Fatigue Design Method Of High Strenth Bolts Based On Fatigue Test Date

With the popularization and application of this structure in industrial factory with suspended crane, the fatigue performance becomes the hot problem to be solved for many years in engineering circle. The high-strength bolt is the most important connection part of grid structure, its stress performance effects the safety of whole grid structure directly. But all the codes within the range of steel construction don't involve the fatigue mechanism of high-strength bolt in grid structure such as "Code for design of steel structures" . (GB 50017-2003) , "Specification for design and construction of grid structure" (JGJ 7-91), "The high-strength bolt used in bolt-sphere of steel grid structure" (GB/T16939-1997), etc.Though it is one kind of shortcut to study fatigue performance by theoretical analysis, various kinds of fatigue formulae which put forward by domestic and international scholar is still differ far from the results of testing greatly at present because of so many fatigue influence factors. But it is fatigue test which to be reliable and direct method acknowledged generally, so this paper sets up the fatigue mechanism which is suitable for the grid structure with bolt-sphere joints and based on the overall systematic statistical analysis on the data of 40Cr high-strength bolts' equal-amplitude and variable-amplitude fatigue test. This paper analyses the influence degree of various kinds of uncertain factors to the fatigue performance of the high-strength bolt. By analysis in detail thispaper founds such conclusions that the stress ratio has not influence to the fatigue of high-strength bolt, that the fatigue performance of 40Cr high-strength bolt now used is too low, it can't be suitable for the grid structure with suspended crane, etc. And paper proposes some suggestions to improve the bolt's fatigue performance.Through the study and analysis of this paper, it will offer the important basis for revising the codes and supplementing clauses; Promote the wide application of the grid structure with bolt-sphere joints at the same time.