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

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-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

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-6

-5

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-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.