Bending Performance of Steel-Reinforced Concrete Beams Strengthened with Highly Ductile Cementitious Composites in the Compression Zone

By replacing ordinary concrete in the compressed zone with high-ductility materials, it is possible to improve the ductility of reinforced concrete beams. The effects of the properties of the materials in the compressed zone and the height of the zone on the performance of steel-reinforced concrete beams were investigated experimentally and theoretically. The performances of the steel-reinforced concrete beams strengthened with slurry infiltrated fiber concrete (SIFCON) in the compression zone were tested by four-point bending experiments. Based on an accurate validation of the experimental results, a parametric analysis using the finite strip method was conducted. The tested results show that after replacing the ordinary concrete in the compressed zone with SIFCON, the strain distribution of the concrete beam cross-section remains linear along the height, adhering to the plane section assumption. An equation was developed using a strip method, and the prediction results showed an error of less than 11% compared to the experimental data. The theoretical calculations predict that the moment–curvature relationship of the beams enhanced with high-ductility-cement-based materials aligns well with the experimental results. This study reveals that adjusting the height, initial modulus, and compressive strength of compressed zone materials effectively enhances ductility, with minimal impact on load-bearing capacity. Increasing the material strength and height improves the ultimate curvature and maximum bending moment. The elastic modulus of the compressed zone has a greater effect on the ultimate curvature than on the maximum bending moment. With a replacement of the compressed zone height of 60 mm (section height 300 mm), the ultimate curvature increases by 177% when the elastic modulus of the material is increased by 2.5 times. The present study provides a calculation method for the retrofitting and reinforcement of over-reinforced concrete beams.