The Earthquake Engineering Online Archive

Effects of torsion on the linear and nonlinear seismic response of structures

Sedarat, Hassan; Bertero, Vitelmo V.

UCB/EERC-90/12, Earthquake Engineering Research Center, University of California, Berkeley, 1990-09-01, 321 pages (577/S42/1990)

These studies focus on the effects of torsion on the three-dimensional linear-elastic and nonlinear inelastic seismic response of multistory structures. The linear-elastic lateral-torsional response of an idealized single-story system to earthquake ground motion, characterized by flat and hyperbolic pseudo-acceleration response spectra, is first discussed. The way that major building codes handle torsion in their simplified regulations is then described. The results of linear-elastic static and dynamic analyses of a seven-story reinforced concrete frame-wall structure are presented, and the importance of factors such as static lateral load profiles, static eccentricity ratio, and accidental eccentricity (as prescribed by the Uniform Building Code) on the lateral-torsional response of structures is discussed. The mathematical modeling of structures for nonlinear analyses is considered. The computer program FACTS and its nonlinear three-dimensional reinforced concrete beam-column element, which are employed in this research, are introduced. Nonlinear static responses of the seven-story structure to two sets of monotonically increasing lateral loads, with triangular and uniform profiles, are studied. A model of a seven-story structure representing typical frame-wall systems is developed. The importance of such parameters as nonuniform distribution of mass (mass eccentricity); unsymmetrical distribution of yielding strength (resistance or strength eccentricity) in the plan of the structure; and intensity of earthquake ground motion on the three-dimensional nonlinear seismic response of a building is discussed in detail. Mass and resistance eccentricities are measured with respect to the geometrical centroid of the structure. Results are presented.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-90-12.pdf (29 MB)