| Both the domestic and foreign earthquake disasters shows that reinforced concrete frame joints will be greatly horizontal shear under vertical load and seismic horizontal force, concrete is shear failure in the core area. The core area of concrete produce diagonal crack or cross crack even fragmentation, In the core area,stirrups outer drum or fracture,longitudinal reinforcement buckling into a lantern shape.Basic magnesium sulfate cement concrete has the very high tensile strength and elasticity modulus,If it is applied to bearing frame structure, can greatly improve the anti-shear capacity of joints, reduce the structural story drift, the research of joints in the framework of seismic performance is particularly important.In order to explore the feasibility of that basic magnesium sulfate cement concrete extended to the framework in the seismic area,three basic magnesium sulfate concrete beam-column interior-joints were tested by different axial compression ratiounder the low-cyclic loading to study their failure modes,hysteresis characteristics,displacement ductility, energy dissipation and stiffness deterioration.And they were compared with the same size and reinforcement Ordinary Portland concrete beam-column interior-joints.the results show:(1) When concrete strength is C30,under the same axial pressure, the secant stiffness of basic magnesium sulfate joint is about 1.25 times that of the ordinary concrete joint, biger than the stiffness of theordinary concrete joint; When the yield, the yield load is equal,but the yield displacement of the beam end of basic magnesium sulfate joint is smaller,it has better displacement ductility. After the test specimen damage, basic magnesium sulfate joint core area does not appear inclined cracks. Still has a high equivalent viscous damping coefficient. Ordinary concrete joint core area has a lot of inclined cracks, the equivalent viscous damping coefficient decline significantly.(2) Experimental results show that the bearing capacity of basic magnesium sulfate joint fully meet the beam-column joint design requirement of the code for design of concrete structure.Proved by the formula of earthquake resistant code, when the structural carrying capacity meets the design requirements, the basic magnesium sulfate frame structure of the elastic interstory drift angle is smaller, and easier to meet the requirement of the code for seismic design of buildings. Through calculating 10 th floor frame structure, compared with ordinary concrete frame structure,the basic magnesium sulfate frame structure is 11% less than ordinary concrete frame structure to resist deformation of the horizontal earthquake by higher rigidity.Under the same seismic wave, ninety-three percent of the displacement of basic magnesium sulfate frame structure is ordinary concrete frame structure, when the strength grade is C35. With strength grade from the C35 to C70,it is right by the numerical simulation of 3 d frame. eighty-three percent of the displacement of basic magnesium sulfate frame structure is ordinary concrete frame structure, when the strength grade is C70.(3) The axial compression ratio obvious influence on the seismic behavior of the Ordinary concrete joint. Too small axial compression ratio of basic magnesium sulfate joint has serious reduced pinch phenomenon,the seismic behavior is poor. Through the control of axial compression ratio of basic magnesium sulfate joint,we found that basic magnesium sulfate joint has the same situation. From the test result of hysteresis characteristics,energy dissipation, stiffness deterioration and deformation of shear angle, This paper argues that axial compression ratio of 0.24 ~ 0.4 belongs to a reasonable axial compression ratio of the basic magnesium sulfate joint, With the improvement of strength grade this advantage is more obvious. |
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