldwide. The reduction in stiffness of the structural members is mainly due to crack formation in members due to shrinkage, creep, bond-slip of the reinforcement, etc. which further aggravates due to large inelastic deformation caused by seismic events. stiffness modifiers for various structural members i.e., beams and columns have been recommended in revised Indian seismic standards (BIS inIS 1893 (Part 1)-2016 Indian Standard criteria for earthquake resistant design of structures, part 1: general provisions and buildings (fifth revision). Bureau of Indian Standards, New Delhi, 2016), however specific guidelines for the same are missing for RC shear walls. This paper presents a comprehensive review of the available effective stiffness recommendation by various national seismic design standards viz., ASCE (ASCE-41 in ASCE/SEI 41-17, seismic evaluation and retrofit of existing buildings. American Society of Civil Engineers, Reston, 2017), Eurocode (Design of structures for earthquake resistance-part 1: general rules, seismic actions, and rules for buildings, 2005), New Zealand code (NZS in NZS 3101:2006 New Zealand Standard Concrete Structures Standard, 2006) and assess the influence of effective stiffness on seismic evaluation of high-rise RC shear wall buildings. It is observed that a significant difference in peak strength is observed with variation in stiffness modifiers of beam and column, whereas their peak strength is not significantly sensitive to the effective stiffness of shear walls due to the higher stiffness of shear walls compared to other structural elements. Conclusion It has been observed that the choice of stiffness modifiers of structural elements influences the seismic performance of RC shear wall buildings in terms of strength, stiffness and plastic deformation capability. Indian seismic design standard BIS (2016) does not prescribe any reduction in gross stiffness to get effective stiffness of shear walls and it is evident from the parametric study that the influence of effective stiffness of the shear wall on the seismic performance of the RC shear wall building is negligible whereas the effective stiffness of beams and columns has a profound effect on seismic behaviour of such buildings.