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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

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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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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

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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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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 >>

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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

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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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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

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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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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.

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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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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

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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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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)

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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

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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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Testing structures in-situ: With common sand bags (A2) or the Belfa vehicle (owner in Germany)

Configuration

Crossing

Testing

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DT methods to find reinforcement in structures

NDT methods are needed in this field !!

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Strengthening decks with CFRP (Future work)

Glueing

Anchoring CFRP(prestressed)

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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 ?