Improving Design for Plan Torsion

摘要

For many years, building codes have required that structures be designed to resist plan torsion seismic demands. The current treatment of plan torsion in ASCE 7-10 uses a metric to quantify torsional irregularity that leads to nonsensical conclusions under certain circumstances, and it is unclear how well this metric correlates with diminished expectations of seismic performance. Furthermore, in regions of high seismicity, buildings exhibiting extreme torsional irregularity are prohibited, which can significantly and unnecessarily disrupt the design process. While the requirement to analyze a structure for both inherent and accidental torsion achieves an important goal, there is room for improvement. This paper presents the findings of an analytical study of single-story structures with variations in torsional eccentricity, ductility, strength, and plan aspect ratio. The seismic performance of each structure is quantified using Incremental Dynamic Analysis (IDA), and the correlation between the degree of torsional irregularity as defined in ASCE 7-10 and seismic performance is investigated. Suggestions for an improved way of quantifying and designing for torsional irregularity are presented.