Alberto Fraile

Measuring dynamic effects on underpasses of high-speed railway lines

Underpasses are common in modern railway lines. Wildlife corridors and drainage conduits often fall into this category of partially buried structures. Their dynamic behaviour has received far less attention than that of other structures such as bridges, but their large number makes their study an interesting challenge in order to achieve safe and cost-effective structures. As ballast operations are a key life cycle cost, and excessive vibrations increase the need of ballast regulation in order to ensure track geometry, special attention is paid to accelerations, the values of which should be limited to avoid track instability according to Eurocode. In this paper, the data obtained during on site measurements on culverts belonging to a Spanish high-speed train line are presented. A set of six rectangular-shaped, closed-frame underpasses were monitored under traffic loading. Acceleration records at different points of the structures are presented and discussed. They reveal a non-uniform dynamic response of the roof-slab, with the highest observed values below the occupied track. Also, they indicate that the dynamic response is important up to frequencies higher than those usually observed for standard simply supported bridges. Finally, they are used to obtain a heuristic rule to estimate acceleration levels on the roof-slab.

A simple approach for the simulations in the mechanical studies of drilled wafers

The mechanical strength of drilled wafers, according to a EWT or MWT structure, is widely influenced by the presence of holes. In the study of the strength of these samples, the holes should be included in the simulations resulting in very heavy models with high calculation times. The traditional mechanical design for ductile materials with holes is based in the application of stress concentration factors. This method is not valid in this case due to the strength dependence on the size of the loaded area. In this paper, a stress concentration surface is proposed getting a much simpler approach for the simulations with drilled samples.