Design And Development Of Large Diameter Bolted Ball Joints In Space Grid Structures And Research On Mechanical Propertie

The bolted ball node spatial grid structure has been widely used in large roof structures such as sports venues,transportation hub buildings,exhibition centers,gas stations,industrial factories,etc.In recent years,the increasing span has become one of the main development directions of spatial grid structures.For spatial grid structures with larger spans of bolted ball nodes,the internal forces of their elements and nodes increase accordingly as well.Therefore,high-strength bolts with large specifications and high bearing capacity are needed for meeting the structural stress requirements.At present,the application of large-diameter bolts in bolted ball joints of spatial grid structures is increasing while there is few research focusing on largediameter bolted ball joints.The current national standard GB/T 16939-2016 “High strength bolts for bolted ball joints in steel grid structures” involves high-strength bolts with a maximum specification of M85,which cannot meet the stress requirements of certain(ultra)large-span bolted ball joints in spatial grid structures.This thesis conducted the following research on the mechanical properties of large-diameter bolted ball joints and their accessories:1.Design of large diameter bolt ball joints and their various accessories.This thesis first confirmed M90×6 、 M100×6 、 M110×6 、 M120×6 types of large diameter bolts with four specifications and then studied their mechanical properties.Next,the dimensions of large diameter bolts,sleeves,and fastening screws were designed based on linear regression method and the size relationship between various accessories of the bolt ball node.2.Research on the Tightening Depth of Large Diameter BoltsThis thesis used a combination of experimental and numerical simulation methods to study the tensile bearing capacity of M68 bolt ball joints with different screwing depths in order to explore the screwing depth of large diameter bolts.The failure modes,load displacement curves,and tensile bearing capacity of bolt ball joints under different screwing depths were obtained,and the variation pattern between the tensile bearing capacity of bolt ball joints and the screwing depth of bolts was given.The results indicate that when the bolt is screwed in at a depth of 1.0d,the ultimate bearing capacity of high-strength bolts can meet the specified requirements.Considering the possible impact of bending moment and shear force on bolts in practical applications,the screwed in depth of large diameter bolts is determined to be 1.1d.3.Experimental Study on the Tensile Bearing Capacity of Large Diameter BoltsTwo typical large diameter high-strength bolts,M100 and M120,were selected to conduct tensile load tests on 10 M100 large diameter high-strength bolts.The results indicate that the tensile load,tensile strength,and failure location of the test failure are all within the specified range.Eccentric sampling tensile test was conducted on three M120 large diameter bolts,and the results show that the tensile strength,elongation,and shrinkage of the sampled specimens can meet the specified requirements.4.Design and Finite Element Analysis of Large Diameter Cone HeadA set of dimensions for the large diameter cone head was designed.In order to verify the rationality of the size of the large diameter cone head using the correct finite element method,a cone head specimen with different bottom thicknesses at both ends was modeled and analyzed.The finite element analysis results were compared with the experimental results of the cone head,and the experimental curve and numerical simulation curve were in good agreement,verifying the finite element modeling and analysis method used in this thesis.Based on this finite element model and analysis method,elastic-plastic finite element analysis was conducted on the large diameter cone heads of two typical bolts,M100 and M120,under tension and compression.The ultimate bearing capacity,stress distribution,and plastic development of the large diameter cone head were obtained through numerical simulation.The experimental results show that the design of the cone head size is reasonable and feasible.5.Standard preparationBased on a series of work such as theoretical analysis,experimental research,and numerical simulation,the group standard “Large diameter high-strength bolts for bolted ball joints” of the China Steel Structure Association was developed.