Report - PEER - University of California, Berkeley

HORIZONTALLY IRREGULAR STRUCTURES: SOME RECENTDEVELOPMENTSA. RUTENBERG 1 and W. K. TSO 2ABSTRACTRecent developments in analysis and design techniques for 1-storey and multistoreyasymmetric structures, including pushover procedures, are reviewed. The relative paucity ofexperimental studies characterizing research in the field until recently, and the present welcomeactivity, are noted. Difficulties in estimating shear demand by either linear models or 1-storeynonlinear ones are illustrated by a case study on a torsionally flexible 10-storey 4-wall system.The need for iteration in applying the static torsional code provisions — resulting from theinterdependence of stiffness and strength — motivated the development of alternative designprocedures leading to more uniform plan-wise displacement distribution. This approach ispresented in some detail.Keywords: Asymmetric structures; Review; Wall-shear; 1-storey models.1. INTRODUCTIONAlmost fifty years have passed since Rosenblueth (1957) and Housner and Outinen(1958) alerted structural engineers to the problem of possible damage caused by therotational response of asymmetric structures during earthquakes. Since then, mostseismic codes have incorporated some form of guidelines for the horizontal allocationof strength among elements commonly referred to as torsional provisions. With thecoming of the computer, an enormous amount of research effort has been devoted toimprove the provisions. Developments up to 2001 can be found in severalpublications (e.g., Rutenberg 1992,Rutenberg and De Stefano 1997, Rutenberg 2002).It is only fair to ask whether the current codified provisions are more effective tomitigate torsional damages since those days, and has our predictive ability improvedconsidering also the availability of very powerful computers? The authors have beenworking in this area over a number of years. This paper is an attempt to answer thesequestions. In the first part of the paper a short review of the more recent developmentsis presented. It is followed by some contributions from the authors, and the paper ends1 Technion-Israel Institute of Technology, Haifa, Israel; E-mail: avrut@tx.technion.ac.il2 McMaster University, Hamilton, Ont. Canada; E-mail: tsowk@univmail.cis.mcmaster.ca369