NONLINEAR SEISMIC RESPONSE OF SOIL-FOUNDATION-STRUCTUREINTERACTION MODEL OF CABLE-STAYED BRIDGES TOWER

摘要

The problem of soil structure interaction in the seismic analysis and design of long-span bridges inseismically active regions is potentially important to highway facilities design. A quite general nonlineardynamic soil structure interaction analysis methodology is developed to estimate seismic responsecharacteristics of cable-stayed bridges tower, in which the effect of the soil flexibility underneath thefoundation and its associated geometric and hysteretic damping are included. Due to rocking response of aspread foundation under a strong near-field ground motion that may result in the foundation uplift and theyield of the underlying soils, both of strain-dependent material nonlinearity and geometrical nonlinearityby base mat uplift are considered. The soil parameters values that are considered in the design process areused to observe the effect of soil nonlinearities upon the tower-pier seismic response. Numerical resultsindicate that force response quantities of the physical sub-structure stiffness tower model can be reducedby considering soil foundation interaction and different soil nonlinearities. The soil yielding below thefoundation and uplift at the interface have significantly contribution to foundation rocking response. Thesoil bearing stress beneath the footing base dramatically increases due to footing base uplift. Thepredominant contribution to the vertical response at footing base comes from the massive foundationrocking rather than from the vertical excitation. The spectrum amplitude at tower top contains only thedominant flexible super-structure frequency and all other frequencies, which present in the massive andrigid sub-structure base level, have been essentially filtered out.