Impact of Soil–Structure Interaction Modeling Simplifications and Structural Nonlinearity on Uncertainty in EDPs: A Case Study on an Existing RC Building in Santiago

This study investigates the impact of modeling simplifications on the uncertainty of seismic response in numerical simulations, focusing on a five-story, asymmetric-plan, reinforced-concrete building in Santiago, Chile, subjected to simulated seismic motions from hypothetical events at the San Ramón fault (SRF). In order to achieve this, a comparative analysis is conducted between a high-complexity reference model and lower-complexity models. The reference model incorporates three-dimensional seismic inputs using the domain reduction method (DRM) and a detailed structural model accounting for material nonlinear behavior. The complexity of the models is systematically reduced to assess the effects of different soil–structure interaction (SSI) modeling assumptions. These assumptions include the use of DRM and plane-wave (PW) input, and also the exclusion of SSI through fixed-base (FB) conditions. For each model, both linear and nonlinear material behaviors are considered. Given the lack of historical records from the SRF, the study employs source-to-structure physical simulation to address seismic performance evaluation as well as its sensitivity to modeling. Simulations are conducted in OpenSees using input motions from 10 realizations of a $M_w=6.7$ event at the SRF, generated with the ShakerMaker Python library. With respect to the reference model, findings indicate that PW assumptions moderately increase uncertainty across different engineering demand parameters (EDPs) and analysis directions. Conversely, FB conditions significantly elevate modeling uncertainty, drastically changing the mean and variance of computed EDPs. A simple EDP sensitivity score is proposed to compare the statistics of computed EDPs, from which a global performance-score is constructed for ranking of models with respect to the reference model. The ranking shows that linear FB models may outperform non-linear FB models, highlighting a complex and nonintuitive relationship between structural nonlinearity and soil flexibility modeling on uncertainty. There are also indications that high-complexity modeling, accounting for the spatio-temporal complexities of the seismic wave-field through the DRM, is needed for responses quantities sensitive to high frequencies. Overall, it is shown that even for this realistic building, located on a very stiff soil, the effects of SSI cannot be neglected as this can produce unpredictable changes in mean and variance of computed EDPs.