An answer to a persisting controversy in earthquake resistant design of asymmetric buildings for torsion

Abstract eng:
One of the persisting controversies associated with the inelastic dynamic, torsional response of asymmetric buildings is whether the so called “critical” elements of the building are those in the “stiff” or the “flexible” sides. The term “critical” is used for the element that exhibits the largest ductility demand during an earthquake, while the terms “stiff” and “flexible” sides indicate those sides of the building that exhibit reduced and increased translational displacements, respectively, as a result of torsion. The published results on this issue in the past are divided between the two possibilities. In this paper, using results from inelastic, earthquake, dynamic analyses of two asymmetric buildings with 3 and 5 stories each, modeled as M.D.O.F. space frames with plastic hinge idealization of their members, it is shown that the critical elements are those at the flexible side. It is further shown that the same conclusion can be obtained using the simplified, one story models, provided that their strengths reflect the total strengths of the real building elements. If, however, the element strengths of the simplified models are determined solely from the earthquake loading, i.e. without accounting for the strength due to gravity loads, as it has been done practically without exception in the past, then the results indicate the elements at the stiff side as the critical elements. This provides a convincing answer to the aforementioned controversy.

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