An elastoplastic finite element formulation for the structural analysis of Truss frames with application to ha historical iron arch bridge

This doctoral thesis presents a structural analysis of the Paderno d’Adda Bridge, an impressive iron arch viaduct built in 1889 and located in Lombardia region (Italy). The thesis falls in the context of a research activity started at University of Bergamo since 2005, that is still ongoing and aims to perform an evaluation of the present state of conservation of the bridge. In fact, the bridge is currently still in service and its important position in the context of transport network will soon lead to questions about its future destination, with particular attention to the evaluation of the residual performance capacity. To this end, an inelastic structural analysis of the Paderno d’Adda bridge has been performed, up to failure. This analysis has been conducted through an autonomous computer code of a 3D frame structure that runs in the MATLAB environment and has been developed within the classical frame of Limit Analysis and Theory of Plasticity. The algorithm has been developed applying the “exact” and stepwise holonomic step-by-step analysis method. It has shown very much able to track the limit structural behaviour of the bridge, by reaching convergence with smooth runs up to the true limit load and corresponding collapse displacements. The main characteristic ingredients of its elastoplastic FEM formulation are: beam finite elements; perfectly plastic joints (as an extension of classical plastic hinges); piece-wise linear yield domains; “exact” time integration. In the algorithm, the following original features have been implemented: treatment of mutual connections by static condensation and Gaussian elimination; determination of the tangent stiffness formulation through Gaussian elimination. These peculiar contributions are presented in detail in this thesis.