EVALUATION OF TORSIONAL PROVISIONS IN SEISMIC CODES

The effects of plan asymmetry on the earthquake response of code-designed, one-story systems are identified with the objective of evaluating how well these effects are represented by torsional provisions in building codes. The earthquake-induced deformations and ductility demands on resisting elements of asymmetric-plan systems, designed according to several different codes, are compared with their values if the system plan were symmetric. The presented results demonstrate that the design eccentricity in building codes should be modified in order to achieve the desirable goal of similar ductility demands on asymmetric-plan and symmetric-plan systems. The design eccentricity should be defined differently for elastic and inelastic systems; in the latter case, it should vary with the design force level or anticipated degree of inelastic action. However, it does not appear possible to reduce the additional element deformations due to plan asymmetry by modifying the design eccentricity; these deformations should be provided for in building design.