Bridge safety testing at EPFL
© Photo: Alain Herzog
To improve the method of checking freeway bridges, the doctoral student Michael Rupf is subjecting concrete beams weighing 10 tons to stress levels up to breaking point. The goal is to validate a future model for predictive calculation.
As well as microtechnology, nanotechnologies and the like, EPFL also performs practical tests of great importance, as shown by the doctoral project of Michael Rupf, from the Structural concrete Laboratory (IBETON), part of the School of Architecture, Civil and Environmental Engineering (ENAC). Commissioned by the Federal Roads Office, this research involves testing the stress resistance of pre-cast concrete beams. These tests are performed on the campus in a large hall. The objective is to develop a model of calculation that will be used in the future checking of freeway bridges.
The enormous project to construct the freeway network in Switzerland took place between 1960 and 1980, and deployed a number of bridges made of pre-cast concrete. The checking of these structures according to current Swiss standards can sometimes cause problems, as theycontain very little shear reinforcement.
What is the impact in relation to the resistance of the bridge if the load is increased; for example, to accommodate an emergency lane? Or if there is rusting in the structure? At what juncture should the bridge be reinforced?
To address these critical safety issues, le doctoral student Michael Rupf and his team are checking concrete beams in the laboratory. These bridge components are deformed by loads applied by precisely defined levels of kilonewtons. Each level corresponds to a given stress resistance. The beam is deformed up to breaking point, and every five seconds a computer measures the strength, movement and tilt of the beam.
A measurement matrix is applied to the beam. At each level, the matrix is measured to the nearest thousandth of a millimeter and the cracks are re-drawn. The data are then sent to a computer. The analysis of the measurements enables an understanding of the behavior of the specimen beam. The model developed using the experience gained will be validated by the trial data. The goal is thus to obtain and refine a robust predictive tool.
The Federal Roads Office has a significant interest in this project, because this calculation tool will allow the validation of the decision whether or not to begin large-scale and costly repair work. It is even more important because – at this point in time – very few data are available.