Accidental Torsion in Multistorey Buildings Due to Torsional Ground Motion—Equivalent Static Procedure and Response History Analysis

ABSTRACT All previous studies on the recommendation, quantification, and assessment of accidental torsion due to torsional ground motion were based on a set of single‐storey buildings and were extrapolated to multistorey buildings either under the assumption of a special class of torsionally coupled buildings (SCTB) or without any scientific rationale. This paper presents a procedure that enables computation of the required accidental eccentricity for a given (general‐class) multistorey building, rather than attempting a generalised recommendation on normalised accidental eccentricity that is independent of the building. Two different frameworks are proposed: one for the equivalent static procedure (ESP) and another for the response history analysis (RHA). The ESP framework considers each storey separately and recommends computing the required accidental eccentricity at the respective storey level, using the recommendations reported by the authors elsewhere for single‐storey buildings. The RHA framework extends that reported by the authors elsewhere for single‐storey buildings by relaxing the SCTB assumptions and instead accounting for the contributions of multiple triplets of torsionally coupled modes. The results from these frameworks are numerically assessed against five buildings (ten‐storied) with various plan layouts and horizontal setbacks, subjected to a suite of recorded events comprising horizontal pairs and the torsional component of ground motion. In a nutshell, this paper presents the first‐ever framework that can address accidental torsion in a given multistorey building without assuming it is an SCTB.