Estimating natural periods of steel plate shear wall frames

A steel plate shear wall (SPSW) with thin, unstiffened web plates is one type of seismic lateral force-resisting system that is gaining popularity. SPSWs are used in low to midrise building construction typically with two or more frames in each orthogonal direction to resist seismic loading combined with gravity framing. The SPSWs therefore control the lateral force response of the building and the building's natural periods of vibration. For design of any seismic load-resisting system, an estimation of the building's first-mode period is necessary to calculate seismic loads and estimate resulting frame drift. This paper presents a method for estimating the first three natural periods of a SPSW with nonuniform properties along its height, accounting for both shear and flexural deformations of the system. The proposed method approximates the SPSW frame as shear and flexural systems separately to determine corresponding frequencies and then combines these frequencies using Dunkerley's equation. A comparison of periods estimated using the approximate method with those obtained from modal analysis of detailed finite-element models suggests that the proposed method is appropriate for estimating the first-mode period of SPSW frames. The proposed method could be valuable for refining the seismic design of these frames or for verifying the results of large, complex steel plate shear wall building models.