Punching of slab–column connections strengthened using external steel shear bolts

This paper describes the use and effectiveness of external steel shear bolts as shear reinforcement for retrofitting of slab–column connections in reinforced concrete (RC) flat plates and also compares the behaviour of slab–column connections with finite-element analysis. Four full-scale test specimens, representing interior slab–column connections in RC flat plates, were cast. Two concrete grades – low strength (14 MPa) and normal strength (28 MPa) – were used. One specimen for each concrete grade was used as a control and the other was strengthened using external steel shear bolts as the transverse shear reinforcement. The slab–column specimens were tested experimentally and their numerical models were analysed using Ansys. The results obtained through static non-linear analysis compared well with the experimental data. Shear strengthening of slabs changed the failure mode of the test specimens from punching shear to flexural mode and increased the ultimate load capacity of the slab–column connection by 64–73%. The shear strengthening also resulted in increased deflections and ductility. Analytical predictions of ultimate load were in good agreement with the experiments.