Author(s)

D. Foppoli

Abstract

The old bridge across the Brenta River in Bassano del Grappa (Italy) is documented since 1209; the current bridge was built by Andrea Palladio in 1569 and it is described in a table of his treatise “The Four Books of Architecture”. The structure was repaired many times because of river floods and damages caused by war, but the one that is admired today is essentially the same bridge designed by the famous architect. The structure is a 5 span truss bridge, made entirely with wooden framework. In recent years significant deformations of the deck have caused concerns about its stability. In 2014 the bridge was subjected to a thorough diagnostic campaign to assess its structural conditions. An accurate survey using laser scanning provided the precise measurement of subsidence and deformation of the current structure, which were recognized as very relevant. To carry out the consequent inspection, it was necessary to have direct access to the structural elements with positioning techniques by ropes. In this way excessive overload to the already damaged bridge and limitations to the passage on the roadway were avoided. This technique also provided an economic saving for the municipality. The direct inspection has allowed close observation of the wooden trusses in order to detect sections, construction details and reinforcing elements (plates, bolts, tie rods). The visual inspection of all structural elements has provided the preliminary survey of the state of degradation of the wood, and additional direct tests were performed by a mechanical drilling instrument (Resistograph). To complete the analysis micro-sampling and macroscopic analysis allowed the identification of the species of wood.

Keywords

timber bridge, laser-scanner, drill resistance