Soil-Structure Interaction Effects on Seismic Assessment of Existing Low-Rise Reinforced Concrete Frames

Abstract eng:
Building structures designed in accordance with older versions of building codes and standards are likely to exhibit unsatisfactory behaviour under seismic loads. Existing structures represent an important part of the built heritage and therefore an economic challenge for current governments, as well as a public security issue for users of these buildings. The assessment of seismic response is most often done assuming fixed-base support conditions, thus ignoring the combined response of structure-foundation-soil system. This approach is considered conservative, but it neglects the great potential to reduce seismic demand imposed on the superstructure through controlled foundation yielding, appropriate mobilisation of bearing capacity or the uplifting at the foundation-soil interface. In order to properly assess the seismic behaviour of existing building structures and to make cost-effective decisions regarding their seismic retrofit, it is necessary to put forward reliable evaluation methods that can preferably account for the integrated seismic response of all system elements: the superstructure, the foundation and the underlying soil. In this study, a three-storey reinforced concrete frame building was designed in accordance with the 1965 National Building Code of Canada and its seismic response was assessed using results of nonlinear time history analysis. The Attention was directed at the impact of soil-structure interaction on the seismic assessment. The selected building geometry represents typical 1970’s school buildings in Quebec, Canada. Consistent with design practices of that era, the foundations were designed for gravity loads only and for two different soil conditions: rock (site class B) and stiff soil (site class D). Initial assessment was carried out using an equivalent static force method and response spectrum analysis considering typical fixed-base conditions. Subsequent more refined assessments were done with 2D nonlinear time history analyses of the superstructure with the soil-structure interface, and were conducted in OpenSees for a set of simulated ground motions compatible with the design spectrum. Soil-structure interaction effects were modelled using the beam-on-nonlinearWinkler-foundation concept. Base shears, roof displacements and displacement profiles are determined and compared to those obtained assuming a fixed-base condition. The foundation displacements and stresses in the soil are examined to assess the consequences on the global structural behaviour. The response of the superstructure is evaluated by tracking the elastic demand in beams and columns.

Conference Title:
Conference Title:
16th World Conference on Earthquake Engineering
Conference Venue:
Santiago (CL)
Conference Dates:
2017-01-09 / 2017-01-13
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 Record created 2017-01-18, last modified 2017-01-18

Original version of the author's contribution as presented on USB, paper 2781.:
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