The Research For The Crack Spacing Of The Reinforced Concrete Beam

From the situation at home and abroad, the current study about crack is focus on the crack width and spacing of the specimens under axial tensile and pure bending moment. The research on diagonal cracks and cracks under complex forces are rare. Although a unified crack spacing formulation of specimens under axial loading and bending moment based on the"Code for design of concrete structures"of China, it's still not clear on the diagonal crack spacing and the distribution of diagonal crack along the beam height and further test research is needed to ensure the mechanism of the diagonal crack development.The main work is summarized as fowling:①19 axial tensile specimens are conducted and main focus is drawn on cover thickness, the influence of d /ρvalue on the crack spacing and the tension stiffening of reinforcement.②7 simple supported beams including one eccentric tension component are conducted and the relative test data within the literature [22][23][24] is collected. Main focus is drawn on the crack spacing distribution varied with the beam depth and the influence of shear-span ratio, d /ρvalue and stirrups on the crack spacing.③The test result is compared with various crack spacing theories and formulations in order to illustrate the utility of these theories and formulations.From the test result and analysis, it's shown that:①Concrete parcels role on the reinforcement can improve the stiffness of steel in tension, reduce the length of the yield curve platform of the stress -strain curve of reinforce. However, we can not change the yield strength of steel. The crack width changes with the cover thickness. The higher rate of reinforcement, the smaller steel stress is.②Axial tension and deep bending component's crack spacing that on the location of the reinforcement are increased with double of the cover thickness, and the diagonal crack space is one time of the cover thickness. Axial tensile component's cracks spacing decreases with the increase in the value d /ρ, decreasing trend of 0.1 times the value. But the bending crack and the diagonal crack of the bending component, the crack space don't change with the d /ρvalue, hang value 150mm. Eccentric tension component's average cracks spacing along the beam high position increased slightly higher, However, the rate of increase and concrete cover thickness not two times the relationship.③The major average crack space of the bending crack along the high position of beam are basically no changes to the constant value 150mm. The crack space of single major bending-shear crack spacing decrease along the beam high position. For the average primary diagonal cracks run below 200mm beam high position, it's crack space maintain the values of about 150mm. While the beam height is over 200mm, the crack spacing decreases along with the beam height increasing.④The prediction of crack spacing on the steel location based on the current china code is better. Bentz applies the formula of CEB-FIP for predicting the cracks spacing along the high position of beam. But their forecast results and the test had a high margin of error. This note that crack spacing and concrete cover thickness can not be directly used for predicting crack space along the high position of beam. Broms theory also applies only to axial tension component's forecasts.