MODEL FOR THE ANALYSIS OF THE SEISMIC BEHAVIOR OF REINFORCED CONCRETE HIGHWAY BRIDGES

A. BARBAT; S. OLLER

Conferencia; COMPUTATIONAL MECHANICS WCCM VI and APCOM?04; 2004

The evaluation of damage caused by seismic action to existing bridges has received an important attention in recent years, because it is the first step towards reducing of casualties and economic losses. In damage detection and evaluation, the application of simple and reliable models has been prioritized, because they are necessary in the multi-analyses required by Monte Carlo simulations. A simplified evaluation model characterizing the expected damage due to seismic action in RC highway bridges with simple pier bents is therefore proposed in this paper. The model is based on the hypothesis of the flexible pier-rigid deck behaviour of the structure subjected to transversal seismic loads. The piers are modeled as continuous elements with distributed mass and infinite axial stiffness, while the girders are perfectly stiff elements concentrating the mass at the top of the piers.The bearings of the girders are modeled as equivalent short elements that work to shear. The soilstructure interaction effect is considered by means of linear springs that represent the rotational stiffness of the soil. Accordingly the model has as many degrees of freedom as the transversal displacements at the top of the piers.The study of the damage produced by the earthquake load is centered on the piers of the bridge, while the dynamic study of the deck can be performed after the structural analysis of the piers in an uncoupled way. The simplified model was developed based on the correlation between the dynamic responses of the proposed model and of the real structure in its first few vibration frequencies. It was also calibrated by using the results of linear and non-linear finite element analyses of the Warth Bridge, Austria.The damage caused by the seismic action is defined by applying an isotropic damage model based on continuum damage mechanics. Using this model, the inertia of the any damaged cross section of the pier is obtained and the evaluation of the damage under seismic actions is based on the modification of the cross sectional inertia of the bridge piers. The maximum damage of the piers is the principal aim of the proposed structural evaluation methodology. A local damage index is used for this purpose, which describes the state of the material at each point of the structure and is based on a constitutive damage law. The proposed model permits a simple, reliable and efficient structural analysis. Example of application of the proposed model to analyze the seismic behavior of the Warth Bridge demonstrates its reliability and efficiency.