Probabilistic Seismic Assessment of Structure, Foundation and Soil Interacting Systems

This report presents research on the probabilistic seismic performance evaluation of a structural-geotechnical interacting system. The system comprises a bridge, its foundation, and the supporting soil. The investigation includes a study on probabilistic performance evaluation methodologies, development of a multiplatform and hybrid simulation framework, verifications of numerical models of structural and geotechnical systems in comparison with measured data, and the derivation of fragility curves of a bridge in Central and Eastern United States. Seismic performance evaluation procedures are studied using a benchmark threestory, reinforced concrete (RC) building structure. Three probabilistic performance evaluation methods are applied: the Monte Carlo simulation, response surface, and SACFEMA methods. The analysis of benchmark structure shows that the effect of random variability in structural materials is small compared to the effect of input ground motion. When Peak Ground Acceleration (PGA) is used as an intensity measure, the derived vulnerability curves highly depend on ground motion sets. Three different simulation methods results in similar vulnerability curves. The computational cost are the most expensive when the Monte Carlo simulation is adopted. Methodologies for soil-structure-interaction analysis are introduced, including the newly developed multiplatform, multiresolution hybrid simulation framework. These methodologies and numerical models of soil-structure-interaction systems are verified through comparison with field measurements and experimental results. The soil-structure interacting system is verified through analyses of a heavily instrumented bridge which recorded several sets of ground motions. The verification study of soil-structure interacting system shows that detailed and meticulously developed analytical models are capable of replicating measurements of the response of complex bridge systems subjected to strong ground motion. Seismic vulnerability curves of a reference bridge in the Central and Eastern United States (CEUS) are derived employing the aforementioned methods with and without soilstructure interaction. A typical highway over-crossing bridge representing one of the most common bridge types in the CEUS is selected. Four different approaches of SoilStructure Interaction (SSI) are tried: (a) Abutments and foundations are assumed to be fixed, (b) Conventional lumped spring approaches are adopted to model abutments and foundations, (c) Lumped springs for abutments and foundations are estimated from Finite Element (FE) analysis of geotechnical system, and (d) Multiplatform simulation is conducted. All four of the methods shows that abutment bearings in transverse direction are most vulnerable components. Failure probability of the bridge system is highly dependent on the failure probability of abutment bearings. Considering that simplified methods for SSI analysis include larger assumptions than fully coupled methods and that the multiplatform simulation is verified with measured responses from instrumented bridge, the use of multiplatform simulation is suggested if computational power and resources for FE modeling are affordable.