| With the development of building industrialization and prefabricated buildings,bolted joints have become one of the widely used joint types in steel structures,and their mechanical properties are essential to ensure the safety of the structure.When an earthquake comes,the structure is subjected to reciprocating plastic deformation,so the low-cycle fatigue behavior of the joints is particularly prominent.High-strength bolts are the key components of the bolted joints,and their low-cycle fatigue properties have an important influence on the fatigue life of the joints.We hope that through reasonable design,the bolts and bolt joints will not be fatigued before the members when the structure is subjected to reciprocating loads.Based on this,this paper investigated the tensile low-cycle fatigue performance of high-strength bolts for steel structures.The main contents are as follows:1.In terms of the bolted gusset plate connections in braced frames,the deformation characteristics of the high-strength bolts were numerically studied.Through multi-scale modeling,the deformation characteristics of the gusset connections and bolts during the storey drift of the braced frame were studied.The influence of different geometric parameters on the plastic deformation amplitude of the bolts was analyzed,while the bending deformation and the shear deformation of the high-strength bolts were evaluated.The overall grasp of the deformation requirements of the bolts was achieved,and the importance of studying the low-cycle fatigue performance of the bolts was clarified.2.In view of the lack of research on the material properties of high-strength bolts in existing studies,the material properties and damage constitutive of the20 Mn Ti B steel used in 10.9S high-strength bolts were experimentally and theoretically studied.Through the tensile test of the smooth bars and the notched bars,combined with the finite element numerical simulation and the commonly used GTN constitutive model of construction steel,the full-range uniaxial constitutive relationship of the steel and the corresponded GTN damage model parameters were obtained.3.Uniaxial tensile and low-cycle fatigue tests on 10.9S high-strength bolts were conducted.Under constant-amplitude load,the fatigue failure modes,failure characteristics and the fatigue fracture morphology of high-strength bolts of different diameters under different loading amplitudes were investigated.The criterion for the fatigue failure of bolts and the fatigue life curve based on the loading amplitude were presented.4.On the basis of the experiment,the methods based on cyclic displacement amplitude,equivalent stress ampliyude,and local equivalent plastic strain were used to evaluate the low-cycle fatigue life of high-strength bolts under tension.It is found that the methods based on the cyclic displacement amplitude and the local equivalent plastic strain can well predict the low-cycle fatigue life of the bolt under tension.At the same time,the fatigue design parameters based on the equivalent stress amplitude were given,which provides a reference for establishing a unified fatigue design theory. |
