Research On Working Mechanism And Design Method Of R.C.Frame Abnormal Interior Joints

Now, the joint design in the current concrete code is mainly based on the general joints' experimental data, and the abnormal joint design is just based on the designer's experience, and it is lack of perfect theoretical foundation. So, working on this kind of abnormal joints has theoretical values and practical useful values.The dissertation focuses on the research of the abnonnal frame interior joints that occur in the reinforced concrete structure of big power plants. Based on the experiment, including plane abnormal interior joints and the whole mode space abnormal interior joints, the dissertation has built separate modes and done the nonlinear finite element analyses about the plane abnormal interior joints; Through the analyses of the anti-shear properties in the joint core, working on the factors of beam section changing, column section changing, the axial compressive ratio, concrete strength, reinforcement in the joint core, and straight across beam restraining effect and so on, the dissertation has discussed the working mechanism and the failure modes of the abnormal interior joints. Controlled by the small core area, the anti-shear capacity of plane abnormal joints is rest with concrete strength, size and reinforcement of the small core area. Due to the diffusion of stress, the big core area works on the small core area with restraining effect, and the restraining effect is reflected on the area ratio of the big core and the small core, namely the restraining coefficient ξ₁ = 1.2 (A_大/A_小) -0.2 (A_大/A_小)². Compared with plane abnormal joints, space abnormal joints are still subjected to the restraining effect of straight across beams. Reference to the experimental data of abnormal joints and the research of general joints, the restraining effect can't be estimated exorbitantly. At the same time, abnormal joints may be failure in the way of four modes, namely the first kind of failure mode: shear failure in small core area; the second: shear failure in the altitudinal gap between big beam and small beam; the third: bending failure in the end of small beam; the fourth: shear failure in the small core area after the small beam yielded. The third kind of failure mode is a perfect mode, and accord with the seismic request of "strong columns and weak beams". The first and the fourth mode all happen in the small core area. Either the first or the fourth mode happening depends on the reinforcement in the joint core. In the design of abnormal joints, the first and the fourth kind of failure mode happening in the small core area and the second mode happening in the altitudinal gap between big beam and small beam all should be prevented. And either the shear failure of small core area or the altitudinal gap between big beam and small beam happens is related with the area of small core, cross area of bottom column and reinforcement in the core and column.Through the analysis of working mechanism and failure modes of interior abnonnal joints, referencing to the general joint design method, taking the complete crack as the design rule, the dissertation has put forward with advices and useful design formulas for the aseismic design of this kind of joints, in the hope of supplying reference for aseismic design in engineering.