Numerical Analysis Of Mechanical Performance Of New Outsourced Joints

Adding layers to existing houses is a housing renovation technology with considerable comprehensive benefits and in line with my country’s national conditions.However,the damping of the upper and bottom structures are very different after the steel structure is added.Adding story joints play an important role in ensuring the cooperative work of upper and lower structures in earthquake.Therefore,this paper takes the new node as the research object,and carries out multi-parameter expansion analysis on its mechanical properties and failure mechanism,and deeply studies the bearing capacity calculation method and restoring force model of the joint,providing reference for the practical application of the joint.The specific research contents and results are as follows:(1)Based on the previous research on the low-cycle cyclic loading test of the new type of outsourcing joints,the finite element model of the new type of outsourcing joints was established,and the nonlinear numerical analysis was carried out.The results were compared with the existing test results from the final failure mode,skeleton curve and stiffness degradation curve.The results show that the comparison error between the seismic performance index of the finite element simulation and the test node is within the controllable range,and the modeling method is more accurate,and the accuracy of the model is higher.(2)Analysis of relevant parameters on the force of the new joint.The multi-group models of axial compression ratio,height ratio of concrete to steel column,reinforcement ratio of longitudinal reinforcement,linear stiffness ratio of beam to column and service time of existing buildings are established for parameter analysis.The analysis shows that:with the increase of axial compression ratio,the connection between the upper and lower parts is closer,and the material performance can be fully utilized.However,if the axial compression ratio is too large,the failure of the joint will be accelerated.Considering comprehensively,the axial compression ratio is 0.16～0.32.When the height ratio of outsourcing concrete to steel column is too small,cracking at the joint of upper and lower concrete The height ratio of outsourcing concrete to steel column should not be less than 0.22.The added of rebar ratio improve the ultimate load of joints,when reinforcement ratio exceeds 1.07%,it will cause the uncoordinated stress deformation of the joint and accelerate the damage of the core area of the joint.,it will cause the uncoordinated stress deformation of the joint and accelerate the damage of the core area of the joint.Reasonable beam-column linear stiffness ratio should ensure the joint function,and the recommended range is 0.24～0.33;With the gradual increase of building service time,the material performance degradation is becoming more and more serious.Therefore,it is suggested that the influence of material performance degradation on the overall performance of the building can be ignored when the new outsourcing joints are used for storey-adding transformation before the service time of the existing building reaches 28 years.(3)Research on the calculation method of bearing capacity of new outsourced joints.On the basis of the relevant parameter research,numerical fitting method is used to establish the mathematical relationship between each parameter and the joint bearing capacity,calculation method of bearing capacity of new outsourcing joints suitable for a certain range.(4)Establish a new outsourced joint resilience model.The skeleton curve and hysteresis curve data obtained by finite element simulation are extracted,and regression analysis is carried out to establish a new type of outsourcing joint restoring force model considering the structural performance degradation,which provides a reference for the whole process dynamic analysis of the joint under the action of earthquake.