Hybrid simulations of a multi-span rc viaduct with plain bars and sliding bearings

This paper deals with the seismic response assessment of an old reinforced concrete viaduct and the effectiveness of friction-based retrofitting systems. Emphasis was laid on an old bridge, not properly designed to resist seismic action, consisting of 12 portal piers that support a 13-span bay deck for each independent roadway. On the basis of an OpenSEES finite element frame pier model, calibrated in a previous experimental campaign with cyclic displacement on three 1:4 scale frame piers, a more complex experimental activity using hybrid simulation has been devised. The aim of the simulation was twofold: (i) to increase knowledge of non-linear behavior of reinforced concrete frame piers with plain steel rebars and detailing dating from the late 1950s; and (ii) to study the effectiveness of sliding bearings for seismic response mitigation. Hence, to explore the performance of the as built bridge layout and also of the viaduct retrofitted with friction-based devices, at both serviceability and ultimate limit state conditions, hybrid simulation tests were carried out. In particular, two frame piers were experimentally controlled with eight-actuator channels in the as built case while two frame piers and eight sliding bearings were controlled with 18-actuator channels in the isolated case. The remaining frame piers were part of numerical substructures and were updated offline to accurately track damage evolution

NUMERICAL UPDATING ON COLLAPSE SIMULATION OF MULTI-STORY BUILDINGS THROUGH HYBRID TESTING

The present dissertation introduces an innovative numerical updating approach within fully simulated hybrid testing with substructuring techniques through collapse. The proposed approach is based on utilizing the measured response from the experimental substructure to update during the test the parameters of the components of the numerical substructure. The main research objective is to improve the ability to predict and simulate collapse through hybrid testing with substructuring techniques. The proposed numerical updating approach demonstrates to be capable of reliably reduce the epistemic uncertainty existent on the calibration of initial component parameters of the numerical substructure, especially when the system is near the limit state of collapse

Performance of shape memory alloy rehabilitated bridge columns under sequential earthquakes

While civil infrastructure systems have played a pivotal role in the provision of essential services and facilities for human life and public society, weaknesses of the systems to natural and man-made hazards has emerged as a major public concern. As a way to improve the resilience and sustainability of the current and future infrastructure systems, utilization of new, smart materials such as shape memory alloy (SMA) in civil engineering application has been drawing keen attention of industry and academia. Among many, active confinement technique using SMA’s shape memory effect (SME) demonstrated a great potential in retrofitting and/or repairing seismically deficient RC bridge columns. In order to gain recognition as an effective seismic retrofit/repair strategy and systemize its application, however, it is necessary to thoroughly study the unique behavior of this new material and its impact on the performance of the structural system under diverse circumstances. In this research, three main objectives are established. First, a series of shake table test is carried out to investigate dynamic responses of SMA retrofitted/repaired RC columns. Two reduced scale (1/6th) RC cantilever columns retrofitted or repaired with SMA spirals at the plastic hinge zones are tested under bidirectional seismic excitations at varying levels of intensity. The dynamic testing is expected to show the realistic seismic behavior of the SMA confined RC columns which were not able to be captured in the previous quasi-static cyclic loading tests. Second, this research also numerically studies the seismic performance of a SMA retrofitted multiple frame bridge when subjected to sequences of main shock-aftershock ground motions. Beyond exploring the responses of the columns at the component level, the impact of retrofitting a single or multiple columns with different levels of confinement pressure on the overall performance of the bridge is studied including interactions with other bridge components such as abutments or expansion joints. Furthermore, the seismic damage status and post-earthquake functionality of the SMA retrofitted bridge after multiple earthquake events are assessed. Lastly, an advanced evaluation method which effectively combines numerical and experimental approaches, named material testing incorporated (MTI) simulation is newly developed. In addition to seismic loading, this new method experimentally derives the realistic material behavior of SMAs at varying situations affected by chemical and/or thermal changes, and incorporates the measured data into the numerical analysis to predict the structure’s overall response