Assessment of the Seismic Behaviour of a Retrofitted Old R.C. Highway Bridge Through PsD TestingExperimental Research in Earthquake Engineering

The 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, 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 detailing and (2) assess the effectiveness of seismic isolation systems as a structural mitigation measure. Two large scale framed piers with two and three levels were re-designed and tested using the PsD method with hybrid (analytical and experimental) simulation. Two test configurations were considered: (1) the as-built bridge layout and (2) the viaduct retrofitted by means of Friction Pendulm (FP) isolators. The seismic performance evaluation was carried out at two limit states, i.e. at serviceability and ultimate limit states. The experimental tests stressed the high structural vulnerability of the viaduct, confirmed 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 significantly because of the pressure due to vertical loads, strong motion velocity and temperature. The reliable evaluation of the friction parameter is of paramount importance to prevent the onset of damage within the framed piers.