ANGULAR EFFICIENCY OF INTENSITY MEASURES

An Intensity measure (IM) characterizes the potential of a ground motion. As a representative of a waveform, the IM's relationship with the structural response of buildings is essential in reducing uncertainties when estimating the structural demand. The efficiency of an IM can be determined by its ability to predict the response of a building accurately. An efficient IM, while capturing the dynamic characteristics of the structure, should be sensitive to the variations in the ground motion that may affect the structural responses. One source of uncertainty that has rarely been addressed before is Angle-to-Angle variability. The common practice of seismic design and assessment is inclined to use only the as-recorded components, neglecting other potential vectors given the constant recording sensor orientations. Therefore, in this study, the efficiency of different IMs is examined concerning their potential to cover Angle-to-Angle variabilities. Angular Efficiency is defined as the competency of an IM in addressing the mentioned variability. To evaluate the Angular Efficiency of IMs, two benchmark moment-resisting steel structures with nonlinear behavior are analyzed under various angles of a set of waveforms. Several Intensity Measures are paired with Maximum Inter-story Drift Ratio and their corresponding relationships are scrutinized to evaluate the seismic response sensitivity of the structures to the ground motion rotation. Additionally, using Modified Cloud Analysis, the fragility functions are developed to study the versatility of each IM in the context of probabilistic seismic assessment. The study proposed the concept of Angular Efficiency to quantify the stated source of uncertainty, compares IMs based on this criterion, and shows the versatility of the Peak Ground Acceleration in this respect.