New Proposal to Incorporate Seismic Accidental Torsion in the Design of Buildings

Abstract

This work studies a new design procedure to account for accidental torsion in buildings subjected to seismic ground motions. The procedure does not require a design accidental eccentricity and it is based on a simple amplification of design parameters obtained from the corresponding model without accidental torsion. The objectives of the study are to present and to evaluate the torsion design proposed procedure. Based on representative low-rise, reinforced-concrete building models subjected to a bidirectional earthquake ground motion, several scenarios of accidental torsion were simulated using the Monte Carlo method. In the first part of the study, elastic analyses of simulated models were carried out to obtain the amplification factor value (Fat). In the second part, nonlinear analyses were performed to evaluate the design proposal based on ductility demands. Main conclusions of the study are: mean values of ductility demands do not significantly change between the torsionally balanced (TB) system and the corresponding one with accidental torsion (TU with Fat = 1.0). However, these mean values decreased about 18% for beams and 16% for columns when the torsion amplification factor (Fat = 1.2) was used in the TU systems. As for peak ductility demands, the unbalance due to accidental torsion leads to increments close to 42% for beams and 54% for columns. On the other hand, the torsion amplification factor Fat = 1.2 reduces the peak values in 25%, approximately, for beams and columns of systems with accidental torsion. Main limitations of the study are: it is based on one bidirectional ground motion (with several incidence angles) and eight structural models.