# Mechanical Analysis of Ground Sleeve
## 1 Introduction  
Compared to cast-in-situ concrete structures, precast concrete structures have the advantages of design-build efficiency, aesthetical versatility, reduced costs, low maintenance, and superior resistance to disasters [1; 2; 3; 4]. However, many long-standing issues of precast structures, such as the defects of the connectors between precast components, always cause difficulties in the construction procedure and safety hazard under service as well as disasters. Although these issues need comprehensive research, most of the existing investigations are related to cast-in-situ structures and the studies on precast structures, especially those that focus on the connectors of precast structures, which have yet to be sufficient. To guarantee the performance of precast concrete structures, the reinforcement bars in components of the structures need to be well spliced. Thus, the grouted splice connector has been widely studiedby researchers from all over the world [5; 6; 7; 8]. For instance, [PERSON] et al. [9] investigated the grouted splice connector, which connected a reinforced precast concrete bridge pier cap and a precast column in America. [PERSON] et al. [10] studied the dynamic response of precast concrete beams connected by the grouted splice connector in China. [PERSON] and [PERSON] [11] conducted an experimental research on the behavior of precast reinforced concrete column-to-column connections made with grouted sleeve splices in Italy. [PERSON] et al. [12] studied the behavior of the precast concrete wall panels, which was connected by a grouted splice connector in Malaysia. Figure 1 is a sketch of a vertically-connected precast concrete shear wall system with a grouted splice connector. A sleeve is embedded at the bottom of the upper precast shear wall in advance during the fabrication process. In the field, the sleeve is placed onto the bar protruding from the top of the lower precast shear wall. Then, grout is poured into the sleeve through the grouting hole until the sleeve is full [13]. The spliced bars must be aligned and positioned at the center of the sleeve for the tensile capacity of the connector to develop fully [14]. The force in one bar is transferred from the grout to the sleeve, and, by the same way, to the other bar [15]. Thus, the grout in the sleeve plays a critical role in force transfer. Therefore, it is essential to completely fill the sleeve inner cavity with grout. According to the specification _JGJ 355-2015_[16], for bars with diameters of 12-25 mm and 28-40 mm, the minimum differences between the sleeve inner diameter and the bar diameter are 10 mm and 15 mm, respectively. However, most sleeve inner diameters designed by practitioners are less than 50 mm [17; 18; 19; 20], since a smaller sleeve diameter will provide sufficient confinement to achieve a higher bond strength between the bar and the grout, which increases the tensile capacity [21; 22]. However, a small sleeve inner diameter always creates difficulties in on-site construction. One problem is that insufficient space between the bar and the sleeve cavity will cause an incomplete fill of grout (Figure 2), which weakens the ability of the connector to transfer force. There is a more serious secondary problem. The protruded bar inevitably leans during transportation and construction. Usually, construction workers need to exert force to correct the inclination of the bar so that the bar can be inserted into the sleeve to align with the other bar. However, when the angle of the incline of the bar is relatively large, and the sleeve inner diameter is relatively small, some workers choose to cut off the inclined bar for ease of construction, which severely weakens the connection performance of the splice. Grout-sleeve bond failure is a typical but undesirable failure mode in grout splice connector [23; 24]. Sufficient bond strength is required between the grout and the sleeve to avoid the slippage of grout from the sleeve.