Research On Mechanical Properties Of Long-span Steel Reinforced Concrete Joints With Haunch Braces

The long-span steel reinforced concrete joints with haunch braces is a new type of frame joints,which is used in the large-span frame structure.It has the following advantages:(1)The haunch braces reduces the span of the large-span beam,thereby reduces the internal force of the frame beams and columns,and the cross-sectional size and reinforcement of the beam and column.It greatly improves the mechanical performance of the joints area;(2)The application of steel reinforced concrete composite structure can effectively reduces the cross-sectional size of the component and improve the economy,while also improving the ductility and bearing capacity of the component.The joints with haunch braces is the key position in the frame structure with complex forces.The research on the mechanical performance of the joints zone is very important.Therefore,the research on the steel reinforced concrete joints with haunch braces is of great significance for the application of this new type of large-span frame structure.The main work and conclusion of this paper is as follows:(1)Two 1:2 scaled side joints specimens with column reinforcement as parameters and two 1:2 scaled middle joints specimens with beam reinforcement as parameters are designed and made.The vertical load tests of these joints specimens are carries out to study the failure morphology,failure mechanism,mechanical performance and strain characteristics of the steel reinforced concrete joints with haunch braces.(2)The vertical load test of the steel reinforced concrete joints with haunch braces is simulated and analyzed by using ABAQUS finite element analysis software.And the failure process and mechanical performance of the middle joints specimens are analyzed from the loaddeflection curve,the deformation characteristics,the concrete damage degree and the stress and strain state of the rebar and steel during the failure process of the specimens.The simulation results are compared with the experimental results to verify the correctness of the numerical model.(3)The tests and finite element analysis results show that the joints specimens has good bearing capacity and ductility performance.The phenomenon of faster development of oblique cracks or faster development of bending cracks occurred during the development process of specimen failure and cracks,which corresponds to the design of reinforcement.The structural failure is mainly concentrated on the intersection of beam and braces of middle joints specimens and the intersection of column and braces of side joints specimens,where is the most unfavorable cross-section of the specimen appears.The strain of rebar and steel and the degree of concrete damage in the joints zone are all very small.It can be seen that the haunch braces are the main force-transmitting member between the beam and the column to transfer the load on the beam to the column,which "weakens" the role of the beam-column joints zone,significantly improves the mechanical performance of the beam-column joints zone,and can easily meet the principle of "stronger joints" in the design.The design of the haunch brace is safe during the entire loading test with the surplus bearing capacity.It has room for optimization.(4)The expansion parameter analysis of the numerical model of long-span steel reinforced concrete joints with haunch braces is carried out to consider the influences of concrete strength,the steel yield strength,the ratio of longitudinal reinforcement of the beam,the ratio of stirrups of the beam,the steel thickness of the web and flange of the haunch braces,the ratio of the longitudinal reinforcement and stirrups of the haunch braces,and the ratio of longitudinal reinforcement of the beam-column joints.Studying the influence trend of each parameters on the static performance of this joints through the analysis of the calculation results under different parameters.On this basis,suggestions are provided for the optimization of joints design and construction.