Effects of torsion on the seismic response of structures

The studies reported herein focus on the effects of torsion on the three-dimensional linear-elastic and non-linear inelastic seismic response of multi-story building structures.; To introduce parameters pertinent to the problem of torsion, 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 discussed. The way that major building codes handle torsion in their simplified regulations is described, and it is clearly illustrated that torsional provisions of most of present building codes are nonconservative.; 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 UBC) on the lateral-torsional response of structures is discussed.; A discussion about mathematical modeling of structures for non-linear analyses is presented. The computer program FACTS and its non-linear three-dimensional reinforced concrete beam column element, which are employed in this research, are introduced. Non-linear static responses of the seven-story structure to two sets of monotonically increasing lateral loads, with triangular and uniform profiles, are studied. Based on the results of this study a realistic model of the seven-story structure, which represents typical frame-wall systems, is developed.; Importance of parameters such as: non-uniform distribution of mass (mass eccentricity); unsymmetrical distribution of yielding strength (resistance eccentricity) in the plan of the structure; and intensity of earthquake ground motion on the three-dimensional non-linear seismic responses of buildings is discussed in detail. Mass and resistance eccentricities are measured with respect to geometrical centroid of the structure. It is illustrated that real non-linear torsional response of structures may be significantly underestimated by a linear-elastic dynamic analysis, especially for large values of static eccentricity ratio and intensity of ground motion. It is also explained how torsional effects on the non-linear response of structures can be reduced by proper distribution of yielding strength in the plan of buildings.; Finally, a summary of the results, pertinent conclusions and a number of code-based recommendations are presented in addition to suggestions for future research regarding torsional effects.