Study On Ultimate Bearing Capacity Of K-joints With Square Hollow Section Of Q690 High Strength Steel

Steel tubular joints are widely used because of their good mechanical properties,clear force transmission route and large bearing capacity.In the steel structure,high-strength steel has a series of advantages,such as high yield strength,high tensile strength,good ductility,high fracture toughness,high impact strength,good wear resistance and good cold bending performance.The use of high strength steel is more and more popular and wide.However,the exact impact of the use of high-strength steel on the strength of joints has been hardly studied,and there is no public design formula for it.Therefore,in this paper,the static performance of Q690 high-strength steel square hollow section K-type gap joint is studied by referring to the current domestic and foreign standard and the research results of relevant steel tube joints,and the failure mode and ultimate bearing capacity are studied.The test results from literatures are as the basic data of validation,an accurate and effective ABAQUS finite element model is established.The main research contents are as follow:Through the established ABAQUS finite element model,the parametric study on the Ktype gap joints of 64 square hollow sections was carried out.Each model is subjected to three load conditions,with a total of 192 finite element models.In the parametric study,the influence of dimensionless parameters of nodes,such as the width ratio of brace to chord(β),the widththickness ratio of chord(2γ),the thickness ratio of brace to chord(τ)and the pre-loading rate of chord(n),on the failure mode and ultimate bearing capacity of nodes is mainly studied.It is found that plastic failure of chord surface and local buckling failure of chord sidewall is the most common failure types.The ultimate bearing capacity of the joint increases with the increase of the width ratio of the brace to the chord β,decreases with the increase of the widththickness ratio of the chord 2γ,decreases with the increase of the pre-loading rate n,and basically remains unchanged with the change of τ.The simulation results are compared with the existing calculation formulas in the three current specifications.The results show that the theoretical calculation results of Chinese steel structure design code and European steel structure design code are relatively conservative and have poor correlation with the finite element simulation results.The theoretical calculation results of CIDECT design guideline 3 are closest to the finite element simulation results,and the dispersion degree is relatively small.However,there is still a certain gap between the numerical ultimate bearing capacity of the joint and the theoretical calculation results of CIDECT design guideline 3.Therefore,this paper modifies the theoretical calculation formula of CIDECT design guideline 3,and puts forward the calculation formula for predicting the design bearing capacity of K-type gap joints with square hollow section of Q690 high strength steel.Through comparison and verification,it is found that the modified theoretical calculation results are in good agreement with the finite element simulation results.