ESTIMATION OF ACCIDENTAL TORSION EFFECTS FOR SEISMIC DESIGN OF BUILDINGS

A procedure is developed for including the effects of accidental torsi on in seismic design of buildings. It has four steps. First, the ratio between the fundamental frequencies of uncoupled torsional and latera l motions of the building is computed. This ratio and plan dimensions are then used to estimate the increase in displacements at the edge of the building resulting from all sources of accidental torsion. Third, from these edge displacements the increase in displacements at the lo cation of interior resisting planes are estimated. Finally, the design forces in structural members are computed by amplifying the forces ig noring accidental torsion by the increase in building displacements de termined previously. This procedure has several advantages over the co de-specified static and dynamic analysis procedures to include acciden tal torsion, such as: (1) The elimination of cumbersome static or thre e-dimensional dynamic analyses to account for accidental torsion effec ts in building design; and (2) the inclusion of the effects of all sou rces of accidental torsion. Two building examples are presented to ill ustrate these advantages as well as the computational steps required t o implement the new procedure.