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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
28
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
32
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