Criteria for Seismic Risk Reduction of Earthquake Resistant Buildings

Most of the existing seismic design codes are based on the empirical knowledge accumulated through systematic earthquake damage data collection and their analysis. Required levels of protection and seismic design forces gradually are increased after each series of catastrophic earthquakes particularly in developed countries. Many efforts have been made through experimental and analytical studies to improve detailing and to increase inelastic capacity of buildings and structures to resist earthquake ground motions with acceptable damage levels. The general believe was that empirically developed seismic design codes contain performance objectives, but usually in a descriptive form that cannot be quantified and that explicit code design for life safety provides adequate damage protection. The main source of damage to structural systems and in particular nonstructural elements are deformations and interstory drifts imposed by earthquake ground motions. Therefore, to control damage, it is necessary to control deformation and particularly to control interstory drift. Thus, achievement of reliable and efficient earthquake resistant design of buildings and structures requires satisfaction not only of the criteria for strength but also the criteria for deformation and reparability which are directly inter-related. Although, there have been proposals to base seismic design on only lateral stiffness, i.e. only controlling the story drift, a practical method of this type of design has been recently developed using damage control criteria based on acceptable level of direct economic losses. Damage control criteria based on acceptable level of direct economic losses is formulated for earthquake resistant structural systems and non-structural elements, considering damage cost of both groups of elements as directly dependant of the structural response mechanism and story drifts to selected earthquake ground motions and their intensities. Two basic categories of ordinary and essential class of buildings are considered. For ordinary buildings governing criteria is damage control defined with the range of maximum story drift for Planning Scale Earthquake scenario, based on building damage data in the past earthquakes, experimental studies and calibration with numerous performance analyses. For essential class of buildings, like schools and health buildings, buildings with high occupancy rate, governing criteria is serviceability limit state defined with the range of maximum story drift for seismic hazard level of Maximum Considered Earthquake scenario, considering them to remain in safe and operational conditions after earthquake disaster. Established criteria is demonstrated with the presented results of seismic performance analysis and damage cost evaluation of the 19 structural systems of essential class of low and high rise buildings and 6 structural systems of ordinary non and earthquake resistant buildings.