Experimental Study on the Mechanical Behavior of Laminated-Rubber Bearing-Concrete Interface

In small-to-medium span highway girder bridges in China, laminated-rubber bearings are typically positioned between the steel plate at the beam bottom and the concrete padstone on the pier/abutment. While relevant specifications indicate that relative sliding can occur at the bearing-steel plate interface, under certain conditions, sliding is more prone to occur at the bearing-concrete padstone interface. To investigate the mechanical behavior of this interface, reciprocating compression-shear tests were conducted under three levels of contact pressure: low (8 MPa), medium (10 MPa), and high (12 MPa). A three-phase deformation and failure mechanism was revealed, a bulging failure criterion was established, the evolution laws of the shear modulus and friction coefficient were quantified, and a friction coefficient attenuation model was developed. The results show that the bearing hysteresis curves are characterized by a parallelogram shape with internal crescent-shaped abrupt loops. Bidirectional damage transfer occurs at the bearing-concrete interface, evidenced by bulging of the rubber cover layer on the bearing and the presence of rubber debris adhered to the concrete surface. In the sliding friction stage, the shear modulus decreases with increasing contact pressure and consistently remains below the code-specified dynamic shear modulus of 1200 kPa. The interface friction coefficient, measured to be below the code-suggested values of 0.25 and 0.30, exhibits a negative correlation with the contact pressure. It is recommended to control the bearing contact pressure below 10 MPa in practical engineering to avoid the risks of a sudden drop in the friction coefficient and bulging failure. The proposed models can provide a reference for the seismic design of small-to-medium span bridges.