Simplified seismic analysis of straight integral frame-abutment bridges

Since the second post-war period, Integral Abutment Bridges (IABs) have become widespread in the construction of overpasses in America and Europe, as they allow to save on the costs of inspection and maintenance of the bearings and deck joints. They are characterized by having an internal continuity constraint between abutments and deck. Their static and dynamic behavior is thus characterized by the strong interaction between structure and soil. Due to these structural characteristics, the analysis models cannot disregard the contribution of the surrounding soil non-linear behavior. While the latter can be modeled by means of a continuous medium with a non-linear constitutive law, such models are very complex and require specialized knowledge and skills beyond those of the average structural designer. The aim of this thesis is therefore the study of simplified two- and three-dimensional models for practice-oriented seismic analysis of integral abutment bridges. The study focused first on a non-linear dynamic model where soil-structure interaction is modeled with non-linear Winkler springs. A comparison with a higher-order three-dimensional finite element model was performed, which allowed calibration and fine-tuning. The same non-linear dynamic model has been implemented both in OpenSEES and in SAP2000, in order to evaluate the sensitivity of the assessed system response to the limitations of commercial softwares and thus to highlight the practical applicability of the model for design. As a further step toward design, even more simplified static models, both non-linear and linear, were established and calibrated against the non-linear dynamic one. Finally the dynamic model was used to carry out a seismic risk analysis of archetypical overpasses with integral abutment on the Italian territory to quantify in probabilistic terms the better performance of these bridges with respect to bridges with traditional seat-type abutments.