Mechanical and Nondestructive Testing to Verify the Effectiveness of Composite Strengthening on Historical Cast Iron Bridge in Venice, Italy

摘要

The oldest cast iron arch bridge built in 1852 in Venice exhibits serious deterioration due to corrosion and cracking of its members. The Municipality accepted a proposal to strengthen it with Aramid fiber reinforced polymers (AFRP) materials. The AFRP materials application aims to arrest cracks and reduce the structure's vulnerability to impact by boats. Tests have already been performed on structural cast iron beams taken from similar cast iron bridges dismantled. Results from four point bending tests showed an increase in strength and a different fracture mode depending on FRP application. Charpy tests showed an increased fracture energy in specimens strengthened with FRP and primer. Utilization of bidirectional and triaxial fabrics was discussed. However this paper is particularly focused on nondestructive testing following the FRP application. Nondestructive testing has been planned both for laboratory test specimens and for a long term monitoring program. Artificial defects, embedded during manufacturing in some test specimens, have been analyzed using the pulsed echo ultrasonic technique, in order to compare the resolving power of different ultrasonic frequencies and probe arrangements. Furthermore, a long term monitoring program has been planned in order to assess bonding performance using ultrasonic and pulloff tests on the overall strengthening and on some test specimens placed in the same environment.