Partial Composite-Action and Durability Assessment of Slab-on-Girder Highway Bridge Decks in Negative Bending Using Long-Term Structural Monitoring Data

This paper uses long-term bridge monitoring data to quantitatively assess the composite action exhibited in slab-on-girder highway bridges and investigates the potential relationship between composite action and deck deterioration over negative bending regions. A three-span highway bridge in Michigan is instrumented with a structural monitoring system to observe the flexural response of the spans to vehicular loads. The monitoring system is designed to offer data for quantitative assessment of the degree of composite action in composite and noncomposite sections of the bridge spans using the position of neutral axis and the magnitude of slip strain as key response parameters correlated to composite action. It is shown that unintended nonlinear partial composite action exists in negative bending regions of the bridge. A calibrated analytical model and a finite-element model are developed based on empirical observation allowing tensile strains in the deck to be estimated under load. Estimated surface strains are compared with those with the design assumption of no composite action at the slab-girder interface. It is concluded that the observed partial composite action results in higher tensile strains in the deck which is a likely culprit to accelerated deck deterioration.