| With the accelerating process of urbanization in China,more and more urban underground space is used.In some projects that can not be excavated in a large area or have a tight construction period,the reverse construction method is often used.In the existing reverse construction method,the connection between the column and the slab is generally welded with the steel sheath on the column reinforcement cage in advance,and then the reinforcement is welded at the steel sheath after excavation to the corresponding elevation.This construction method has the advantages of complex process,high cost,slow construction progress and easy fire,which is harmful to the health of workers.Therefore,a new type of ring beam joint is proposed in this paper,which solves the disadvantages of the above traditional construction methods.Two traditional steel ring plate joints and two new ring beam joints are made respectively.The mechanical properties of the two joints are analyzed through axial compression test and quasi-static test.Through the analysis of strain,the similarities and differences of the two joints are compared.The main contents and conclusions of this paper are as follows:（1）Starting from the shortcomings of the existing steel ring plate joints,a new type of ring beam joints is designed.The ring beam joint uses the reinforcement planting process and surrounds the hoop around the periphery of the column,which has the advantages of simple construction process,low cost and no welding process.（2）Axial compression and quasi-static tests were carried out on the specimens of two different joints.During the axial compression test,the two specimens were damaged under the axial pressure of 2150 k N,but the damage of the ring beam joint was relatively mild,and the damage of the steel ring plate specimen was brittle.In the quasi-static test,the cracking load of both joints is 41.5k N,but the cracking displacement,yield displacement,peak load,peak displacement,failure load and failure displacement of ring beam joints are increased by 33%,30.5%,12.4%,27.3%,11.8% and 18.8% respectively.The ultimate damage degree of steel ring plate specimen is more serious than that of ring beam method specimen,and the total energy consumption of ring beam method specimen is about 66% higher than that of steel ring plate method specimen;（3）The internal strain of the joint is analyzed by using the strain gauge embedded in the specimen.The internal stress distribution of the steel ring plate specimen joint is uneven,the stress near the column end is large,and there is basically no stress and strain at the bottom of the joint away from the column end.The internal stress of the ring beam method joint is more uniform than that of the steel ring plate method joint,the difference between the upper and lower stress in the joint is small,and the stress transmitted to the raft is more regular.（4）Both methods can meet the requirements of structural bearing capacity.The joint stiffness of steel ring plate specimen is too large,and the synergistic deformation capacity of steel sleeve and concrete is poor,resulting in stress concentration at the end of column,which is easy to cause serious plastic damage when encountering large load.The stiffness of ring beam joint is smaller than that of steel ring plate joint,but its cooperative deformation ability is good,which can give full play to the performance of members to a greater extent. |
