Assessment of the seismic behaviour of a retrofitted old R.C. highway bridge through PsD testing

RETRO project aims at studying the seismic behaviour of existing reinforced concrete (RC) bridges and the effectiveness of innovative retrofitting systems. A typical as-built RC highway viaduct, which was designed primarily for gravity loads, has been analysed experimentally. The objective of the laboratory test program is twofold: 1) improve the knowledge of the non-linear behaviour of RC framed piers without seismic details and 2) assess the effectiveness of seismic isolation systems as structural mitigation measures. Two large scale framed piers with two and three storeys were re-designed and tested using the PsD method with hybrid (analytical and experimentally) simulation and sub-structuring technique. Two test configurations have been considered: 1) the as-built bridge and 2) the vi-aduct retrofitted by means of Friction Pendulm (FP) isolators. The seismic per-formance evaluation has been carried out at two limit states, i.e. at serviceability and ultimate limit state. The experimental tests stressed the high structural vulner-ability of the non-conforming viaduct caused by the extensive shear damage in the transverse beams and the fix-end rotation effects generated by the bond slip of plain steel bars in the columns embedded in the foundation. The effectiveness of the isolation system with FP devices was also demonstrated. Nevertheless, the friction of the FP devices is a critical response parameter which may vary signifi-cantly because of the pressure due to the vertical loads, strong motion velocity and temperature. The reliable evaluation of the friction parameter is of paramount im-portance to prevent the onset of damage within the framed piers