Investigation of the Fatigue Life of Steel Base Plate to Pole Connections for Traffic Structures to Pole Connections for Traffic Structures Pooled Fund Project 9‐1526 F lt D K lF k F aculty: Dr. KarlFrank Graduate Students: Nick Richman, Andrew Stam Stephen Pool Andrew Stam, Stephen Pool, James Kleineck, Luca Magenes
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Investigation of the Fatigue Life of Steel Base Plate
to Pole Connections for Traffic Structuresto Pole Connections for Traffic Structures
Pooled Fund Project 9‐1526
F lt D K l F kFaculty: Dr. Karl FrankGraduate Students: Nick Richman,
Andrew Stam Stephen PoolAndrew Stam, Stephen Pool,James Kleineck, Luca Magenes
OutlineOutline
• Test Method• Test Method
• Weld Details Tested
• High Mast Results
• Design Guidelines• Design Guidelines
• Galvanizing!?
• Weld Repair
Mast Arm Setup
x
M
P
M0 10 1
16'
High Mast ResultsHigh Mast Results
Typical Socket ConnectionFillet Welded Connection
Ø1.87" See Detail
Ø30.00"Ø36.00"
Variable Thickness
Socket with External Collar
Ø1.88" See Details
Ø30.00" 12.00" SleeveThickness=
Ø36.00"3.00"
0.375"
Stool Connection
Full Penetration Weld DetailsFull Penetration Weld Details
T W iSee Detail
Texas Wyoming
0.75"
.2545 degrees
.75 x .31
.62 x .37
.25
Seal Weld
0.25" ThickBacking
Variable Thickness
BackingRing
0.25"
3.00"
Full Penetration With External Collar/Ground SleeveCollar/Ground Sleeve
11/16" x 3/8"
1/4"
45°
0.88"0.38"
7/8" x 3/8"0.69"0.38"
.25"30°11/16" x 3/8"
0.69"
0.88"0.38"
7/8" x 3/8"
0.25"0.25" ThickB ki
.38"
0.25"
BackingRing
A100
Sockets: Base Plate Thickness
AB
CD
EEE'
e (ksi)
1.5"
10
ess Rang
2"
Str
3"
Among 8‐Bolt Specimens
1
10,000 100,000 1,000,000 10,000,000 100,000,000
Cycles
A100
Sockets: Base Plate Thickness & Bolts
AB
CD
EEE'
e (ksi) 8 Bolt 1.5"
12Bolt 1 5"
10
ess Rang 12 Bolt 1.5
8 Bolt 2"
12B lt 2"
Str 12 Bolt 2"
8 Bolt 3"
1
10,000 100,000 1,000,000 10,000,000 100,000,000
Cycles
A100
Sockets: Base Plate Thickness & Bolts
AB
CD
E 8B l 1 5"EE'
e (ksi)
8 Bolt 1.5"
12 Bolt 1.5"
10
ess Rang 8 Bolt 2"
12 Bolt 2"
Str
8 Bolt 3"
16 Bolt 3"
1
(Lehigh)
10,000 100,000 1,000,000 10,000,000 100,000,000
Cycles
Bending of Base Plate and Mast WallBending of Base Plate and Mast Wall
Full Pen Details ‐ FractureFull Pen Details Fracture
• Fatigue Strength Increases with:Fatigue Strength Increases with:– Thicker Base Plates– Smaller Internal Holes in Full Penetration Details
• High Mast‐Combination of Thick Base Plates, Small Hole, 12 anchor rods, and External , ,Collar Produces Category C Fatigue Strength
• Bolt Pattern Not Significant on Mast Armsg• Full Penetration Weld on Mast Arm‐ Category D or better with 2 in. base platep
Thirty‐three Inch Diameter High M t P f SMast Performance Summary
The Last Specimens?The Last Specimens?• Pair of 33” HMIP for last tests of
l d f d jpooled fund project
• Poles identical in fabrication
• One specimen, 33‐3‐12‐TX‐SG‐A, was galvanized, the other 33‐3 12 TX SB B was left black3‐12‐TX‐SB‐B was left black
• Ultrasonic Testing revealed that the 33‐3‐12‐TX‐SG‐A specimenthe 33‐3‐12‐TX‐SG‐A specimen contained small cracks
Pre Test Inspection
• 33‐3‐12‐TX‐SG‐A
Pre Test Inspection
33 3 12 TX SG A had cracks on every bend except atbend except at seam weld
• Testing resulted in• Testing resulted in a lower‐than‐anticipated fatigueanticipated fatigue performance
Typical Initial CrackTypical Initial Crack
Test Results
• 33‐3‐12‐TX‐SG‐A
Test Results
33 3 12 TX SG A only cycled 81,326 times before developing large fatigue
kcracks• Tested back to b k i h bl kback with black specimen
Research History• 33‐3‐12‐TX‐SB‐B UT indicated no signs of initial cracking
• 33‐3‐12‐TX‐SB‐B did not k fcrack after
81,326cyclescycles
• Two Additional Galvanized SpecimensGalvanized Specimens Tested From Another Supplier
Initial Test ResultsInitial Test ResultsA
B
100
CDE
E'
(ksi)
10
Stress Ran
ge (
Nom
inal S
33‐3‐12‐TX‐SG
1
33‐3‐12‐TX‐VG
33‐3‐12‐TX‐VG (Flipped)
1
10,000 100,000 1,000,000 10,000,000 100,000,000
Cycles
Fatigue Crack Bend 5Fatigue Crack Bend 5
Fracture Surface Bend 5Fracture Surface Bend 5
Fatigue Crack
Initial Crack
Crack Depth at ToeCrack Depth at Toe‐3/32 in.
Initial Crack Bend 5Initial Crack Bend 5
Initial Crack at Bend 12 OpenedNo Fatigue Damage
Dark Area‐Initial Crack
Cracks at Weld SeamTested after Cracking at Bend 5
Shallow Initial CracksShallow Initial Cracks
Longitudinal Seam Weld at CornerNo Initial Cracks!
Possible Cracking CausesPossible Cracking Causes
• Source currently unknownSource currently unknown– State of art described in report written by Thomas J Kinstler: Current Knowledge of the Cracking ofJ. Kinstler: Current Knowledge of the Cracking of Steels During Galvanizing
– Largely speculative with general rules of thumbLargely speculative with general rules of thumb which are not fully developed scientifically
Possible Cracking Causes
• Investigated five potential causes of cracking– Bend radius of shaft
– Base Plate Volume to Shaft Volume
– Liquid Metal Embrittlement / Chemistry of Bath and Base Metal
– Hardness testing
– Thermal Stress Analysisy
Bend Radius Study
• Variable radii per sample
Bend Radius Study
Variable radii per sample
• Variable radii per manufacturer
G d b S d i i f• Governed by ASTM and American Institute of Steel Construction Design Manual– For hot‐dip galvanized structural steel products, ASTM 143 recommends bend radius ≥ three times the member thicknessthe member thickness
Bend Radius StudyBend Radius StudyHigh Mast/Pole Data
*Asterisk denotes existence or indication of initial cracks
Bend Radius StudyMast Arm DataThickness Avg Inside Bend
Bend Radius Study
Specimen NameThickness
(in)Avg. Inside Bend
Radius (in)R/T
10‐2R‐EC‐PG‐A 0.179 0.48 2.67
10‐2R‐EC‐PG‐B 0.179 0.35 1.98
10‐2S‐WY‐PG‐A 0.179 0.65 3.60
10‐2S‐WY‐PG‐B 0.179 0.67 3.72
10‐3R‐WY‐PG‐A 0.179 0.42 2.33
12‐2R‐EC‐PG‐A 0.179 0.42 2.32
12‐2R‐EC‐PG‐B 0.179 0.35 1.98
12‐3R‐WY‐PG‐A 0.179 0.42 2.32
VII 1 0 188 0 47 2 49VII‐1 0.188 0.47 2.49
VII‐2 0.188 0.47 2.49
VII‐3 0.188 0.47 2.49
VII‐6 0.188 0.68 3.61
VII‐7 0.188 0.65 3.49
Bend Radius Study ConclusionsBend Radius Study Conclusions
Cracked SpecimensCracked Specimens
Specimen Name Radius/Thickness
33‐3‐12‐TX‐SG‐A* 4.64
33‐3‐12‐TX‐VG‐A* 4.08
33‐3‐12‐TX‐VG‐B* 3 92
• Cracked Specimens Had Larger R/t ratio then
33‐3‐12‐TX‐VG‐B 3.92
many uncracked specimens
• Radius/Thickness ratio does not seem to be a contributor to cracking
Base Plate to Pole Wall Volume Ratio Comparison
• Relationship between base plate weight (volume) and bottom 12” of shaft weight (volume) noticed in comparing designs that did and did not result in
ki i T C k i B Pl t W ld 30 Ycracking in Toe Cracks in Base Plate Welds – 30 Years Later by Richard Aichinger and Warren Higgins
• Shows that as this ratio increases the “Event• Shows that as this ratio increases the Event Probability” also increases in a nearly linear trend
• We have interpreted “Event Probability” as number• We have interpreted Event Probability as number of cracks divided by number of inspected bends
Percentage of Cracks Found in the Field and Laboratory versus Volume Ratio of Base Plate to Shaft
150'‐80mph60%
70%
Cracks
33‐3‐12‐TX
40%
50%
Bend
s with C
30%
40%
f Inspe
cted
B
100'‐80mph
125'‐80mph
175'‐80mph
10%
20%
ercentage of
175 80mph
24‐3‐16‐TX/WY0%
0 2 4 6 8 10 12 14
Pe
Base Plate to Shaft Volume (Bottom 12") Ratio
• No Correlation Found Between Volume Ratio and Cracks Discovered.
Chemistry AnalysisChemistry Analysis
• Pelco Structural and Steel Ameron UnionPelco, Structural and Steel, Ameron, Union Metals, and Valmont samples taken from high masts for chemical testing at Chicago Spectromasts for chemical testing at Chicago SpectroService Laboratory, Inc
• Steel chemistry differed slightly from• Steel chemistry differed slightly from fabricator to fabricator
• Field Repair SMAW• Field Repair ‐ SMAW– More than 1,467,734 cycles
F il f d b f ld ( b l )– Failure forced to base of weld (at base plate)
• Shop Repair ‐ FCAW– Nearly 1,893,306 cycles, deemed class D run out
Thermal StudyThermal Study
KHF
Thermal StudiesThermal Studies
• Galvanizing InstrumentationGalvanizing Instrumentation– Thermocouples attached to identical high masts during galvanizing
– Data recorded fromtwo separategalvani ersgalvanizers
– Indications of severetemperature gradienttemperature gradientbetween shaft andbase plate
81 of 10
Current WorkCurrent Work
• Finite Element Thermal Stress AnalysisFinite Element Thermal Stress Analysis– Thermal Conductivity Studies to Develop Heat Flow Between Bath and High Mast PolesFlow Between Bath and High Mast Poles
– Parametric Studies to Look at Effect of Base Plate Mass to Pole Mass Upon Thermal StressesMass to Pole Mass Upon Thermal Stresses
• Additional Full Size Specimens to Measure Temperature Response of Ground SleeveTemperature Response of Ground Sleeve Specimens and Development of Cracks