| Earthquake is the biggest threat to structural safety.Although seismic behavior of steel structure is expected to be high,a large number of steel structure buildings suffered brittle failure due to joint cracking in Northridge earthquake and Kobe earthquake,which exposed the problem of seismic performance in joints,and started a more extensive and in-depth study of steel structure beam column joints.Researchers first proposed a design method based on the concept of ductility design.This kind of joint can avoid brittle failure,but it is gradually replaced by the components-based design method due to many shortcomings,such as difficult to repair,low energy consumption efficiency,sudden change of bearing capacity and so on,but the latter’s manufacturing process is complex,and its energy consumption efficiency is still low.Based on the concepts of buckling restraint and damage control,a C-shaped buckling restrained energy dissipation beam column joint is proposed.The joint is constructed of prefabricated column cantilever beam,and the energy-dissipating plate is used as a "fuse" to connect the beam segment to control the damage;The results show that the C-shape constraint can limit the buckling deformation of the energy dissipation plate and make the plate plastic deformation and dissipate energy;At the same time,the beam flange as a part of the constraint can simplify the joint structure and save the building space.Then two kinds of shear resistant construction of energy dissipation plate with stiffener and end dentate constraint are proposed to control the shear deformation and avoid the adverse effect of shear deformation.The seismic performance of joints is studied by theoretical analysis,experiment and finite element analysis,the details and some conclusions are listed as follows:(1)The energy dissipating plate and the restraint plate of the beam-to-column connection are taken out as an energy dissipation device to study the effect of shear deformation.Firstly,the deformation process of the energy dissipation plate in the C-type buckling restrained energy dissipation device is analyzed.The energy dissipation plate is regarded as an axial compression member subjected to transverse concentrated load.The calculation formulas of critical load and shear deformation are given.The calculation results are in good agreement with the experimental results.Taking the shear deformation of instability as the dividing point,the shear deformation is divided into large shear deformation and small shear deformation.The energy-dissipating plate is unstable under large shear deformation,and strength failure occurs under small shear deformation.According to the factors that affect the shear deformation,two shear design methods of energy-dissipating plate with stiffeners and end dentate constraints are proposed,and the corresponding design suggestions are given.(2)The low cycle tension-compression cyclic tests are carried out on the rectangular restraint specimen J,the primary form specimen P,the energy-dissipating plate with stiffener specimen S1,S2,the dentate restraint specimen D1,D2,D3,D4 and the energy dissipating-plate with stiffener and dentate restraint composite specimen DS.The test results show that the dentate buckling restraint can control the shear deformation of the energy-dissipating plate,the hysteretic curve is full,the bearing capacity is stable,the energy dissipation capacity is strong,and the fatigue performance is better than that of the specimen J;The results show that the performance of the specimen S1 and S2 is good in the early stage of loading,but worse in the later stage due to crack or welding stress,but better than that of the specimen P.(3)The experimental analysis focuses on the hysteretic and energy dissipation properties of dentate restraint specimen D1,lengthened serrated specimen D2,strengthened bottom plate specimen D3,asymmetric dentate restraint specimen D4,energy-dissipating plate with stiffener and dentate restraint specimen DS.The results show that the serration length has little effect on the bearing capacity,stiffness and ductility of the specimens,and the energy dissipation performance is good,but the stability of the bearing capacity is poor under fatigue loading.The bearing capacity of the reinforced base plate is slightly lower than that of the stiffener specimen of the energy dissipation plate,and the stiffness degradation is faster,but the ductility is good,the energy consumption is more,the energy consumption efficiency is also high,the shear deformation is well controlled,and it is basically stable around 2.5mm,and its fatigue performance is also the best,the fatigue hysteretic curve is full,and the fatigue life is longer.(4)A finite element model of specimen D1 is established,and the finite element results of the model are in good agreement with the experimental results.The finite element analysis results show that the short free buckling length and the small clearance between the energy dissipation plate and the outer shell will have adverse effects on the fatigue performance of the energy-dissipating plate.The average strain on the energy-dissipating plate should be less than1.5%,and the design clearance should be 2.5 ～ 3.5mm.If the thickness of the bottom plate is too small,the shear deformation of the energy dissipation plate can not be controlled.The distance between the sawtooth and the base plate determines the joint length of the sawtooth.The larger the joint length of the sawtooth,the greater the adverse effect on the performance of the specimen.Therefore,the distance between the base plate and the sawtooth length should be controlled to reduce the joint length of the sawtooth.When the bottom plate is broken at 1 / 4 of the energy dissipation plate,the specimen has the best performance.(5)The dentate buckling restraint energy dissipation device is applied to the connection and the corresponding finite element model is established.The finite element results show that the hysteretic behavior of the two devices is basically the same.In order to verify the conclusions of the parameter analysis,the serrated length of the joint is reduced,and the broken position of the beam section corresponds to 1 / 4 of the energy dissipation plate.The optimal dentate buckling restrained joint is established,which shows that the optimized joint has good energy dissipation performance and can improve the fatigue performance of the joint. |
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