| Various external factors such as natural disasters and environmental erosion often have adverse effects on reinforced concrete beams during the service period.So reinforced concrete beams must be repaired because of insufficient concrete protective layer thickness,corroded stirrups in the beam,durability degradation and insufficient bearing capacity.Although many studies have been done on the shear reinforcement of durable degraded reinforced concrete beams at home and abroad,maintenance and reinforcement of durable degraded reinforced concrete structures is still one of the main tasks facing structural engineering,in which researches on methods and means of improving shear performance are also very important.The research on the shear behavior of reinforced concrete beams strengthened with U-shaped stirrups was still very little at present.Therefore,the strengthening technology and theory of U-shaped stirrups are still to be further studied.In this paper,the shear behavior of reinforced concrete beams strengthened with U-shaped stirrups was studied by static load failure test of 8 reinforced concrete beams and theoretical analysis.The main contents and conclusions are as follows:(1)The electrochemical corrosion mechanism of reinforced concrete beams was expounded,and the influence of corroded steels on the structures’ bearing capacity was introduced from three aspects.Introduced 4 kinds of shear analysis theory and the shear transfer mechanism of reinforced concrete beams in detail,and discussed the establishment,application condition,the mechanical relation and the features of model theory comparatively.Finally,expounded the basic reinforcement theory and main reinforcement method of reinforced concrete beams and is,and summarized the main features and the application scope of the commonly used reinforcement method.(2)The static bearing failure test of 8 reinforced concrete beams was carried out to analyze the ultimate bearing capacity,deformation capacity and stiffness’ change law of reinforced concrete beams before and after strengthening with U-shaped stirrups.The results show that the arrangement of U-shaped stirrups in this paper can inhibit the development of main oblique cracks,U-shaped stirrups can inhibit the development of inclined main cracks,delay the development of cracks,and improve the shear cracking load and ultimate shear capacity of reinforced concrete beams.Compared with the contrast beams,the average increase rate of cracking load and ultimate load was about 16%and 27%respectively.With increase of corrosion rate,shear and yield time of the beam stirrups and reinforcement stirrups were in advance.The development of stirrups pull strain in reinforced beams was lagging behind the contrast beam.The development and extension of the diagonal crack can be limited,the maximum deflection of the beams was improved effectively and the stiffness and ductility of the beams was ameliorated by reinforcement of U-shaped stirrups.(3)Based on regression analysis of experiment data about shear behaviors of reinforced concrete beams strengthened with U-shaped stirrups,the formula to calculate the shear capacity of corroded reinforced concrete beams was verified.And then obtained shear strength comprehensive impact coefficient of reinforced U-shaped stirrups by the regression fitting.A formula to calculate the shear capacity of corroded reinforced concrete beams strengthened with the U-shaped stirrups was established with the relevant literatures,and the calculated results coincidences well with the experiment results.It was shown that the formula have a certain value and can be used to estimate the shear capacity of corroded reinforced concrete beams strengthened with U-shaped stirrups,which can be used as a reference for the reinforcement design of reinforced concrete beams. |
