1

COLD BENDING RESEARCH NEEDS

UNIVERSITY OF BALAMAND RESEARCH COUNCIL

JUNE 23rd, 2004

Courtesy S. Kozel

2

OUTLINE

• MOTIVATION

• PROPOSED METHOD

• PREVIOUS WORK

• CURRENT WORK

• FUTURE WORK

3

Cut Curving

Flange

Scrap

Flange

Flange

4

Fit-Up

Flange

WebPressure Applied During Fit-up

Fitting Jig

Flange

Pressure Applied During Fit-up

5

Problems ?

- Costly because of excessive waste

- Too much scrap for sharp curvatures

- Used for mild curvatures (R 300m)

- Fit-up operation too complicated

6

Heat Curving

Continuous Intermittent V-Heating

HEATED AREA

7

8

9

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.

10

3-ROLLERS BENDING

PINCHING PINCHING ROLLERROLLER

Courtesy AISC

11

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

12

13

MIAMI METROMOVER PROJECT

14

TAMPA STEEL1: Hydraulic jack (bot. flange)2: Hydraulic jack (top flange)3: Longitudinal arms4: Steel plate 5: Clamps

TAMPA STEEL

15

PROPOSED CONCEPT

8R

Lδ

2

max

L

1 2 3 4 5 7 6

2

3 5

6

max = 4

x

22max xRRδδ

16

FULL-SALE DEMOFULL-SCALE DEMO

17

Top Flange Bending

S

18

Bot Flange Bending

1: Jack2: Head3: Plate4: Angle5: Support6: String Line 7: Stiffener

1

23

4

5

6

7

19

FORMULATION

PARAMETERS:

- Load Frame Spacing S

- Bending Loads Ptf, Pbf

- Deflection within span S

- Segment Length Li

- Number of Segments n

- Offsets

S

PtfLi

20

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

21

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

22

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

23

SEGMENT LENGTH Li

S

4RΔLi

2Li

Radius R

S

[m-1][m+1]

[m]

S

L2 iConstant

tf

8R

l2

2Li2Li/S

24

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

25

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

26

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

27

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

28

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)

29

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

30

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

31

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.

32

Current Work

• Theoretical Investigation: 3D Finite Element Modeling

33

STRAIN

STRESS

y

Fy

max 10 y

Loading

Un-Loading

residual 8.5 y

Current Work

Strain Hardening

34

Current Work

- Effects of Cold Bending on Steel mainly fracture

characteristics:

- Perform Visual

Inspection using

NDT Techniques

35

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

36

ASSESSMENTS

37

38

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

39