Research On Stiffness Reduction Coefficient Of Semi-rigid Joints Of Precast Concrete Frame Structure

The development of prefabricated buildings is the mainstream of future architecture under social demand,and the nodes of prefabricated structures are constrained by the mechanical performance system to restrict the development of prefabricated joints.The application of prestressed concrete to the assembly type can effectively improve the seismic performance of the assembly structure.The nodes of the pre-compressed concrete frame structure are semi-rigid nodes,and its rigidity degradation has an important impact on the structure.At present,in the "Specifications for the Design of Concrete Structures",a uniform reduction factor is used to reduce the stiffness of the members at one time.In fact,the deterioration of the stiffness of the nodes is constantly changing according to the damage and damage accumulation of the members and materials It is necessary to carry out multistage reduction at different stages of stress.Therefore,based on the test,this paper establishes a finite element model of the results of pre-assembled concrete with semi-rigid joints,analyzes the effects of concrete,axial compression ratio,and different beam-column stiffness ratios on the stiffness degradation of the joints;analyzes repeated loads at low cycles As well as the stiffness degradation law of semi-rigid beam-column nodes in the model under frequent and rare earthquakes,it is found that the stiffness degradation is a dynamic process,and it is more practical to adopt different stiffness reduction coefficients for different stages in multiple stages.Situation;summarizes the reduction coefficients of the three stages of stiffness degradation and the relationship between the displacement angle between layers and the reduction of stiffness under the action of earthquake.The reduction factor of node stiffness under low cycle repeated load is: the stiffness reduction factor of the first stage is about 0.7;the stiffness reduction factor of the second stage is about 0.4;the third stage is Liang Kai The stiffness reduction coefficient is about 0.2;the first-stage reduction coefficient of the stiffness reduction under the earthquake is about 0.77,and the second stage is about 0.38.In summary,due to the reduction calculation with an error of less than 10% during the calculation,the rigidity reduction factor is roughly synthesized and estimated.The reduction factor in each stage: 0.7-0.8 in the first stage;0.35-0.4 in the second stage;and about 0.2 because the structure has almost failed in the third stage.The stiffness obtained by the multi-stage reduction is close to the actual degraded stiffness,which can help to study the mechanical properties of semi-rigid nodes later.