LNECdurati.lnec.pt/pdf/ICDS12_Presentations/F1_4_RAntunes.pdf · DURABLE STRUCTURES LNEC Lisbon 31...

DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012


STRENGHTENING AND REPAIR OF MOSTEIRÔ BRIDGEJoão Pinho, José David, Ricardo Antunes


MOSTEIRÔ BRIDGE – OVERVIEW

• Mosteirô Bridge: landmark bridge designed by the renowned Portuguese engineer Mr. Edgar Cardoso

• Built in 1973: replacing steel bridge to be submerged by Carrapatelo Dam water

• Length: 194 m / Width: 9.0 m

ICDS12 International Conference DURABLE STRUCTURES: from construction to rehabilitation LNEC • Lisbon • Portugal • 31 May - 1 June 2012

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MOSTEIRÔ BRIDGE – DECK

• Continuous box-girder

• Spans: 42 + 110 + 42 m

• Solid slabs / Truss web

• Reinforced concrete + Post-tensioned concrete (top slab)


MOSTEIRÔ BRIDGE – PIERS

• Casing and raising of the masonry piersof the previous bridge with reinforcedconcrete.

• Central pier partially demolished


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MOSTEIRÔ BRIDGE - ABUTMENTS

Casing and raising of the masonryabutments of the previous bridge withreinforced concrete

Bearings tied to the abutments through vertical high-strength steel bars, to withstand upward forces

Fixed abutment Free abutment


MOSTEIRÔ BRIDGE – REPAIR WORKS IN THE 1990s

• 1992: Breaking of steel bars connecting the deck to the bearings at the fixed abutment

• Main repair works:

• Replacement of broken high-strength bars

• Strengthening of deck-abutment connection with four external PT cables


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PROJECT STAGES

• Data collection

• Detailed inspection

• Underwater inspection

• Detailed geometric survey

1. Inspection and characterization

2. Evaluation of structural safety

3. Strengthening and repair – Design

4. Strengthening and repair – Construction

• Preliminary design

• Detailed design

• Detailed topographic survey

• Bathymetry survey

• Concrete characterisation tests

• Geotechnical investigation


INSPECTION AND CHARACTERIZATION - MAJOR DEFECTS FOUND

Strong vibration under heavy vehicle traffic

Major transverse cracks in bottom slab at

central span

Vertical deformation at middle of central span

(16 cm)


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INSPECTION AND CHARACTERIZATION - MAJOR DEFECTS FOUND

Unleveled expansion joint at fixed abutment (2 cm)

Transverse cracking in diagonals in tension

Concrete spalling near the bearings at fixed

abutment


EVALUATION OF STRUCTURAL SAFETY

Goal: Understand origin of structural problems

• Model 1: Same assumptions as the original design and standards

• Model 2: Modern calculation methods and standards

Conclusion: Major effects were overlooked in the original design

• Increase of bending moments at middle of central span due to creep

• Seismic action (not required by the standards)


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ULTIMATE LIMIT STATES

EVALUATION OF STRUCTURAL SAFETY - CONCLUSIONS

Insufficient tension strength in bottom slab at the central span

• Tension stresses much higher than strength

• Probable yielding of rebars

• Loss of slab stiffness -> overall reduction of structural stiffness

Insufficient strength of horizontal connection between deck and fixedabutment

Insufficient strength of diagonals in tension (central span)

• Not designed to withstand seismic action


SERVICEABILITY LIMIT STATES

EVALUATION OF STRUCTURAL SAFETY - CONCLUSIONS

• Linked to excessive tension

• Reactions at bearings near zero for permanent loads

• Insufficient stiffness of deck-abutment connection (provided only byvertical PT cables)

• Loss of stiffness of bottom slab led to higher forces in the connection

Cracking in bottom slab at central span

Defective vertical connection between deck and abutments


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STRENGTHENING AND REPAIR WORKS - OVERVIEW

• Strengthening:

• Bottom slab (central span)

• Diagonals

• Connections between deck and abutments

• Partial demolition of submerged pier

• General repair and maintenance works (concrete, bearings…)

Focus: Strengthen the bridge with minimal aesthetic impact


STRENGTHENING AND REPAIR WORKS – BOTTOM SLABEXTERNAL POST-TENSION CABLES

• Goals: Restore stiffness

Ensure compliance with SLS criteria

• 10 external PT cables inside the box girder

• Minimize aesthetical impact, avoid reduction of river traffic clearance


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STRENGTHENING AND REPAIR WORKS – BOTTOM SLABCFRP PLATES

• Goals: Provide tension strength to comply with ULS criteria

Control of cracking

• 48 CFRP plates on both faces of the slab


STRENGTHENING AND REPAIR WORKS – DIAGONALS IN TENSION

• 48 diagonals intervened

• Steel plates in internal faces (minimize aesthetic impact)


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STRENGTHENING AND REPAIR WORKS – CONNECTION DECK-ABUTMENT

• Goal: Ensure compression of bearings for service loads

Reduce risk of fatigue in PT cables

Reduce vibrations

• Two additional PT cables at each abutment

• Anchored in truss system connected to the deck’s cross beam


CONCLUSIONS

Some decades ago, high relative cost of materials led engineers to search for theirmaximum optimisation

Simplified approaches required by limited calculation methods could lead to overlooking some effects (in this case, creep)


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CONCLUSIONS

Deep structural strengthening achieved with minimal aesthetic impact


CONCLUSIONS

“Cocktail” of different technologies proved to be the best approach

Post-tension Reinforced concrete

Carbon fiber plates Steel


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MAY 2012

THANK YOU!


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LNECdurati.lnec.pt/pdf/ICDS12_Presentations/F1_4_RAntunes.pdf · DURABLE STRUCTURES LNEC Lisbon 31...

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