the effect of overload of a bolted connection on its ... · double gusset plate bolted connections...
TRANSCRIPT
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The Effect of Overload of a Bolted Connection on its Fatigue Life: A
Case Study
Presenter: Leon D. Wegner
Authors: Shahin Shadlou, Leon D. Wegner, Timo Tikka
www.usask.ca
Building on Our Growth Opportunities May 27 – 30, 2015Miser sur nos opportunités de croissance REGINA, SK
PresenterPresentation NotesWill talk about the overload, but in some ways I’ll present a bit of a play-by-play of the study and provide some lessons learned along the way.
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Plan View of Typical Mine Shaft
Sample 2
Sample 1Background
Static Design:• Concentric + torsional components
Design for Fatigue• Limited guidelines• Conservative approach Accelerated fatigue testing
Cage
Skip Skip
PresenterPresentation NotesPut the presentation into context … need to describe the steelwork in a typical mineshaft. In a typical mineshaft, ore, people, and equipment is carried between the mine level and the surface by conveyances. Skips carry the ore. The cage carries people and equipment. The conveyances are guided by vertically oriented HSS sections, which are supported periodically by horizontal steel sets – bunton sets. In this case, a bunton set consists of a main bunton beam, to which is connected shorter beams supporting the guides. Double gusset plate bolted connections are used, designed for slip-critical conditions. As a conveyance travels, if there is any mis-alignment in the guide, the conveyance will shift from side to side and exert repetitive horizontal slam loads on the bunton sets. Leads to eccentrically loaded connections. So the connections must be designed for fatigue over the life of the mineshaft.Static design of eccentrically loaded connections – good guidelines – distribute forces by considering a superposition of concentric and torsional components.
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Outline• Description of test program• Results of initial fatigue tests• Overload incident and immediate effects• Finite element analysis and results• Post-overload fatigue tests & results• Conclusions
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Test Program - Summary
• Sub-assembly of “Sample 2”
• Subjected to simulated cyclic slam forces from payload skips
• Accidently subjected to 1 cycle of overload (5 times the design load)
PresenterPresentation NotesSlip critical design
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Test Setup
1782
629
2083
296
2292
1003
• Load applied with 250 kN hydraulic actuator
• 6 LVDTs to monitor displacement • 32 strain gauges used to monitor
strains on the gusset plate
PresenterPresentation NotesMore complete view of the setup.Interest is the performance of the gusset plate connection.
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Test Stages
Test Stage Load (kN) Number of cycles Events
Stage 1 42.6 1 million --Stage 2 85 1 million --
OVERLOAD 215 1 --Stage 3 93 1 million Bolt breakageStage 4 103 1 million --Stage 5 113 0.5 million Bolt breakage
PresenterPresentation NotesFocus on effects of the overload, but will also summarize results at other stages.
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Results – Stages 1 & 2
Load-point Displacement (mm)
(positive value is downward)
Stage 1 (42.6 kN)Support bolts re-tightened
PresenterPresentation NotesDisplacements varied from 0.6 or 0.7 mm to 2.7 to 2.8 mmShift associated with re-tightening of support boltsGradual increase in displacement, range constantStage 2 similar to Stage 1
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The Overload Incident
0
50
100
150
200
250
0 5 10 15 20 25
Forc
e (k
N)
Displacement (mm)
Force-displacement of overload incident
215 kN5 times the design load!
Permanent Displacement
PresenterPresentation NotesSoftware error – transfer from load-control to displacement control (lesson!)215 kN (5 x the design load)Permanent displacement observed at load-point
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Damage Due to the Overload
Clip angle 2
Clip angle 1
PresenterPresentation NotesDetailed investigation conductedSlippage between gusset plates and boltsSlippage of clip angles
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Damage Due to the Overload
• Bolt slip• Contact between bolt shank
and bolt-hole
PresenterPresentation NotesScratches on the bolt shank and damaged threads confirm that the bolt came into contact with the hole.
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Finite Element Analysis x=y=z=0
Rx=Ry=Rz=0
Applied load
• Purpose: to estimate share of load carried by each bolt
• Linear-elastic analysis using ABAQUS
• Symmetric model
• Tie constraint at bolt locations
• Hard contact elsewhere, with 0.5 friction coefficient
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Finite Element Results
0
20
40
60
80
100
0 1 2 3 4 5
Forc
e (k
N)
Load-Point Displacement (mm)
Experimental data
FEA data
Comparison of FE and experimental results
Exaggerated deformation (20 times) under 81.6 kN load
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Finite Element Results
Finite Element ResultsThe share of load carried by each bolt• Critical load for slip = 26%
PresenterPresentation NotesBased on FE results, 5 bolts experienced load close to slip valueAll except bolt 2 had slippedOther bolts also slipped. Believed to be secondary to slip of other bolts.Coating of some contact surfaces was partially worn off, which could lead to premature slippage.
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Experimental Results – Stage 3 (93 kN)
• Bolt #19 broke• Four bolts were loosened
Broken bolt
Half of the broken bolt
Loosened bolt
Loosened bolt
Loosened bolts
PresenterPresentation NotesNote that the broken bolt was carrying a tensile load.
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Experimental Results – Stage 3 (93 kN)
Vertical load-point displacement
Increase in rangeLoosening of bolts
ShiftBreakage of bolt
Vertical load-point displacement
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Fracture Surface of the Broken Bolt
Ratchet marks- Crack initiation
Higher roughness- Fast fracture
Smooth surface- Fatigue crack growth
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Experimental Results - Stages 4 & 5 (103 kN & 113 kN)
• No incident during Stage 4• Stage 5 stopped at 500,000 cycles, failure of two bolts at the support
outside the region of interest
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Conclusions• Good fatigue behaviour at design load and double the design load• Immediate effect of over-load:
• Bolt slip, leading to contact between bolt and edge of hole• Damaged coating of slipped surfaces
• Effect of over-load on fatigue performance• Bolt contact possible reduction in fatigue resistance• Bolt loosening and fatigue failure of bolt
• Confirmed (in approximate manner) critical load for bolt slip• Pay attention to components not necessarily considered most critical or
even along the main load path
PresenterPresentation NotesWhat did we learn?
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Acknowledgements
www.usask.ca
Building on Our Growth Opportunities May 27 – 30, 2015Miser sur nos opportunités de croissance REGINA, SK
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www.usask.ca
Building on Our Growth Opportunities May 27 – 30, 2015Miser sur nos opportunités de croissance REGINA, SK
BackgroundOutlineTest Program - SummaryTest SetupTest StagesThe Overload IncidentDamage Due to the OverloadDamage Due to the OverloadExperimental Results – Stage 3 (93 kN)Fracture Surface of the Broken BoltExperimental Results - Stages 4 & 5 �(103 kN & 113 kN)Conclusions