bridge deck behaviour
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Austroads Bridge ConferenceAustroads Bridge Conference 200 20044HobartHobart MayMay 200 20044
Bridge Deck Behaviour Revisited
Doug Jenkins
Interactive Design Services
OverviewOverview:: 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 TechnologyChanges in Computing Technology
1976 Text based punched
card input 200 nodes; grillage
Linear static analysis
Printed text output
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 SystemsSpeed of Computer Systems Prof. E.L. Wilson Prof. E.L. Wilson
http://www.csiberkeley.com/support_technical_papers.htmlhttp://www.csiberkeley.com/support_technical_papers.html
1960 1970 1980 1990 2000 2010
Year
0.1
1
10
100
1000
10000
100000
Rel
ativ
e P
erfo
rman
ce
Main Frame Desktop Trend
Computer Performance1963 - 2003
AnimationAnimation
Hambly commentsHambly 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
Features of AnalysesFeatures of Analyses Downstand
Grillage Plates with downstand
beams
3D Brick models
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
Grillage 1aGrillage 1a
Grillage 1bGrillage 1b
Grillage 1cGrillage 1c
Grillage 2Grillage 2
Grillage 2 - detailGrillage 2 - detail
Plate Slab with Downstand BeamsPlate Slab with Downstand Beams
Brick ElementsBrick Elements
Brick Elements - detailBrick Elements - detail
Deflections at mid-span
-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
0 2 4 6 8 10 12 14
Position, m
De
fle
cti
on
, mm
Grillage 1a Grillage 1b Grillage 1c Grillage 2 Plate slab Brick
Top Face Stress
-2500
-2000
-1500
-1000
-500
0
0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00
Position, m
Str
es
s, k
Pa
Grillage 1a Grillage 1b Grillage 1c Grillage 2 Plate slab Brick
Bottom Face Stress
0
500
1000
1500
2000
2500
3000
3500
4000
4500
0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00
Position, m
Str
es
s, k
Pa
Grillage 1a Grillage 1b Grillage 1c Grillage 2 Plate slab Brick
Beam and Plate Analysis – Deflected ShapeBeam and Plate Analysis – Deflected Shape
Beam and Plate Analysis – Long. StressBeam and Plate Analysis – Long. Stress
Brick Elements – Long. StressBrick Elements – Long. Stress
Brick Elements – Cutting PlaneBrick Elements – Cutting Plane
Brick Elements – Cutting Plane, Selected ElementBrick Elements – Cutting Plane, Selected Element
Link SlabLink Slab
Deflections at mid-span
-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
0 2 4 6 8 10 12 14
Position, m
De
fle
cti
on
, mm
Grillage 1c Grillage + Link Plate Plate + Link
Brick Brick + Link No hinges
AnimationAnimation
Dynamic AnalysisDynamic AnalysisDeflection at mid Span, Outer Beam
-0.012
-0.010
-0.008
-0.006
-0.004
-0.002
0.000
0.002
0.00 0.50 1.00 1.50 2.00 2.50
Time, S
Def
lect
ion
, m
Plate dynamic Brick Dynamic Plate static Brick Static
AnimationAnimation
Summary of findings in paperSummary of findings in paperAdvantagesAdvantages
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 paperSummary of findings in paperNo Longer a ProblemNo Longer a Problem
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 paperSummary of findings in paperDisadvantagesDisadvantages
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 Review Hambly commentsHambly 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
RecommendationsRecommendations
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 non-standard features.
Consider the use of non-linear analysis and slab membrane action - potential for significant refinement of deck slab design.
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