Strengthening mechanism of channel steel plate for notched concrete beams against fracture: Test and numerical study

Concrete structures are intentionally built with notches or incomplete joints in many engineering practices to deal with complex loading conditions. It is of great significance to improve the crack resistance and the installation of a channel steel plate ahead of the purpose-built notch (or joint) tip may serve such a purpose. This paper presents an investigation into the strengthening mechanism of installing a channel steel plate at the head of a notch for concrete beams against opening mode fracture failure. Both test and numerical studies have been undertaken and particular attention is given to the effects of key factors on the load carrying capacity and the failure pattern. Two types of three-point bending tests were conducted on concrete beams with or without channel steel plate reinforcement for a comparison study. The test results demonstrated the capability of channel steel plate measure for increasing the beam load capacity, and the interface debonding and matrix cracking were responsible for the eventual failure of reinforced concrete beams. Correspondingly, finite element based numerical models were established to investigate the progressive cracking in test beams and the strengthening mechanism by the installation of a steel plate. A damage-plasticity material model was used for simulating the cracking development in concrete, whilst two different approaches were adopted for the steel-concrete interface modelling: one assumed a perfect bond while the other incorporated a discrete thin layer of interface to allow for potential debonding and slippage. A comparison between the numerical and test results was given, and the effects of key factors on the performance of beams with steel plate measure were investigated through parametric numerical studies. The paper ends with some discussions on the strengthening mechanism and conclusions.