Probabilistic Study on Accidental Torsion of Low-Rise Buildings

A probabilistic study on accidental torsion is presented. Multistory shear systems, representative of low-rise buildings and subjected to bidirectional earthquake ground motions are considered. Ductility demands of lateral resisting elements (LREs) due to uncertainties on (1) center-of-mass locations, (2) LRE stiffness, and (3) LRE yield forces were studied. Building code recommendations on accidental torsion as well as the effects of both eccentricity and lateral-force reduction factor are assessed. Results indicate that considering one random variable in the accidental torsion problem can lead to larger ductility-demand probabilities of exceedance than using two or more variables. Individual effects of each one of the variables considered are not superimposed when all variables take place at the same time. For systems designed for torsion, ductility demands of LREs decreases for increasing eccentricities. Increments of yield forces and decrements of probabilities of exceedance due to the use of increasing values of factor β associated with the accidental eccentricity are presented.