section 2 pt systems - post-tensioning institute...unbonded and bonded pt comparison applications:...
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SECTION 2
PT SYSTEMS
DEVELOPED BY THE PTI EDC-130 EDUCATION COMMITTEE
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OUTLINE Unbonded and Bonded Post‐Tensioning
Comparison Unbonded Post‐Tensioning: Systems and equipment Function of the coated tendon Construction
Bonded Post‐Tensioning: Various systems, components and equipment Function of the grouted tendon Construction
Post‐Tensioning Applications
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UNBONDED AND BONDED PT COMPARISON
Unbonded Post‐Tensioning (PT) Tendon is not bonded to the surrounding concrete PT force is transmitted to the structure by means of the
anchorages. Bonded Post‐Tensioning (PT) Tendon is bonded to the concrete Bond is achieved throughout the length of the tendon
by a cementitious matrix called grout. Bond between the strand and the concrete is achieved through the duct after grouting
PT force at every section is a function of the deformation of the concrete (strain compatibility)
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UNBONDED AND BONDED PT COMPARISON
Applications: both systems are used in building and civil structures (bridges, containment structures, etc…) In USA, unbonded is more common in buildings Bonded is more common in civil structures Both systems can be used as external post‐tensioning
Performance and durability: both systems provide comparable satisfactory results
Selection of a system depends on: Availability Economics Specific needs of each project
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MAJOR CONSTRUCTABILITY DIFFERENCES
Unbonded Bonded
Fabrication of tendons in plant (extrusion & cutting to specific length)
Necessary Not necessary but possible
Placement
Very practical and flexible. Easy to handle and does not necessitate heavy equipment
Very practical and flexible. Depending on application and system used, may require heavy equipment and reduced flexibility
Grouting Not Applicable Necessary
Stressing Single strand stressing
Typically multi-strands with high stressing forces.Single strand stressing in specifc systems
Demolition Requires special care Straight forward (similar to regular reinforcement)
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UNBONDED SYSTEMS Monostrand PT systems: Coated strand Coated anchors Encapsulation accessories Wedges
Coated Anchor
Grease Cap
Coated Strand
Lockable Sleeve
Wedge
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UNBONDED PT COATED STRAND
The process of coating the strand is called extrusion
Coated strand 7‐wire PC strand: ultimate strength fpu= 270 ksi Plastic sheathing: High Density Polyethylene (HDPE) or Polypropylene (PP) PT coating: Corrosion inhibiting grease
Tendon Section
Plastic Sheathing
7-Wire Strand
PT coating (Corrosion
inhibiting grease)
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UNBONDED PT ANCHORAGE Encapsulated anchorage Prevent water infiltration and corrosion Monostrand steel anchor coated with corrosion protection Lockable encapsulation sleeves Encapsulation cap to cover strand tails (ends) Plastic pocket former
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STEEL WEDGE Wedges are responsible of locking the strand after stressing so it holds the force
Wedges are made of steel and have ductile core to adjust to strand shapes
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FUNCTION OF STRAND COATING• Function of the PT coating
– Allow a bond free movement of the strand inside the sheathing.
– Increase protection against corrosion and provide a non-conductive environment for corrosion
– Reduce friction between the strand and sheathing
• Function of the sheathing– Provide corrosion protection to the strand– Provide encasement against damage and
moisture penetration
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UNBONDED PT STRESSING EQUIPMENT
Monostrand Stressing Jack
Stressing Pump Gauge
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UNBONDED PT CONSTRUCTION
Tendon fabrication (PTI certified plants)
Site installation Inspection and concrete
placement Stressing operation
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UNBONDED PT FABRICATION Tendon extrusion
and cutting to length Tendon bundling Tendon color coding
& labeling Loading and shipping
to site
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UNBONDED PT INSTALLATION Placing of formwork Fixing of anchors to
side formwork Installing chairs to
profile heights shown on PT drawings
Installing reinforcement and PT tendons
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UNBONDED INSPECTION AND CONCRETE CASTING
Inspect reinforcement and PT installation according to drawings
Cast concrete Thorough vibration
around anchorages Avoid damaging PT
tendons Proper curing
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UNBONDED PT STRESSING Remove edge formwork Prepare tendons for
stressing Check achieved concrete
strength Stress tendons using
calibrated monostrandequipment
Fill out elongation records Approve elongations Seal tendons and patch
pockets
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BONDED PT SYSTEMS Several systems exist with main components being: Bare Strands or Bars Steel Anchorage Assemblies (bearing plates and wedge plates);
proprietary designs Plastic or Galvanized Metal Ducts Steel Wedges
Typically multistrands encased in grouted duct Bonded systems also known as grouted systems
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FUNCTION OF GROUTED DUCTS
• Function of the duct– Maintain a voided path for strands
during construction– Transfer the bond between the grout &
the concrete– Act as additional corrosion protection
against penetration of moisture and chemicals
• Function of the grout– Provide a continuous bond between the
strand and the duct– Increase protection against corrosion– Provide a non-conductive environment
for corrosion
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Wedges Wedge Plate
Duct
Deviation Cone (Optional)
Bearing Plate
BONDED PT SYSTEMS• High capacity multistrand systems used in civil structures and
transfer beams or slab construction• Main components
– Bare strands– Multistrand anchorage
assembly– Round corrugated duct– Grout accessories
(cap, shut‐off valvesvents, etc…)
– Wedges
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BONDED PT SYSTEMS
WedgesWedge Plate
Duct
Deviation Cone (Optional)
Bearing Plate
• Flat systems used typically in thin concrete elements and slab construction
• Main components– Bare strands– Multistrand anchorage
assembly– Flat corrugated duct– Grout accessories
(cap, vent tubes, etc.)– Wedges
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BONDED PT SYSTEMS Bar systems: PT bar Steel anchor Duct Grout accessories
Monostrand grouted system Single strand anchor Round duct Wedge Grout accessories
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Stressing Pump
BONDED PT STRESSING EQUIPMENT
Grouting Machine
Stressing Jack Strand Pusher
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BONDED PT CONSTRUCTION Installation Inspection and concrete placement Stressing operation Grouting operation
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BONDED PT SYSTEMS INSTALLATION
Placing of formwork and side shutter
Fixing of bearing plates Placing of ducts and
reinforcement Profiling ducts according to
drape specified on PT installation drawings
Placement of strands inside duct (can be done before or after casting of concrete)
Beam/Bridge Construction
Slab Construction
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INSPECTION AND CONCRETE PLACEMENT
Inspect reinforcement and PT installation according to placement drawings
Cast concrete Thorough vibration around
bearing plates Avoid damaging PT
tendons Proper curing
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BONDED PT SYSTEMS STRESSING
• Stress tendons using calibrated equipment
• Fill up elongation records
• Approve elongations
• Remove edge formwork• Prepare tendons for stressing• Check achieved concrete strength
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BONDED PT SYSTEMS GROUTING
Check ducts for blockage
Grout and seal tendons
Record grouting results
Check vents for grout adequacy
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PT APPLICATIONS: 2‐WAY SLABS
Photo Courtesy of Seneca Structural Engineering Inc.
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PT APPLICATIONS: TWO‐WAY SLABS
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PT APPLICATIONS: SLABS‐ON‐GROUND
Ribbed Foundation
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PT APPLICATIONS: SLABS‐ON‐GROUND
Uniform Thickness Foundation
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PT APPLICATIONS: MAT FOUNDATIONS
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PT APPLICATIONS: INDUSTRIAL FLOORS
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PT APPLICATIONS: PARKING STRUCTURES
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PT APPLICATIONS: GROUND ANCHORS
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PT APPLICATIONS: STORAGE STRUCTURES
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PT APPLICATIONS: BARRIER CABLE
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PT APPLICATIONS: STRENGTHENING
Photo courtesy of Seneca Structural Engineering
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PT APPLICATIONS: STRENGTHENING
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PT APPLICATIONS: SPLICED GIRDERS
Photos courtesy of: