DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
STRENGHTENING AND REPAIR OF MOSTEIRÔ BRIDGEJoão Pinho, José David, Ricardo Antunes
DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
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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DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
MOSTEIRÔ BRIDGE – DECK
• Continuous box-girder
• Spans: 42 + 110 + 42 m
• Solid slabs / Truss web
• Reinforced concrete + Post-tensioned concrete (top slab)
DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
MOSTEIRÔ BRIDGE – PIERS
• Casing and raising of the masonry piersof the previous bridge with reinforcedconcrete.
• Central pier partially demolished
ICDS12 International Conference DURABLE STRUCTURES: from construction to rehabilitation LNEC • Lisbon • Portugal • 31 May - 1 June 2012
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DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
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
DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
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
ICDS12 International Conference DURABLE STRUCTURES: from construction to rehabilitation LNEC • Lisbon • Portugal • 31 May - 1 June 2012
LNEC
• ICDS1
2
DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
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
DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
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)
ICDS12 International Conference DURABLE STRUCTURES: from construction to rehabilitation LNEC • Lisbon • Portugal • 31 May - 1 June 2012
LNEC
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2
DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
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
DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
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)
ICDS12 International Conference DURABLE STRUCTURES: from construction to rehabilitation LNEC • Lisbon • Portugal • 31 May - 1 June 2012
LNEC
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DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
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
DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
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
ICDS12 International Conference DURABLE STRUCTURES: from construction to rehabilitation LNEC • Lisbon • Portugal • 31 May - 1 June 2012
LNEC
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DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
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
DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
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
ICDS12 International Conference DURABLE STRUCTURES: from construction to rehabilitation LNEC • Lisbon • Portugal • 31 May - 1 June 2012
LNEC
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DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
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
DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
STRENGTHENING AND REPAIR WORKS – DIAGONALS IN TENSION
• 48 diagonals intervened
• Steel plates in internal faces (minimize aesthetic impact)
ICDS12 International Conference DURABLE STRUCTURES: from construction to rehabilitation LNEC • Lisbon • Portugal • 31 May - 1 June 2012
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DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
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
DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
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)
ICDS12 International Conference DURABLE STRUCTURES: from construction to rehabilitation LNEC • Lisbon • Portugal • 31 May - 1 June 2012
LNEC
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2
DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
CONCLUSIONS
Deep structural strengthening achieved with minimal aesthetic impact
DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
CONCLUSIONS
“Cocktail” of different technologies proved to be the best approach
Post-tension Reinforced concrete
Carbon fiber plates Steel
ICDS12 International Conference DURABLE STRUCTURES: from construction to rehabilitation LNEC • Lisbon • Portugal • 31 May - 1 June 2012
LNEC
• ICDS1
2
DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012
MAY 2012
THANK YOU!
ICDS12 International Conference DURABLE STRUCTURES: from construction to rehabilitation LNEC • Lisbon • Portugal • 31 May - 1 June 2012
LNEC
• ICDS1
2