World Engineering Congress 2010, 2 nd 5 th August 2010, Kuching, Sarawak, Malaysia Conference on Engineering and Technology Education

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1 STRUCTURAL PERFORMANCE OF SPLICE SLEEVE CONNECTOR WITH VERTICAL AND SPIRAL REINFORCEMENT BAR UNDER DIRECT TENSILE LOAD Shuhaimi Shaedon 1, Ahmad Baharuddin Abd Rahman 2, Izni Syahrizal Ibrahim 3, Zuhairi Abd. Hamid 4 1 Master Student, Faculty of Civil Engineering, Universiti Teknologi Malaysia,81300, Skudai, Johor 2 Associate Professor, Dept. of Structure and Material, Faculty of Civil Engineering, Universiti Teknologi Malaysia, Skudai, Johor 3 Lecturer, Dept. of Structure and Material, Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81300, Skudai, Johor 4 Executive Director, Construction Research Institute of Malaysia (CREAM), Construction Industry Development Board (CIDB), Kuala Lumpur shuhaimi_z@yahoo.com.my ABSTRACT A splice sleeve connector is used to splice two reinforcement bars with their ends aligned adjacently, ensuring continuity in load transfer between them. Its tensile resistance relies on the interactions among reinforcement bars and bonding material. In this study, a series of twenty seven splice sleeve connectors with vertical and spiral reinforcement bars were tested under incremental tensile load until failure. The proposed specimens were different between each other in terms of quantity of vertical bars used and diameter of spiral. They were provided to resist the grout from slipping out of the sleeve. Their performance under direct tensile load was evaluated based on the load-displacement relationship, ultimate loading capacity, displacement and failure mode. Basically, four modes of failures were observed through the testing; (1) bar fractured, (2) bar slippage (3) grout fractured and (4) bar slippage and grout fractured as bond failed. The results show that the specimens with three and four vertical bars were better than the specimens with two vertical bars. Despite of providing interlocking effect to resist the grout from slipping out of the sleeve, these spiral and vertical bars also responded to the inclined stress that was generated due to force diversity caused by the splice bar, inducing excessive compressive stress to the sleeve connector. From the load-displacement curves and failure modes, eighteen of the specimens presented satisfactory result because of the long development length and the configuration of spiral and vertical bars had created more confinement effect to keep the grout and reinforcement intact. Finally, the understanding of the causes of failure obtained from the study provided essential information for further study in developing more reliable splice sleeve connector. Keywords: splice sleeve, vertical bar, bond, spiral reinforcement, failure mode. INTRODUCTION The behaviour of connections in a building structure can determines the performance of precast concrete structures. During erection of precast concrete structures, connections between precast component must be supervised and done properly. This way, the intended behaviour of a connection can be achieved. Currently there is a method that have been accepted to connect the precast structural members using mechanical connector. A grouted splice sleeve connector is a type of mechanical connectors that have been in use for the past two decades in North America, Europe and Japan to connect precast concrete members [1]. Some common applications of mechanical splices in precast concrete structures include column-to-base, wall-to-wall, columnto-column, beam-to-beam connections are shown in Figure 1. The splice sleeve connector can be utilized as connection system and also as alternative to the conventional bar lapping system. The splicing reinforcement bars extruded from structural element to ensure continuity among them. Mahdi Moosavi, Ahmad Jafari, Arash Khosravi, (2003) stated that bond may be defined simply as the gripping effect of an annulus (usually concrete or cement) on an embedded length of a steel bar (smooth or deformed) to resist forces tending to slide the bar longitudinally [2]. Besides, in reinforced concrete design, bond was recognized as a critical parameter because in most of the cases, the failure is not due to the excessive tension in the bar, but rather related to slip [3]. Hence, to prevent the reinforcements bar from slipping out of the sleeve, the spliced zone should be strong and able to generate bond strength that is greater than the tensile capacity of its reinforcement bars.

2 Figure 1: Application of mechanical splices (source In addition, for shear resistance, splice sleeve connectors have the advantages as its sleeve can also be utilized to resist shear force instead on relying solely onto the effective shear area contributed by the vertical reinforcement bars. Based on their tensile resistance, the feasibility of splice sleeve connectors as connection system in precast concrete structures also can be evaluated. This paper presents the tensile test results of twenty seven splice sleeve connectors. Their performance was evaluated based on their load-displacement curves, ultimate tensile capacities, corresponding displacements at ultimate states and failure modes. The feasibility and practicality of the proposed connectors in precast concrete load-bearing wall systems are examined based on the response and performance of the connector. MATERIALS AND METHODS In this study, a series of PVC pipe sleeve connectors (ES-Series) with spiral and vertical reinforcement bars was used to splice Y16 bars (reinforcing bars) as an alternative for conventional lapping system. A total of twenty seven specimens were proposed and tested experimentally under incremental tensile load. The proposed specimens were different from each other in terms of the quantity of vertical bars used and diameters of spiral. They were provided to resist the grout from slipping out of the sleeve. The proposed specimens were varied because of to study and compare the effects contributed by these parameters to the bond performance. They were also designed to trigger mechanical interlocking effect to the grout that bonded onto the reinforcement bars. Figure 2 shows the detail of the specimens tested in the laboratory. The splice sleeve connectors were made of 45 mm, 55 mm, and 65 mm diameters of spiral reinforcement bars with 4Y10, 3Y10 and 2Y10 vertical bars at each of diameters. Figure 3 shows the appearance of the connectors without the PVC pipe in the laboratory. All vertical bars were welded onto the inner of the spiral reinforcement bars surface. The anchorage length of the reinforcement bars embedded in the sleeve was fixed at 200 mm, with the total length of the connector and spiral was 400 mm. Figure 2: Details of proposed specimens

3 Figure 3: Proposed specimens in laboratory (ES-Series). Sample Preparations Figure 4 shows the preparation of the specimens before casting. A wooden frames were prepared to hold the splice sleeve connector, as well as the reinforcement bars upright to the intended positions before the filler were poured to fill the sleeve connectors. All reinforcements have been centrally inserted in a 110 mm diameter PVC pipes. The PVC pipe with the spiral and vertical reinforcements were arranged in vertical position. Before that, the bottom steel bar of Y16 were aligned at the central axis of the sleeve connector followed by the top Y16 steel bar, contacting to each other at mid span before they were tied to the wooden frames. Since the embedment length is 200 mm, hence, no gap between the two ends of the tensile bar. High strength non-shrinkage grout was mixed and poured into the splice sleeves connector to fill the spaces between the reinforcement bars and the sleeves. The grout act as a filler for load transferring material to bond the reinforcement bars, thus preventing them from slipping out of the sleeve. 6 cubes for the filler has been prepared for the compressive test to be tested at 7 days. PVC Figure 4: Preparation of specimens for casting

4 Loading and Instrumentation As the grout hardens and achieved the intended strength of at least 50 N/mm 2 at 7 days, tensile tests were carried out using DARTEC 500 kn testing machine. Figure 5 shows the setup of the hydraulic actuator for the direct tensile test. Specimens were placed vertically on the platform before applying at both ends of the reinforcements. The rate of pulling force was 0.2 kn/s throughout the testing. The data obtained from the testing consisted of load (kn) and displacement (mm) for the tested specimens. The variation of load was plotted against displacements for analysis. Figure 5: Tensile test setup RESULTS AND DISCUSSION Tensile Performance Table 1 summarizes the tensile performance of the ES-specimens under incremental load in terms of ultimate tensile capacities, P (kn), corresponding displacements at ultimate states, δ (mm), ultimate yield force, P u from BS8110 and ACI (kn), strength ratio and also the failure modes. From this test, an adequate mechanical splice should provide excellent bond that should behave similarly as a continuous steel bar. Rationally, the steel bars spliced in the sleeves should fracture outside of the sleeve instead of slipping. However, ACI 318 and AC 133 only require the minimum bond strength of least 125% of the specified yield strength of the spliced steel bars and 108% for BS 8110[4][6]. In terms of axial force and stress of the bars, the specimens that were able to sustain up to 103 kn or N/mm 2 would be considered adequate for ACI. The result shows that all the specimens with 3 and 4 vertical bars inside the spiral which is 18 specimens presented satisfactory tensile performance and had their reinforcement bars fractured before they slipped with their ultimate tensile capacities ranged from kn to kn. While for the other 9 specimens with 2 vertical bars inside had their reinforcement bars slipped, grout fractured or both with their ultimate tensile capacities ranged from kn to kn. In this test, the ultimate loading capacities of the specimens were governed by the tensile resistance of the reinforcing bars and bond capacity between the grout and the reinforcement bars. It indicates that the anchorage length with 3 or 4 vertical bars provided for splicing was adequate.

5 Specimens Failure Load, P (kn) Table 1: Tensile performance of the test specimens Displacement, δ(mm) ACI [1.25fyAs] BS 8110 [1.08fyAs] P 1.25fyAs P 1.08fyAs Failure Modes Bar slip & ES (1) Grout Fractured ES (2) Grout Fractured Bar slip & Grout Fractured ES (3) ES (1) Bar Fractured ES (2) Bar Slipped ES (3) Bar Fractured ES (1) Bar Fractured ES (2) Bar Fractured ES (3) Bar Fractured ES (1) Bar slip & Grout Fractured Bar slip & Grout Fractured ES (2) ES (3) Grout Fractured ES (1) Bar Fractured ES (2) Bar Fractured ES (3) Bar Fractured ES (1) Bar Fractured ES (2) Bar slipped ES (3) Bar Fractured ES (1) Grout Fractured ES (2) Grout Fractured ES (3) Grout Fractured ES (1) Bar Fractured ES (2) Bar Fractured ES (3) Bar Fractured ES (1) Bar Fractured ES (2) Bar Fractured ES (3) Bar Fractured Although, the configurations of the specimens were varied in terms of spiral diameters, the specimens gave similar results in terms of ultimate tensile capacities. Thus, it is recognized that the diameter of the spiral gave relatively insignificant effect to the tensile performance in this situation. The amount of vertical bars and average compressive strength of the grout of N/mm 2 had significantly enhanced the bond performance, making it possible of achieving their intended bond strength within the anchorage length of 200 mm. Therefore, the strength of the grout that bonded onto the reinforcement bars became the factor that governed the tensile performance of these specimens. Basically, the tensile capacity of the proposed specimen was governed by five major factors, as illustrated in Figure 6 and described as follows: (a) tensile capacity of reinforcement bar which lead to the bar fracture, (b) bond resistance between the grout and the reinforcement bars which will lead to the bar slippage, (c) bond resistance between the grout and the reinforcement bars and also tensile resistance of the grout which will lead to the bar slippage and grout fracture, and (d) tensile resistance of the grout which will lead to grout fracture.

6 Figure 6: Factors that governs the tensile resistance of the specimens Failure Modes and Causes Through this test, four major modes of failure were observed, namely bar slippage and grout fractured (Figure 7), grout fractured (Figure 8), bar slippage (Figure 9), and bar fractured (Figure 10). Specimens ES (1), ES (3), ES (1), ES (2), ES (3), ES (1), ES (2), ES (3), ES (1), ES (3), ES (1), ES (2), ES (3), ES (1), ES (2) and ES (3) provided excellent bond with steel bars that outperformed the tensile capacity of steel bars, and therefore, the steel bars fractured outside of the sleeves. The spliced steel bars in those specimens fractured out of the sleeves between kn and kn. It is known that the bond between the reinforcement bars and the grout was mainly contributed by the mechanical interlocking effect between the grout keys, spiral and vertical reinforcement, embedded length of the bar and the bar ribs, preventing it from slipping out of the sleeve. Many researchers, such as Clark (1946), agreed that the relative ribs area (bearing area/shear area) provides significant influence to the bond performance [5]. This is because the interaction between the steel bars and the grout is due to the interlocking effect between the bar ribs and the grout keys. The interlocking between the bar ribs and the grout keys engaged shear areas to resist the pulling force generated by the hydraulic actuator. Therefore, due to the sufficient anchorage length of reinforcement bars in the sleeve connectors, which 200 mm, and the amount and location of vertical bars use which in the inner side of the spiral reinforcement, the specimens were able to accumulate sufficient bond stress to resist the spliced bars from being pulled out of the sleeve. Therefore, the steel bars fractured when they achieved their ultimate capacity. The results indicate the importance of the bond between the spiral reinforcement and the grout that bonded onto the reinforcement bars, as it could directly influenced the tensile resistance of the specimens. Besides, specimens ES (2) and ES (2) provided slightly less efficient bond with steel bars, and therefore their steel bars slipped at high pulling forces. There were also lack of interlocking mechanism between the reinforcement bars. The spliced steel bars in both specimens, slipped out of the sleeves at kn and kn respectively. In comparison with the other specimens in this group which are (diameter=45, amount of vertical bars=3) and (diameter=55, amount of vertical bars=4) shows that the failure mode was bar fractured. It is shows that, the failure happened due to the problem in arrangement of the spiral reinforcement and vertical bars in the sleeve connectors, then the specimens were unable to accumulate sufficient bond stress to resist the spliced bars from being pulled out of the sleeve. Meanwhile, specimens ES (2), ES (3), ES (1), ES (2), and ES (3) provided less tensile resistance of the grout which will lead to the grout fractured. Figure 8 shows the failure mode of tested specimens, where its sleeve connector fractured at mid length under tensile load. The failure was due to poor tensile resistance of (a) grout, (b) spiral and vertical bars, and (c) Y16 steel bars. Therefore, insufficient vertical bars which is only two also led to inadequate shear area to resist the steel bars from slipping out of the sleeve.

7 While, for specimens ES (1), ES (3), ES (1) and ES (2) provided less bond resistance between the grout and the reinforcement bars and also tensile resistance of the grout which will lead to the bar slippage and grout fractured. These failure may happen due to poor tensile resistance of (a) grout, (b) spiral and vertical bars, and (c) Y16 steel bars will lead to grout fractured. Also, with only two vertical bars they led to bar slippage because of inadequate shear area to resist the steel bars from slipping out of the sleeve. From the observation, specimens that underwent bar fractured offered the largest tensile capacities that make them more preferable as compared to other specimens that had their bars slipped and grout fractured before achieving the bar tensile capacities. Figure 7: Bar slipped & Grout Fractured Figure 8: Grout Fractured \ Figure 9: Bar slipped Figure 10: Bar Fractured Load-displacement behaviour Figure shows the load-displacement relationship of the tested specimens, categorized into three main groups. Each group have different diameter of 45 mm (Figure 11), 55 mm (Figure 12) and 65 mm (Figure 13). A line that indicates the requirements of ACI 318 is marked at 1.25 times the specified yield strength of steel bars. The load-displacement curves describe the loading behaviour of the specimens. Ideally, the specimens should behave similarly as a continuous steel bar, enduring through stages of elasticity, yielding process, plasticity and ultimate failure.

8 Figure 11:Load displacement curve of the specimens up to 60 mm displacement (Spiral Diameter 45mm) Figure 12:Load displacement curve of the specimens up to 60 mm displacement (Spiral Diameter 55mm)

9 Figure 13:Load displacement curve of the specimens up to 60 mm displacement (Spiral Diameter 65mm) The interpretations of the load-displacement curves are discussed as follows: 1. The initial bond-slip is the immediate slip of steel bars as soon as the load is applied. In this case, negligible initial bond-slip was observed. This characteristic is essential and is preferable to prevent sudden settlement of the precast elements during installation. 2. The stiffness of the specimens is represented by the slope of the load-displacement curves before yielding. Specimens of all diameters with three and four vertical bars gave better stiffness as compared with two vertical bars because of the development load-displacement followed closely to the steel bars. Excellent bond was generated, preventing the steel bars from slipping out of the sleeves. Only two specimens fail due to bar slippage, where as the others fail due to bar fractured. The specimens with two vertical bars only presented high stiffness at the initial stage. Then, the stiffness decreased gradually after approximately 90 kn. It was due to progressive propagation of inclined cracks under less efficient grout confinement. 3. The yielding point is detected upon the first significant decrease of the stiffness of the specimens. From the graphs, the specimens started to elongate upon yielding of the spliced steel bar at the load ranging from 80 kn to 90 kn. It is essential to ensure the bond strength are always greater than the yielding strength of its reinforcing bars, as the bar yielding strengths are usually employed during analysis and design stages. 4. Ductility is the characteristic of a metallic material to endure a certain degree of deformation before failure. Generally, it is preferred that the ductile component to yield first before ultimate failure. In this study, all of the specimens except the specimens with two vertical bars, presented ductile behaviour, where their steel bars elongated for at least 10 mm to 15 mm after yielding before failure. This characteristic is essential in precast concrete structure applications, to ensure visual warnings are detected in the case of failure, particularly in terms of deformations and cracks propagations of the precast concrete elements. Ductile behaviour ensures precautions and remedies are taken immediately in case of structural failure. 5. The ultimate capacity are governed by the bar tensile capacity (bar fractured) and bar-grout bond capacity (bar slippage), of which was weaker. The tensile capacity of these specimens ranged from 110 kn to 115 kn and are higher than the 125% of specified yield strength required by the codes. Therefore, they are accepted as an adequate mechanical splice.

10 CONCLUSIONS In this study, a total of twenty seven splice sleeve connectors were tested experimentally under incremental tensile load. Their performances were evaluated in terms of load-displacement graphs, ultimate loading capacities, displacements and failure modes to determine their feasibility in actual construction. It is found that all the tested specimens were feasible except for ES (1), ES (2), ES (3), ES (1), ES (2), ES (3), ES (1), ES (2), and ES (3) due to poor ductility and low ultimate load capacity, respectively. The results shows that the proposed splice sleeve connector can be used to confine and splice two discontinuous steel bars at 200 mm, which was only 37% of the required 540 mm (35ø) specified by BS8110 [6], provided that adequate interlocking mechanism is provided to resist the grout from slipping out of the connector. It was also found that when adequate vertical bars were used they can trigger reaction from the sleeve reinforcement nearby, leading to more efficient confinement effects to enhance the bond performance. ACKNOWLEDGEMENT The authors are gratefully to CIDB (Construction Industry Development Board) and CREAM (Construction Industry Research Institute of Malaysia) for the financial support under research grant Vot The experimental programs were conducted at the Structural and Material Laboratory of Faculty of Civil Engineering, University Technology Malaysia. The contribution of the technical staff is also acknowledged. REFERENCES [1] Amin Einea, Takashi Yamane, Maher K. Tadros (1995) Grout-Filled Pipe Splice for Precast Concrete Construction. PCI Journal. [2] Mahdi Moosavi, Ahmad Jafari, Arash Khosravi, (2003) Bond of cement grouted reinforcing bars under constantradial pressure. Mining Engineering Department, Faculty of Engineering, The University of Tehran, Tehran, Iran. [3] Mahdi Moosavi, Ahmad Jafari, Arash Khosravi, (2003) Bond of cement grouted reinforcing bars under constantradial pressure. Mining Engineering Department, Faculty of Engineering, The University of Tehran, Tehran, Iran. [4] American Concrete Institute (2005). Building Code Requirements for Structural Concrete (ACI ) and Commentary (ACI 318r-05). America, ACI 318. [5] Clark, A. P. (1946). Comparative Bond efficiency of Deformed Concrete Reinforcing Bars. Proceeding of, Detroit, Michigan, ACI Journal. [6] British Standard BS :1997, Structural use of concrete Part 1: Code of practice for design and construction [7] Shaedon, S, Abd. Rahman, A. B, Ibrahim, I. S, Abd. Hamid, Z (2009) Performance of Splice Sleeve Connector with Spiral Reinforcement Bar under Direct Tensile Load. Proceedings, 2 nd Construction Industry Research Achievement International Conference, Kuala Lumpur. NOMENCLATURE P ultimate tensile capacities (kn) P u ultimate yield force (kn) δ corresponding displacements at ultimate states (mm)