NEHRP Clearinghouse

Title
Torsional Effects in Structures Subjected to Strong Ground Motion.
File
PB90226960.pdf
Author(s)
Lu, S.; Hall, W. J.
Source
National Science Foundation, Washington, DC., April 1990, 201 p.
Identifying Number(s)
UILU-ENG-89-2006
Abstract
The purpose of the study was to increase the understanding of torsional behavior in low-rise frame buildings and to assess its importance in the gross response of such buildings. One aspect of this investigation centered on understanding the strong coupling between translational and torsional response with closely spaced frequencies (including the beating phenomenon arising from modal instability); the study is believed to be the first conclusive theoretical demonstration of the beating phenomenon arising in the manner noted. It was found that the dynamic apmlification factor in torsion (as measured by static eccentricity) was about 2.5. With the use of a theoretical model encompassing nonlinear material behavior, it was possible to predict the torsional effects in two low-rise buildings and to compare such results with response data recorded in these buildings in the 1987 Whittier Narrows Earthquake. The low-rise moment-resisting frame-building studies indicated that the fundamental frequencies identified earlier herein are usually not well separated, and if possible, to prevent damage arising from torsion (usually late in the response process), the translational frequency should be kept smaller in relation to the torsional frequency, to ensure that the fundamental translational mode is dominant.
Keywords
Earthquake resistant structures; Framed structures; Torsion; Whittier Narrows Earthquake; Mathematical models; Dynamic response; Buildings; Earthquake engineering; Theses; Structural analysis