Unintended composite action in beam and slab bridges

Beam and slab bridges which consist of a reinforced concrete deck and supported by steel beams are one of the most common types of highway bridges in use today. Before the advent of welding, most of these bridges were built without the use of any mechanical connectors to resist the horizontal shear at the steel-concrete interface during bending. However, reports from bridge tests have shown that composite action was found to develop in beam and slab bridges which were not compositely built. Based on the available literature and test reports on the subject, this paper attempts to investigate this phenomenon and the factors which could influence the existence of non-composite action.

The existence of natural or chemical bond was found to be the most important factor in determining whether a non-compositely built beam and slab system can be counted on to act compositely. Even though natural or chemical bond has been shown to be very effective in transmitting horizontal shear, it is also unreliable due to its susceptibility to fatigue loading, shrinkage, thermal stresses, impact, and uplift forces.