Approximate bridge deck acceleration response from train loading using a spectral approach

In bridge dynamics the current practice is time domain analyses; consequently, there are specific requirements on load model formulation as well as computational intensity. This paper explores a spectral approach to evaluate bridge deck acceleration using an envelope spectrum as a moving correlated load, allowing evaluation for an ensemble of model trains rather than the traditional individual ones. Effects of bridge deck load distribution and of track defects and vehicle imperfections are included. Two loads are used as examples, the existing Eurocode high speed load model (HSLM)-A model load as well as a broad-band load in terms of a white noise. The method is applied on two bridge types, simply supported structures and short-span integral portal frames where the effect of soil–structure interaction is included. The results demonstrate that using an envelope load spectrum has potential to estimate the bridge deck acceleration levels of ordinary structures using a reduced number of simulations. In addition, it offers a potential to use spectral densities in model load development and use of measured data from real traffic. Further simplification shows that for ordinary short-span bridges, at a given damping ratio and at a given acceleration level, an approximate modal mass can be estimated.