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10th June 2010
The process of reexamination of concrete infrastructures constructed before 1975
Shear capacity old concrete structures, scope of Rijkswaterstaat(MOT), TNO Research and Delft University of Technology(InfraQuest-Centre for Roads and Infra)
Ane de Boer Ministry of Transport, Centre of Infrastructure
the Netherlands
Scope of Research2 10th June 2010
Contents
• Introduction• Vehicle Load Development vs Development Recommendations• Examples Accidents/Incidents ?• Research history recommendations Netherlands• Scheme of actions reexamination old structures• Material research• WIM research: Vehicle / Axles measurements trends• Structural research• Testing structures in situ• DT/NDT methods• Future work: strengthening structures• Questions to this audience
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Scope of Research3 10th June 2010
Why a research of the condition of concrete bridges?
• Why are there problems withconcrete strutures ?
• Structures are getting older; 60% are build before 1975
• Increase of traffic volume and load till 2000
• Increase asphaltload (ZOAB)• Change in design and safety
philosophyand
• Incidents in foreign countries
Scope of Research4 10th June 2010
Birthyear of concrete viaducts/bridges
Total 3500 structures Highwayswhere 60% build before 1975
100
200
300
400
500
600
700
0
< 195
0
1951
-1955
1956
-1960
1961
-1965
1966
-1970
1971
-1975
1976
-1980
1981
-1985
1986
-1990
1991
-1995
1996
-2000
2001
-2005
Period
Num
ber [
-]
Viaduct over HighwayViaducts in HighwayBrug Fixed – Concrete smallBrug Fixed – Concrete large
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Scope of Research5 10th June 2010
1950
1960
1970
1980
1990
2000
2007
2005
Heavy weight vehicles Design Bridges viaducts
Fatigue cracks steel bridges; 1997 movable part Brienenoordbrug
Introduction Eurocode (2002)
VB 74: strong change in concrete mechanics behaviour
VOSB 1963; traffic load lanedependancy
Using sidelane highways – checksconcrete structures to the Eurocode
Hollandse bridge problems!
Rapid increase numberof highways
60% structures < 1975
Widewheels
Numbers 50 ton <
Increase of Widewheel vehicles
Numbers 50 ton >
Slow lane: Daily Passing Heavy Vehicles= 10.000 !!
Increase axle-load8 -> 10 ton
Numbers 50 ton <<
Increase mass “solo” vehiclesNumbers 50 ton >>
Scope of Research6 10th June 2010
Incident Montreal bridge collapse (October 2006)
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What happens?• Viaduct from 1970 with precast girders• Brittle crack (!) in support after 36 years operation• Large maintenance works in 1992 (joints and asphalt changes)• Understanding of faults (!)
1985 1992 2004
Scope of Research8 10th June 2010
Example in the Netherlands(cracks, only damage!):In-situ prestressed box-girder bridge• Inspections: Shearcracks in webs• In motorway RW 50; Bridge over the river Rhine near Arnhem• Built in the period 1968-1971
How safe is this bridge ?• Current traffic heavier then the
traffic in the design period
• Thickness asphalt layer (±30 cm instead of 12 cm) to keep a smooth surface, locally extra deflections at the hinges !!
• Shear cracks in the webs
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Scope of Research9 10th June 2010
Scope of Research10 10th June 2010
Shear Cracks in webs box-girder(two-cell)
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Research Overview History of NL-Recommendations• Engineering judgement based on actual loads, but checks on old material
recommendations: Reinforced concrete 1912, 1918, 1930, 1940, 1950, 1962 Prestressed concrete …………………………………………1962, 1967 Structural concrete ……………………………………………………1974, 1978, 1995
• Pro: no real differences regarding trendfactors in recommendations• Contra’s:
1) lack of knowledge at engineers old recommendations2) complex design coupling new to old3) law says: checking structures to the actual recommendation
• Solution: 1) translate the old design philosophy to the modern partial safety factors(load and material) and2) translate old material properties to modern characteristic material properties
Need: Recommendation Existing Bridge Structures
Scope of Research12 10th June 2010
Inventory state of art structures- Photo’s, QuickScan calculation- Result: Structure condition index
Reanalysis of the structure- Beam or slab analysis- Result: Modified Structure condition index
DrillingDrilling concrete concrete cylinderscylinders corescores fromfrom the the structurestructure-- CompressionCompression and and tensiontension teststests-- ResultResult: : ActualActual materialmaterial behaviourbehaviour forfor input input nextnext analysisanalysis
Refine analysis of the structure- 3D structure/solid analysis of the structure- Result: Remodified structure condition index
Nonlinear and/or probabilistic analysis- Result: Ultimate structure condition index
Scheme of actions for reexamination existing structures
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Scope of Research13 10th June 2010
Approach: Phase 1 Inspection and inventoryTotal number relevant structures (including steel)
Type structure numberViaducts in highway 1515Viaducts over highway 930Bridges 711Tunnels & culverts 544Aquaducts 8Ecoducts 7Total 3715
Total constructed <1976 2020
Main categories: Slabs, Prefabricatedgirders, Box-girder bridges, Tunnels, Culverts, T-girdersDetails: dapped girders, support area, reinforcement details, etc.
Scope of Research14 10th June 2010
Research topicsMaterial property research1. Actual material measurements2. Test loading in lab(relation old and
new concrete[28-days strength] 3. Long term factor 4. Concentrated load distribution in
slabs)
5. Design philosophy for existingstructures
6. Complex analysis; nonlinear and probabilistic, guidelines
7. Test load in-situ(sand bags vs Belfavehicle)
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Scope of Research15 10th June 2010
Material Research
• Cores 140 structures– Development strength concrete, compression and tension– Number of cores per structure– Minimum strength per category
• Statistical research – Number of structures per category known as built
• Categories: Slabs, Prefabricated girders, Box-girder bridges, Tunnels, Culverts, T-girders
– Number of structures per category unknown as built(no drawings, no design analysis anymore)
• DT / NDT reinforcement geometry
Scope of Research16 10th June 2010
Material Research: Standard deviation distribution “old” compression strength
Standard deviation [N/mm2]
Cum
ulat
iflo
wer
-bou
ndfa
ilure
[-]
T-beamsSlabs, tunnels, culvertsBox-girders and thin inner slabs
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Scope of Research17 10th June 2010
Complex analysis: NLFEA and Probabilistic approach
Conclusion QuickScan and refinement calculations:Many differences in judging existing structures at consultancy offices and engineers.
Beside the partial safety factors of load and material:There is a need for a partial model factor !!
A need for:• Guideline NLFEA analysis based on lab experiments in the past relatedto (prestressed) girders and (prestressed)slabs will be coming end 2010 • Guideline is based on the MC1990, in future MC2010(draft available)• Scheme of how to deal with a probabilistic analysis(or Safety Formats)
Scope of Research18 10th June 2010
Vehicle Load Research: Evaluation trends passing Vehicles/Axles(TNO) NEN6700:
βt = 3.6; αLoad = -0.7; ISO2394:PULS= ф(-0.7×3.6)=0.006Lifetime: 100 yearsIncident/year: 100/0.006=1/16000Incident/day:1/16000×365=1.7×10-7
Number vehicles:Slow lane 10.000 / dayIncident vehicle:1.7×10-7/10-4= 1.7×10-11
Axles: ± 4 Axles / vehicleIncident axles:1.7×10-11/4= 0.425×10-11
Trend: 1998 similar to 2008
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Concrete research: Comparison old and new girders (DUT)
• Development over 50 year oldcompression strengthversus the development of the tension strength similar at newYoung concrete ?• Opportunities Acoustic Emissionas additional tool to lab/in-situtests and FEA
Scope of Research20 10th June 2010
Concrete research: Lab Testing concentrated load distribution (DUT)
• Differences distribution length of concentratedloads to point supports orline supports ?
• Variation in reinforcementratio, compressionstrength concrete, loadarea
• Opportunities AcousticEmission as additional tool to lab/in-situ tests and FEA
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Scope of Research21 10th June 2010
Testing structures in-situ: With common sand bags (A2) or the Belfa vehicle (owner in Germany)
Configuration
Crossing
Testing
Scope of Research22 10th June 2010
DT methods to find reinforcement in structures
NDT methods are needed in this field !!
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Scope of Research23 10th June 2010
Strengthening decks with CFRP (Future work)
Glueing
Anchoring CFRP(prestressed)
Scope of Research24 10th June 2010
Questions to this audience
Looking to the development of the structural recommendations of all different in the EU countries or worldwide raises the question:
1) Is it possible to setup an overall recommendation for existing structures (as appendix to the MC 2010)
ór
2) Is it preferable to setup a framework for reexamination of existing concrete structures ?
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