Bridges

The modern procedure for concrete bridge deck analysis typically employs commercial computer programs to analyse load effects on bridge girders using the Finite Element Method (FEM). Essentially, these programs are developed based on the displacement method, predominantly calculating node displacements and converting them to load effects at the nodes or to stresses (solid work) of bridge elements. Recently, grillage models have been frequently used for concrete bridge deck analysis due to their simplicity in undertaking structural analysis. However, using grillage models for complex superstructures, such as those with super T beams and box girders, is significantly more challenging. Guidelines for developing grillage models for these girder types can be found in Edmund Hambly’s 'Bridge Deck Behaviour' (1976) and Eugene J. O'Brien et al.'s 'Bridge Deck Analysis'.

Successful grillage modelling of these superstructures necessitates numerous assumptions regarding the properties of the grillage members. For instance, in a grillage model of the bridge deck consisted of the super T girders, primary beams are located at the centroid of composite super T beams despite the voids present, and transverse deck slabs are idealised as perfect transverse members, disregarding both flanges.

While 3D solid brick element models offer the most accurate simulation of deck bridge behaviour, they are resource-intensive, demanding substantial effort in both model development and post-processing, in contrast to grillage models. For rapid structural analysis, grillage models should be employed with reasonable assumptions based on structural mechanics and a firm grasp of the underlying parameters within commercial programs. Thus, it is essential that bridge designers understand structural analysis techniques and verify load effects before use.

This paper aims to present and compare the structural analysis of live load effects and live load distributions for a super T bridge superstructure, utilising both a 3D solid brick element model and grillage models. Based on the findings, best practice approaches will be recommended for the rapid development of effective grillage models for undertaking structural analysis of this type of bridge superstructure.