Abstract
The paper deals with the proposal and application of a procedure for the seismic retrofit of an existing multispan prestressed concrete girder bridge defined explicitly for the use of friction pendulum devices as an isolation system placed between piers top and deck. First, the outcomes of the seismic risk assessment of the existing bridge, performed using an incremental noniterative Nonlinear Static Procedure, based on the Capacity Spectrum Method as well as the Inelastic Demand Response Spectra, are described and discussed. Then, a specific multilevel design process, based on a proper application of the hierarchy of strength considerations and the Direct Displacement-Based Design approach, is adopted to dimension the FPD devices. Furthermore, to assess the impact of the FPD nonlinear behaviour on the bridge seismic response, a device model that reproduces the variation of the normal force and friction coefficient, the bidirectional coupling, and the large deformation effects during nonlinear dynamic analyses was used. Finally, the paper examines the effects of the FPD modelling parameters on the behaviour of the retrofitted bridge and assesses its seismic response with the results pointing out the efficiency of the adopted seismic retrofit solution.
Highlights
It is well known that a great portion of the Italian road system has already been built and a remarkable number of existing bridges, currently in exercise on the national road network, were designed and realized without any sort of earthquake resistant criteria
Rubber bearings have been extensively used in base isolation systems, sliding bearings with curved sliding surfaces have recently found some applications, with several studies having investigated their effectiveness in protecting bridges from damage caused by strong earthquakes
As in the previous paper [19], the procedure is firstly based on the preliminary seismic risk assessment of the bridge in existing state carried out using an incremental noniterative approach inspired by the Capacity Spectrum Method and Inelastic Demand Response Spectra proposed by Fajfar [21]
Summary
It is well known that a great portion of the Italian road system has already been built and a remarkable number of existing bridges, currently in exercise on the national road network, were designed and realized without any sort of earthquake resistant criteria. As in the previous paper [19], the procedure is firstly based on the preliminary seismic risk assessment of the bridge in existing state carried out using an incremental noniterative approach inspired by the Capacity Spectrum Method and Inelastic Demand Response Spectra proposed by Fajfar [21] This approach, following the PBEE criteria, allows directly correlating the seismic performance levels to the different intensities of seismic action. The bridge seismic retrofit according to the new seismic actions required by the current Italian Code [2] was achieved by means of a seismic protection strategy based on the use of friction pendulum device (FPD) as an isolating system placed between the top of the substructure elements and the deck With this aim, a rational approach to the design of curved-surface friction isolators for the seismic rehabilitation of the bridge was proposed and applied. The outcomes point out the feasibility and efficiency of the retrofit solution adopted and the effect of the FPD modelling parameters on the seismic response of the retrofitted bridge is discussed
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