In this research, an energy formulation is proposed for the evaluation of pore pressure generation, incorporating the influence of the initial state of static stresses, both normal and shear, prior to cyclic loading. The proposed model focuses on obtaining a law of evolution of pore pressures under cyclic loading in saturated soils regardless of their susceptibility or not to liquefaction. The energy approach developed in this research extends previous energy based models developed for granular soils (susceptible to liquefaction and without initial static shear stress) incorporating: a) the integration in the formulation and interpretation of both the work dissipated and consumed during the dynamic process; b) the normalization of the formulation considering initial static stresses both normal and shear; c) obtaining and validating the model parameters with conventional tests of cyclic shearing equipment. The proposed model was validated with 116 cyclic simple shear tests under different in situ vertical effective stresses and different combinations of static and cyclic shear stresses. However, the model can be easily calibrated for other soils with cyclic simple shear tests without static shear stress, widely used in laboratories with dynamic equipment.

The performance of reinforced concrete buildings subjected to earthquake excitations depends on the structural behaviour of the superstructure as well as the type of foundation and the properties of soil on which the structure is founded. The consideration of the effects due to the interaction between the structure and soil- foundation alters the seismic response of reinforced concrete buildings subjected to earthquake motion. Evaluation of the structural response of buildings for quantitative assessment of the seismic fragility has been a demanding problem for the engineers. Present research deals with development of fragility curve for building specific vulnerability assessment based on different damage parameters considering the effect of soil- structure interaction. Incremental Dynamic Analysis of fixed base and flexible base RC building models founded on different soil conditions was conducted using finite element software. Three sets of fragility curves were developed with maximum roof displacement, inter storey drift and plastic energy dissipated as engineering demand parameters. The results indicated an increase in the likelihood of exceeding various damage limits by 10-40% for flexible base condition with soft soil profiles. Fragility curve based on energy dissipated showed a higher probability of exceedance for collapse prevention damage limit whereas for lower damage states, conventional methods showed higher probability of exceedance. With plastic energy dissipated as engineering demand parameter, it is possible to track down the intensity of earthquake at which the plastic deformation starts, thereby providing an accurate vulnerability assessment of the structure. Fragility modification factors that enable the transformation of existing fragility curves to account for Soil-Structure Interaction effects based on different damage measures are proposed for different soil conditions to facilitate a congenial vulnerability assessment for buildings with flexible base conditions.