A proposed methodology for the design and characterisation of concrete screw anchors

In recent years the construction fixings industry has begun to look to the concrete screw anchor to alleviate lengthy installation cycles and expansion issues, whilst introducing temporary fixing capability and suitability for use in cracked concrete. The screw anchor, often used in heavy-duty structural applications, operates on a mechanical interlock principle by creating a threaded cut in the substrate. Previous research has revealed this operational principle to show similarities to both expansion and chemical anchors-the two predominant fixings systems in current construction practice. Still in its infancy, the product lacks a certified test procedure and program for attaining technical approvals. This paper describes the development of an improved methodology for analysing the performance of the concrete screw anchor both physically and theoretically. Having reviewed the current test procedures, a range of products available on the market were assessed manually in the interest of developing an understanding of product operation. Standard test approaches were then customised to suit the unique product characteristics, before continuing to gather performance data. This research work then focuses upon theoretical performance calculation. Currently two theoretical models are potentially applicable to the concrete screw anchor; the concrete capacity method and the bond strength calculation method. Through comparison of the physical test data and the two current theoretical models, realisation of partial conformity with each model pointed towards promising routes for future research and a foundation for improved design of the product.