Test and evaluation of bending resistance of UHPC-grouted sleeve anchored joints

The joint is a complex bending member connecting the lining precast block, and it is also the weakest and key part of the prefabricated underground structure in the construction and operation stage. Its bending performance directly determines the bearing capacity of the structure. Based on the construction convenience and good mechanical properties of ultra-high performance concrete (UHPC) grouting sleeve connection technology, two kinds of UHPC grouting sleeve anchorage joints, symmetrical joint and staggered joint, were designed in this study. The bending performance of the joint was studied by full-scale model test and numerical method, and the contribution of three influencing factors to the ultimate bending capacity of the joint was evaluated by machine learning. The results show that the maximum opening of symmetrical joint (9.67 mm) is 1.06 times that of staggered joint (9.12 mm). Increasing the axial force can improve the bending capacity of the joint, but excessive axial force (such as 500 to 750 kN) will reduce the bearing capacity. The flexural capacity can be enhanced with the increase of concrete strength, but the deformation before failure will be reduced above C60. The Shapley Additive Explanations (SHAP) analysis indicates that the number of sleeves arranged on the tension side contributes the most to the model, accounting for 52.1%. Considering the actual compression direction of the joint in practice, increasing the number of sleeves on the tension side can reduce joint opening amount and maximize the ultimate bending capacity of the joint without additional construction time or cost.