Deformation capacity of over-reinforced concrete beams strengthened with highly ductile fiber-reinforced concrete

Highly ductile fiber-reinforced concrete (HDC) was applied to strengthen the compression zone of over reinforced concrete beams to improve the deformation capacity and avoid brittle failure. HDC possess the high ultimate compressive strain. This paper aims to propose a deformation-based approach for predicting the thickness of the strengthening layer to guide design. The flexural experiments on over-reinforced concrete beams strengthened by HDC were conducted. The results showed that HDC-strengthened beams failed in a ductile mode. HDC exhibited higher effectiveness in improving the deformation capacity than normal concrete (NC) with the identical thickness of the layer. The better deformation capacity can be achieved by a larger thickness of the strengthening layer in the case of ensuring the coordination work between the layer and original beams. A mechanical calculation method for the deflection corresponding to the cracking, yielding, peak, and ultimate state of the beam was presented. Comparison deflections showed that the calculated value had good agreement with the test result. Finally, the deformation-based approach for predicting the thickness of the strengthening layer was proposed. This approach ensures the deformation capacity and ductility of the strengthened beam simultaneously. It is useful in the selection of an appropriate strengthening scheme at the design stage.