Bridges

Lower bound elastic analysis of bridge deck slabs, culverts, and stiffened kerb slab bridges is commonly a conservative approach that is not often consistent with the observed abilities to support heavy vehicles. Upper bound yield line theory provides an alternative to better inform the reliability of bridges at the ultimate limit state. This paper explores these different approaches as part of the risk-informed assessment of slab bridges.

This paper presents a novel application of yield line theory developed for assessing heavy vehicle access to reinforced concrete stiffened kerb bridges. The derivation of tricky virtual work equations becomes more accessible by utilising 3D equations of the yield lines and connecting surfaces to define the rigid plastic deformed shape of yield line patterns. This facilitates the reliable automatic calculation of the internal and external virtual work, without the need to explicitly derive the virtual work equations for all yield line shapes. This also allows different yield line patterns to be readily assessed by defining the geometry of the structure, the yield lines, heavy vehicle wheel positions, and local yield strength of the elements. This geometric approach enhances the reliability of bespoke yield line models and enables different yield line patterns to be investigated efficiently.

Variations in the yield line pattern can be systematically investigated to identify the weakest failure mechanisms and build confidence that low estimates of the upper bound solutions have been identified.

The paper presents the background to traditional yield line theory and comparisons between yield line assessment and tests conducted to failure. The novel geometric method is presented and illustrated through examples from the assessment of stiffened kerb bridges for heavy vehicles of all shapes and sizes. The paper also discusses observations from the risk-informed assessment of this network and the implications for the sustainable access by heavy vehicles.