Abstract
Engineering practitioners do not usually include soil-structure interactions in building design; rather, it is common to model and design foundations as embedded joints with joint–based reactions. In some cases, foundation structures are modeled as rigid bodies, embedding the first story into lower vertical elements. Given that the effects of underground floors on the seismic response are not generally included in current building design provisions, it has been little explored in the literature. This work compares and analyzes models to study the effects of different underground stories modeling approaches using earthquake vibration data recorded for the 16–story Alcazar building office in downtown Viña del Mar (Chile). The modeling expands beyond an embedded first story structure to soil with equivalent springs, representing soil-structure interaction (SSI), with varying rigid soil homogeneity. The building was modeled in a finite element software considering only dead load as a static load case because the structure remained in the framing stage when the monitoring system was operating. The instruments registered 72 aftershocks from the 2010 Maule Earthquake, and this study focused on 11 aftershocks of different hypocenters and magnitudes to collect representative information. The comparisons between empirical records and models in this study showed a better fit between the model and the real vibration data for the models that do consider the SSI using horizontal springs attached to the retaining walls of the underground stories. In addition, it was observed that applying a stiffness reduction factor of 0.7 to all elements in deformation verification models for average-height buildings was suitable to analyze the behavior under small earthquakes; better results are obtained embedding the structure in the foundation level than embedding in the street level; the use of horizontal springs with Kuesel’s model with traction for the analysis of the structure yields appropriate results; it is necessary to carefully select the spring constants to be used, paying special attention to the vertical springs. Even though the results presented herein indicate that the use of vertical springs to simulate the SSI of the base slab can result in major differences concerning the real response, it is necessary to obtain more data from instrumentation across a wider variety of structures to continue to evaluate better design and modeling practices. Similarly, further analyses, including nonlinear time-history and high-intensity events, are needed to best regulate building design.
Highlights
Designing structures requires adequate modeling of its different elements, loads, and— especially in earthquake-prone countries like Chile—simulations of the seismic loads
The huge relative errors obtained for models considering vertical springs at the base of the foundation can be attributed to a poor calibration of the spring constant used
The complex process that is required to validate and accurately define this parameter, and the high sensitivity that the numerical analyses performed shown to this parameter, make it unsuitable for design purposes to model the structure using vertical springs, at least until further studies regarding the calibration of the spring constant makes easier to define it
Summary
Designing structures requires adequate modeling of its different elements, loads, and— especially in earthquake-prone countries like Chile—simulations of the seismic loads. Comparisons of the effect of underground floors on the building’s response to real–world data have been seldom reported, given the few instances where instrumentation was already placed in a building when significant or useful events were registered for data processing While studies, such as [26,30] have investigated SSI effects through system identification techniques of buildings from earthquake data, only a few studies [16,17,21] to the best of the authors’ knowledge, have focused on the influence of underground levels in the seismic analysis of buildings and only the former oriented to practical engineering applications. Each model’s results were compared to determine the best approximation to the recorded building response and to evaluate if more rigorous foundation modeling may contribute to better engineering practice
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