Study On Fracture Properties Of Widen Flange Section And Dog-bone Section Joint In Steel Frame

For a long time,the traditional beam-column connections are generally considered to have good seismic performance,however,the earthquake of Northridge in the United States and Kobe in Japan,a large number of welded steel beam-column joints occurred brittle fracture,did not show the expected ductility.After the earthquake,the scholars put forward a new joint form based on beam end plastic hinge shift and made a lot of research,but most of the design of the new type of joint is considered from the aspect of seismic performance,considering the possibility of fracture is relatively small.In order to improve the mechanical performance of the traditional joints,in this paper,the connection with widened beam flange and dog-bone section joint are studied,combined with the hysteretic properties and fracture,the design of the parameters and the weakening parameters of the joints are discussedIn this paper,the connection with widened beam flange and dog-bone nodes are studied,three-dimensional finite element models are established with different parameters,by applying cyclic loading at the end of the beam,the cracking of the weak points of the joints was analyzed by the stress triaxiality,equivalent plastic strain index and the rupture index and combined with hysteretic performance of node parameters recommended values are given in the range.In addition,based on the theory of metal fatigue and ductile fracture,the initiation of the initial crack in this weak crack location is quantitatively calculated on the butt welds of the connection with widened beam flange and dog-bone joint,the influence of the parameters of the diffuser on the crack growth is analyzed from the point of view of the crack developmentIn this paper,the above results show that: The change of the length of the diffuser and the expanded wing is less affected by the hysteretic behavior of the connection with widened beam flange,but its value is too small or too large will increase the weld through the hole at the crack may also cause the end of the weld crack growth rate led to the node prone to macroscopic cracks,but its value is too small or too big will increase the crack of the weld through hole,at the same time,the crack propagation rate increases at the end of the weld,leading to the occurrence of macroscopic cracks,the wider of the width,the more can restrain the development of weld cracks;For dog-bone section joint,the the farther away from the column flange,the plastic hinge displacement effect is better,but it is disadvantageous to fracture resistanc.The greater the weakened length and the weakened depth,the rate of crack growth at the end of the connection is slower,the lower the probability of node cracking,but it will cause the loss of bearing capacity of the joint.Based on the above analysis,in this paper,the range of the design parameters of the widen flange section and the parameters of the dog-bone section join are given,Which can provide some theoretical support for the seismic design and fracture analysis of reinforced joints.