## 1 Introduction  
The precast concrete structure has attracted spectacular attention in the engineering field for its high quality, low cost, high construction speed and low carbon emission characteristics [1, 2, 3]. Manufactured in the factory, the precast concrete elements are assembled on site after the transportation. The industrialization ensures the quality of the element itself but the connection among different elements in situ affects the performance of the overall structure. Thus, the connections become the key to ensure the precast structure being of a high quality. The connections in precast concrete structure can be multiple, and in most cases, the connection of the steel bars is significantly important. Different methods have been advanced to process the connection of steel bars. In the late 1960s, [PERSON] proposed the grouted sleeve-splice connection [4]. Ever since that, numerous pieces of research have been conducted. The mechanical performance of grouted sleeve splice under monotonic [5, 6, 7, 8, 9] and cyclic [10, 11, 12] loading have been conducted through experimental and numerical investigations. In addition, the mechanical performance of precast concrete members connected by a grouted sleeve splice including a shear wall [13, 14, 15] and a column [16, 17, 18, 19] are studied and the results demonstrate that the structural members with grouted sleeve splice show as good a structural performance as those cast-in-place. Apart from grouted sleeve splice, [PERSON] [20] proposes the grouted spiral-confined lap connection and applies it to the steel bar connection of the precast shear wall [21; 22] and beam-column-slab joints [23]. Through experimental and numerical investigations, the structural reliability of such a connection is proved. It should be noted that the grouted sleeve splice connection and grouted spiral-confined lap connection are the most widely used connection methods in the Chinese engineering field. However, these two methods may be disadvantageous in some cases. Grouting is needed either for grouted sleeve splice or grouted spiral-confined lap connection and it is a type of concealed construction process for which the construction process cannot be supervised directly and visibly. The difficult on-site inspection can result in poor construction quality as well as grouting defects. Through experimental investigations, reduction in the tensile capacity of grouted sleeve splice due to grouting defects has been validated [24; 25]. Additionally, [PERSON] [26] discovered that the defects can post adverse effects on the mechanical performance of the overall precast concrete shear wall including the bearing capacity dropping by 32% and the energy dissipation decreasing by 35% compared with the non-defect shear wall. Reduction effects can be also observed for the precast column connected by a defective grouted sleeve splice [27; 28]. Although several methods have been proposed to detect the grouting defects such as the impact-echo method, X-ray method, damping vibration method and so on, these methods need embedded sensors or specific testing instruments with the assistance of professionals, which causes inconvenience and increases the costs during construction. Additionally, even if the defects are detected, it is difficult to repair the defects with the structures being undamaged. Overall, the unseen defects cause a challenge for detection and repair, which may impair the reliability of precast RC member behavior. Apart from the grouting defects, the construction speed of the grouted sleeve splice or grouted spiral-confined lap connection can be limited by a low construction error tolerance. The on-site connection of precast concrete members needs the lifting of, then placing the concrete members into the design position. For grouted sleeve splice or grouted spiral-confined lap connection, after lifting, the steel bars in the precast member need to plug into the sleeve or grouting holes of another precast member and this inserting process requires a high degree of accuracy in geometry.