Study On The Post-fire Performance Of Space Lattice Structures With Welded Hollow Spherical Joints

Space lattice structure is a grid-like structure formed by a number of rod and joints with standardized shapes and sizes.It possesses such advantages such as light weight,low material consumption,beautiful shape,large space stiffness,simple in construction and installation,thus has become one of the most widely used large-span structural forms.Fire hazard is one of the main disasters that cause damages to building structures.At present,the research on fire resistance of space lattice structures mainly focuses on their behavior under high temperature,while their residual performance after fire exposure are rarely studied.To accurately assess the fire damage and post-fire safety of space lattice structure,this thesis explored the post-fire performance of structural materials,connection joints and the overall structure.The main research contents and achivement are as follows:(1)Experimental and modelling study on the post-high-temperature mechanical properties of the structural materials commonly used in space lattice structureExperiments were conducted to investigate the post-high-temperature mechanical properties of the domestic structural materials commonly used in space lattice structure,including hot-rolled steels,cold-formed steels,high-strength steel tie rods,cast steels,high-strength steel wires and structural aluminum alloys.A total of more than 1000 specimens were tested.The effects of exposure temperatures,cooling methods,strength grades and cyclic heating-cooling process were considered.Associated mechanical properties including stress–strain curves,elastic modulus,yield strength,ultimate strength,and ductility level were obtained and their change trends with exposure temperatures were analyzed.Based on the experimental results,predictive equations were proposed to calculate the post-high-temperature elastic modulus,yield strength,ultimate strength of the structural materials,and the post-high-temperature stress-strain models were further established.(2)Experimental study on the residual behavior of welded hollow spherical joints after fire exposureExperiments of 24 welded hollow spherical joints after uniform heating-cooling and of 12 welded hollow spherical joints after ISO-834 standard heating-cooling were conducted to reveal their post-fire residual behavior.The effects of exposure temperatures(or the highest fire temperatures),cooling methods,steel grades and load eccentricity were considered.The temperature development of the joint during whole fire process was measured.And the post-fire mechanical behaviors,such as failure modes,load–displacement curves,load-steel tube rotation curves,initial axial stiffness,yield loads,load-bearing capacities,ductility level,and strain distribution,were obtained and further analyzed.(3)Numerical study and practical calculation method of the post-fire residual behavior of welded hollow spherical jointsFinite element models of the welded hollow spherical joints after both the uniform heating-cooling and ISO-834 standard heating-cooling were developed using the ABAQUS software,and the accuracy of the models were validated against the experimental results.The parametric analysis were further conducted to investigate the effects of exposure temperatures,cooling methods,steel grades,load eccentricity and geometric parameters on the load-bearing capacity and initial axial stiffness.Practical calculation formulas of the load-bearing capacity and initial axial stiffness of the joints after both of the two fire conditions were proposed,and application scope of the formulas were recommended.(4)Study on the post-fire behavior and safety assessment method of the space lattice structure based on whole-process-analysisBased on ABAQUS,the whole-fire-process structural analysis method of the space lattice structure was established.The whole-fire-process behavior of a single-layer reticulated shell was investigated.The parametric analysis were further conducted to study the effects of the highest fire temperatures,uneven temperature field distribution,support stiffness,joint stiffness,initial load ratio,and shell geometry on the stability carrying capacity of single-layer reticulated shell,and corresponding simplified calculation formula was proposed.In view of the shortcomings of the existing method,a post-fire safety assessment method of space lattice structures was proposed,which combines both the on-site investigation and whole-process analysis...