Lutz Karl Heinz Hermanns

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.

Study of the effect of different hole sizes on mechanical strength of wafers for back contact solar cells

Drilling process on wafers to produce EWT or MWT solar cells is a critical fabrication step, which affects on their mechanical stability. The amount of damage introduced during drilling process depends on the density of holes, their size and the chemical process applied afterwards. To quantify the relation between size of the holes and reduction of mechanical strength, several sets of wafers have been prepared, with different hole diameter. The mechanical strength of these sets has been measured by the ring on ring bending test, and the stress state in the moment of failure has been deduced by FE simulation.

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.

Comportamiento de las fábricas no estructurales en el terremoto de Lorca

En lo que sigue se describen los efectos del terremoto del 11 de mayo de 2011 en las fachadas y particiones de los edificios de Lorca y se analiza la interaccion entre estos elementos, tradicionalmente considerados como no-estructurales, y la propia estructura. Las observaciones de campo se justifican a partir de los resultados de algunos modelos numericos simples y de todo ello se concluye la importancia fundamental de las fabricas en el comportamiento de los edificios durante el terremoto