Reliability Assessment of Using the Equivalent Lateral Force Method to Estimate Elastic Seismic Responses with Accidental Torsion Effects

Reliability Assessment of Using the Equivalent Lateral Force Method to Estimate Elastic Seismic Responses with Accidental Torsion Effects

Model building codes require consideration of accidental eccentricity in addition to the existing eccentricity in order to reflect accidental torsion effects on the seismic responses of buildings. In some model building codes, accidental eccentricity is multiplied even further by the torsional amplification factor Ax in order to minimize the discrepancy between the statically and dynamically estimated responses. This study investigates the reliability of using the equivalent lateral force method to estimate elastic seismic responses with code-specified accidental torsion effects. To achieve this aim, the discrepancy curves that represent the exceedance probabilities of the difference between the statically and dynamically estimated elastic seismic responses are first developed. The discrepancy curves for 3-story, 9-story, and 20-story example buildings are then constructed and investigated accordingly. Besides the building height, the investigated buildings vary based on four frequency ratios: 0.7, 1.0, 1.3, and 1.6. The existing eccentricity ratios of the investigated buildings range from 0% to 30%. The assessment results of this study clearly indicate that the torsional amplification factor Ax specified in some building codes generally provides conservative estimates of displacement for medium-rise and high-rise buildings.