Pseudo-dynamic test of an old R.C. highway bridge with plain steel bars - part I: Assessment of the “as-built” configuration.

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. In particular, an experimental test campaign is performed at ELSA Laboratory of JRC (Ispra, Italy). Two piers (scale 1:2.5) are tested using the PsD technique with sub-structuring; the modelling of the entire viaduct is considered along with the non-linear behaviour of each pier, due to bending, shear on the transverse beams and strain penetration effect at the column base. Comprehensive numerical investigations have shown the high vulnerability of the bridge. Consequently two isolation systems (yielding-based and friction-based bearings) have been designed. The work is subdivided in two parts: the present paper is devoted to on-going activities of “Retro” project regarding the assessment of the viaduct in the as-built configuration, whereas the second part is dedicated to the analysis of the effectiveness of isolation systems. In this paper the results of a numerical investigation and the results of PsD test confirm that the response of the pier is highly affected by the behaviours of local details. In particular, a generalized failure of the transverse beams and beam-column joints has been detected. This means that the original structure does not comply with the requirements of the modern seismic codes for the collapse limit state, particularly because of the potential for brittle shear failure in some beams of the bridge piers. Therefore seismic isolation of the bridge deck has been examined, in the companion paper, as possible protection systems