Study On The Compressive Strength Of Welded Hollow Ball Joints After Corrosion

With the rapid development of national economy in the past 30 years,steel structures with good performance have been widely used in the construction field,In recent years,a large number of large-span space steel structure buildings constructed in the initial stage of the reformation and opening have gradually entered the later stage of their design working life.Therefore,it is necessary to pay enough attention to their durability.And corrosion is an important factor affecting the durability of steel structures,so it is of great significance to study the mechanical properties of steel structures after corrosion.As one of the widely used joints in space grid structure,there are few researches on welded hollow ball joints' mechanical properties after corrosion at present.In order to provide a reference for the safety performance and service life evaluation of the hollow ball joint grid frame and similar structures,this paper studies the pressure-resistant performance of welded hollow ball joints after corrosion,mainly including the following four parts:1.Study on pit corrosion morphology distribution of steel surfaceIn order to study the effect of the pitting phenomenon on the steel surface on the stress distribution and bearing capacity degradation of hollow ball joints,this paper conducted a full investigation on the pitting phenomenon on the surface of Q235 steel under three corrosion modes,namely natural corrosion,corrosion in the wet environment of the swimming pool and accelerated corrosion by electrification.We used optical digital microscope to geometrically measure the distribution of corrosion pits on steel surface under various corrosion modes,summarized and established the probability analysis model of the geometric size of corrosion pits on steel surface under these three typical environmental corrosion modes.2.Establishment of welding ball joint model affected by corrosionBased on "Technical specification for space frame structures" size for common hollow ball node design,and based on the ANSYS platform,The study establishes welding hollow ball joint model considering the influence of welding residual stress and initial bending component,and proposes the effective corrosion pit simulation method,which offers method for the analysis of similar joints after corrosion.3.Study on the influence of pit corrosion on mechanical properties of jointsAnalysis should consider the effect of local corrosion pit or not is the key to the analysis of steel structure after corrosion.In order to explore the influence of pit corrosion distribution on the mechanical properties of hollow ball joints under compression in detail,this paper analyzes the parameters of the ring range,depth and size effect of corrosion on hollow ball joints with pit corrosion distribution under three typical corrosion environments,namely natural environment,wet environment of swimming pool and electrified accelerated corrosion environment,and obtains the influence of pit setting on the bearing capacity of the joint.4.Study on bearing capacity degradation of locally corroded ball jointsBased on the refined finite element model of the corroded joint,the corrosion position,the corrosion shape and the corrosion depth are taken as the indexes to analyze the parameters of the weld hollow ball joint after local corrosion so as to explore the influence law of each key corrosion parameter on the joint bearing capacity degradation.A formula for calculating the bearing capacity degradation rate of welded hollow ball joints after corrosion is given on this basis,which can take the influence of corrosion location,shape,depth and pit corrosion into consideration,and provides technical reference for similar structure joint design.