Analysis Of RC Beams Bonding Plates Reinforced By Active Unloading

A large number of bridges need reinforcement and reconstruction because of various internal and external factors and service for long time when transport construction develop rapidly. Based on loading features of RC beams, the section cracking is difficult to avoid and will cause the degradation of stiffness, capacity and durability. Engineer at home and abroad put forward a series of bridge reinforcement methods. However the methods have some defects. This paper presents active unloading reinforcement, and the mechanical properties after reinforcement are studied. The main contents are as follows.Firstly 19 groups of experiments are done with loading machine, include 17 groups of reinforced beams with different unloading degree and different plates, 2 groups of nude beams. Failure modes, mid-span deflection curves and strains of plate, steel bar, concrete were recorded in the tests. The test results showed that plate reinforcement can improve the stiffness and ultimate bearing capacity effectively, but The effect of different plate reinforcement is different obviously. The cracking load, utilization ratio of sheet and strain lag of plate of unloading specimens are better than preloading specimens. The advantages of unloading are different for different plates.Then a finite element analysis(FEA) model was established, in which the nonlinear material, glue layer, the contact behavior of concrete and glue layer and unloading degree were considered. experiment result were used to proving the precision of the FEA model and results shows well.Thirdly, the effect of initial strain on the bearing capacity and stiffness of beams were proposed through theoretical derivation. The FEA model were used to study the mechanical property of beams with plates under more unloading degrees which includes the failure mode, stiffness, the stains of concrete, plate and steel bar. The optimum unloading degree of each plate were found.Based on the experimental data, the stiffness contribution coefficient of plates were proposed, and verified by finite element calculation. It shows that the coefficient has a certain precision, and can be used in practical engineering.