2014 VIRGINIA CONCRETE CONFERENCE
Presented by:
Teddy S. Theryo, P.E.
Parsons Brinckerhoff
COMPLEX BRIDGES
March 7, 2014
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Background / Motivation
Field Observation
PT Tendon Flexible Material Filler Practices in
France / Europe
Potential Applications in the US as Alternative to
Cement Grout
Design Perspectives
Construction and Maintenance Perspectives
Conclusions
Timeline of PT Durability Issues in the US
1999-2003: PT corrosion / durability issues related to bleed
water in grout
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Niles Channel Bridge, Florida Keys
Mid-Bay Bridge, Destin, FL.
Sunshine Skyway Bridge , Tampa Bay, FL.
Seabreeze Bridge, Daytona Beach, FL.
Varina-Enon Bridge, Richmond, VA
2010-2013: PT corrosion / durability issues related to chloride
contamination in grout and soft grout.
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Ringling Bridge, Sarasota, FL
Wonderwood Bridge, Jacksonville, FL
I – 4 / Crosstown Connector, Tampa, FL
I-95 / I-295 Interchange , Jacksonville, FL
Background / Motivation
THE SCAN TOUR MEMBERS AT PROJECT SITE IN FRANCE
Scan Tour Objectives (October 2013)
 To observe the injection of wax in PT tendons in a
segmental bridge during construction
 To seek information on flexible material filler used as
Corrosion protection with regard to material
properties spec., policy and potential maintenance
issues
 To seek information on site implementation such as
Cost and construction issues.
Erection tower
Segment lifter
LGV SEA TOURS BORDEAUX BRIDGE UNDER CONSTRUCTION
MEETING WITH IFSTTAR / LCPC
IFSTTAR : The French Institute of Science and Technology for Transport, Development and Networks
MEETING WITH SETRA
SETRA: French Technical Department for Transport, Roads and Bridges
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Background / Motivation
Field Observation
PT Tendon Flexible Material Filler Practices in
France / Europe
Potential Applications in the US as Alternative to
Cement Grout
Design Perspectives
Construction and Maintenance Perspectives
Conclusions
OVERALL VIEW OF STORAGE YARD
Wax heater & pump equipment
Power generator
WAX HEATER AND POWER GENERATOR
A SEGMENT WAS BEING LIFTED
Wax injection hose
INJECTING HOT WAX INTO PT DUCT
Wax volume measurement device
Wax injection hose
HOT WAX INJECTION EQUIPMENT
Wax temperature indicator
TEMPERATURE MEASUREMENT DEVICE
Deviator
External Tendon
Diabolo void
A SCHEMATIC SHOWING A DRAPED TENDON BEING INJECTED WITH WAX
Sealing
leakage duct
DUCT REPAIR PRIOR TO WAX INJECTION
Wax
WAX SAMPLE
Inlet
INJECTING HOT WAX INTO PT DUCT
Outlet (vacuum device)
HOT WAX INJECTION IS IN PROGRSS
VACUUM DEVICE
Diabolo void
Abutment
Maintenance Room at
Abutment
End Diaphragm
Wax raw material
Portable wax heater & pump equipment
Courtesy of DSI International
Vent tubes at high point
Vent tube at end cap
Injection Point
Courtesy of DSI International
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Background / Motivation
Field Observation
PT Tendon Flexible Material Filler Practices in
France / Europe
Potential Applications in the US as Alternative to
Cement Grout
Design Perspectives
Construction and Maintenance Perspectives
Conclusions
CHRONOLOGY
 Between 1994 and 2005, five bridges in France had external
PT tendons that ruptured:
1994 (9 years old)
1997 (14 years old)
2001 (8 years old)
2001 (10 years old)
2005 (20 years old)
 All tendons are bare strand bundles in HDPE duct with cement grout
 Cause of failure: excessive bleeding and formation of soft grout (white
damp paste) in ducts
 The white paste was shown at high points in the duct and caused stress
corrosion at these locations and ultimately failure of tendon
19 STRANDS EXTERNAL
GROUTED TENDON AFTER
CUTTING (courtesy of
IFSTTAR)
External tendons buckling
deformation /whipping after
rupture
The failure mode of grouted external tendon is brittle and without warning !
 February 2001: SETRA issued new requirements which led to
the abandonment of cement grout in external tendons.
 2002: European Technical Approval Guide (ETAG) 013 on
Prestressing System was published.
ETAGs were established by European Organization for Technical
Assessment (EOTA)
 June 2002: ASQPE was created. Its mission to qualify
prestressing Systems that conform to ETAG 013, including
processes and services.
 2013: French regulations for concrete structures were revised.
Grease filler is prohibited, except mono-strand greased and
sheathed.
NEW FILLER MATERIALS
Requirements: External tendon be easily removed and replaced
led to the development of soft filler products such as grease and
wax and also provide tendon protection. If the duct is breached
and strands are corroding, then soft fillers allow individual strand
to break and release their energy individually, rather as a single
tendon as in case of cement grout.
Two systems have been developed to meet the above
requirements:
1. Bare strands bundle in HDPE duct filled with wax (90% of
current installations). Wax was selected, since grease was
considered unstable (separation between soap and oil).
1. Mono-strand Greased & Sheathed bundle in HDPE filled with
cement grout prior to stressing.
wax
(a)
(b)
Alternative Tendon System Used in France (a) Bare strands in HDPE duct with Petroleum
Wax Filler (b) Monostrand Greased & Sheathed Bundle Inside HDPE Duct and Filled with
Cement Grout
WAX INJECTION TESTING
In 2004 LCPC (IFSTTAR) conducted tests on
flowability of wax during injection. This was due to
problem encountered with injection and cooling.
During injection, if the wax cools sufficiently in the
duct, then it thicken and results in additional back
pressure, which can leaks or burst. The wax is
typically heated to 110 Deg C (230 Deg F).
MOCK-UP WAX INJECTION (courtesy of IFSTTAR)
HDPE BURST DURING WAX INJECTION (courtesy of IFSTTAR)
Variation in Wax Viscosity at Elevated Temperature (courtesy of IFSTTAR)
PUMPING PRESSURE
 Pumping pressure ≤ 6 bars (90 psi): Potential leaks are
minimized.
 15 bars (225 psi) ≤ Pumping pressure ≥ 6 bars (90 psi):
Potential leaks and deformation.
 Pumping pressure ≥ 15 bars (225 psi): Potential duct
bursting.
Measured Pressure During Wax injection in Mock-up (Chantier)
and in actual Bridge Tendon (courtesy of IFSTTAR)
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Background / Motivation
Field Observation
PT Tendon Flexible Material Filler Practices in
France / Europe
Potential Applications in the US as Alternative to
Cement Grout
Design Perspectives
Construction and Maintenance Perspectives
Conclusions
 External Tendons
(span by span)
 Multi Spans Draped / complex Internal Tendons
(CIP bridge, spliced girder bridge, straddled beam)
 Very long Internal Tendons
(Pontoon Bridge)
Internal Bonded tendon
SPAN BY SPAN SEGMENTAL BRIDGE
Internal unbonded tendon
Internal unbonded tendon (typ.)
Pretensioned strands
POST-TENSIONED SPLICED GIRDER BRIDGE
INTERNAL BONDED TENDON
INTERNAL BONDED TENDON
INTERNAL UNBONDED TENDON
CAST-IN-PLACE BRIDGE ON FALSEWORK
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Background / Motivation
Field Observation
PT Tendon Flexible Material Filler Practices in
France / Europe
Potential Applications in the US as Alternative to
Cement Grout
Design Perspectives
Construction and Maintenance Perspectives
Conclusions
Design Impact
 Use in External Tendons: No impact
(Both cement grout or waxed tendon is considered unbonded)
 Use in Internal Tendons: 10 % to 15 % total strands
increased
(Unbonded tendon has lower tendon stresses at
Ultimate Limit State)
Design Strategy to minimize Impact: combination of
bonded and unbonded tendons
Comparison in structural behavior between bonded
(grouted) and unbonded tendons
Loads vs Deflections
Tendon stresses (fps) at Ultimate Limit State
(unbonded is lower than bonded at critical sections)
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Background / Motivation
Field Observation
PT Tendon Flexible Material Filler Practices in
France / Europe
Potential Applications in the US as Alternative to
Cement Grout
Design Perspectives
Construction and Maintenance Perspectives
Conclusions
PROS
 Fast wax filling / injection in the duct ( required only 2 to 3 minutes to fill a
long tendon)
 No wax testing required on site
 Tendon replaceability and restressability possible
 Safe environment in case of strand / strands rupture for external tendons
CONS
 Required special safety measures for personnel during hot wax (230 Deg. F)
filling
 Required special equipment (heating and pumping)
 Required thicker HDPE duct thickness
 Wax material is about 7 (seven) times more expensive than cement grout
 Potential hot wax bursting and duct bulging / deformed
Deviator
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5.
6.
7.
Background / Motivation
Field Observation
PT Tendon Flexible Material Filler Practices in
Europe
Potential Applications in the US as Alternative to
Cement Grout
Design Perspectives
Construction and Maintenance Perspectives
Conclusions
1. Petroleum wax filler is a better option than grease.
2. Petroleum wax is more stable than grease for tendon
protection.
3. Petroleum wax can provide similar corrosion
protection compared to cement grout or grease.
4. External unbonded tendons improve personnel safety
in case of tendon rupture.
5. Both waxed and greased & sheathed monostrand
tendons are viable alternatives to cement grouted
tendons.
6. Waxed tendon can be for internal tendon.