Constant Amplitude Fatigue Properties Of M20 Torsional Shear Type High Strength Bolts Subjected To Eccentric Tension For Fabricated Steel Structures

Bolted connections have become one of the most widely used connection forms in assembled steel structures due to the advantages of easy installation,high reliability and high load-bearing capacity.Accumulated fatigue damage is the main failure mechanism of bolted connections,and the sudden and catastrophic nature of fatigue damage has made the fatigue problem a widespread concern among scholars.In actual engineering,it is more common to see bolted group eccentric tensioned connections than uniaxial tensioned connections.However,there is no corresponding connection category parameter in the Steel Structure Design Standard(GB 50017-2017),and the fatigue calculation parameters of the connection categories Z11 and J2(i.e.,bolts subjected to axial tensile action and bolts subjected to pure shear action)in the standard cannot meet the requirements for fatigue life assessment of bolts in this force state.(1)This paper takes the specimen of the new assembled column-based joint connected to the beam through the high-strength bolt extended end plate as the carrier.Fatigue tests,finite element analysis and related theoretical studies were conducted on a group of eccentrically tensioned torsion-shear type M20 high-strength bolts.The main work are as follows:(2)The loading device matched with AMSLER fatigue tester was designed,and the normal-amplitude fatigue performance of M20 torsion-shear type high-strength bolts eccentrically tensioned for assembled steel structures was studied through the test.And 9normal-amplitude fatigue data and 1 variable-amplitude fatigue data were obtained.(3)Based on the analysis and summary of the calculation methods and research results of high-strength bolts and sled force in the connection of the extended end plate,ABAQUS software was used for solid modeling analysis,taking into account the material nonlinearity,geometric nonlinearity,high-strength bolt pretension and contact between the components,etc.(4)With the thickness of beam end plate and column,bolt pre-tension and bolt diameter as parameters,the joints and bolts deformation and stress clouds of 9 groups of specimens at the corner of 0.082 rad and the tensile stress distribution and changes of bolts at different locations during the whole loading process were obtained.Accordingly,the influence of each parameter on the tensile performance of the bolt group was investigated for the high-strength bolt extended end-plate connection.(5)The macroscopic to microscopic comparative analysis of nine constant amplitude fatigue fractures and one variable amplitude fatigue fracture was carried out by using TM3000 electron microscope,which revealed the fatigue damage mechanism of the eccentric tensile damage of the high-strength bolt group.The fatigue fractures all showed three regions with different morphological characteristics: fatigue source region,extension region and transient fracture region.(6)Finally,based on the guidance of domestic and international design codes,the theoretical study of the force transmission mechanism of the column-based joint and the bearing capacity of each component is carried out to provide reference for promoting the standardized design of the column-based joint.