| The joints of beam-to-column extended end-plate connection have been widely used in steel structure,but high-strength steel is often used in the column and end-plate because of structural space limitation or steel saving.Due to the advantages of high-strength steel,its future applications will be more extensive and the strength of steel is also improving.However,most of the current research on the beam-to-column joints of steel frames is based on the ordinary strength steels.When the high-strength steel was used in the joints of beam-to-column extended end-plate connection,due to the characteristics of high-strength steel such as high yield ratio and short yield platform,the mechanical properties of the joints are bound to be affected to some extent.In order to standardize the safe use and optimal design of this kind of joints,it is necessary to do a lot of research on the joint performance of high-strength steel beam-to-column extended end-plate Connections,to understand the regularity of how different parameters affect the performance of the joints,and then to summarize the regularity and seek breakthroughs in theory and design methods.Therefore,this paper designed and finished the static loading tests of 8 different structure of T-stubs（4 used high-strength steel and 4 used ordinary strength steel）,and 3 different structure of high-strength beam-to-column extended end-plate connection joints.After using the test results to verify the correctness of the finite element method of ABAQUS,34 different parameters of T-stubs and 13 of high-strength beam-to-column extended end-plate connection joints were analyzed by using the finite element analyse.Then the influence of mechanical properties of the joints because of different thickness of end-plate,column flange,column web and the different bolt spacing was carried out,and the results showed that:（1）A relationship of （?） existed in the critical end-plate thickness of different failure modes between high-strength steel and ordinary steel T-stubs.And the bearing capacity of high-strength steel T-stub is increased by 23%on average compared with ordinary steel,but the ultimate deformation capacity is reduced by 54%,and it is characterized by sudden brittle failure.（2）It is suggested that the design of high-strength steel T-stub’s failure mode should be B-type and more inclined to A-type,that means the end-plate thickness should be slightly greater than the critical thickness th,1,also the bolts of higher strength grade should be used to match it.（3）It is suggested that the end-plate thickness of high-strength steel joints should be designed as the end plate yield and bolt failure and more inclined to the end-plate controled failure mode,and a ratio about 0.6 of end-plate thickness to bolt diameter is suggested.（4）When the bearing capacity of the column is satisfied,it is suggested that the thickness of the column flange or the column web can be reduced appropriately,and the thickness ratio of the column flange or the column web to the end plate can reach 0.625,so that the ultimate bending moment of the joint is basically unchanged and the rotation capacity greatly increases.（5）The third row of bolts can be considered when calculate the bearing capacity of high-strength steel beam-to-column extended end-plate connections.At the same time,this paper makes theoretical analysis on the initial stiffness and ultimate bearing capacity of joints based on the component method.It is found that the component method can be well applied to high-strength steel joints,but the prediction of ultimate bearing capacity of T-stub or joints with end-plate mainly controlled is 20%～22%lower.Finally,concerning the characteristics of non-obvious yielding platform of high-strength steel,a modified theoretical formula for calculating the ultimate bearing capacity of high strength steel is proposed.Then it is verified with a large number of finite element analyse results that the predicted value of this method is 5%～16%lower,which means the results are more accurate. |
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