Predicting Inelastic Torsional Response with the Inclusion of Dynamic Rotational Stiffness

Abstract eng:
Inherent to the development of performance-based seismic design and assessment techniques, is the need to adequately predict the inelastic displacements of structures. To date, research has provided a range of prediction approaches based on 2 and 3-dimensional representations. While the 2-D response can often be adequately assessed for design using simplified hand-predictions, the 3-D cases have tended to rely on push-over techniques that do not capture the effects of the rotational inertia on the diaphragm twist that develops in asymmetric structures. This paper presents the basis of a new approach for estimating, by hand calculation, the expected maximum torsional response of buildings with in-plan asymmetry. Fundamental to a prediction procedure is the quantification of the apparent twist restraint that is a result of the rotational mass inertia of the floor diaphragm. The derivation of this dynamic torsional restraint is presented here. For a series of simple structures subjected to sinusoidal pulse inputs, comparative results between recorded inelastic time-history and predicted response are presented. For realistic eccentricity cases the predictions are shown to provide sufficiently accurate estimates of response for use in design.

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