Concrete Cracking in Composite Bridges: Tests, Models and Design Proposals

Concrete cracking affects the durability and the mechanical behaviour of steel concrete composite bridges. The main results of an experimental and theoretical study that focused on the mechanical bahaviour of steel-concrete composite bridges under non-monotonic service loading are presented. Three 7.2 m long cracked composite beams were tested and a numerical model was developed (the Non-Linear Model). This model is used to evaluate the difference between the real behaviour of continuous composite bridges and the behaviour determined with a simple model that does not consider the influence of the cracked concrete. The tests and the Non-Linear Model demonstrate that tension stiffening of cracked concrete is counteracted, under non-monotonic service loading, by the plastic behaviour of the concrete-reinforcement bond. In addition, the coincidence of transverse reinforcement with the location of cracks as seen in tests means that the influence of the concrete between cracks on the crack widths is less than 10%. Finally, the design proposals based on this analysis that have been developed in order to be used by practising engineers are summarised.