The Earthquake Engineering Online Archive

Inelastic seismic response of structures with mass or stiffness eccentricities in plan

Bruneau, Michel; Mahin, Stephen A.

UCB/EERC-87/12, Earthquake Engineering Research Center, University of California, Berkeley, 1987-09-01, 303 pages (530/B785/1988)

The basic concepts inherent to the response of torsionally coupled systems are reviewed, and the pertinent equations of motion are derived. A literature review emphasizes the lack of agreement between different researchers on how variations in the fundamental parameters influence the response. Systems with only two lateral-load-resisting elements are selected for study. A tentative classification scheme is proposed for various types of inelastic torsionally coupled systems. For mass and stiffness symmetric systems having elements with different yield capacities, torsional coupling is created by the desynchronizing inelastic element responses, despite the existence of symmetry in the elastic domain. An extensive parametric study demonstrates that the element ductility levels remain within reasonable bounds, provided the ratio of uncoupled frequencies is not excessively large and the yield level of the weaker element is accurately estimated. A similar extensive parametric study is conducted for initially eccentric systems. A procedure is formulated to ensure a fair comparison between the coupled system and an equivalent single degree-of-freedom system. Preliminary results indicate that the findings in relation to both initially symmetric and eccentric systems may also be applied to equivalent multi-element single-story systems, systems with various types of element models, and multistory systems.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-87-12.pdf (26 MB)