Pseudo-Dynamic test of an old R.C. highway bridge with plain steel bars - part II: Investigation on the effectiveness of isolators

The “Retro” project funded by the European commission within the Series-project aims at studying numerically and experimentally the seismic behaviour of an old existing reinforced concrete bridge with portal frame piers and the effectiveness of different isolation systems. An experimental test campaign is planned to take place at ELSA Laboratory of JRC (Ispra, Italy). Two piers (scale 1:2.5) in non-isolated and isolated configuration are designed to be tested using the PsD technique with sub-structuring. The work is subdivided in two parts: the present paper is devoted to the analysis of the “isolated” configuration whereas a companion paper illustrates the results of the “as-built” case. Friction pendulum systems (FPSs) were utilized as isolation devices for the bridge continuous deck. They have been currently designed and characterized using a Direct Displacement design approach. The effectiveness of the isolated bridge has been validated through dynamic non-linear analyses both on refined and simplified numerical models of the bridge. A comprehensive numerical investigation and the results of the on-going PsD experimental activities have shown the high effectiveness of both the isolation systems in reducing the damage level of the piers, especially limiting slippage of reinforcements due to the presence of plain steel bars and the shear damage in the transverse beams, already noticed in the “as-built” configuration of the viaduct