Abstract
Rocking shallow foundations can be used as an effective seismic isolation means to reduce earthquake-induced damage to structures by utilizing nonlinearities arising from base uplifting and soil yielding. A number of studies have been devoted to the proposal of inelastic displacement ratios for estimating the maximum inelastic displacement demands on yielding structures on rocking shallow foundations for seismic evaluation purposes. However, there is a lack of methods for estimating structural deformations associated with damage to structures, which are usually measured using structural drift ratios. Since drift ratios of structures on rocking foundations consist of contributions due to foundation rocking, it is necessary to figure out whether these rocking rotations should be removed from structural drift ratios to obtain effective structural drift ratios related solely to structural straining. A comprehensive parametric analysis is carried out in this study to quantify the contribution of foundation rocking. Based on the results, a structural displacement ratio is proposed to estimate effective structural drift ratios excluding foundation rocking rotation, and an empirical expression is provided so that effective structural drift ratios can be directly obtained using available expressions for the inelastic displacement ratios of rocking shallow foundations.
Highlights
Foundation rocking isolation has been shown to be an effective means to reduce seismic damage to structures by utilizing foundation nonlinearities through rocking motions, including geometrical nonlinearity due to base uplifting and material nonlinearity due to soil yielding [1]
The results suggest that the stronger the superstructure is compared to the foundation, the less deformation the superstructure is likely to experience compared to the foundation, which leads to higher contribution of the foundation rocking to the drift ratio (DR)
The effective structural drift ratios could be estimated by applying Rs to the maximum displacement demands on structures supported by rocking shallow foundations which could be determined using readily available expressions for inelastic displacement ratios
Summary
Foundation rocking isolation has been shown to be an effective means to reduce seismic damage to structures by utilizing foundation nonlinearities through rocking motions, including geometrical nonlinearity due to base uplifting and material nonlinearity due to soil yielding [1]. Using a large number of nonlinear response-history analyses, Ghannad and Jafarieh [23] concluded that code expressions of inelastic displacement ratios for fixed-base structures, in most cases, underestimated actual displacement ratios for uplifting systems They were the first to propose empirical expressions to estimate inelastic displacement ratios for yielding structures with bilinear hysteretic behavior on rocking shallow foundations. Maximum displacement demands on a yielding soil–structure interaction (SSI) system can be estimated using inelastic displacement ratios, it is sometimes more desirable to evaluate seismic damage to structures and foundations separately This is because damage limit states for structures and foundations are separately well defined and readily available. A structural displacement ratio is proposed to estimate effective structural drift ratios, excluding foundation rocking rotation, and an empirical expression is provided so that effective structural drift ratios can be directly obtained using available expressions for the inelastic displacement ratios of rocking shallow foundations
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