Effects of waste tyre steel fibres on the ultimate capacity of headed studs in normal concrete

Headed shear studs are used to transfer longitudinal shear along the interface of steel and concrete. Concrete around shear studs cracks or crushes due to high bearing stress causing premature loss of shear capacity. The effects of adding waste tyre steel fibres to reduce cracking and crushing of normal concrete around shear studs in composite construction were studied. Two normal concrete classes were labelled P1 and P2, and four fibre contents, 0 %, 0.5 %, 1 %, and 1.5 % were added to both classes. Eight pushout specimens were cast for determination of the ultimate capacity of the shear studs, four for each concrete class, with all fibre contents. The test results of the shear capacity and slip capacity were compared with those from Eurocode-4 and AASHTO LRFD. Results showed that the addition of waste tyre steel fibres increased the ultimate capacity of the shear studs by 2.2 %, 9.6 %, and 5.9 % for P1-0.5, P1-1 and, P1-1.5 respectively, and by 14.7 % and 9.9 % for P2-0.5 and P2-1 respectively, as compared to their controls, and improved the failure mode of the concrete from brittle to ductile. Furthermore, the addition of 1 % fibres to class P1 concrete and 0.5 % fibres to class P2 concrete transformed the failure mode from concrete crushing to studs failure. This indicated the contribution of the fibres in preventing cracking around the localised areas of shear studs and hence enhancing the stress-bearing capacity of concrete, which in turn increased the ultimate capacity of the studs. This study, therefore, provides a solution for users of normal concrete in composite construction and shows that the equations provided by AASHTO LRFD and EC 4 can still apply to the ultimate capacity design of shear studs embedded in waste tyre steel fibre-reinforced concrete. Compared with the experimentally obtained bearing capacities, AASHTO LRFD is confirmed to be the closest and EC 4 is more conservative.