An answer to an important controversy and the need for caution when using simple models to predict inelastic earthquake response of buildings with torsion

Abstract

SUMMARYThis paper presents evidence that the extension of conclusions based on the widely used simplified, one story, eccentric systems of the shear-beam type, to actual, nonsymmetric buildings and consequent assessments of the pertinent code provisions, can be quite erroneous, unless special care is taken to match the basic properties of the simplified models to those of the real buildings. The evidence comes from comparisons of results obtained using three variants of simplified models, with results from the inelastic dynamic response of three-and five-story eccentric buildings computed with detailed MDOF systems, where the members are idealized with the well-known plastic hinge model. In addition, a convincing answer is provided on a pertinent hanging controversy: For frame-type buildings, designed in accordance with the dynamic provisions of modern codes (such as EC8 or IBC2000), which allow reduced shears at the stiff edge due to torsion, the frames at the flexible sides are the critical elements in terms of ductility demands.

The role of overstrength on the seismic performance of asymmetric‐plan structures

“…3 The results of these studies have contributed significantly to the understanding of torsion phenomena resulting from the inelastic seismic response of asymmetrical systems. They have usually employed single-story shear frames for simplifying the rigorous analytical work.…”

Predicting displacement demand of multi-storey asymmetric buildings by nonlinear static analysis and corrective eccentricities

“…However, comparisons between results from single-and multi-storey models have shown significant qualitative differences in the predicted responses, thus raising doubts about conclusions based on the oversimplified single-storey models. Four peculiarities of actual multi-storey buildings are generally not properly simulated by single-storey models [23][24][25][26][27][28]. Indeed, in real buildings: (1) member stiffness, strength and yield deformation are related to each other; (2) members have a significant overstrength because of the use of many loading conditions; (3) member yielding causes a gradual reduction in the lateral stiffness of the frames because of the structural redundancy; (4) higher modes of vibration have a non-negligible influence on the seismic response.…”

Rot Index for Assessing the Torsional Effect on the Seismic Performance of Rc Buildings

“…Myslimaj and Tso [11,12] proved that the torsional effects can be alleviated for asymmetric wall-type systems by locating the centre of strength and the centre of rigidity on the opposite sides of the centre of mass. Anagnostopoulos et al [13] pointed the inadequacies of the simplified one-story, shear-beam type systems for predicting the inelastic response of real, asymmetric, multistory frame buildings, subjected to torsion due to earthquake motions and consequently for deriving general conclusions about torsional provisions of the codes.…”