Study On Fire Resistance Of Fully Welded Box-Type Column-H-Beam Joints

With its light structure,large strength and rigidity,isotropy,easy production and installation and many other advantages,steel structure buildings have been widely used in various stadiums,large-span industrial plants and high-rise steel structure buildings in recent years.However,affected by its own high thermal conductivity,specific heat capacity,thermal expansion coefficient and other physical parameters,the fire resistance of steel structure buildings is poor compared with traditional reinforced concrete buildings,and in recent years,the fire of steel structure buildings has caused a large number of casualties and property losses.In the steel structure building in the beam and column node as a link between the various components,its fire resistance performance for the structure itself in the fire to maintain the overall stability and integrity of the vital role,in recent years of various types of steel structure building fires in the example of illustration: if the node damage in the fire can easily lead to the collapse of the building.Due to the late start of China’s steel structure fire resistance research,and the preliminary research mostly focused on the fire resistance of a single component,the joint fire resistance research in the design code is very rare.In the traditional design,designers only check the stiffness and strength of the node at room temperature when designing,ignoring the large deformation of the structure at high temperature and the influence of material property changes on the structure.Therefore,the study of the deformation failure mode and mechanical properties of joints in fire is an important prerequisite for structural fire resistance design.Through a large number of experimental data,it is shown that the all-welded rigid beam and column connection nodes have good hysteresis performance,high plastic deformation ability,and the damage degree of all-welded rigid joints in earthquakes is significantly better than that of other joint forms during earthquakes.Today’s research direction mainly focuses on semi-rigid nodes,and the fire resistance of fully welded rigid joints is less studied,and mostly focuses on finite element simulation.The fully welded joints are mostly welded by H-shaped steel columns(or I-beams)and H-beam beams for construction,but the moment of inertia of H-beams or I-beams in the two vertical directions of the section is quite different,and there are strong and weak axes.Compared with open sections such as H-shaped steel or I-beam,the closed section of box-type column section has excellent bending stiffness and torsional rigidity,so it is widely used in high-rise steel structure buildings and large industrial plants.Based on this,this paper conducts fire numerical simulation research on full-size fully welded outstretching cantilever beams,which mainly includes the following contents:1.Collect and sort out the relevant research on nodal fire resistance at home and abroad in recent years,provide direction guidance for this topic,and compile the high temperature mechanics,physical parameters and related mathematical models of steel required for this research.2.ABAQUS finite element software was used to select material parameters according to Eurocode 3,and parametric analysis was carried out on the fully welded box column-H beam node based on the ISO-834 standard heating curve.By setting the influence of column stiffeners,different load ratios,controlling different heating surfaces,spraying fireproof coatings and other variables on the fire resistance of the node,the key factors affecting the fire resistance time of the node are specifically determined through parametric analysis.3.Using the knowledge of heat transfer and material parameters,the temperature field analysis of the finite element model is carried out and the sequential thermalmechanical coupling simulation is carried out,and the deformation cloud map,node temperature cloud and Mises stress cloud map of the node area are obtained,and the relationship curve of the node temperature and rotation angle with respect to time is extracted,and the relationship between node performance and time under fire is obtained.The following results are obtained by finite element simulation according to the above conditions:1.The existence of stiffeners can alleviate the temperature rise of the node domain and improve the stress redistribution to a certain extent,which is an important influencing factor affecting the fire resistance of fully welded nodes,and the fire resistance time of nodes with stiffeners is improved.2.The load ratio is a key factor affecting the fire resistance of the joint,the higher the load ratio,the lower the fire resistance of the structure.From the temperature-rotation curve,it can be seen that the angle rate of the node with a higher load ratio at the same temperature is significantly greater than that of the node with a lower load ratio after500°C.3.The selection of the fire surface is the key factor affecting the fire resistance of the node,and the fire resistance of the three-sided fire node is significantly improved than that of the four-sided fire node.4.The presence of fireproof coating significantly reduces the transmission of the surface temperature of the node to the interior and improves the fire resistance time.