Effect Of Casting Defects On Mechanical Properties Of Steel Structure With Cast Steel Nodes

Cast steel nodes have beautiful appearance, flexible modeling and smooth transition, each branch angle can be selected to adapt a variety of complex shapes. Also Cast steel nodes are completed by one time casting, the overall performance is excellent, so they are particularly suitable for pipes and nodes in three-dimensional stress state joins, which have been widely used in engineering in recent years. Due to the limitation of the casting process and the influence of environmental factors, the cast steel nodes often have internal and external defects such as crack, sand, shrinkage, porosity and so on. The existence of defects will affect the mechanical properties of cast steel nodes and the whole structure to a certain extent. For the current research of cast steel nodes, consider casting defects little. The current assessment of the quality of steel castings, steel castings is concerned according to the most serious defects in the local area, while for others the defect distribution on steel castings lack the necessary attention. Such "In partial consideration of the whole," the evaluation method is not comprehensive, it might give the overall structure of cast steel nodes and the calculation of the mechanical properties and bring judgment bias.This paper takes the truss bridge with cast steel nodes as the engineering background, numerical simulation method was used to study the influence of casting defects on the mechanical properties of cast steel nodes and integral truss structures.The main research contents are as follows:(1) This paper introduces the production process and production process of cast steel nodes, classifies the defects of cast steel, and explains the cause of defect formation.(2) Using modeling software Solidworks to establish a three-dimensional solid model consists of steel trusses and steel casting defects node, successfully solve the modeling of complex intersecting shapes and internal three-dimensional defects.(3) Through the establishment of entities at different locations defect cast nodes, research for the steel and cast steel truss structure node static mechanical properties of a single casting defects is done.By establishing the distribution of defects in the cast steel nodes, the finite element method to study the casting defect size, location and distribution of the static mechanical properties of cast steel nodes and truss structures affected.(4) Stress distribution by extracting the defect at the location of cast steel nodes analyzed to obtain a single casting defect due to differences in location on the fatigue properties of cast local node under constant amplitude fatigue loads. In addition, a single casting defect size for cast steel joint performance of local fatigue is explored; By finite element analysis obtained at the same quality level as whole and loading conditions, effect on the casting defect distribution for fatigue properties of cast steel nodes is researched.(5) Using steel equivalent node contains the elastic modulus to characterize the distribution of defects, and make the modulus of elasticity of ordinary steel (steel and joist materials) and cast steel materials to random variables, using the structure of maximum stress and maximum displacement to characterize the strength and stiffness of the structure, explores the steel joist and steel material elastic modulus randomness for truss structural strength and stiffness properties through Monte Carlo simulation. Also, under the circumstance that steel joist and section modulus of elasticity remain unchanged, effect of randomness of casting defects for static structural steel truss Reliability is studied. Finally, take the cast steel node as study object from the overall model, make the equivalent elastic modulus of the cast node to the local position as random variable, Studied for effect of casting defects randomness on local node static reliability.Research shows:(1) Under elastic range, casting defects have a certain influence on the mechanical properties of the cast steel nodes and the whole truss structure, the impact depends on the size of the defect size, location, distribution and structural loading. Overall, the casting defect sizes, different locations and distribution, have a greater impact for cast steel joint stress distribution (especially the stress distribution within the local area defect), while impact on the overall structure and the stress distribution is relatively small. (2) Size, location and distribution of casting defects have substantially no effect on the steel truss structure node and stiffness properties. (3) Size, location and distribution of casting defects have greater impact on fatigue properties of cast steel nodes. (4) The sensitivity of cast steel elastic modulus is greater than the sensitivity of the pipe section and the elastic modulus of I-beams, steel elastic modulus randomness impact the overall performance of the truss structure should be paied attention. When judging the quality of steel castings, it is not comprehensive that only based on the size of casting defects, cast steel nodes safety assessment should be considered at the sanme time. That is, considering the plurality of distribution of defects, using the entire node "field" partial replacing "assessment Box". According to the density and size distribution of defects, castings are divided into different areas. A comprehensive assessment of the region is achieved according to the multi-factor comprehensive evaluation of the results area defects. Finally, all the danger zone on the node of a comprehensive assessment to determine the level of security throughout the casting node. (5) Randomness of casting defects has significant impact on Static Reliability of both cast steel nodes local and the overall truss structure.When judging the quality and safety of steel castings, it is not comprehensive that only based on the size of casting defects, it should also be considered at the location of the defect state of stress. Recommendation for cast steel joint safety assessment, consider the distribution of the plurality of defects, with the entire node "field" partial substitution "assessment Box"; According to the density and size of the defect distribution, make the castings into different regions, each region recording all detected defect; Comprehensive assessment based on multivariate defect region results in the region conduct a comprehensive assessment of the risk of deficit number of regions, as a dangerous area; Finally, all the danger zone on the node of a comprehensive assessment to determine the level of security throughout the casting node.