New Structural Irregularity Assessing Index for Seismic Torsional Vibration

Abstract

In this paper, an energy ratio, i.e. the ratio of torsional energy to lateral energy, is introduced as a new index to assess torsional irregularity of structures. Torsional regularity of structural configuration in elastic range is essential in keeping low level torsional responses of structures to withstand earthquake ground motion. By using a response spectrum method, a simplified one-storied model with different dynamic characteristics is studied to investigate different properties of the energy ratio. The energy ratio is found to be able to reflect the effects of large eccentricity and the closeness of lateral and torsional periods, which are two main sources of intense torsional vibration. Applicability of the energy ratio is further demonstrated by discussions on other code-specified assessing indexes, i.e. the coupled period ratio and the drift ratio. Deduced from the limits of the drift ratio specified in the China's codes, the required magnitudes of the energy ratio for irregularity assessment are proposed. Based on computer programs for structural design, the computation procedures are proposed for the energy ratio of real structures, and the application is then provided with a reinforced concrete structure as an example.

Keywords

torsional irregularity torsional vibration energy ratio seismic design

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