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

The Retro TA project funded by the European commission within the Series-project aims at studying the seismic behaviour of existing reinforced concrete (RC) bridges and the effectiveness of innovative retrofitting systems. The research activity focuses on old bridges, designed chiefly for gravity loads. Towards this aim, the seismic vulnerability of an old Italian viaduct with portal frame piers (Rio Torto Viaduct) is evaluated and an isolation system is designed using both yielding-based and slide spherical bearings. Some results of predictive numerical analyses, both for “as-built” and “isolated” configuration are illustrated and discussed. The work is subdivided in two parts: the present paper is devoted to the analysis of the “as-built” configuration. The structure is assessed through dynamic analyses. To do so, the Italian guidelines for the seismic assessment of existing bridges, proposed within the Reluis research program (2005-2008), are employed. Progressive damage using natural records is estimated and failure modes of the system components are accurately analyzed. The assessed systems is found sub-standard; it isthus deemed necessary to utilize an adequate retrofitting system such as seismic isolatio