Mechanical behavior of composite joints for connecting existing concrete bridges and steel–concrete composite beams

In a technique of widening existing concrete bridges with steel–concrete composite beams, the old existing concrete bridge and new composite beam was connected by a composite cross beam with a composite joint. Since there have been no experimental studies on the mechanical behavior of composite joints, six specimens were tested. Based on the existing methods, the shear strength of the interface of the old and new concrete was calculated. The results showed that the shear failure of the interface between the old and new concrete is the failure mode of the composite joint and the interface between the steel plate and new concrete is always in good condition. There was nearly no slip between the old and new concrete before the bonding failure of the interface. The interface between the old and new concrete has good ductility and high strength. Based on the constitutive law of the materials, the simplified three stage mechanical model was proposed and the load–slip relationship was also predicted. Comparison between theoretical and test results has showed that the theoretical method has good accuracy. The ultimate shear strength of the interface was determined by the strength of the concrete, roughness degree and friction coefficient of the interface, and the normal stress could increase the ultimate shear strength. The residual shear strength of the interface was determined by the embedded bars, and the ratio and yield strength of the embedded bars were the main influence factors. At last the practical design method was proposed.

► The test on six composite joints was carried out. ► The theoretical model was proposed with good agreement. ► The mechanical behavior of composite joints was analyzed in detail. ► The simplified method for practical design was proposed.