The Theoretical And Experimental Research On Fatigue Performance Of High Strength Bolt Connection In Grid Structure With Bolt Sphere Joint

The application scale and number of the grid structure with BSJ(bolt sphere joint)has been the first rank at home and abroad as one of large span structures.Repeated varied amplitude by suspending cranes loads in industrial field resulted in the fatigue of the grid structure with BSJ.The fatigue of the grid structure with BSJ refers to the fatigue of bars,conical-head,sealing plate, sphere and high strength bolt connection.the latter is the key to fatigue failure. Due to few theoretical and experimental researches,the relevant codes for their fatigue design methods are in greatly needs at home and abroad.So the designer has no clause to obey.It largely restrains large-scale applying to the industrial buildings under suspending cranes loads.Supported by National Scientific and Natural funds(59908005,50678109),the fatigue behaviour of HSB(high strength bolt)connection in grid structure was studied theoretically and experimentally.The main study contends,methods,achievements and innovations are as follows:1.Eight kinds of 40Cr HSB connection which are M14,M20,M24,M30, M33,M39,M52 and M60 were studied by ANSYS FEA with 20 nodes of Solid 95 and the influence of bolt diameter,lift angle,thread root fillet radius and bolt sphere were researched quantitatively.Besides,the stress concentration factor and the fatigue notch coefficient,formula for HSB connection have been established in the first time,the latter numerical range is 4.35-4.89.The results pointed out that the relations between stress concentration and fatigue original,explain the reason that why the fatigue strength of HSB connection is very low and lay a theoretical foundation for fatigue design methods on the basis of hot stress and hot stress amplitude.2.The constants amplitude fatigue tests of 32 HSB in M20 and M30 two sizes were taken by use of Sweden AMSLER fatigue machine and self-design loading equipments which are stable and efficient,19 effective broken points,9 unbroken points that surpass 2 millions times and 4 uncommon broken points were gotten.It have gathered 35 national constant amplitude fatigue test data in this paper,including 33 effective broken points and 2 unbroken points that surpass 2 millions times.With 52 domestic effective test data regression analysis, S-N curve slash part of the equation is gotten and the horizontal part of S-N curve is obtained rely on 11 unbroken experimental data.So far,it has gotten a relative common HSB connection's fatigue curve—S-N at home and abroad.3,It has established the constant amplitude fatigue design methods of HSB connection in grid structure with BSJ by adopting four design parameters of nominal stressσ_max,hot stressσ_h,nominal stress amplitudeΔσand hot stress amplitudeΔσ_h.Based on N=2×10⁶,[σ₀^P]=46.0MPa,[σ_0h^P]=200Mpa,[Δσ]=34 Mpa and[Δσ_h]=148 Mpa.The fatigue strength BSJ equals about its yield strength 5.1%,ultimate tensile strength 4.6%and design tensile strength 10.7%.and it put forward that the HSB connection is the Ninth supplemented in the Table 6.2.3-2 in《codes for design of steel structure》(GB50017-2003)3.While finishing the HSB connection experiments under constant amplitude,the 21 HSB in M20 and M30 fatigue specimens were tested for variable amplitude fatigue behaviour in" low-high","high-low", "low-high-low","high-low-high" and "random programmed" five typical loading forms and 21 effective broken points were gotten,it is the first time at home and abroad.The fatigue life calculation was made by applying Miner law and Corten-Dolan law based on the gotten experimental data,most of D value of which is more than one,and the discreteness of Corten-Dolan law is far behind Miner law,it is stated that the fatigue life calculation that adopts Corten-Dolan law is more reasonable.4.The 40 typical fracture section,including 12 constant amplitude and 8 variable amplitude fracture section in M20,and 10 and 10 of respectively in M30.The HSB connection fatigue mechanism under constant and variable amplitude are mainly showed by image analyzing with magnifier and electron microscopy and showed the typical fatigue fracture characters,which are original zone,intermittent disconnection and developed zones.The fatigue fracture random of varied amplitude is often far greater than that of constant amplitude.5.Using fracture mechanics,it has calculated the fatigue life of 40Cr HSB in M20 and M30 under constant amplitude and compared with the experimental data,they had a good relevance,but the former majority is less than the latter, and error in 20%.The initial crack length has a large influence on the crack development life,when the initial crack length is one times larger than before, the crack development life is shorten about 50%.Fracture toughness has small influence on fatigue,when fracture toughness is one times than before,crack development life only 10%larger than before.