The Earthquake Engineering Online Archive

Investigation of the seismic response of a lightly-damped torsionally-coupled building

Boroschek, Ruben L.; Mahin, Stephen A.

UCB/EERC-91/18, Earthquake Engineering Research Center, University of California, Berkeley, 1991-12, 262 pages (520/B67/1991)

The earthquake behavior of lightly damped, torsionally coupled moment-resisting steel space frames is investigated by analyzing the recorded three-dimensional response of a regular 13-story steel frame building located in San Jose, California, and by performing several elastic and inelastic computer analyses of this and similar structures. Several earthquakes have been recorded in the case study building. Of these, three earthquakes are considered in this report: the 1984 Morgan Hill, the 1986 Mt. Lewis, and the 1989 Loma Prieta events. During these events, the building responded severely, though no structural damage was observed. The recorded responses of the structure were unusual, characterized by long duration, narrow-banded periodic motions with strong amplitude modulation; large displacements and torsional motions; large amplification of the input ground motions; and slow decay of the building's dynamic responses. Three-dimensional linear and nonlinear numerical models of the complete structure are developed to simulate the recorded responses and to study the effects of changes in various parameters. The dynamic analyses consider unidirectional as well as bi-directional input motions with and without torsional input excitations. A best-fit model employing standard analysis and design procedures is identified. The parameters affecting the correctness of the response are determined. The effects of such factors as inelastic behavior, amount of equivalent viscous damping, additional plan eccentricities, and input motion characteristics on the overall response of the structure are studied. Typical design code recommendations for this type of structure are also evaluated.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-91-18.pdf (19 MB)