## 1 Introduction  
Compared with traditional cast-in-place structures, prefabricated structures have been increasingly used due to their environmental friendliness, low cost, and fast construction speed with the rapid development of building industrialization [1]. At present, the sleeve grouping connection is the most widely used rebar-splicing technology, since it can achieve a reliable connection between prefabricated components [2]. As shown in Figure 1a, two rebars located in a line are placed in the center of the sleeve and connected by non-shrinkage grouping material to form a whole. Since [PERSON] [3] invented the grouting sleeve technology for splicing rebars, researchers have carried out extensive experimental studies on the performance of grouted splice connectors under uniaxial tension and cyclic loads [4; 5; 6; 7; 8]. The effects of different load conditions and research parameters, such as rebar diameter, sleeve dimension, anchoring length, and grouting defects, etc., on the mechanical properties of the connectors were evaluated, and the results showed that the grouted splice connectors with reasonable design parameters met the requirements of strength, stiffness, and ductility. In order to study the reliability of grouted splice connectors in components, the seismic performance of prefabricated columns and walls connected by grouted splice connectors has been extensively investigated [9; 10; 11; 12; 13; 14; 15; 16; 17; 18], and the results showed that the prefabricated components connected with grouted splice connectors had reliable seismic performance. Furthermore, some recommendations for seismic design of prefabricated components were put forward. However, to ensure the bearing capacity of the connector, the inner diameter of the sleeve is usually small, which undoubtedly causes an increase in the difficulty of construction. Further, it is difficult to ensure the alignment of the rebars during construction, which will lead to the occurrence of grouting defects [8; 18]. Since the two rebars are discontinuous in the sleeve, the section in the middle of the sleeve is the weak part under stress. Therefore, a complicated process and more expense are required to properly treat the inner wall of the sleeve. Based on the above situation, [PERSON] [19] proposed a new type of grouted sleeve lapping connector, referred to as APC (all vertical members precast in concrete structures) connector. APC connectors are divided into two types, among which the type-I connector is composed of two overlapping rebars, grouting material, and a sleeve, as shown in Figure 1b, and the type-II connector shown in Figure 1c consists of four overlapping rebars, grouting material, and a sleeve. Due to the opposite direction of the force on the lapped rebars in the sleeve, the forces on the sleeve (grouting material) cancel each other out. Therefore, the APC connector has lower requirements on the performance of the sleeve and the grouting material, that is, the inner wall of the sleeve does not need special treatment, and the grouting material grade can be C60 instead of the traditional grouting material C80. Moreover, the inner diameter of the type-I sleeve is generally 25 mm to 30 mm larger than the diameter of the rebar. The larger gap makes the maximum aggregate particle size of the grouting material up to 4.75 mm. As a result, compared with the traditional grouted splice connector, the APC connector has the advantages of large fault tolerance, convenient construction, easy and compact grouting, and low cost. In order to explore the mechanical properties of APC connectors, [PERSON] et al. [20; 21; 22; 23] conducted uniaxial tensile tests of type-I and type-II connectors, and studied the failure mode, ultimate bearing capacity, force-displacement curve, and sleeve strain. It was recommended that the lap length of the type-I connector was 12.5 d, and the lap length of the type-II connector with the diameter of the rebar less than 25 mm was 18 d (where d is the diameter of the rebar).