Pull-Out Tests on Stainless Steel Connectors for UHPC-Insulated Sandwich External Wall Panels

Ultra-high performance concrete （UHPC）， known for its high durability and excellent mechanical properties， has been increasingly applied in building external protection systems in recent years. To accommodate the requirements of such systems in different regions， a UHPC high-efficiency insulated sandwich external wall panel has been developed， in which diagonal stainless steel trusses are used as connectors between the inner and outer wall panels. To study the connection performance of these stainless steel truss connectors， six groups of pull-out specimens were fabricated. The variables considered include the height of the connectors， the embedment depth， and the influence of the placement order of the connectors. The results showed a three-stage failure progression （elastic， crack development， and failure） in the specimens. The presence of fibers effectively delayed the development of cracks in these specimens.The placement order of the connectors significantly influenced fiber distribution. Placing the connectors in place before casting the UHPC outer leaf panel effectively improved the bearing capacity of the specimens， and good ductility was observed during the failure stage. The specimens also exhibited a large safety margin. Variations in the height of the connectors had little influence on the bearing capacity and deformation capacity of the specimens. However， an increase in embedment depth from 15 mm to 20 mm raised the peak bearing capacity by 64% to 117% and enhanced the ductility by 48% to 153%， while also providing a greater safety margin.