Research On Rebar Splicing System By GDPS Grout-Filled Coupling Sleeve

With the development of building and housing industrialization, many researchers have made a great deal of studies on the implementation of precast concrete constructions. The application of this type of structures in China started to emerge from the slump and improved in recent years. The reliable rebar splicing is the critical step for the seismic behavior of monolithic precast concrete structure. The reinforcing bars can be spliced by a grout-filled coupling sleeve or lapped in grout-filled hole, and the former can be used more widely due to its non-restriction by the diameter of the spliced bar, the type of the loading and the height of the building. However, nowadays the much higher cost of the grouting splice compared to the conventional coupler system used in cast-in-place structure has became one of the main factors impeding the acceptance and implementation of precast concrete structure in China.Supported by National "Twelfth Five-Year" Plan for Science and Technology (No.2011BAJ10B03), this paper dedicated to develop a novel grouting coupler and studied the structural performance, working mechanism and influencing parameters on the behavior of the grouted splice using this new coupler through experimental method and theoretical analysis. The main work and achievements are drawn as follows:1. A comparison analysis was made between different grouted sleeves fabricated by different enterprises, and also the latest development and research status of the grout-filled pipe splice technology was analyzed and concluded. Based on the above work, deficiencies of the current studies on the behavior the grouted splice were put forward and this can help to provide ideas and lay the foundation of the study on this novel grouted splice.2. A new type of grout-filled coupling sleeve was presented and named as Grouted Deformed Pipe Splice (GDPS sleeve). The sleeve was fabricated with a low-alloyed standard seamless steel pipe through cold rolling techniques. This makes the sleeve is convenient for fabrication with little waste of steels.The configuration of GDPS sleeve is featured by the concentric ribs on the inner surface and the concentric inverted trapezoid grooves on the outer surface, which can improve the bond strength between the sleeve and inner grout as well as the sleeve and surrounding concrete. Through pullout test and cyclic test, the ultimate tension load, residual deformation and distribution of the bond stress along the bonded length were studied. The test results showed that providing an embedment length of seven times of bar diameters, the strength and residual slip of the grouted splice can meet the relevant requirements specified in various codes home and abroad, and hereby the feasibility of this new coupler was verified.3. According to the variation and distribution of strains in outer surface of the sleeve, the confining mechanism of GDPS sleeve was studied. Meanwhile, based on the contact analysis theory, the load transverse process of the grouted splice was stimulated using finite element analysis program-ANSYS. The stimulation results clearly shows the distribution of the sleeve strain at axial and radial direction, and the variation of contact pressures acting on the inner concentric ribs with the increase of the pullout load. At last, this paper proposed a method for estimating the bond capacity of the spliced bar that quantitatively reflects the confining effect of the sleeve based on the test and stimulated results, and the calculated value showed a good agreement with experimental value.4. The grout working as a bonding material has great influence on the structural performance of the grouted pipe splice. Through physical and mechanical properties test, the flexural strength, compressive strength, size effect, fluidity and expansion rate of the grout were studied, and the aging strength and the relation between the compressive strength and flexural strength were also derived. Then, utilizing the thick-walled-cylinder model and the test results of the strains in the sleeve during the curing stage, the nominal elastic modulus and expansion rate, and the contact pressures between different components were calculated, and verified by the pullout test under incremental tension load. Eventually, based on the calculated elastic modulus and the thick-walled-cylinder model, the maximum sleeve diameter to wall thickness ratio, the maximum thickness of the grout layer, the relation between the sleeve diameter to wall thickness ratio and interfacial contact pressure and also the relation between the grout thickness and the contact pressure were derived.5. For the intention to study the influence of inner cavity structure and cross-sectional dimension of the sleeve, strength of the grout and embedded length of the bar on the performance of grouted splice, ninety-five splice specimens with different parameters were prepared and tested under tensile load. According to the test results of ultimate load and load-displacement curve, a parametric analysis on the structural performance of the splice was conducted. At last, a design method for the grouted splice with GDPS sleeve were proposed, including the calculation of inelastic segment length, detailing requirements of the inner cavity structure and a five-parameter empirical formula for the bond capacity of spliced bar, which shows a good agreement with experimental results.6. For the popularization and application of GDPS sleeve and to resolve construction details of the application of the grouted splice in practical engineering, the rebar stop, sealing plug and sleeve setter were developed. Meanwhile, in order to ensure the construction quality of grouted bar splicing, a series of construction technique were advanced.