Composite action in non-composite beams

Slab-on-girder bridges were a common form of bridge construction prior to the 1960s. In the design of these structures, it was assumed that there is no interaction between the steel beams and concrete deck as no mechanical form of shear connection was used. Due to the age of these structures, and recent increases in allowable live loads, load tests have been carried on several non-composite slab-on-girder bridges in order to assess their remaining strength. The load tests show that there is a measurable degree of interaction present and that the remaining strength is greater than anticipated. Several factors not accounted for in current assessment techniques contribute to the unintentional composite action observed. Due to the absence of mechanical shear connectors, the only mechanism available to transfer the longitudinal shear forces between the steel and concrete components is friction along the interface. The results of simply supported slab-on-girder beam tests were used to isolate interface friction from the other factors contributing to the reserve strength observed. This has lead to the development of a new mathematical assessment technique referred to as the Non-Composite Mixed Analysis Fatigue Approach that is used to quantify the effect of interface friction on the remaining fatigue strength or endurance of these structures.