Period‐Dependent Effects in Seismic Torsional Response of Code Systems

Abstract

The primary objective of code torsional provisions is to limit to acceptable levels the element ductility demands and deformations in plan‐eccentric structural systems. Such levels are determined from well‐established seismic design criteria applied to the appropriately defined reference systems. Information is available from comprehensive recent studies focusing on the effectiveness of code torsional provisions in meeting that objective. The major controlling factors have been identified as the total design strength incorporated in plan‐eccentric structures and its code‐dependent distribution among the lateral load‐resisting elements. The results and conclusions of these related studies have been based on a comparison of the response of elements in plan‐eccentric systems with that of the corresponding element in the selected reference system. This paper demonstrates that when a reference model is adopted that adheres rigorously to the design regulations of codes, including provisions for so‐called accidental torsional effects, significant period dependency of inelastic seismic torsional response behavior is revealed. To demonstrate this, a reevaluation of the equivalent static torsional design procedures of codes is presented.