Pseudo-Dynamic Testing Based on Non-linear Dynamic Substructuring of a Reinforced Concrete BridgeExperimental Research in Earthquake Engineering

The assessment of the seismic performance of an old concrete bridge was conceived within the RETRO Transnational Activity funded by the SERIES research project. The installation of isolation devices -one per column- for each pier portal frame interposed between the cap beam and the deck was proposed as seismic retrofit, fully complying with Eurocode 8 requirements. A comprehensive set of hybrid simulations was conceived to simulate the dynamic response of the existing 400 m span Rio Torto Viaduct, both in the isolated and the non-isolated cases. In order to support the pseudo-dynamic test design, a refined fiber based FE model of the bridge was implemented in the well-known OpenSEES software; time history analyses highlighted appreciable nonlinearities in the dynamic response of the system under the Serviceability Limit State (SLS). As a consequence, a Numerical Substructure (NS) capable of reproducing such nonlinear behaviour was deemed necessary. Nonetheless, implementation issues relevant to the typical solving time dictated by the controller time step, made the use of complex fiber based FE models not suitable for testing purposes. In this perspective, the paper presents the design of a suitable NS, which is based on a rational and nonlinear reduction of the aforementioned OpenSEES Reference Model (RM). Moreover, in order to impose a consistent degradation of physical and numerical piers, a testing procedure based on recursive identification and model updating sessions is proposed. The numerical tools and simulations developed in the project are presented and discussed.