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Concrete In Australia : March 2013
22 Concrete in Australia Vol 39 No 1 Tensile tests on edge-lifting anchors inserted in precast concrete panels* Safat Al-Deen and Gianluca Ranzi -- School of Civil Engineering, University of Sydney Raymond Ian Gilbert -- School of Civil and Environmental Engineering, University of NSW Rod Mackay-Sim -- Unicon Systems Precast concrete panels are a cost-efficient and effective form of construction, with simple erection procedures and tight production control. Panels are usually prepared on casting moulds, either in a factory or on site. Before pouring, special devices are inserted into the moulds to be used subsequently for all lifting and handling operations of the finished panels. ese devices are usually referred to as "lifting inserts", or "lifting anchors". e common types of inserts include round-bodied anchors and, in Australia, "hairpin" plate inserts. ese are placed either on the face of a panel or on its thin-side edges (edge-lifting). Edge-lifting is preferred by the construction industry because it optimises handling, storing, transportation and erection. In this context, this paper presents an experimental study carried out to investigate the behaviour of anchors used for edge-lifting when subjected to tension. As part of this work, 12 concrete precast samples were prepared and tested using three different types of anchors. e panels had a thickness of 150 mm. e initial part of the paper describes the preparation of the samples followed by the outline of the test set-up and presentation of the experimental results, providing details on the failure modes observed during the tests. 1.0 INTRODUCTION Precast concrete solutions are widely used in the construction industry due to their simple erection procedures and tight production control. Precast concrete panels are usually prepared on casting moulds, either in a factory or on site. Special devices are inserted into the moulds before concrete pouring to facilitate all lifting and handling operations for the finished panels. ese devices are usually referred to as "lifting inserts", or "lifting anchors". e thickness of these precast wall panels is usually controlled by the requirement for the fire rating, typically 100 mm to 200 mm. ese thin panels are predominantly cast horizontally and tilted up about one edge into the vertical or near vertical position for erection. e lifting inserts are placed on the thin side edges of the panel (edge-lifting). In Australia, edge-lifting is preferred by the construction industry because it optimises handling, storing, transportation and erection. e most popular edge-lifting anchors are made from steel plate in a "hairpin" shape of length 200 mm to 400 mm, which can accommodate between the legs of the hairpin one layer of shrinkage reinforcement as commonly specified in practice. e typical preparation of a precast panel starts from the placement of the lifting anchors and reinforcement in the casting mould, followed by the pour of the concrete. After the hardening and curing of the concrete, the capping of the lifting insert is removed and the anchor is ready for use. For the actual lifting operation a specialised hook, referred to as a lifting clutch, is connected to the insert. Common lifting operations undergone by a panel include its lifting from the casting moulds at an early age of the concrete, which usually takes place by lifting it along its long edge, or prior to its final placement, in which case, for example when dealing with wall panels, it is usually rotated to be erected with its long edge vertical. ese precast walls usually serve for one or more of the following functions: (i) to provide stability to the overall structure by acting as shear walls; (ii) to carry and transfer vertical loads, and (iii) to act as protection barriers in the case of a fire 1-3. From a structural viewpoint the strength of the anchoring system is governed by either the capacity of the anchor or by failure of the concrete. Some of the factors governing its capacity include the shape of the anchor, panel geometry, location and embedment of the anchor, and the strength of concrete at the time of lifting. While extensive research has been devoted to date on the understanding of the behaviour of anchoring systems embedded in the concrete, representative for face lifting, eg 4-15, only limited work has been published to date in the open literature dealing with edge-lifting by means of "hairpin" inserts , eg 16-18. In this context, this paper presents an experimental study carried out to investigate the behaviour of anchors used for edge-lifting when subjected to tension. 2.0 EXPERIMENTAL PROGRAM 2.1 Overview e experimental setup and testing procedure were designed to reflect the stringent production schedules sometimes adopted in precast factories, in which panels poured horizontally are lifted within one day from casting into a vertical position for storage. For this reason, samples were * is paper was first presented at Concrete 2011, the conference of the Concrete Institute of Australia. It is republished with permission.