Probability Analysis On Strong Shear Weak Bending Design Of Reinforced Concrete Frame Beam

Present-day "strong shear weak bending" design, mainly based on engineering experience, is one of important ductility assurance measures of reinforced concrete frame beam. Although some scholars try to evaluate the present-day design method by probability analysis, it is obviously defective in method and concept. Based on probability and structural reliability theory, "strong shear weak bending" design of reinforced concrete frame beam following the current seismic design code GB 50011-2001 is studied thoroughly in this thesis. It aims to know the probability of no failure in the current "strong shear weak bending" design method, and give some amendment advice on "strong shear weak bending" design method according to analysis results.The major contents are summarized as follows:(1) Reinforced concrete frame beam reliability analysis and ductility seismic design method are stated in general. The difference of ductility design method of reinforced concrete frame beam between GBJ11-89 and GB50011-2001 code is compared and analyzed.(2) The probability analysis method for "strong shear weak bending" design of reinforced concrete frame beam is presented. According to the relation between shear failure and bending failure in "strong shear weak bending", the performance function, exactly reflecting "strong shear weak bending" of reinforced concrete frame beam, is established. The probability distribution and statistical parameters of basic variables are discussed by probabilistic computation. The probability of no failure of "strong shear weak bending" design is described by reliability index.(3) For office building and housing, influences of ratio of variable load nominal value to permanent load nominal value ρ₁, ratio of representative values of gravity load to earthquake action nominal value ρ₂, ratio of real bending capacity to calculated bending capacity α and shear-enlarged coefficient η_vb on reliability index of reinforced concrete frame beam are systematically analyzed. It aims to know the reliability level in the current "strong shear weak bending" design method.(4) On the basis of calibration method, this paper evaluates the reliability level of "strong shear weak bending" design of reinforced concrete beam, and provides target reliability index for the first, second and third class beams respectively. Target reliability index can be control index adopts, in the process of probability analysis on "strong shear weak bending" design of reinforced concrete frame beam.(5) The application scope of "strong shear weak bending" design method is limited, by analyzing reliability index. Finally, the amendment of shear-enlarged coefficient of the first, second and third class beams is presented by taking account of target reliability index.Based on firm theories, the probability analysis method on "strong shear weak bending" design of reinforced concrete frame beam is presented. It overcomes the theory defect of current analysis method. Presented target reliability index can be defined as probability control criterion on "strong shear weak bending" design of beam. And the amendment of shear-enlarged coefficient will provide reference to revision of relevant state standard.