Experimental Study on Shear Performance of Composite Connectors for Precast Concrete Sandwich Insulation Walls

To address the issue that traditional connectors struggle to balance mechanical and thermal insulation performance, while meeting the force transfer and thermal insulation requirements of precast concrete sandwich insulation walls, a composite thermal insulation connector composed of “steel tube-epoxy resin-rubber-cross steel bar” is designed. Taking the insulation layer thickness (75 mm, 95 mm, 115 mm) and the planar arrangement of connectors (1×1, 2×1, 3×1, 2×2) as two control variables, unilateral shear tests are conducted to systematically investigate the influence laws of the above variables on the shear performance of the connectors. The test results show that as the insulation layer thickness increases from 75 mm to 115 mm under 2×2 arrangement, the shear bearing capacity of a single connector decreases from 28.66 kN to 20.02 kN, with a maximum reduction of 30.1%. The core reason is that the extension of the cantilever segment significantly increases the bending-shear stress at the anchorage end. As the connector arrangement changes from 1×1 to 2×2, the overall interface stiffness and ultimate bearing capacity show a linear increase. Under the 75 mm insulation layer thickness, compared with the 1×1 arrangement, the stiffness of the 2×2 arrangement increases by 212%. However, affected by uneven anchorage, the average bearing capacity of a single connector decreases by a maximum of 38.2%, presenting a nonlinear relationship between “quantity and efficiency”. The insulation layer exerts a stress buffering effect through the interface bonding effect. The comparative test of group S-95-3 shows that pre-removal of the insulation layer reduces the shear bearing capacity of the specimen by 17.3%. The failure process of the connector exhibits four-stage characteristics of “microcracking-propagation-peak-failure”, and the core failure mode is a composite mode of steel tube bending-shear failure, cross steel bar pull-out, and concrete anchorage failure. The thickness of the insulation layer and the arrangement of connectors have significant influences on the shear performance of the composite connectors. It is necessary to balance the number and efficiency of connectors to ensure the interface bonding quality of the insulation layer.