Models for Lateral Dynamic Interaction of High-Speed Trains and Bridges

In this work a methodology for analysing the lateral coupled behavior of large viaducts and high-speed trains is proposed. The finite element method is used for the structure, multibody techniques are applied for vehicles and the interaction between them is established introducing wheel-rail nonlinear contact forces. This methodology is applied for the analysis of the railway viaduct of the R´ıo Barbantino, which is a very long and tall bridge in the north-west spanish high-speed line.

Reduction of Nutrient Losses with Eroded Sediments by Post-Fire Soil Stabilisation Techniques

After an experimental fire in steep shrub land in a temperate–humid region (north-west Spain), the effects of two post-fire stabilisation treatments (grass seeding and straw mulching) on the chemical properties of eroded sediments,and the amount of nutrients lost with them, we reevaluated relative to control burnt soil, over a period of 13 months. Total C and N concentrations, and d 13 C, indicated that sediments were mainly contributed by charred plant and litter material. The highest concentrations of extractable base cations in the sediments occurred during the first 3 months following fire, especially for Na and K. As treatments had little or no effect on nutrient concentration in sediments, differences in nutrient losses were due to the 10-fold lower sediment production in mulching compared with other treatments. In control and seeding treatments, the accumulated amounts of nutrients lost with sediments were 989–1028kgha 1 (C), 77kgha 1 (N), 1.9–2.4kgha 1 (Ca), 0.9–1.1kgha 1 (Mg), 0.48–0.55kgha 1 (NH 4 þ –N), 0.39–0.56kgha 1 (K), 0.19–0.34kgha 1 (Na) and , 0.1kgha 1 (P and NO 3 –N) . These values accounted for 22–25% (total C and N) and 5–12% (NH 4 þ –N, Ca, P and Mg) of available nutrients in ash, and 1.0–2.4% of those in ash þ topsoil. As nutrient and sediment losses were strongly correlated, the reduction of the latter by mulching application leads to an effective decrease of post-fire nutrient losses.