wind loading on historic covered bridgescovered bridges
TRANSCRIPT
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Wind Loading on Historic Covered BridgesCovered Bridges
F Michael Bartlett J Peter C KingF. Michael BartlettCivil & Enviro. Engg.
J. Peter C. KingBoundary Layer Wind T l L bWestern Engineering
London, CanadaTunnel LaboratoryLondon, Canada
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This Afternoon’s RoadmapThis Afternoon s Roadmap
• Introduction• Introduction• Existing Wind Provisions for
C d B idCovered Bridges• Wind Tunnel Tests• Data Analysis
– “Cladding” (Roofing and Siding) Loadsg ( g g)– Forces in Main Members
• ConclusionsConclusions
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This project p jinitiated in
OhioOhio…
8th Historic Bridge Conference, Columbus, April 2008
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A gap between bridges and buildings…
• AASHTO Guide Specifications for• AASHTO Guide Specifications for Design of Pedestrian Bridges (1997) specifies 3 6 kPa (75 psf)specifies 3.6 kPa (75 psf)– Seems excessive! May require
t th i d t l ithstrengthening end portals with structural steel
• ASCE Minimum Design Loads for Buildings and Other Structures less stringent
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Some confusion in practiceSome confusion in practiceBridge Source Design LoadBridge Source Design LoadBurkeville Lee & Brenner
(2008)0.58 kPa (12 psf)
Hutchins Bicja (2008) Walls: +/-1.41 kPa (29 psf)Roof: +0.33/-0.88 kPa
(+7/-18 psf)(+7/-18 psf)AASHTO (1997) 3.6 kPa (75 psf)
Research Objective: What load should be used?What load should be used?
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Western’s Boundary Layer Wind T l L b tTunnel Laboratory
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“Boundary Layer”
ucdavis.edu
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Maumee River Bridge in tunnel
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Getting by with a little help from our friends…
H l T & A i t I• Hoyle, Tanner & Associates Inc. graciously provided:
– Drawings of a representative historic covered bridgehistoric covered bridge
– STAAD computer model
– Thoughtful feedback and advice throughout the project!throughout the project!
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H t hi C d B id b fHoyle, Tanner & Assoc., Inc.
Hutchins Covered Bridge – before rehabilitation
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1:40 model by David Mizzeny
204 pressure taps in204 pressure taps in roof, walls, soffit
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P i it M d l Di i WTProximity Model Disc in WT
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Test ProgramTest Program
10 i d• 10 wind angles
• 3 water• 3 water clearances
• 3 side opening ratios
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Data AnalysisData Analysis
• Cladding pressures• Cladding pressures• Main member force effects• Worst cases for walls with:
– small openingsp g– any water clearance
wind from any direction– wind from any direction
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30 psf 35 psf
Peak Positive NetRoof End
Peak Positive Net Cladding Pressures
Side 45 psf
Soffit
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-80 psf40 psf
-75 psf-40 psf
Peak Negative NetRoof End
Peak Negative Net Cladding Pressures
35 psfSide
-35 psf
Soffit
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Hurricane Hugo, North C li 1989Carolina, 1989
Gable Roof Damaged Hip Roof UndamagedGable Roof Damaged Hip Roof Undamaged
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Member Forces Analysis
Time historyTime history of pressures
Time historyTime history of member
forcesforces
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Comparison of Member ForcespMember
(Force type)WT
AASHTOWT
ASCE 74 5 (Force type) AASHTO ASCE 71 (F) 0.56 0.762 (M) 0.65 0.84
14 5
3 (M) 0.61 0.834 (F) 0.67 1.034 (M) 0.62 0.70
2( ) 0 6 0 0
5 (F) 0.64 0.905 (M) 0.66 0.94Avg 0 63 0 86Avg. 0.63 0.86
3ASCE 7 stringentASCE 7 stringent
AASHTO very stringent
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ConclusionsConclusions1. Check main wind-load resisting g
members using wind loads from ASCE 7 as those specified in pAASHTO (1997) are excessive.
2 The 3 6 kPa (75 psf) press re2. The 3.6 kPa (75 psf) pressure specified by AASHTO is accurate for cladding suctions at the ridge andcladding suctions at the ridge and eave at the end of the roof but is excessive elsewhereexcessive elsewhere.
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Paper AvailablePaper Available
Mizzen D King J P C and BartlettMizzen, D., King, J.P.C., and Bartlett, F.M. (2010): “Wind Loading on Historic Covered Bridges” Proceedings of theCovered Bridges . Proceedings of the 8th International Conference on Short and Medium Span Bridges Niagaraand Medium Span Bridges, Niagara Falls, Canada.
Request from: [email protected]
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Acknowledgementsg• D. Mizzen and T. Scott, Western
Engineering U/G Thesis Students • J. Bicja, S. James and M. Low, Hoyle, j , , y ,
Tanner & Associates Inc., Manchester, New Hampshire , p
• B. Schmidt, Dillon Consulting Ltd., London CanadaLondon, Canada
• Natural Sciences and Engineering Research Council of CanadaResearch Council of Canada
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Questions?Q
West Montrose Covered Bridge, Waterloo Region, Ontario (T. Scott photos)
Later: f m bartlett@uwo caLater: [email protected]