PERFORMANCE BASED SEISMIC DESIGN OF PIERS OF REINFORCED CONCRETE BRIDGES

Julian R.; Fernandez-Davila V.I. · World Conference on Earthquake Engineering proceedings (2021)

Resumen

In Peru, there is a great demand for bridges with reinforced concrete piers, which arc designed for resistance (force-based methodology). Currently, the seismic design is based on displacements due to its close relationship with structural damage. It is for this reason that it is necessary to know the capacity of lateral displacement of the bridges, and compare it with the demand for displacement to know the level of performance according to the regulations used. The objective of this research is to present an empirical expression to calculate the lateral displacement capacity of the reinforced concrete piers from a paramctrically defined bridges family. It is known that nonlinear static analysis (NSA) - Pushover is a powerful tool to calculate the displacement capacity of a structure and in this particular case of bridges. The analysis Typc-NSA was performed in the longitudinal and transverse direction of the bridge to determine the lateral displacement capacity in all the cases studied. In addition, the ductility criteria and the verification were considered in the analysis so as not to consider the P-Dclta clTcct on the piers, according to Caltrans [ I ]. The family of bridges used in the research is made up of continuous bridges of three span with two intermediate piers, composed of columns of circular cross-section of reinforced concrete. Three-dimensional modeling of the bridges was performed, using the following elements: area clement in the superstructure, and frame clement in the piers. In addition, it was considered that the superstructure is supported on the infrastructure and considering an isolator compose by neoprcne layers between both, the columns of the piers were considered to be fixed into the base and the flexibility of the cap beam that connects them at the top end was taken into account. Also, the lateral restraint in the abutment and the seismic control devices in the intermediate piers that restrict both transverse and longitudinal movement during the occurrence of an earthquake was considered. The parameters considered were the following: the height of the intermediate columns, the number of columns in each pier, and the amount of vertical reinforcement of the columns. It was observed that in both directions of analysis of the bridge, the capacity for lateral displacement of the bridge decreased as the amount of vertical reinforcement for geometrically equal piers increased and that the lateral displacements were better related to the height of the piers. For this reason, the formulas developed for the calculation of lateral displacement arc related according to the height of the pier and are affected by the limitations of ductility and the not need to consider the P-Dclta effect, according to the recommendations indicated in Caltrans [ I ]. Finally, the proposed formula may be used in the prc-sizing stage of reinforced concrete piers, allowing the seismic design by displacement to be more expeditious, because the lateral displacement capacity obtained by this formula has a margin of average error of 5% in the longitudinal direction and up to 5% in the transverse direction, compared to the displacement capacity obtained from an NSA, decreasing the iterative process involved in seismic design by displacements.

Instituciones: Universidad Nacional de Ingeniería