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COLD BENDING RESEARCH NEEDS
UNIVERSITY OF BALAMAND RESEARCH COUNCIL
JUNE 23rd, 2004
Courtesy S. Kozel
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OUTLINE
• MOTIVATION
• PROPOSED METHOD
• PREVIOUS WORK
• CURRENT WORK
• FUTURE WORK
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Cut Curving
Flange
Scrap
Flange
Flange
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Fit-Up
Flange
WebPressure Applied During Fit-up
Fitting Jig
Flange
Pressure Applied During Fit-up
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Problems ?
- Costly because of excessive waste
- Too much scrap for sharp curvatures
- Used for mild curvatures (R 300m)
- Fit-up operation too complicated
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Heat Curving
Continuous Intermittent V-Heating
HEATED AREA
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Problems ?- Trial and error process relying on uneven
expansion/contraction.
- Takes time to heat and much longer to cool
down.
- Results not known till AFTER cooling.
- If it is not right, process must be repeated.
- Ties up shop, slow and costly.
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3-ROLLERS BENDING
PINCHING PINCHING ROLLERROLLER
Courtesy AISC
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Bridges: Current Status ?• Not allowed by AASHTO, concerns:
- Cracking, Fracture
- Flange Upsets
- Dimples
- Web Crippling
• No criteria is available
• Depends on skill and knowledge of fabricators
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MIAMI METROMOVER PROJECT
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TAMPA STEEL1: Hydraulic jack (bot. flange)2: Hydraulic jack (top flange)3: Longitudinal arms4: Steel plate 5: Clamps
TAMPA STEEL
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PROPOSED CONCEPT
8R
Lδ
2
max
L
1 2 3 4 5 7 6
2
3 5
6
max = 4
x
22max xRRδδ
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FULL-SALE DEMOFULL-SCALE DEMO
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Top Flange Bending
S
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Bot Flange Bending
1: Jack2: Head3: Plate4: Angle5: Support6: String Line 7: Stiffener
1
23
4
5
6
7
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FORMULATION
PARAMETERS:
- Load Frame Spacing S
- Bending Loads Ptf, Pbf
- Deflection within span S
- Segment Length Li
- Number of Segments n
- Offsets
S
PtfLi
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LOAD FRAME SPACING (S)
Based on lateral bracing limit:
S = 14.4c for Grade 250 steel
S = 12.2c for Grade 345 steel
For unsymmetrical sections use ctf
Load P
Comp. side
Flange
S = Lp
Fla
ng
e
Wid
th 2
c
yt F
E1.76rS
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BENDING LOADS (Ptf, Pbf)
From simple beam plastic load analysis:
S
ct4FP
2fy
Mp = Fytfc2
Fytfc
4
PSM p
P
S
c
c
Fytfc
Constant
Top Flange: Ptf based on ttf, ctf
Bot. Flange: Pbf based on tbf, cbf
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DEFLECTION
216Ec
S13FΔ
2y
Load P
S
Plastic Hinge
tf
bf
ctf cbf
Ptf Pbf
tf bf
set = cte = tf
bf ???
P Pbf
(not in this scope)
Set P = Pbf,
Load in cycles
m=tf/bf
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SEGMENT LENGTH Li
S
4RΔLi
2Li
Radius R
S
[m-1][m+1]
[m]
S
L2 iConstant
tf
8R
l2
2Li2Li/S
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NUMBER OF SEGMENTS n
iL
S-Ln
n
S)-(LLi
Round-down to the nearest even integer
nLi
1 2 3 4 5 n+1 n
Length L
a a
Line of symmetry
adjust
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OFFSETS ii, ij
55
1 2 3 4 5 6
22
23 33
24 34 44
45
Load: 4
25 35
7
Load: 3
Load: 2
Load: 5
Load: 6
26 3646 56 66
1in
n
1)i(iδ4δ
3maxii
j
1ij2maxiiij n
1jn
n
1)-(iδ8δ
max
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FABRICATION AIDS (LOADS)
100 200 300 400 500 600 700
0.2
0.4
0.6
0.8
1.0
P/tfc2 (kN/cm3)
S (cm) G 250
G 345
G 400
215cm
0.46kN/cm3
Ptf =0.462.5152 = 260kN,Pbf =0.465252 = 1440kN
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FABRICATION AIDS (Deformations)
c (cm2)
S (m)
100 200 300 400 500 600 700
0
10
20
30
40
50
60
S (cm)
G 250
G 345
G 400
S = 215cm
3.5cm2
tf = 3.5/15 = 0.23cm,bf = 3.5/25 = 0.14cm
1.650.14
0.23
Δ
Δ
bf
tf
round-up to 2
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FABRICATION AIDS (Multiple Load)
/(S2/c)105
S (m) R/c (cm/cm)
G 250 G 345
G 400
90 100 110 120 130 140 150 160
1
2
3
4
5
6
7
8
9
10
Px/tfc2/S(kN/cm2)
Bot. Flange load
= (tf – bf)=0.09cm
[/(S2/c)]105 = 4.9.
2up)(roundΔ
Δ
bf
tf
4.9
97 Px=975(25)2/215=1400k
N
(kN/cm2)
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250 750 1250 1750 2250 2750 3250
0.00
0.25
0.50
0.75
1.00
1.25
1.50
FABRICATION AIDS (Segments)
Li/S cm/cm)
S (m) R/c (cm/cm)
G 250
G 345G 400
80015
12000
c
R
tf
800
Li=0.25215=53.75cm
n=(1200–215)/53.75= 18.3
Round-down to n=18.
Li=(1200–215)/18= 55 cm
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SUMMARY
- Development of a standardized cold curving
procedure.
- Relationships (loads vs. deformations),
Fabrication Aids are now available.
- Limits are set on maximum strains (plastic)
Note: Residual stresses may be released by
heat treatment
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PUBLICATIONS• Sen,R., Gergess,A. & Issa,C. “Finite Element Modeling of Heat-Curved I-Girders”
ASCE Journal of Bridge Eng, Vol. 8, No. 3, May/June 2003,pp.153-161.• Gergess A. & Sen R. (2003). “Simplified Heat-Curving Analysis”. Journal of
Transportation Research Board, No. 1861, Construction, pp. 101 - 114 • Gergess, A. & Sen, R. “Inelastic Response of Simply Supported I-Girders
Subjected to Weak Axis Bending,” Proceedings of the International Conference on Structural Engineering, Mechanics and Computation, Cape Town, South Africa, Edited by A.Zingoni, Vol. I, pp 243-250, 2001.
• Gergess, A. and Sen R. “Fabrication Aids for Cold Straightening Structural Steel Girders”. AISC, Engineering Journal (in press), 2004.
• Gergess, A. and Sen R. “Cold Curving Un-symmetric Un-stiffened Steel Girders, Journal of Constructional Steel Research, London, UK (in press), 2004.
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Current Work
• Theoretical Investigation: 3D Finite Element Modeling
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STRAIN
STRESS
y
Fy
max 10 y
Loading
Un-Loading
residual 8.5 y
Current Work
Strain Hardening
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Current Work
- Effects of Cold Bending on Steel mainly fracture
characteristics:
- Perform Visual
Inspection using
NDT Techniques
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Property ASTM A709
Grade 345
ASTM A709
HPS 485W
Plate Thickness up to 5 cm (2 in.) up to 10 cm (4 in.)
Yield Strength 345 Mpa (50 ksi) 485 Mpa (70 ksi)
Tensile Strength min. 404 MPa
(min. 58 ksi)
620 – 758 MPa
(90 – 110 ksi)
Min. Elongation
5 cm (2 in.) 21% 19%
Toughness: CVN
Fracture Critical
Zone 3
35 m-N @ -12C
(25 ft-lbf @ 10F)
6.35 cm (TO 2.5 in.)
47 m-N @ -23C
(35 ft-lbf @ -10F)
6.35 cm (TO 4in.)
AASHTO Requirements
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ASSESSMENTS
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Acknowledgments
• Samuel & Julia Flom Fellowship: USF
• Dr. Rajan Sen
• Ronald Medlock, Texas DOT “Performance and
Effect of Hole Punching and Cold Bending on Steel Bridges”.
Research project conducted by University of Texas at Austin and
Texas A&M University, 2003.
• TRB/AASHTO/NSBA
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