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

The “Retro” project funded by the European commissi on 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 eff ctiveness of different isolation systems. An experimental test campaign is performed at ELSA Laboratory of JRC (Ispra, Italy). Two piers (scale 1:2.5) in non-isolated and isolated co nfiguration are tested using the PsD technique with sub-structuring. The work is subdivi ed in two parts: the present paper is devoted to the analysis of the “isolated” configura tion whereas a companion paper illustrates the results of the “as-built” case. Friction pendul um 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 ef fectiveness 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 inv estigation and the results of the ongoing PsD experimental activities have shown the hi gh effectiveness of both the isolation systems in reducing the damage level of the piers, specially limiting slippage of reinforcements due to the presence of plain steel b ars and the shear damage in the transverse beams, already noticed in the “as-built” configurat ion of the viaduct.