مهندسی عمران شریف (Aug 2016)
INFLUENCE OF THE MASS ECCENTRICITY ON THE MARGIN OF SAFETY AGAINST THE COLLAPSE OF RC-SMF BUILDINGS UNDER EXTREME EARTHQUAKES
Abstract
Safety assessment of a building is important in recognition and control of seismic hazards in high earthquake risk areas. The margin against collapse and the probability of failure are important indicators, which are mostly used to examine building safety against collapse. Evaluation of these indicators in a building is part of its collapse assessment under strong ground motion that may cause more modern buildings to collapse. Collapse assessment studies have often been carried out on symmetric buildings. Most research into plan-asymmetric buildings tries to introduce methods to control undesirable demands due to torsion-induced motion, or to suggest a proper design strategy in order to reduce torsional effects on structural responses. However, such studies are often carried out using simple building models and are inadequate for modelling realistic multi-story buildings in the inelastic range. So, this study tries to examine the influence of plan-asymmetry on the collapse performance of buildings that have been designed based on building codes. 5, 10 and 20\% mass eccentricities are proposed as plan-asymmetric building models and collapse safety is investigated on 5- and 10-story reinforced concrete special moment frame buildings by assessing collapse probability and the collapse margin ratio. The inelastic behavior of the frame elements is modeled using lumped-plasticity hinges at the ends of each element. The parameters of the inelastic behavior model of these hinges are calculated by empirical calibration equations regarding the design details of structural elements. According to the results, the probability of collapse reduces as the mass eccentricity increases. The trends of the collapse margin also show that the increase of mass eccentricity improves the collapse safety of the proposed buildings. This is because the building models show torsionally stiff behavior as the mass eccentricity increases. Although the collapse capacity decreases by increasing building height, it does not considerably influence the variation of the proposed safety measures.
