Soil-foundation compliance evidence of the “Chiaravalle viaduct”

This paper describes some notable aspects demonstrating the contribution of the soil-foundation compliance on the measured dynamic response of the Chiaravalle viaduct subjected to ambient excitations. The viaduct, linking the SS76 with the airport of Ancona (in Central Italy), is 875 m long and consists of four r.c. kinematic chains separated by joints. The deck is constituted by three beams supported by column bent piers constituted by two circular r.c. columns founded on a continuous footing on six concrete piles. Ambient vibration measurements have been performed to determine experimental natural frequencies and mode shapes of the viaduct before a scheduled seismic rehabilitation of the structure; data have been used to calibrate a numerical model for the retrofit design. Experimental modal properties are evaluated by means of Operational Modal Analysis; due to the great length of the viaduct, different configurations of sensors placed on the deck are used to evaluate the overall behavior of the viaduct and the Pre Global Estimation Re-scaling method is adopted in order to merge the different parts of mode shapes relevant to each configuration. Furthermore, with reference to the transverse behaviour, some tests are performed in correspondence of one pier, measuring accelerations of the foundation cap (both translational and rotational components) and the pier bent, in order to identify contribution to the transverse modal displacement due to the elastic deflection of the pier and the foundation rocking. Results of dynamic tests are interpreted through a 3D Finite Element model of the viaduct. Firstly, a conventional fixed base model is considered, then a model including the Soil-Structure Interaction problem is developed in order to improve consistency between numerical and experimental results. The numerical model including Soil-Structure Interaction is able to capture the foundation rocking, experimentally detected, and provides modal parameters in good agreement with the experimental ones.