Behaviour of Intermediate Moment Resisting RC Frame Structures Under The Influence of P-Delta Effect

Abstract

Among the different categories of RC frames based on the implemented ductile detailing of the members, Intermediate Moment Resisting Frame (IMRF) is imparted with medium ductility capacity. Buildings with IMRF are intended to be used in Indian Seismic Zone III which refers to moderate level of seismic risk. Although past research has focused extensively on seismic behaviour of non-ductile and fully ductile moment resisting frames, very few studies on IMRF behaviour have been carried out. Also, the influence of P-Delta (P-?) effect on nonlinear behaviour of RC frame buildings has been studied to a limited extent. The present study aims to study the influence of imposed displacement pattern on the nonlinear behaviour of IMRF considering the P-? effect. Initially, single RC frame building five-storey with symmetrical floor plan, is designed as per the relevant Indian guidelines considering possible IMRF behaviour. Although the detailing of frames with medium ductility is absent in the current Indian Code IS: 13920-2016, the same has been carried out as per the draft IS: 13920. Displacement-controlled nonlinear static analysis or pushover analysis is carried out for the designed frames. For the distribution of imposed displacement pattern along the height of the frame, 4 different profiles are adopted, namely (a) parabolic as per IS: 1893 (Part 1) – 2016, (b) uniform, (c) fundamental mode shape and (d) triangular. It is found that under P-? effect, the initial lateral stiffness and base shear capacity get reduced for all the frames. The same can be correlated with the higher lateral displacement Thus, the absence of P-? effect causes overestimation of base shear capacity for the IMRF. The initial global stiffness predicted by the IS: 1893 (Part 1) – 2016 is the least among the lateral stiffness observed under all the load patterns. However, the uniform displacement profile provides the maximum base shear capacity of IMRF among all the load patterns.