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This paper studies the impact of spatially varying ground motions on the responses of a railway bridge. The evaluation of the seismic hazard for a given site is to estimate the seismic ground motion at the surface. This is the result of the combination of the action of the seismic source, which generates seismic waves, the propagation of these waves between the source and the site, and the local conditions of the site. Firstly, the seismic ground motions are modelled by assuming the base rock motions of the same intensity and modelling them with a filtered Tajimi-Kanai power spectral density function and a spatial ground motion coherency loss function. Then, the power spectral density function of ground motion on surface is derived by considering the site amplification effect based on the one-dimensional seismic wave propagation theory. A comparison between the bridge responses to uniform ground motion, to spatial ground motions with and without considering local site effects is established. Discussions on the seismic ground motion spatial variability and local site conditions effects on structural responses of railway bridge are made.

This paper presents a method that allows calculating the elastic critical stress for the distortional buckling mode, based on the buckling mode classification of typical lipped channel columns. In our case, Cold-Formed Steel Lipped Channel Columns are subjected to compression. Moreover, in order to consolidate the important findings of this work, a comparative study was carried out to assess the reliability of various distortional buckling models that are provided by different design Standards. It was found that the American and Australian approaches, given in the codes of practice, are closer to the Finite Strip Method than to the European method. An analytical solution was proposed for the determination of the distortional buckling stress on the basis of a statistical method; it corresponds to lipped channel sections with a flange width to web width ratio b/h ranging from 0.1 to 1, and a lip width to web width ratio c/h between 0 and 0.5. After comparison with the results given by the finite strip method for pure distortional buckling, it turned out that the proposed approach provides a reasonable prediction for the elastic distortional buckling stress for lipped channel sections subjected to compression. In fact, this method gives better results than the American approach.

Thin-walled structures have an increasingly large and growing field of application in the engineering sector, the goal behind using this type of structure is efficiency in terms of resistance and cost, however the stability of its components (the thin walls) remains the first aspect of the behavior, and a primordial factor in the design process. The hot rolled sections are known by a consequent post-buckling reserve, cold-formed steel sections which are thin-walled elements also benefit, in this case, it seems essential to take into account the favorable effects of this reserve in to the verification procedure of the resistance with respect to the three modes of failures of this type of structure. The design method that takes into account this reserve of resistance is inevitably the effective width method. The direct strength method has been developed to improve the speed and efficiency of the design of thin-walled profiles. The latter mainly uses the buckling loads (for Local, Distortional and Global mode) obtained from a numerical analysis and the resistance curves calibrated experimentally to predict the ultimate load of the profile. Among those, the behavior of a set of Cshaped profiles (highly industrialized) is studied, this type of section is assumed to be very prone to modes of local and distortional instability. The outcome of this investigation revealed very relevant conclusions both scientifically and practically.