R.C.DE VEKEY and K.TARR Building Research Establishment
The objective of this series of tests was to measure any change in performance resulting from relaxation associated with mechanically fixed metal expansion anchor type wall ties. Two makes of ‘expanding anchor’ type replacement wall ties were tested in tension and in compression. Tests were carried out at as soon as possible after installation
and as close as possible to 24h after installation. The ties were fixed into a wall of Fletton common bricks, representing one leaf of a cavity wall, following manufacturers’ instructions. Only a single end connection of each tie was tested. For each tie the load/displacement behaviour was measured, and four values of load capacity extracted from the data corresponding to deflections of 0.1, 0.5, I and 5mm. The value at 5mm was deemed to he the ultimate strength if the tie had not failed at a smaller deflection. Each set of test results was produced from ten tie tests. Analysis of these results showed that there was no statistically significant difference between immediate strengths and those after 24h, In the case of Type H ties in tension however, there was a larger scatter of results than is desirable and a 30% reduction of the mean ultimate strength between the Oh and 24h point. The reduction in characteristic strength was sufficient to suggest that the 24h value would be better to use in design and this experience has been embodied in advice given in the BRE Digest 401 on quality in remedial tie installation practice.