Load-bearing characteristics of fibreglass uplift anchors in weathered rock

Pull-out destructive tests on six fibreglass anchors and four steel anchors for resisting the uplift of foundations in medium-weathered granite were conducted. The test results revealed two modes of shear failure for the anchors: at the interface between the anchor rod and the mortar interface (the first interface) and at the interface between the mortar and surrounding rock (the second interface). With M32.5 mortar and a 2 m anchorage length, the ultimate pull-out bearing capacity of the fibreglass anchor rods and steel rods of 28 mm diameter was 225 kN and that of fibreglass anchor rods of 32 mm diameter was 250 kN, which satisfied engineering requirements. An exponential-power-linear function model was established that better described the load-slip curves of the anchor rods. The average bond strengths at the first and second interfaces were found to be 1.50-1.54 MPa and 0.32-0.37 MPa, respectively, which were slightly lower than those for steel rods. The average bond strength at the second interface of the fibreglass anchor rods increased with the rod diameter.