Researchers from two Australian universities are working to enhance safety and predictability in concrete construction projects by testing the strength and resistance to pull-out failure of screw anchors increasingly used in Asia-Pacific building, construction and infrastructure projects.
The researchers at Edith Cowan University (WA) and Swinburne University of Technology (Vic) are using powerful Enerpac industrial hydraulics to test, measure and accurately predict the tensile loading capacity and failure point of screw anchors used to connect structural and non-structural elements to concrete.
The series of hundreds of tests involved in the ongoing programme use an Enerpac RRH307 double-acting 30t-capacity hollow pull-cylinder mounted in a reaction frame with load cells, displacement transducers and strain gauges to measure results of multiple tests, including predicting the tensile strength of screw anchors failing under pull-out failure mode.
The test rig developed by the School of Engineering researchers from both universities is powered by an Enerpac ZU Series portable electric pump with a powerful 1.25kW universal electric motor featuring high oil flow and bypass pressure. This provides the portability, reliability and power-to-weight ratios required to conduct multiple tests to the point of bolt destruction in many cases.
The hydraulic tools involved are the same types used extensively in demanding industries using screw anchors, including building and construction; infrastructure and civil engineering; road and rail bridges and other structures; and mining, oil and gas and bulk handling facility construction and testing.
“Screw anchors are gaining popularity in construction and infrastructure because of their simplicity of installation, ability to bear load straight after installation, and ease of removal,” says Enerpac WA Territory Manager Bert Heinrich. “The universities are ensuring through their ongoing work that this trend proceeds with maximised safety, facilitated by carefully documented programmes of thorough testing from which to develop equations that predict safe load capacities using the expanding variety of screw anchors available today.”
The testing conducted by the two universities involves multiple types and diameters of screw anchors, using concrete of different compressive strengths and age. Aspects of the research compare results achieved in experiments with the predicted values of the concrete capacity design (CCD) method.
A reaction frame with a clear span of 500mm is used to support the hollow cylinder jack and a hollow load cell. According to ETAG 001-Annex A (2013), this span can be used for testing anchors with effective embedment depth of up to 125mm, say the researchers at Edith Cowan University. The Enerpac RRH cylinder involved is one of a range in capacities from 30-145t for testing, maintenance and tensioning applications.
The ZU Series electric pump used for loading is one of a broad range of Enerpac ZU portable electric pumps with two-speed pump design for rapid set up then powerful application of force. A needle valve is used to control the loading rate and to apply the load slowly. The displacement is measured using a transducer positioned on top of the head of the screw to measure displacement of the anchor relative to the concrete surface during loading.
Holes are drilled using a rotary hammer drill and anchors are installed using an impact wrench up to just before the head of the anchor reached the top of the fixture. For consistency of installation, all of the anchors are tightened using a calibrated torque wrench to a maximum permissible torque value recommended by the anchor manufacturer. The holes are cleaned using an air compressor and a vacuum before anchor installation.
The ongoing test programme has been supported by the Australian Engineered Fasteners and Anchors Council and, in WA, by a concrete supplier that provided general-purpose concrete material for the 1.4 x 1.4m slabs used there.
“This is an outstanding example of practical test work being conducted by universities working with industry to ensure the highest standards of safety and reliability in major areas of building and infrastructure engineering,” says Heinrich.
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