Operating conditions of an ancient Roman bridge: inspections and vibration analysis

Object of the research activities reported within this paper is one of the best-preserved and famous roman structures of Padova: San Lorenzo bridge. It was built between 47 and 30 BC on the river Medoacus (the old flow of the Brenta river) and over its long history it was gradually incorporated into medieval and modern structures. Thanks to the archaeological excavations carried out in 1938 it was totally rediscovered and currently it is located below the modern roadway. In July 2013, after the survey of some detachments of stone from the intrados of the arch bridge, the municipality gave the task to the University of Padova to carry out an investigation campaign to study its health state. Aim of this work was to define the structural conditions of the bridge, control its degradation state and define possible actions to be implemented. Starting from historical research and geometrical survey, it was possible to investigate the past interventions and define a detailed damage pattern. Thermographic and georadar tests were per- formed confirming the high level of humidity affecting the structure due to water infiltrations. In addition, a dynamic monitoring system was installed in order to control the vibration level transmitted by the traffic on the masonry structures of the roman bridge. Time histories collected over about 20 days were processed and used for vibration analysis and verifications according to national and European standards (UNI 9916, DIN 4150). The outcomes of vibration monitoring gave the possibility to identify the type of vehicles that induce higher levels of vibrations and to control the daily and weekly intensity of traffic over the structure. The work constitutes the basis for any actions to be implemented in agreement with Padova municipality and the ministry of Cultural Heritage for an effective maintenance and conservation plan of the monument.