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Concrete In Australia : March 2013
30 Concrete in Australia Vol 39 No 1 A plate type edge-lift anchor: Influence of reinforcing configurations on failure loads* Andrew Barraclough -- Doctoral Student, Curtin University of Technology Natalie Lloyd -- Senior Lecturer, Curtin University of Technology AS3850 Tilt-up Concrete Construction 1 is the current standard for design of lifting anchors and bracing in Australia. However, this standard does not provide a recommendation for calculating the capacity of edge-lifting anchors (normally placed in the edge of thin wall elements) which are commonly used in the precast industry throughout Australia. ese anchors may experience a load under tension or combined tension and shear during the lifting process. e American Concrete Institute (ACI) 318-08M Building Code Requirements for Structural Concrete 2, the Precast Concrete Institute (PCI) Design Handbook -- Precast and Prestressed Concrete 3, and Comité Euro-International Du Béton (CEB) Design of Fastenings in Concrete 4 include provisions for general anchorage configurations (such as multiple face lift anchors) rather than what are typically seen in edge-lifting anchors. Not only are anchor configurations for edge lifting anchors different from those described in these standards, but the reinforcement around the anchor can vary significantly to those denoted in standards. is paper is an evaluation of pull out test data for edge lift anchors in thin walled elements. Using the formula in the ACI 318-08M 2, developed predominantly for footed anchors, comparisons of the predicted capacity and the test pull-out capacity of the edge-lift anchors is made. Data is presented on 154 tests; the variables tested include concrete compressive strength at time of testing and the provision and arrangement of reinforcement. In addition to the edge-lift anchors, 90 face-lift footed anchors were also tested and some of the more relevant data is presented for these tests. 1.0 INTRODUCTION Edge-lift anchors (lifting inserts) are used to transfer lifting loads between steel and concrete. Unlike footed lifting anchors that have been investigated by numerous researchers worldwide, including work focused on anchoring either to reinforced or prestressed concrete 5,6,7, edge-lift anchors are relatively unexamined in published research. e most advanced knowledge regarding anchorage to concrete is included in ACI 318-08M Appendix D 2, CEB Design of Fastening in Concrete 4 and PCI Design Handbook 3. Recommended design solutions are also included in ACI 318-05 Appendix B that were meant to ensure the ductile behaviour of cast-in-place anchors 8. e ACI standard requires the tensile strength of the anchor to be less than or equal to the tensile strength of an idealised concrete cone surface Figure 1. ACI-349 Guide to the concrete capacity design (CCD) method -- Embedment design examples 9 in turn, incorporates the approaches presented in ACI 318-05 Appendix D 8. is paper summarises the pull-out failure data (under direct tension loads applied in a load controlled manner) of 154 edge-lift anchors embedded in concrete panels with and without reinforcement provided near the anchor. Various configurations of reinforcement were tested in conjunction with the edge- lift anchors; including with or without a shear bar, with or without panel mesh and with or without a perimeter bar. e configurations were chosen on the basis of common standard practice and recommendation. Grade 350, 16 mm thick edge- lift plate anchors were tested in direct tension by pull-out tests of the anchors in 150 mm thick, 2 m x 2 m panels. e tests were conducted using normal weight Portland cement concrete with a compressive strength at the time of testing of at least 10 MPa and up to 40 MPa. e minimum strength recommended for lifting is 15 MPa but lower compressive strengths were included as a lower bound that may occur in practice. e pull-out failure loads were compared to the predicted capacities as determined by design provisions provided in ACI 318-08M Appendix D (2008) 2 which have been developed from the basis of extensive footed anchor tests. 2.0 PREDICTIVE STRENGTH EQUATIONS AND THEIR HISTORICAL DEVELOPMENT Two similar methodologies exist to predict brittle tension failure of an anchor, being the 45° cone method and the concrete capacity design (CCD) method, being a square- pyramidal failure surface with 35° inclination. For the 45° cone method the concrete strength of an anchor is calculated assuming a conical surface (Figure 1) taking the slope between the failure surface and the concrete surface as 45°. As the depth of embedment of the lifting insert increases, the area of the conical section increases proportionally up to the point of full embedment. Following this capacity guideline and test data, Nelson Stud Welding 10 stated that an embedment depth of eight to 10 times the anchor shank diameter, for footed anchors, was required for the concrete breakout strength to be * is paper was first presented at Concrete 2011, the conference of the Concrete Institute of Australia. It is republished with permission.