Transcript Training

Austroads Bridge Conference 2004
Hobart May 2004
Bridge Deck Behaviour
Revisited
Doug Jenkins
Interactive Design Services
Overview:
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Changes in computing technology
Illustration – dynamic analysis animation
Features of alternative analysis methods
Hambly’s comments on FE analysis
Summary of findings in paper
Examples of advanced analysis techniques
Conclusions
Copy of presenation:
www.interactiveds.com.au
Changes in Computing Technology
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1976
Text based punched
card input
200 nodes; grillage
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Linear static analysis
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Printed text output
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2004
Interactive graphical
input
100,000 nodes; 3D
brick elements
Non-linear and dynamic
analysis
Interactive, animated
graphical output
ftp://download.intel.com/research/silicon/moorespaper.pdf
Speed of Computer Systems
Prof. E.L. Wilson
http://www.csiberkeley.com/support_technical_papers.html
Computer Performance
1963 - 2003
Relative Performance
1 00 00 0
1 00 00
1 00 0
1 00
10
1
0 .1
1 96 0
1 97 0
1 98 0
1 99 0
2 00 0
Y ear
M a in F ra m e
D e sk top
T re n d
2 01 0
Animation
Hambly comments
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Powerful and versatile analytical ... with a sufficiently
large computer,
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Often requested by clients, or proposed to a client,
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Cumbersome to use and is usually expensive.
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Choice of element type can be extremely critical
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Full time occupation which cannot be carried out ...
by the senior engineer responsible for the design.
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Unlikely to have time to understand or verify ... data.
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Difficult to place his confidence in the results
Features of Analyses
Transverse variation in the
level of the neutral axis.
Transverse and
longitudinal in-plane
forces
Distortion of beam
members
Torsional and distortional
warping effects
Local bending effects
Model skew decks exactly
Downstand
Grillage
Plates with
downstand
beams
3D Brick
models
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Grillage 1a
Grillage 1b
Grillage 1c
Grillage 2
Grillage 2 - detail
Plate Slab with Downstand Beams
Brick Elements
Brick Elements - detail
Deflections at mid-span
-2
-3
0
2
4
6
8
10
12
14
-4
Deflection, mm
-5
-6
-7
-8
-9
-10
-11
-12
Position, m
Grillage 1a
Grillage 1b
Grillage 1c
Grillage 2
Plate slab
Brick
Top Face Stress
0
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
Stress, kPa
-500
-1000
-1500
-2000
-2500
Position, m
Grillage 1a
Grillage 1b
Grillage 1c
Grillage 2
Plate slab
Brick
Bottom Face Stress
4500
4000
3500
Stress, kPa
3000
2500
2000
1500
1000
500
0
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
Position, m
Grillage 1a
Grillage 1b
Grillage 1c
Grillage 2
Plate slab
Brick
Beam and Plate Analysis – Deflected Shape
Beam and Plate Analysis – Long. Stress
Brick Elements – Long. Stress
Brick Elements – Cutting Plane
Brick Elements – Cutting Plane, Selected Element
Link Slab
Deflections at mid-span
-2
-3
0
2
4
6
8
10
12
-4
Deflection, mm
-5
-6
-7
-8
-9
-10
-11
-12
Position, m
Grillage 1c
Brick
Grillage + Link
Brick + Link
Plate
No hinges
Plate + Link
14
Animation
Dynamic Analysis
Deflection at mid Span, Outer Beam
0.002
0.000
0.00
0.50
1.00
1.50
2.00
Deflection, m
-0.002
-0.004
-0.006
-0.008
-0.010
-0.012
Time, S
Plate dynamic
Brick Dynamic
Plate static
Brick Static
2.50
Animation
Summary of findings in paper
Advantages
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Transverse distribution of live loads - significantly
reduce maximum design stresses in longitudinal
members.
Distribution of wheel loads - more accurate estimate
top slab bending moments, without the need for
introducing separate local analyses.
Analysis of secondary effects such as differential
temperature and shrinkage
Ends of skew decks and link slabs modelled more
exactly, including three dimensional effects.
Summary of findings in paper
No Longer a Problem
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Finite element models may now be produced and
analysed using standard computing equipment in a
shorter time than a grillage analysis would have
taken in the recent past.
The accuracy of complex models may be checked
against grillage analysis, or individual elements may
be checked against simple analysis methods.
Three dimensional contour plots of stresses or plots
of the deformed shape of structures are easily
produced, allowing engineers not directly involved in
the analysis to review the results, and check the
validity of the model.
Summary of findings in paper
Disadvantages
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More difficult to extract member actions,
particularly for large elements such as bridge
beams.
Design engineers must be trained in the use
of complex software to use it efficiently.
Verification process may be more difficult,
particularly if detailed analysis has resulted in
lower design actions than a simpler analysis.
Review Hambly comments

Powerful and versatile analytical ... with a sufficiently
large computer,

Often requested by clients, or proposed to a client,

Cumbersome to use and is usually expensive.

Choice of element type can be extremely critical

Full time occupation which cannot be carried out ...
by the senior engineer responsible for the design.

Unlikely to have time to understand or verify ... data.

Difficult to place his confidence in the results
Recommendations
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Standard analysis procedure:- Plate slab
model with longitudinal beam members
Use pre and post-processor software,
specifically designed for bridge decks.
Use brick models to further refine the design,
or to investigate the behaviour of nonstandard features.
Consider the use of non-linear analysis and
slab membrane action - potential for
significant refinement of deck slab design.