Load-slip behaviour of L-shape rebar shear connectors in steel-concrete composite members

Abstract

In steel-concrete composite beams, at the interface between steel beam and concrete slab shear connectors are provided to resist the horizontal shear between the two components. This study presents an experimental investigation on the performance of L-shape rebar shear connector embedded in solid concrete slab through push-out test under static axial compression. The test program consists of sixteen push-out specimens. The specimens were designed to investigate the effects of height, length, diameter of the rebar connector and concrete compressive strength (40 and 50 MPa) on the shear capacity of a composite member. The experimental results are presented and discussed, focusing on the failure modes, load-slip behaviour, ultimate shear capacity, slip at the steel concrete interface and ductility of the shear connector. Two types of failure behaviour are observed from the push-out tests: shearing of connector and cracking-crushing of concrete slab. Shearing failure is observed in specimens with lower bar diameter (10 and 12 mm) and was brittle in nature as compared to the failure of specimens with larger bar diameter (16 and 20 mm). In specimens with larger bar diameter failure is caused by cracking and crushing of concrete surrounding the connector.

The ultimate capacities and slip values at failure of the push-out specimens are significantly influenced by the diameter of the rebar connectors. For specimens with 40 MPa concrete the increase in ultimate capacity was found to be 69%, 105% and 118% when the rebar diameter is increased from 10 mm to 12 mm, 16 mm and 20 mm, respectively. This improvement in capacity is found to be higher for 50 MPa concrete. Therefore, benefits of increasing the rebar diameter increases with the increment in concrete strength. It is also observed from the test that the height and length of the L-shape rebar connector do not have significant effect on the load-slip behaviour of the push-out specimens. Concrete strength has a significant effect on the shear resistance of rebar shear connector and failure mode for larger diameter bars. For 20 mm diameter connectors increasing the concrete strength from 40 MPa to 50 MPa resulted in 16% increase in the ultimate load. When the failure mode is concrete crushing, the increase in the compressive strength of concrete led to an increase in the ultimate load capacity of rebar connectors.

Moreover, the experimental results are compared to the capacity prediction equation for headed stud connectors in the AISC 360-16 specification. A modified equation is recommended for rebar shear connector incorporating a correction factor of 0.7 to the AISC 360-16 design equation of stud connector. Finally, it is recommended that, the L-shape deformed rebar connectors with diameter not less than 16 mm can be effectively used in composite beams to transfer the longitudinal shear at the steel concrete interface.