Prediction of load carrying capacity of bridges using equivalent SDOF system analysis

A practical approach to assessing load carrying capacity of slab-on-beam bridges is developed in this paper. This method works by transforming the actual structural system with infinite degree of freedom (DOF) into an equivalent numerical model with a single degree of freedom (SDOF), and then performing the dynamic analysis of this SDOF model. During the transformation from the structural system with infinite DOF to SDOF system, load distribution factors are first calculated using the formula suggested by AASHTO, with a materially nonlinear finite-element model. Making use of the resulting load distribution factors. analysis of the entire structural system can be simplified into the investigation on behaviour of a single key beam. Then, applying the most adverse combination of loads to the key beam, a so-called pushover curve, describing the relation of the resultant loads and the biggest deflection, and a normalized deflection curve for the assumed shape function can be derived for the Amplification of the key beam into a SDOF system-The load carrying capacity of the structural system is eventually determined by the nonlinear dynamic analysis of this SDOF system subjected to an equivalent time-dependent concentrated load, taking into account the effect of moving loads. A practical example is presented to demonstrate the detail procedure of this approach.