Study on Tensile Mechanical Properties of Cast-In-Place Wet Joints in Steel-Concrete Composite Beam

The wet joint, a critical component in prefabricated steel-concrete composite beams (SCCBs), is typically subjected to tensile stresses during service. Consequently, its crack resistance directly governs the serviceability and durability of the SCCB. This study investigates the use of an early-strength, low-shrinkage basalt-fiber-reinforced concrete (BFRC) as a wet-joint material. Axial tensile tests were conducted on four wet-joint specimens, with crack width development, stress distribution, and cracking load monitored. A finite element model was established and validated against experimental results, and a modified formula for predicting the cracking load of BFRC slabs was proposed. The results indicated that the wet joint–precast concrete interface was the weakest link. Under increasing load, cracks initiating at this interface developed into primary cracks in the concrete deck. Compared to normal concrete, the early-strength, low-shrinkage BFRC demonstrated superior performance in enhancing crack resistance at the joint interface during the initial crack development stage, with an optimal basalt fiber volume fraction of 0.3%. The proposed cracking load formula incorporated a wet-joint influence coefficient and a fiber influence coefficient for modification. Based on experimental and finite element simulations, the joint influence coefficient was determined to be 0.725. The fiber influence coefficients were calibrated to be 0.15 and 0.045 for fiber volume fractions of 0.3% and 0.6%, respectively. Within the parameter range covered in this study, this modified formula exhibited favorable prediction accuracy for the cracking load and crack width development of cast-in-place wet joints in SCCBs under axial tension.