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DURABLE STRUCTURESLNEC Lisbon 31 May - 1June 2012


STRENGTHENING AND REPAIR OF LANHESES BRIDGEJoo Pinho, Jos David, M anuel Lorena, Alexandre Portugal


BRIDGE DESCRIPTION

Lanheses bridge is a 1218 m long structure.

It is a beam slab continuous deck, supported by pendulum piers.

9 piers are located in the main river channel of Lima River.

The bridge was designed by the renowned Portuguese engineer Prof. Edgar Cardoso.

It was built between 1977 and 1981.

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

LNEC

ICD

S12


BRIDGE DESCRIPTION - DECK

The bridge has a total of 41 spans, with typical spans of 30 m and lateral spans of 24 m.

The deck is 11.50 m wide and is a post-tensioned concrete structure (with post-tension in both directions).

It has 4 longitudinal beams with variable heights.

The deck is fixed to South abutment by hinges, and dilates freely in the longitudinal direction at piers and at North abutment.


BRIDGE DESCRIPTION - PIERS

Piers are reinforced concrete blades.

They have a pendulum functioning hinged in both ends.

The hinges are materialized by lead plates and mechanical studs.

Foundations: Each pier has a single alignment of 4 piles 0.8 m.


LNEC

ICD

S12


BRIDGE DESCRIPTION - ABUTMENTS

It is a wall abutments, with approximately 7 m of height and 10.3 m of extension.

The cill beam is supported by counterforts and wing walls.

The foundations are composed of 18 piles 0.8 m.

Concrete dead ground blocks located on the back of abutments, under the the road embankment, are anchored by tendons to the abutments, to withstand the horizontal loads.

In the South abutment: the deck is laid on lead plates, fixed by mechanical studs.

In the North abutment: the deck is laid on steel rollers.


REHABILITATION DESIGN - OVERVIEW

1st Phase: Inspection and characterisation

Data collection.

Detailed visual inspection.

Underwater inspection.

Topographic and bathymetric survey.

River bed material characterisation tests.

Concrete characterization tests.

Geotechnical investigation.

Sonic tests on piles.

2nd Phase: Design of bridge strenghtening and repair

Evaluation of structural safety.

Hydraulic and river morphology studies.

Geotechnical studies.

Preliminary design.

Detailed design.


LNEC

ICD

S12


INSPECTION AND CHARACTERISATION MAJOR PROBLEMS FOUND

A strong riverbed widespread scouring occurs, with movements of the protection of the riprap embankments, with exposed piles.

The river flow was concentrated between protections.

A large scour hole was identified, downstream of the bridge section.



Defective structural functioning of hinges, between deck and piers: Crushing of the lead plates, with direct contact between concrete surfaces. Crushing and delamination of concrete. Exposure and corrosion of rebars.

Deterioration of concrete occurs at several members.


LNEC

ICD

S12


A general degradation of the construction joints.

Degradation of the connection between deck and the fixed abutment.


Major cracks at supports of deck s cross beams.


EVALUATION OF STRUCTURAL SAFETY - APPROACH

1. Following the standards applicable at the time of the original design.

2. Following the current applicable standards in Portugal.


LNEC

ICD

S12


EVALUATION OF GLOBAL STRUCTURAL SAFETY FINAL CONCLUSIONS

The deck does not comply with the limit state of decompression, required for post-tensioned concrete members.

Unstable equilibrium of the piers extreme sensitivity to horizontal loads.

Reduction of piles capacity in the piers located in the main riverbed, due to loss of confinement.

Insufficient penetration of the piles in substratum.

Insufficient strength for seismic loads of abutment piles, counterforts and connections with the deck.

Insufficient global strength for seismic loads.


A MODIFICATION OF THE STRUCTURAL SYSTEM WAS DECIDED

Eliminate the Problems of former structural system, that consisted:

The existing extreme sensitivity of the structure to horizontal loads.

An eventual collapse of one pier, or breaking of deck-abutment connection, couldcause a chain reaction and collapse of the whole bridge.

The Adopted Solution consisted: modifying the structural system, withminimum intervention on the bridge: The deck remained fixed to South abutment. The piers were fixed to the foundations. The hinges were replaced by sliding bearings at piers.


LNEC

ICD

S12


STRENGTHENING AND REPAIR WORKS

Modification of structural system: by eliminating of the pendulum functioning of the piers.

Strengthening of piers foundations.

Strengthening of cross beams at piers.

Replacement of bearings.

Strengthening of the fixed abutment and of the connection between the fixed abutment and the deck.

Strengthening of deck with external post-tension.

Protection of piers against scour and protection of entire riverbed with riprap.

Treatment of scour holes.

Concrete repair and treatment.


STRENGTHENING OF FOUNDATIONS OF PIERS

Micro-piles: high-strength steel tubes 127 mm x 9 mm have been installed.

The micro-piles were connected to a new pile cap extension, embedding the existing one.


LNEC

ICD

S12


FIXATION OF PIERS TO FOUNDATION

The connection of piers to the foundation was made integral.A reinforced concrete casing above the pile cap was executed.


STRENGTHENING OF CROSS BEAMS AT PIERS

The cross beams were widened to take into account: The deviation of vertical alignment of piers. The need to accommodate the top plates of the new bearings.


LNEC

ICD

S12


REPLACEMENT OF BEARINGS AT PIERS

A temporary support of the deck was required.

The auxiliary system allow restoring the pier verticality.

Installation of elastomeric bearings: sliding in the longitudinal direction and blocked in the transverse direction.


STRENGTHENING OF THE FIXED ABUTMENT

The strengthening of the fixedabutment was executed to withstandthe seismic loads.

High-strength steel bars, wereinstalled, to connect the deck to theabutment.


LNEC

ICD

S12


DECK STRENGTHENING WITH EXTERNAL POST-TENSION

The deck was strengthened by external post-tensioning to ensure the complianceto serviceability limit state.

Four cables at each span were installed.


SCOUR TREATMENT AND PROTECTION OF RIVER BED WAS IMPLEMENTED

Demolition and removal of riprap embankments and of the sheet pile walls around piers.

Installation of a general riprap protection on the regularized riverbed.

BEFO RE

AFTER


LNEC

ICD

S12


CONCLUSIONS

THE STRUCTURAL VULNERABILITY OF THE EXISTING PENDULUM-PIERSYSTEM OF THE BRIDGE WAS ELIMINATED.

THE IMPROVEMENT OF SEISMIC CAPABILITY OF BRIDGE WASACHIEVED.

THE DRAMATIC PROCESS OF SCOURING AND EROSION THATENDANGERED THE GLOBAL STABILITY OF THE BRIDGE WASELIMINATED.

THE PROCESS OF RIVERBED STABILIZATION HAS STARTED.


MAY 2012

THANK YOU!


LNEC

ICD

S12

f1_2_jpinho

Documents

bridge description abutments

bridge section

design of bridge strenghtening

pendulum piers

detailed design

north abutment

river flow

south abutment