Performance-based analysis of concrete and steel-concrete composite box-girder bridges

Abstract eng:
This article investigates the performance of concrete and steel-concrete composite box-girder bridges. The first advantage of the box-girder typology lies in a high stiffness and strength for minimum weight. In addition, box-girder sections exhibit high torsional rigidity and therefore they are very suitable to be used for curved spans. In a first phase, we consider some aspects related to steel decks. As a result, one existing steel-concrete composite boxgirder viaduct that has to be retrofitted is analysed. In detail, the finite element (FE) model of the bridge as originally designed is developed. A main issue of the research is represented by the calibration of the FE model used for a subsequent reliability analysis. The uncertainties related to the mass and in particular to the stiffness of the bridge are very high owing to an advanced corrosive degradation of the steel inside the box. With this regard an in-situ outputonly ambient vibration dynamic identification test of the bridge is carried out. The results of the test are subsequently used to perform the FE model updating. Moreover, by using the updated FE model the study is completed by performing a reliability analysis in order to assess the residual performance of the bridge. In a second phase, we focus on the seismic behaviour of the substructure of box-girder concrete bridges endowed with different curvature in the horizontal plane. Since box-girders are commonly used in curved bridges, the study of the seismic behaviour of columns results particularly interesting. In detail, we investigate how the seismic demand of a concrete box-girder bridge composed of single bent columns modifies by changing the curvature in the horizontal plane. As a result, three types of bridges are studied: (a) one with low lateral stiffness; (b) one commonly employed in the design practice and (c) one with high lateral stiffness. Thus, a probabilistic seismic demand analysis is performed by considering different radii, including the straight bridge case. The bin approach is used to select a representative ground motion scenario. The drift ratio is analysed with respect to two intensity measures. Hence, preliminary design equations are provided in order to quantify the expected amount of amplification of the drift demand with respect to the straight solution.

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