2.5 Effect of flexural cracking on plate end shear stress in FRP-strengthened beams

For concrete beams strengthened with bonded FRP plates, failure often occurs as a result of local delamination at the end of the plate. Conventionally, such a failure mode has been ascribed to the presence of stress concentrations at the plate cut-off point, leading to failure of concrete in its vicinity. In the literature, various models have been developed to compute the elastic shear and normal stresses at the plate, and different failure criteria have been proposed. However, the predicted failure loads based on plate end shear and normal stresses are often in poor agreement with experimental data. This is due to the assumption of perfectly elastic behaviour up to the ultimate failure load. In reality, flexural cracking often occurs along the concrete beam, causing significant changes in the stress distribution at the FRP/concrete interface. In this work, experimental and analytical results will be presented to illustrate the change of interfacial stress distributions as loading is increased to induce flexural cracks beyond the end of the plate. Based on observations from the results, we found that the average shear stress over a given distance from the plate end could be a parameter governing delamination failure. An approximate method to calculate such an average stress was proposed. The computed values of critical shear stress were found to be similar for tested beams of various sizes.

• INTRODUCTION

• EFFECT OF CRACKING ON PLATE END STRESSES

• DISCUSSION

• AN APPROXIMATE METHOD TO CALCULATE THE AVERAGE PLATE END SHEAR STRESS

• PREDICTED AVERAGE SHEAR STRESSES AT FAILURE BY THE APPROXIMATE METHOD

• CONCLUSION

• REFERENCES