| On the basis of keeping the original structure of the beam-column joint area,the dog bone joint partially weakens the beam section at a certain distance away from the surface of the column flange,so that the position of the plastic hinge deviates from the joint area.The joint has better plastic rotation capacity,and full hysteresis curve under the action of earthquake.However,when the load-bearing column fails due to accidental loads such as fire,explosion,impact,etc.,the joints mainly bear the vertical load passed from the superstructure,and the stress state is quite different from that of the earthquake.At present,there are few actual projects using this joint form,and the research on its continuous collapse performance mostly focused on pure frames.And also,the specific joint parameters have no systematic research on the impact of continuous collapse performance.Therefore,it is of great theoretical significance and practical value to study the anti-continuous collapse ability of the composite beam structure of dog-bone joints considering the influence of composite floor.The main research contents and conclusions in this paper are as follows:(1)The finite element software ABAQUS was used to model and analyze two existing composite beams of plane steel frame.The bearing capacity curve,side column displacement curve and failure mode obtained from numerical simulation were compared with that of the test results to verify the reliability of the finite element simulation method.(2)Combined with the actual project,a full-scale dog-bone joint beam structure and a traditional joint beam structure was established.The whole process of dog bone joint destruction were systematically studied,including failure mode,bearing capacity changes,normal column lateral displacement,fracture cross-section stress,beam-column connection location the development of strain and resistance mechanisms.The results show that the fracture position of the steel beam of the dog bone joint appears at the weakened area at the proximal end of the failed column,the weakened area of the flange acts as a "fuse",and the fracture position of the steel beam of the traditional joint appears at the beam-column connection.And cracks from the bottom flange extending upward along the cross-section until the entire beam breaks,the bearing displacement of the dog bone joint has increased by more than 1.4 times compared with the traditional joint.Moreover,when the steel beam is completely broken,the limit displacement value is significantly increased,showing a relative good ductility.(3)Twenty-three specimens of dog beam joint composite beam structures with different parameters were designed and modeled by ABAQUS.The distance between the weakening starting point and the surface of the column flange,the length of the weakened area,the weakened depth,and the reinforcement ratio were analysed.And the influence of the five factors of the failure position of the column on the anti-collapse performance of the dog bone joint has been obtained.The results show that when the distance between the weakening starting point and the surface of the column flange is greater than 0.5 times the width of the beam flange,the ultimate displacement and ultimate bearing capacity of the substructure are basically the same;when the length of the weakened area is 0.8 times the beam height,the substructure can obtain an ideal continuous collapse resistance Capacity;the effect of weakening depth on the continuous collapse of dog bone joints is greater than the other two weakening parameters.When the weakening depth is greater than 0.22 times the beam flange width,the substructure does not enter the catenary stage before the lower flange breaks;The increase of the reinforcement ratio improves the ultimate bearing capacity of the composite joint,but the reinforcement capacity is negligible when the reinforcement ratio is less than 0.5%;compared with the failure of the corner column,when the side column and the inner column fail,there is at least a set of symmetrical The beam is connected to the node,and the exertion of the suspension cable mechanism makes the bearing capacity of the substructure much higher than that of the corner column.(4)An improved scheme for adding arc-shaped side plates in the weakened area was proposed.The comparison and analysis of the parameters of the side plate through 25 specimens show that the ratio of the side plate area to the weakened area is 0.25～0.67.The plate can effectively improve the ultimate bearing capacity and ultimate displacement of the substructure.The destruction position of the steel beam is not affected,which can make sure the design criterion of "strong joint and weak member".Also,the optimal reinforcing effect can be obtained when the ratio is 0.67. |
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