Estimation of Story Stiffness in Multi-Storey Frame Buildings

Abstract eng:
Presence of stiffness irregularity, in conjuncture with strength irregularity, along building height leads to undesirable behavior during severe earthquake shaking, including localization of lateral deformations in select stories and initiation of storey collapse mechanism. Thus, seismic design codes recommend simple quantitative check using storey stiffness, to identify presence of stiffness irregularity along building height. This requires estimate of lateral stiffness of each storey along the height of the building, but the procedure to estimate the same is not specified in design codes. Consequently, in practice, several methods are used to estimate storey stiffness. In theory, there exists a unique value of stiffness of a given storey in a multi-storey building, but estimates using different methods give different results; the difference arise due to the inherent assumptions in the methods. Therefore, there is a need to compare and ascertain a method using which storey stiffness can be estimated with adequate accuracy. Storey stiffness estimates from seven available methods are compared, and their strengths and limitations discussed. A method involving use of fundamental natural mode of oscillation of structure seems to be most accurate, as it does not entails any simplifying assumption.

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