Tests on two 18-years-old prestressed thin walled roof elements

The paper presents the experimental tests carried out on two prestressed thin walled V-shaped elements, used over a period of 18 years as the roof of an industrial building and removed after having exhibited marked deflections and crack patterns. The experimental program, including material characterization, impact load and ultimate static load tests, is aimed at evaluating the actual load carrying capacity of the elements. The survey of the elements geometry, with special attention to imperfections, is presented; then results of the impact load test, namely the fundamental frequencies and modal shapes of free vibration, are reported. Successively, the results of static load tests up to failure are discussed. Due to the small thickness of the cross section walls, second order effects strongly interact with the global failure mechanism. The combination of dynamic impact and ultimate static load tests allowed the calibration of an accurate finite element model, accounting for both mechanical and geometrical nonlinearities, capable to predict the behaviour of the elements up to collapse and useful to design repairing and strengthening works.