Undercut anchorage in dimension stone cladding

Abstract

This paper analyses undercut anchorage technology, in particular its behaviour and performance as a fixing system for dimension stone cladding of rainscreen façades. Based on a number of mechanical tests using various types of Portuguese stone – three igneous, two sedimentary and one metamorphic – a study was carried out to investigate the relationship between the flexural strength and breaking load of specific and very common stone types. Several physical and mechanical characterisation tests and 130 pull-out tests with 6 and 8 mm cone bolt threads were performed to determine the pull-out load failure on six different stone types: three granite, two limestone and one marble. Finite-element stress analyses were carried out, and the test results were the basis for calibrating a simple formula that can be used to estimate the stone's breaking load at the undercut anchorage. Stress concentration factors are proposed to take into account the undercut drill hole geometry and the specific properties of each type of stone. Stone specimens from the same batches were subject to pull-out force tests using dowel anchorages, whose values were then compared with the breaking load of undercut anchorages. Results are discussed and conclusions are drawn based on tensile stress values by comparing the test results, the finite-element method and the proposed semi-empirical formulations for the same breaking load.