Chiew Sing-Ping

School of Civil and Environmental Engineering

NANYANG TECHNOLOGICAL UNIVERSITY

9 July 2015

Pipe Strut vs. Laced Strut

Pipe Strut vs. Laced Strut

Laced Strut

2

Pipe Strut

PLAXIS Soil-Structure Interaction Analysis

3

Wall (Beam element)

Strut (Bar element)

4

Wall max BM = +82.6 kNm/m

and -107.8 kNm/m

Distribution of wall

bending moments

dhmax = 68.9 mm

Wall deflection profile

PLAXIS Soil-Structure Interaction Analysis

5

compression is -ve

Strut forces

PLAXIS Soil-Structure Interaction Analysis

Pipe Strut vs Laced Strut

Part 1: What is Pipe Strut?

• Production Process: ERW, Spiral, UOE

Press-Forming & Roll-Forming

Part 2: Why use Pipe Strut?

• Design of Pipe Strut vs. Laced Strut

• Section Efficiency Study

Part 3: How to use Pipe Strut?

• Pipe Connectors for Fixed and Free Ends

6

What is Pipe Strut?

7

SPIRAL-WELDING

UOE PRESS-FORMING

ELECTRIC-RESISTANT WELDING

ROLL-FORMING

How to produce a pipe?

ERW – Electric Resistant Welding

8

UOE Press-Forming

9

Spiral Welding

10

Why use Pipe Strut?

Design of pipe strut according to EC3

1. Section classification

2. Non-dimensional slenderness

3. Buckling curve

4. Reduction factor

5. Buckling resistance

11

1

1

i

Lcr

yf2359.931

0

,

M

y

Rdb

AfN

22.015.0

22

1

formed cold 49.0

finishedhot 21.0

Design of Laced Strut

12

2 types of built-up struts

Laced Strut Battened Strut

Chord

Batten Lace

Module

Design of Laced Strut

Efficient Laced Strut:

• Iz’z’ ≥ Iyy

• z’ ≥ y (affected by module length a)

• Strong laced members

13

z'

y y

z'

Design of Laced Strut

Section properties of laced strut with two identical members

Effective second moment of area:

(EC3-1-1,§6.4.2.1)

14

cheff AhI2

050.

Ach Area of the chord

h0 distance between the centroids of chords

Design of Laced Strut

15

chzzAhI

2

05.0'' 2

ychyy iAI

15.05.0

2

2

0

2

2

0''

ychy

ch

yy

zz

i

h

Ai

Ah

I

I

20 yi

h

radius of gyration about y-axis

Effect of Global Stiffness

Buckling modes:

16

20 yi

h20

yi

h

Out-of-plane

buckling In-plane

buckling

Effect of Module Length ‘a’

Buckling mode with inappropriate module length between

lacing members:

17

Local In-plane

chord buckling

Effect of Laced Member

Buckling modes with weak laced members:

18

Laced

member

buckling

Torsional

buckling

Section Efficiency Study

19

Strut force

(kN/m)

Strut

spacing (m)

Force

(kN)

160 6 960

210 6 1260

250 6 1500

290 6 1740

700 6 4200

1000 6 6000

1300 6 7800

2000 6 12000

2300 6 13800

2500 6 15000

Strut

Strut length L

h

Strut spacing @ 6m c/c

Strut Force

Compressive Resistance 6000 kN

20

Strut L

(m) Pipe λ

Weight

(kg/m)

12 711×12 0.56 207

15 762×12 0.65 222

20 813×12 0.81 237

25 914×12 0.90 267

30 965×12.7 1.03 298

35 1016×14.3 1.14 352

40 1067×14.3 1.24 370

45 1067×16 1.39 415

50 1168×16 1.42 455

55 1219×16 1.49 475

60 1219×20 1.63 591

Strut L

(m) Laced λy

Weight

(kg/m)

12 610×229UB101 0.57 222.6

15 610×229UB113 0.7 248.6

20 610×229UB125 0.93 275.2

25 610×305UB149 1.12 328.2

30 686×254UB170 1.23 374.4

35 838×292UB176 1.22 387

40 914×305UB201 1.29 442

45 914×305UB224 1.43 493

50 1016×305UB249 1.48 548

55 1016×305UB272 1.58 598

60 1016×305UB314 1.73 691

Weight kg/m for pipe and laced struts for various length

Grade S275

Compressive Resistance 6000 kN

21

0

100

200

300

400

500

600

700

800

10 20 30 40 50 60 70

We

igh

t (k

g/m

)

Strut length (m)

Pipe

Laced

Compressive Resistance 12000 kN

22

Strut

L (m) Laced λy

Weight

(kg/m)

12 838×292UB194 0.41 426.6

15 838×292UB194 0.51 426.6

20 914×305UB201 0.65 442

25 1016×305UB222 0.76 488.4

30 1016×305UB249 0.89 547.1

35 1016×305UB272 1.01 599

40 1016×305UB314 1.15 691.5

45 1016×305UB393 1.29 864

50 1016×305UB437 1.43 961

55 1016×305UB487 1.56 1071

60 3/1016×305UB393 1.72 1297

Strut

L (m) Pipe λ

Weight

(kg/m)

12 1016×16 0.39 395

15 1016×16 0.49 395

20 1016×16 0.65 395

25 1168×14.3 0.71 406

30 1168×16 0.85 455

35 1168×19 0.99 540

40 1219×20 1.09 591

45 1320.8×19 1.13 611

50 1320.8×22.2 1.25 711.6

55 1320.8×27 1.39 860.6

60 1320.8×30.2 1.51 960.3

Weight kg/m for pipe and laced struts for various length

Grade S275

Compressive Resistance 12000 kN

23

300

500

700

900

1100

1300

1500

10 20 30 40 50 60 70

We

igh

t (k

g/m

)

Strut length (m)

pipe

Laced

Resistance & Slenderness vs. Steel Grade

24

Strut

L (m) Pipe

Weight

(kg/m)

Slenderness λ Resistance (kN)

S275 S355 S460 S275 S355 S460

4 323.9×6 47 0.41 0.47 0.53 1564 1986 2602

8 355.6×6.3 54.3 0.74 0.84 0.96 1570 1887 2396

12 406×7.1 70.3 0.98 1.11 1.27 1672 1864 2167

15 457×7.1 79 1.09 1.23 1.4 1678 1821 2032

20 457×10 110 1.46 1.66 1.89 1503 1557 1671

25 508×12 147 1.65 1.87 2.13 1630 1674 1775

30 508×16 194 1.99 2.25 2.57 1533 1560 1632

35 508×25 298 2.36 2.68 3.04 1708 1730 1794

40 508×32 376 2.73 3.1 3.53 1638 1655 1707

Design resistance of strut = 1500kN

Suitable pipe sections with unit-weight (kg/m) for various

strut length are given below

Resistance & Slenderness vs. Steel Grade

25

Sle

nd

ern

es

s

0

0.5

1

1.5

2

2.5

3

3.5

4

0

500

1000

1500

2000

2500

3000

0 5 10 15 20 25 30 35 40 45

Re

sist

ance

(kN

)

Strut length (m)

S275 S355 S460

Slend275 Slend355 Slend460

When the slenderness is beyond the range of 1.0 - 1.5, the

high strength steel contributes little to compression

resistance.

Sle

nd

ern

ess

Influence of Steel Grade

Design resistance =1500 kN

Suitable pipe sections with different steel grade

26

Strut L

(m)

S275 S355 S460

Pipe Weight

(kg/m) Pipe

Weight

(kg/m) Pipe

Weight

(kg/m)

4 323.9×6 47 273×6 39.5 219.1×6.3 33

8 355.6×6.3 54.3 323.9×6.3 49.3 273×8 52.3

12 406×8 78.6 355.6×8 68.6 355.6×8 68.6

15 406×10 98 406×8 78.6 355.6×12 101

20 457×10 110 457×10 110 406×14 135

25 508×12 147 508×12 147 457×14.2 155

30 508×16 194 508×16 194 508×16 194

35 508×25 298 508×25 298 508×25 298

40 508×32 376 508×32 376 508×32 376

Influence of Steel Grade

27

0

50

100

150

200

250

300

350

400

0 10 20 30 40 50

we

igh

t (k

g/m

)

Strut Length (m)

S275 S355 S460

Advantages of Pipe Strut

Design of pipe strut is simpler; lesser chance of making

a mistake

Smaller diameter pipe strut will not be competitive

Larger diameter pipe strut can span longer and/or take

higher strut force without any intermediate restraint

(i.e. no king post, runner beam or splay; hence, higher

productivity)

No clear advantage in using higher grade steel because

design govern by buckling for long span strut

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How to use Pipe Strut?

29

Mast Section Fixed End Free End for manual

pre-loading

Hydraulic

Jack

Automatic hydraulic

system

Connector

Example of Free End – Type 1

30

Common specification: Φ800*1450 mm

Adjustable range: 0-30 cm

Example of Free End – Type 1

31

Detachable End

Example of Free End – Type 2

Steel wedge to lock the strut after pre-loading

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Example of Free End – Type 3

33

Example of Free End – Type 3

Typical connection between Free End and Waler

34

Filling pile

Waler

Steel pipe

Free End

Detachable End

Hydraulic Jack

Hydraulic Jack

Steel wedge

Bolted connection

Example of Fixed End

35

Twin

Waler

900mm

700mm

500mm

300mm 500mm

Flexible Cone Connectors

36

Stiffener

Flexible cone

connector

Twin

Waler

Flexible Cone Connectors

37

500mm φ

300mm φ

Stiffener

Connection between Mast Sections

Bolted connections and connectors

38 Bolts

Connector

Concluding Remarks

Use of laced struts in Singapore is highly developed

and efficient because of our many years of experience

of MRT construction.

For pipe strut to be more competitive and productive, it

has to space wider and span longer without any

intermediate restraint.

This will naturally lead to the use of larger diameter

pipe struts.

However, pre-loading and connection design will be

more challenging.

Some clever device for manual or automatic pre-loading

and flexible connectors will have to be developed.

39