Stress history generation for truss bridges using multi-level models

A technique is described for the automatic computation of numerical stress histories in the steel truss railway bridges, caused by the passage of pre-defined trains. The 3-D frame of the bridge is combined with finite element method plate/shell sub-models of selected details. The effects of joint rigidity and interaction of structural elements are taken into account by the global model. Joint geometry is introduced by the local sub-models. Connection nodes in the global beam model correspond to the end cross-section centroids of the sub-model. Their displacements are interpreted as imposed deformations on the sub-models. The load cases for the global model simulate the passage of two vertical unit forces along the stringers. The load cases for the sub-model are imposed unit deformations. Combining these, and applying train loads, numerical stress histories are obtained. The method is illustrated by test load results of an existing railway bridge.