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Concrete In Australia : September 2013
62 Concrete in Australia Vol 39 No 3 Testing of reinforcing bar couplers By Gary Connah -- Technical Manager, Ancon Building Products 1.0 INTRODUCTION e use of reinforcing bar couplers in reinforced concrete construction is on the increase. Couplers are selected for various reasons, where lapped splices are impractical due to congestion of reinforcement, at construction joints and increasingly for practical considerations to enable buildability, thereby simplifying construction. is article provides a brief overview of the testing related to mechanical reinforcing bar couplers and the background for such tests. 2.0 LOAD TRANSFER Generally, the transfer of load between reinforcing bars is achieved by lapping or splicing the bars. e load transfer mechanism for laps is by cementitious bond. e effectiveness of lap connections is dependent upon the type of bar and the strength and quality of the concrete. Additionally, as the bars are laid side by side, the load transfer is indirect; couplers provide a direct in-line load transfer. Load testing the performance of lapped joints is expensive and time dependent, as the reinforcement has to be cast in concrete. It is therefore seldom undertaken in practice. In contrast, mechanical couplers are generally subject to extensive testing to meet the requirements of specific national standards, technical approvals or those of a state or national infrastructure owner. 3.0 TESTING AND STANDARDS e international standard ISO 158351 specifies both the technical requirements and test regimes for reinforcement couplers. is ISO standard has been adopted in part by many bodies worldwide and is combined with local requirements, resulting in a number of local standards which often demand additional or modified product testing. e standards applied in Australia and New Zealand are shown in Table 1. Additionally, reinforcing bar couplers are subject to continuous audit and product testing under quality assured technical approval schemes. e main technical requirements for reinforcing bar couplers are: • Limitation of permanent set under static forces, often referred to as slip; this is necessary to limit cracking of concrete. • Tensile strength and ductility under static forces; this is necessary to provide a factor of safety. • Cyclic loading performance; necessary for structures in seismic (earthquake) regions. • Fatigue performance; necessary for structures subjected to repeated loading, such as bridge decks. e first two are considered essential for building construction applications; cyclic and fatigue performance are additional requirements for specific structures. 4.0 PERMANENT SET All concrete structures will crack. e degree of the cracking under load is controlled by reinforcement provided by the designer. Design procedures are well-established in codes and regulations. For spliced joints the most commonly agreed limit is 0.1 mm. One current test procedure is to load a splice in tension from zero load, to a load equal to 60-70% of the reinforcing bar specified yield strength (Re), then return the load to zero (see Figure 1). e permanent set is then recorded for the splice. e measurement of permanent set is obtained by taking readings from two or three averaging Linear Variable Differential Transducers (LVDTs) over a gauge length, Figure 2. 5.0 TENSILE STRENGTH AND DUCTILITY A margin of safety against failure of a splice is required and it is also desirable that a degree of ductility is available at the splice location in a structure. Lack of ductility will result in little warning of possible sudden failure of the connection. Ductility is particularly important when designing couplers for use in structures subject to seismic loading. e properties of the reinforcing bar used in conjunction with a coupler have a direct effect on the overall performance of the splice. In Australia and New Zealand, the three ductility classes ISO 15835:2009 Steels for the reinforcement of concrete. Reinforcement couplers for mechanical splices of bars. AS 3600:2009 Concrete structures. NZS 3101:2006 Concrete Structures Standard. Part 1 The Design of Concrete Structures. AC 133:2010 Acceptance Criteria For Mechanical Connector Systems For Steel Reinforcing Bars NZTA Bridge Manual Bridge Manual (SPM022) Third edition (2013) -- Draft. RMS -- 9M3835 Approval of Mechanical Reinforcing Bar Splices. VicRoads -- BTN 2011 / 001 Bending, Splicing and Welding of Grade 500 Reinforcement. TMR Test Method Q481 Testing of Mechanical Reinforcing Bar Splices -- Draft. Table 1. Current documents with splice requirements.