On the inelastic torsional response of single-storey structures under bi-axial excitation

Abstract

SUMMARYAn attempt has been made to explore the general trends in the seismic response of plan-asymmetric structures without any restrictions imposed by a particular code. Systems with structural elements in both orthogonal directions under bi-directional excitation were studied. Idealized single-storey models with bi-axial eccentricity were employed. The systems were torsionally sti and, in the majority of cases, mass-eccentric. The main ÿndings are: in general, inelastic torsional response is qualitatively similar to elastic torsional response. Quantitatively, the torsional e ect on the exible side, expressed as an increase of displacements due to torsion, decreases slightly with increasing plastic deformation, unless the plastic deformations are small. The response on the sti side generally strongly depends on the e ect of several modes of vibration and on the in uence of the ground motion in the transverse direction. These in uences depend on the structural and ground motion characteristics in both directions. Reduction of displacements due to torsion, typical for elastic torsionally sti structures, usually decreases with increasing plastic deformations. As an additional e ect of large plastic deformations, a attening of the displacement envelopes in the horizontal plane usually occurs, indicating that torsional e ects in the inelastic range are generally smaller than in the elastic range. The dispersion of the results of inelastic torsional response analysis is generally larger than that of elastic analysis.

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

“…Some exceptions appeared in 2/50 hazard level. A remarkable observation, also noticed by other researchers [26,27], for both test examples considered is that maximum diaphragm rotations do not usually occur at the same time as maximum translations.…”

A review of research on seismic behaviour of irregular building structures since 2002

“…Marušic and Fajfar (2005) investigated the elastic and inelastic response of massasymmetric multi-storey steel frame buildings under bi-directional ground motions. According to Peruš and Fajfar (2005), results evidenced a qualitatively similar elastic and inelastic response, as shown by Fig. 6, with the exception of the stiff edge in the direction undergoing lower plastic deformations in torsionally stiff buildings, and, the same edge, though in the weaker direction, in torsionally flexible ones.…”

“…In the inelastic range, torsional effects may result to be either larger or smaller than the elastic displacements, depending on the frequency content of the input ground motion. Generally, Peruš and Fajfar (2002) found a decrease for flexible structures and an amplification for stiff structures (short periods range), according to the shape of response spectrum.…”

“…2), since differences between elastic and inelastic response are more pronounced in the translational part of motion, rather than in the rotational one. However, quantitatively, the change in response depends on the Peruš and Fajfar (2005) magnitude of inelastic deformations. In particular, normalized inelastic to elastic displacements at the flexible edge generally decrease with increasing ductility, except for very small values (below 2).…”

“…The N2 method controls the target displacements and distribution of deformations along the height of the building, whereas the linear dynamic analysis is used to define the torsional amplifications of lateral displacements. Use of linear dynamic analysis was justified by the assumption that, at the flexible edge, the elastic envelope of lateral displacements is conservative with respect to the inelastic ones (Peruš and Fajfar 2005). …”