A COMPARISON OF THE PRESENT SEAOC UBC TORSIONAL PROVISIONS WITH THE OLD ONES/

The seismic response of single storey asymmetric structures modelled a s two-degree-of-freedom elastic-perfectly plastic oscillators and desi gned using the design eccentricity formula of the present Uniform Buil ding Code (UBC) torsional provisions, which first appeared in the 1988 edition, is compared with designs based on the earlier UBC 1979. Chan ges in the total strength requirement and its distribution among the r esisting elements are examined, and the effects of these changes on th e ductility demand of three- and five-element systems are evaluated. I t is shown that for two levels of the strength reduction factor R (= 4 ;1) the ductility demands predicted for systems designed according to the UBC 79 provisions are in most cases similar to those for UBC 88 sy stems, with the exception of torsionally flexible systems - mainly mas s eccentric and, to a much lesser extent, stiffness eccentric systems. In view of the relative complexity of the UBC 88 provisions, a modifi cation of the simpler UBC 79 ones is proposed which results in the UBC 79 torsionally flexible systems behaving in a similar and often bette r manner than their UBC 88 counterparts. (C) 1997 Elsevier Science Ltd .