Behavior of steel-plate concrete wall-reinforced concrete slab joint with UHPC-strengthened lap-splice connection

The comprehensive integration of modular technology is the crucial pathway for advancing the upgraded Hua-long Pressurized Reactor (HPR1000). However, previous studies are limited and numerous challenges remain concerning the modular curved steel-plate concrete (SC) wall-reinforced concrete (RC) slab joint. This paper focuses on the behavior and design of the SC wall-RC slab joint through large-scale tests and numerical simulation. Two UHPC-strengthened non-contact lap splice (NS) connections, including versions with normal and headed rebars, were proposed to ensure effective load transfer and modular construction performance. The test results indicated that the four joint specimens subjected to cyclic loading did not experience lap splice failure but instead suffered interface shear failure and shear failure of the RC slab under shear-span ratios of 1.5 and 3.0, respectively. The excellent load transfer performance demonstrated by these two NS connections validates them as effective methods for this joint, with lap lengths of 21d for normal rebar and 13d for headed rebar deemed adequate. Besides, the developed three-dimensional FE model with non-linear spring element accurately simulated the test failure modes and F-Δ curves. The parametric study results recommended that the volumetric steel ratio of tie-bar should not be lower than 1.03 %. The tension of longitudinal rebars for normal and headed rebars can be fully transferred within 80 % of the designed lap length. Furthermore, a complete design method was established based on the load-transfer model, encompassing interfacial shear, lap length calculation and tie-bar configuration, and is applicable to SC-to-RC connections or joints.