Experimental Research On Behaviors Of Reinforced Concrete Beams With 500MPa Steel Bars

500MPa steel bars is a new type steel bar which has high-strength and strong ductility. This kind of steel bar has been widely used in foreign countries. But it hasn't been taken in by Code for design of concrete structures (GB 20010-2002). In order to take the internationalization into reality as soon as possible and popularize this new kind of steel bar in engineering area of our country, the experiment researches should be done on the characteristic of reinforced concrete members with such steel bars. However, such concrete beams, applying higher tensile steel as reinforcement, may appear oversized cracks which cannot satisfy the requirement for applicability and durability. Therefore, the research on the performance of such high strength reinforced concrete beams is meaningful.Based on the experimental research on reinforced concrete beams with 500MPa steel bars, the development of crack and the different factors which affect the crack width are discussed. Moreover, six groups of members with welded wire fabric near the concrete surface have been designed and compared with bending capacity, deformation and crack width. From the test results, it is indicated that this kind of members with 500MPa steel bars can work well as the common RC flexural members and the formula in Code for Design of Concrete Structures can be used to calculate bending capacity, deflection and crack width, but the calculated crack width should be calibrated. Furthermore, welded wire fabric can not only be used to control the development of crack but also make the beams to meet the limit of maximum crack width. On basis of the experimental results, using the basic calculated principle and method of concrete, a formula which can be used to calculate the bending capacity and deflection of the concrete beams with welded wire fabric safely has been given out.Further, according to the distribution character of the surface cracks of reinforced concrete beams, it is shown that the expansion process of concrete beams under load can be described with such nonlinear theories as fractal geometry. Therefore, fissure dimensions on the surface of concrete beams can be used to describe the state of cracking damage under the influence of various stresses. Moreover, a relationship has been established between the fissure dimensions and the damage variable. Therefore, fractal geometry theory can provide a new thought and method for the study of the cracking and breakage of concrete structures.Based on reasonable theoretical models and the experimental results, a formula which can be used to calculate the diagonal crack width of reinforced concrete beams has been given out. It is shown that the calculated results are feasible and safe by comparing the results between experiment and calculation.