# Mechanical Analysis of Ground Sleeve
## 1 Introduction
However, a strong enough bond cannot form for a smooth sleeve inner surface because of the relatively weak chemical bond between the sleeve and the grout [15]. Hence, numerous fabrication methods for sleeves have been developed to improve the bond strength between the grout and sleeve in grouted splice connectors, such as welding bars to the sleeve inner surface and tapering the sleeve head [14], threading the inner surface of the sleeve [25], and producing ribs on the interior surface of the sleeve [18; 19; 26]. The complexity of these sleeve configurations requires advanced casting technology to fabricate the sleeve. In addition, the manufacturing cost of these sleeves is relatively high. Figure 1: Sketch of the grouted splice connector. To avoid the difficulties caused by the small inner diameter of the sleeve and lower the production cost of the sleeves illustrated above, [PERSON] and [PERSON] [27] developed a grouted sleeve lapping connector. The sleeve of this connector is cut from a standard pipe section and does not require additional fabrication, which is both economical and simple to produce. In addition, its inner diameter is up to 70 cm. In the grouted sleeve lapping connector, the two main bars are lapped, and the pipe is set along with the grout around the lapping splice to provide transverse confinement. A schematic of the grouted sleeve lapping connector is shown in Figure 3. The construction process of the grouted sleeve lapping connector is similar to that of the grouted splice connector. The sleeve in the upper precast shear wall is placed onto the bar protruding from the lower precast shear wall. Thus, the two main bars are lapped. Then, grout is poured into the sleeve through the grouting hole until the pipe cavity is full. Although the grouted sleeve lapping connector offers the advantages of a large sleeve inner diameter and low sleeve manufacturing cost, it is unknown whether the tensile capacity of the grouted sleeve lapping connector is larger or smaller than that of the grouted splice connector and if there is a difference between the failure modes of the two connectors. Thus, it is meaningful and essential to conduct experimental research to study the differences in tensile capacity and failure modes between the two connectors. There are many significant typical mechanical properties of grouted splice connectors, such as the mechanism of force transfer [28], the bond stress distribution along the embedded length [13], and the confining mechanism [18]. In-depth studies of these mechanical properties have been conducted for the grouted splice connector [29; 30; 31; 32; 33; 34], which significantly promotes the application of this connector. Similarly, research on the mechanical properties of the grouted sleeve lapping connector must be conducted to provide a theoretical basis for its popularization. A previous study on the grouted sleeve lapping connector focused on its feasibility and working mechanism, and two equations were developed to calculate the average lapping bond stress and the critical lap length using linear regression [27]. Many principal mechanical properties--the load transfer mechanism, the force state on the cross section, and the bond stress distribution along the lapped bars--were not investigated. Figure 3: Sketch of grouted sleeve lapping connector. Figure 2: Incomplete fill of grout in grouted splice connector. To fill in the gaps that were left by the previous study, 16 grouted sleeve lapping connectors and three grouted splice connectors were tested under monotonic conditions. Since the subject of this research is to study the mechanical behavior of the grouted sleeve lapping connector, the test on three grouted splice connectors can be considered as a reference, in which the purpose is to conduct a comprehensive analysis of the grouted sleeve lapping connector. The differences in the tensile capacity and the failure modes between the two connectors were studied, and the origin of these differences was explored.