Bending Behavior Experiment of RC Beams with U-shaped Steel and Concrete Composite Reinforcement

To study the flexural performance of reinforced concrete beams strengthened with anchored U-shaped steel and concrete composite, five beams and one unstrengthened beam were designed for the bending test. The major design parameters were included loading history, longitudinal length of shaped-steel, thickness of shaped-steel and screw bolt space. The loading instrument was 1 000 kN beam-column loading system, the strains were collected by static strain analysis system, and the deflections were measured by electromechanical dial indicators. The section strains, mid-span section deflections, the slippages between shaped-steel and old concrete, cracking propagation of test beam under loads were respectively measured. Based on the assumption of plane cross-section, the formulas of bearing capacity of the test beam were derived, the results of model test and theoretical analysis were compared. The experimental results show that compared to unreinforced contrast beams, the cracking moment and ultimate bending capacity of RC beams strengthened by anchored U-shaped steel and concrete composite can be increased by 50% and 1 time respectively, The longitudinal reinforcement length of steel- plate have obvious effects on the reinforcement effect, the greater the range of reinforcement, the more significant the stiffness increase; The shear strength of the section at the truncated part of the reinforcement should be fully considered in the reinforcement scope to avoid the failure mode of the specimen from plastic bending to brittle shear failure mode; comparing the results of test beams with screw bolts spacing of 15 cm and 30 cm, it is found that as long as the screw bolts spacing meets the structural requirements, there is little influence on the bearing capacity of specimens, but certain obvious influence on the development of cracks; The closer the screw bolts spacing is, the smaller the development of cracks will be; With increase in the area of the added steel plates, the flexural bending capacity is also improved. In view of the flexural bending capacity of reinforced concrete beams by moderate destruct form, the calculation formula for the ultimate bending capacity is derived.The relative difference between the theoretical value and experimental value is within 10%. © 2020, Editorial Department of China Journal of Highway and Transport. All right reserved.