An experimental and numerical investigation on the cyclic response of a portal frame pier belonging to an old reinforced concrete viaduct F. Paolacci* ,† and R. Giannini Department of Structures, University of Roma Tre, Italy SUMMARY This paper deals with the assessment of the seismic response of a portal frame pier belonging to an old rein- forced concrete viaduct. A series of tests, consisting of cyclically imposed displacements, were carried out on three 1:4 scale mock-ups. The objective of the experimental campaign is twofold: (1) identification and evaluation of the local failure mechanisms and (2) calibration of a numerical model including all observed nonlinear phenomena. The experimental results show that the shear strength of the transverse beam and of the beam–column joints characterizes the post-elastic behavior of the piers. Other phenomena, like bond-slip and buckling of the longitudinal bars of the columns, typical of old reinforced concrete structures have also been observed. Finally, a numerical model, built in OpenSEES, was calibrated to reproduce in a satisfactory way the experimental results and to provide a reliable tool for the evaluation of the seismic response of the pier. Copyright © 2011 John Wiley & Sons, Ltd. Received 15 October 2010; Revised 23 August 2011; Accepted 2 September 2011 KEY WORDS: existing bridges; experimental activity; plain steel bars; cyclic response; shear modeling; bond-slip; nonlinear analysis 1. INTRODUCTION The seismic vulnerability assessment of existing and new lifeline systems, especially transportation systems, is becoming of paramount importance in resilient social communities. In Italy, majority of the highway transportation systems were built in the late 1960s and early 1970s and thus designed primarily for gravity loads. As a result, such systems do not include seismic details and hence their structural performance is frequently inadequate under earthquake ground motions. The perception of the risk associated with the seismic vulnerability of bridge structures, on the part of both authorities and professionals, is quite a recent acquisition. The first document concerning the assessment of existing bridges (‘Retrofitting Guidelines for Highway Bridges’) was published by the US Federal Highway Administration 12 years after the spectacular failures of bridges during the San Fernando earthquake of 1971 [1]. The substantial deficiencies of bridges in California shown during the Loma Prieta earthquake of 1989 induced the US Federal Highway Administration, Multidisciplinary Center for Earthquake Engineering Research (MCEER), Caltrans, and other agencies to fund other comprehensive research programs to investigate a certain number of topics related to the seismic assessment and retrofit of bridges [2, 3]. In Europe, the European standards include a document for the seismic design of new bridges, namely the Eurocode 8 Part 2 [4] but do not cover existing bridges. Within this framework, the need for a further thorough study is becoming urgent and is deemed necessary, especially on account of the strategic nature of transportation infrastructures. *Correspondence to: F. Paolacci, Department of Structures, University of Roma Tre, Italy. † E-mail: paolacci@uniroma3.it; giannini@uniroma3.it Copyright © 2011 John Wiley & Sons, Ltd. EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS Earthquake Engng Struct. Dyn. 2012; 41:1109–1127 Published online 28 September 2011 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/eqe.1175