Analytical model for deck-on-girder composite beam system with partial composite action

In a deck-on-girder composite beam system, the deck and supporting girders work together to effectively provide loading capacity. This system has been widely used for bridges, buildings, and other structures. Effective flange width is typically used to reduce a threedimensional behavior of the composite beam system to the analysis of a T-beam section with a reduced width of deck. Current studies, including AASHTO specifications, are mainly focused on concrete decks with full-composite action. This paper presents a closed-form solution to study the composite beam system, which considers different degrees of composite action (DCAs) between the deck and supporting girders and can be applied to decks with orthotropic materials. The analytical model is verified through close correlations among test, finiteelement, and analytical results for two T-beams with concrete and fiber-reinforced polymer (FRP) decks, in terms of both deflections and stress distributions. A parametric study is then conducted by using the analytical model to study the effects of DCA, deck stiffness, and aspect ratio on effective flange width. Finally, a simplified method is proposed to analyze the composite beam system with different DCAs, which can be used for design purposes.