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Buckling Behaviour of Steel Truss-wongjeeraphat
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Buckling behavior of Steel TrussBuckling behavior of Steel Truss
Rangsan Wongjeeraphat
by
Rangsan Wongjeeraphat
Supervisor: DrTodd HelwigSupervisor: Dr.Todd Helwig
STEER
The Common Conference CenterJ J Pickle Research Campus
March 4, 2010
J.J. Pickle Research CampusThe University of Texas at Austin
Study Objectivey j
To improve the understanding of the stability To improve the understanding of the stability behavior of truss systems
To study the requirements for both lateral and torsional bracing requirements for truss and torsional bracing requirements for truss system
Truss Behavior
C
PPP
TT
The truss system consists of a collection of axial loaded members to form a flexural system. Therefore question often arise about the truss behaving like a column or more often arise about the truss behaving like a column or more like a beam
Design of brace for trussg
AISC S ifi iAISC SpecificationIn the appendix 6 of commentary section on stability bracing for columns and beamsbracing for columns and beams
Truss Bracingg
Several factors affect truss buckling behavior:
Internal factors: Out‐of‐plane stiffness of web elementspThe axial compressive loads in the chordsThe alignment of the vertical and diagonal web elements
External factors:The local and global initial imperfectionsLoad location and positionLoad location and positionType of bracesLocation of braces on the cross‐section
Overview of Experimental Programp g
The experimental program includes several t ti t i l di
Lateral stiffness test
testing stages, including:
Lateral stiffness testLoad height effect test
Top chord loading Bottom chord loading
Tests on torsional bracing systemBracing at top chord Bracing at top chord Bracing at bottom chord (Pony Truss)
Tests on lateral bracing system
Truss System with Lateral Bracing y g
P P Lateral brace
link
(Stiffness = 0.2, 0.5, 0.8 kip/in)
Height adjustable to ffchange stiffness
Lateral brace system
Truss cross‐section at brace point
Truss System with Lateral Bracing y g
P P
linklink
Lateral brace system
Truss cross‐section at brace point
Truss System with Torsional Bracing y g
Bottom chord loading case Top chord loading caseg
P P
p g
Torsional brace
P P
Truss cross‐section at third point
Torsional brace
Truss cross‐section at third pointthird point third point
Truss System with Torsional Bracing y g
Gravity Load Gravity Load Simulator
Torsional brace
Bottom chord loading test with 3 small torsional braces at bottom chord
Load‐Lateral Deflection Curve
72‐ft span
14 0
12.0
14.0
8.0
10.0
ad (kips)
4.0
6.0
Total Loa Top chord ‐ Bottom chord loading test
Bottom chord ‐ Bottom chord loading test
Top chord ‐ Top chord loading test
0.0
2.0
Bottom chord ‐ Top chord loading test
0.0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Lateral Deflection (in)
Results of buckling test
Lateral Deflection at mid span top chord
gWith lateral braces
60
70
Lateral Deflection at mid span top chord
No Lar Br
40
50
kips)
1 Lat Br K = 0.2 k/in
1 Lat Br K = 0.5 k/in
1 Lat Br K = 0.8 k/in
2 Lat Br K =0.2 k/in
2 Lat Br K = 0 5 k/in
20
30
Total Loa
d ( 2 Lat Br K = 0.5 k/in
2 Lat Br K = 0.8 k/in
10
20
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Lateral Deflection (in)
Results of buckling testg
Lateral Deflection at mid span top chord
With torsional braces
60
70Lateral Deflection at mid span top chord
40
50
kips)
No Tor Br: BC Load
2 Sm Tor Br at BC: BC Load
30
Total loa
d (k 3 Sm Tor Br at BC: BC Load
2 Lrg Tor Br at BC: BC Load
No Tor Br: TC Load
2 Sm Tor Br at TC: TC Load
3 S T B t TC TC L d
10
20 3 Sm Tor Br at TC: TC Load
2 Lrg Tor Br at TC: TC Load
0
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5
Lateral deflection (in)
Current work
• Developing the FEA model• Verify the model with the laboratory test resultsVerify the model with the laboratory test results• Parametric study
FEA model with 3 large torsional braces at bottom chord with
bottom chord loading
Summaryy
The load height effect exists in truss and causes the truss system to behave similar to a beamthe truss system to behave similar to a beamAdding the proper lateral and torsional bracing stiffness as well as the proper number of braces p pis necessary to improve the buckling capacity of a truss. Th ff ti f ddi l t l b The effectiveness of adding a lateral brace decreases with an increase in the number of the bracesAdding torsional braces is more effective in top chord loading cases than in bottom chord l dloading cases
THANK YOUTHANK YOU
Question ?
