Modal identification of a prestressed concrete bridge through ambient vibration tests

The results of modal identification and finite element model updating of an existing precast concrete (PC) bridge are presented. The aim of the study is to discuss the influence of prestress on the natural frequencies of the structure in the framework of linear isotropic homogeneous elasticity and geometric nonlinearity. To this end, an experimental campaign has been carried out on an existing PC bridge, consisting of two ambient vibration tests carried out to measure the vertical accelerations of the deck induced by traffic. The modal parameters of the structure have been identified by means of the classic Enhanced Frequency Domain Decomposition (EFDD) method. The results of the model updating, performed via a first order optimization technique, allow pointing out the sensitivity of the structural modal properties with respect to variations of the relevant design parameters including the prestressing force.