Flexural behavior of steel-UHPC composite beams with different connectors in negative moment

This paper investigates the flexural performance of steel-ultra-high performance concrete (UHPC) composite beams with different types of connectors (normal studs and rubber-sleeve studs) and concrete types (normal strength concrete, UHPC and slag UHPC) in the negative moment region. The feasibility of the application of environmentally friendly UHPC in composite beams is analyzed and a moment-curvature calculation model for composite beams is developed. The cracking moment calculation formula is proposed based on the plane section assumption, and the reliability of the method is verified. The results show that UHPC can significantly improve the flexural performance of the structure in the negative moment region, but the change in the type of UHPC has less effect on the flexural performance. Slag UHPC reduces price, reduces environmental impact and is viable for structural applications. The rubber connectors can change the strain distribution of composite beams in the early loading period and improve the cracking resistance of composite UHPC slabs. The moment-curvature model developed in this paper can effectively identify the change characteristics of the structure during the loading process, and then determine the characteristic moment of the structure. Comparison of the equations for cracking moments shows that the cracking loads on the structure are overestimated if the interface between the concrete slab and the steel beam is assumed to be free to move.