Influence of soil-structure-interaction in shear-wall RC buildings fragility curves

It has been widely recognized that soil-structure interaction (SSI) can have a significant effect on structural performance during seismic response. This effect varies depending on structural and local site characteristics, meaning that general conclusions, relevant to a large class of structural and site characteristics, cannot be drawn. Therefore, SSI must be considered on a case-by-case basis. In this study, the seismic performance of a typical Chilean shear-wall reinforced concrete (RC) building is assessed, considering fixed-base and SSI response, using a two dimensional numerical model. The geometric and material characteristics of the building are chosen to be representative of a 20-story RC residential building. Such characteristics include wall density, story weight per unit area, inter-story height, length and width of walls, reinforcement ratio for the boundary elements and wall web, among others. Its design followed the Chilean seismic code provisions. The numerical model of the prototype RC building was developed using the program OpenSEES, wherein fiber-based beam elements using non-linear materials were considered. SSI effects were incorporated by modeling the site using a linear continuum approach discretized by two-dimensional quadrilateral finite elements. Materials were chosen consistent with a class B site (Vs30 > 500 m/s), according to the Chilean site classification of the NCh433 seismic code, which is common in some populated cities in Chile, such as Santiago. Also, a fixed-base model was developed for comparison.Fragility curves were obtained through incremental dynamic analysis (IDA), using a set of 34 acceleration ground-motion records obtained from the Chilean National Seismic Center. Different damage measures were extracted from the simulations, e.g.: inter-story drift, floor acceleration, axial load levels measured in the walls, among others. Two sets of fragility curves were obtained considering the inter-story drift of the first floor, one for a fixed-base model and the second, for a model including SSI. The results shown in this study showcase the importance of SSI effects in the structural response of shear-wall RC buildings in Chile. The inclusion of SSI effects in fragility curves is of importance to damage evaluation and risk assessment studies, which use the fragility curves as an input. © NCEE 2018.