Probabilistic assessment of ground motion rotation impact on seismic performance of structures

In the common application of ground motions in seismic design and assessment, it is mainly inclined to leverage merely as-recorded components. However, the as-recorded data is restricted by the recording sensor orientations, implicitly neglecting other potential vectors, which can be readily calculated using a rotation matrix. Meanwhile, there exists a debate on the extent of the importance of such consideration on various aspects of seismic assessment outcomes. This study, using a measure of entropy, shows why and how rotating the ground motions matter, and to what extent the rotation can alter the structural seismic assessment results probabilistically, in the context of performance-based earthquake engineering. In this regard, two benchmark structures are analyzed and the sensitivity of their seismic behavior to the records' rotation is demonstrated using Sa(T1) and Maximum Inter-story Drift Ratio as the pair measures. It is revealed that the precise estimation of fragility functions is affected by the number of angles, unachievable using moderate ground motion sets at solely as-recorded angles. Fragility functions are developed through Cloud Analysis, and the impact of sample size and ground motion rotation on them is studied. Also, a simple yet versatile procedure is proposed to incorporate the mentioned impact in a cost-saving manner. In this regard, Sa,RotD50, which is a well-known seismological measure, is proven to contribute to the incorporation of waveform angular effects adequately. The proposed method is assessed in terms of its estimation precision in comparison with other single random angles probabilistically.