Minimum required separation gap for adjacent RC frames with potential inter-story seismic pounding

Abstract

The aim of this study is to correlate the seismic performance of a real RC frame structure at different seismic demand levels with the separation gap that would be inadequate against pounding with an adjacent shorter and stiffer structure. In this direction 882 nonlinear step by step seismic analyses have been performed. The first part of this study includes the evaluation of the inter-story (floor to column) pounding problem at nine seismic demand levels, using for each level 14 seismic excitations that have been properly scaled. The examined cases are inter-story pounding cases between an 8-story RC frame and a 3-story RC frame - wall structure or a 3-story rigid barrier (very stiff structure) while the adjacent structures are considered to be in contact from the beginning. The seismic performances of the structures without the pounding effect have also been evaluated. The results of the assessment indicate that: (a) at all the examined levels of the seismic demand, the local performance of the external column of the tall building that suffers the impact from the upper floor slab of the adjacent shorter structure is the most important issue in the inter-story pounding phenomenon, (b) this column is always in a critical condition due to shear action and in the case of pounding with the 3-story rigid barrier this column appears to be critical due to high ductility demands as well, (c) the level of the seismic demand that is used to assess the pounding problem on the local performances of the critical column that suffers the hit, altered the developing requirements for flexural and shear capacity of the column. Thereafter, the minimum required gap distance against pounding between the adjacent structures has been estimated taking into account two different criteria: (a) avoidance of the shear failure in the critical column that suffers the hit and (b) complete avoidance of the contact between the adjacent structures. The separation gap is evaluated at all the seismic demand levels for both pounding cases. In comparison to the Eurocode 8 provisions the results of this study indicate less conservative separation gap distances between the adjacent structures at different levels of seismic demand.