The Fourth bridge over the Grand Canal in Venice: From idea to analysis and construction

The new Fourth bridge over the Grand Canal, designed by the Spanish architect Santiago Calatrava; which was recently completed in Venice, is characterized by some original solutions in the Venetian panorama of traditional bridge design. Its stunning elevation, on a single 80 m span depressed "Vierendeel" arch with a span/rise ratio of 1/16, implies an extraordinary challenge for the foundation system in the muddy Venetian soil. The cross section of the bridge presents an open star-shaped layout with a central triangular steel box girder, thus implying a remarkable torsional deformability. The loose mechanical properties of the Venetian soil, together with the peculiar intrinsic structural and geometric characteristics of the footbridge, imposed a careful revision of the original design and some modifications aimed at achieving a globally stiffer structure without any alteration to its external outfit. The footbridge was pre-assembled and loaded prior to erection trying to simulate its final condition in terms of external restraints. In this phase a monitoring instrumentation was installed in order to better investigate its response. The erection design was conceived in order to take into account the extremely bounding conditions of the project area. A set of full-scale static tests of the structure was carried out before and after the erection to check the behaviour of the bridge.