Mixed steel-concrete structures are very interesting and attractive to bridge engineers, who are eager to promote technological innovation. In cable stayed bridges, the ratio of the side spans to center span becomes extremely small, and this causes negative reaction at the side spans. To alleviate this problem, mixed structures composed of steel girders for center span to minimize its dead loads and reinforced or prestressed concrete girders for side spans as counterweights have been recently proposed. Further, the idea had been successfully implemented for Normandie bridge in France and Tatara bridge in Japan.
The purpose of this work is to provide a general nonlinear finite element model to analyze the mechanical joints for mixed structural systems. Two-dimensional plane stress elements having two degrees of freedom at each node are used to idealize both steel and concrete components. Line interface elements having both normal and shear stiffnesses are placed at the interface between steel and concrete elements. The steel elements are modeled using an elastic-perfectly plastic model with a Von Mises yield criterion. The concrete behavior under compression is modeled using an elasto-plastic model with a Drucker-Pager yield criterion and associated flow rate. The concrete in tension is modeled using a smeared cracking model with tension cut-off, tension softening and variable shear retention. Analytical models for three mechanical joints are investigated in this paper. The analytical results are compared with the experimental ones. The comparison shows that the proposed model is accurate enough to predict the behavior of the mechanical joints. Finally, a new mechanical joint for mixed structures is proposed.
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