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Lean Construction

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Title: Lean Construction


1
(No Transcript)
2
By Dr. Attaullah ShahSwedish College of
Engineering and Technology Wah Cantt.
  • CE-407
  • Lec-01
  • Structural Engineering

3
Course Outline
  • Prestressed concrete.
  • Prestressed VS reinforced concrete.
  • Types of prestressing.
  • Losses in prestressing.
  • Analysis and design of simple prestressed
    concrete members.
  • Introduction to various prestressing systems.
  • Bridge Engineering
  • Types of bridges. Site selection. .
  • Bridge loadings. Load distribution on bridge
    deck.
  • Introduction to design of deck for a simple
    concrete bridge.

4
  • Advanced Structural Analysis.
  • Definition of matrices and determinants.
  • Stiffness method.
  • Truss element, Beam clement, Plantation of
    stiffness sub matrices of multiple ended
  • members.
  • Flexibility method.
  • Introduction to structural dynamics.

5
Assignment No.1
  • This is a group presentation assignments which
    will be required to be presented in next class
  • Group 1 Define pre-stressing in concrete, the
    rationale and philosophy, types
  • Group 2 Explain application of the pre-stressed
    concrete in modern structures.
  • Grooup-3 Write a detailed note on the use of
    pre-stressed concrete in Pakistan with examples
    of real life.

6
PRESTENSIONING POST- TENSIONING
  • METHODS OF PRESTRESSING IN CONCRETE

7
What is a pre-stressed concrete
  • Prestressed concrete is a particular form of
    reinforced concrete.
  • Prestressing involves the application of an
    initial compressive load on a structure to reduce
    or eliminate the internal tensile forces and
    thereby control or eliminate cracking.
  • With cracking reduced or eliminated, a
    prestressed section is considerably stiffer than
    the equivalent (usually cracked) reinforced
    section.
  • Prestressing may also impose internal forces
    which are of opposite sign to the external loads
    and may therefore significantly reduce or even
    eliminate deflection.

8
PRESTRESSED CONCRETE
  • PRINCIPLE Using high tensile strength steel
    alloys producing permanent pre-compression in
    areas subjected to Tension.
  • A portion of tensile stress is counteracted
    thereby reducing the cross-sectional area of the
    steel reinforcement .
  • METHODS - a) Pretensioning
    b)Post-tensioning
  • PRETENSIONING - Placing of concrete around
    reinforcing tendons that have been stressed to
    the desired degree.
  • POST-TENSIONING - Reinforcing tendons are
    stretched by jacks whilst keeping them inserted
    in voids left pre-hand during curing of concrete.
  • These spaces are then pumped full of grout to
    bond steel tightly to the concrete.

STEEL BARS BEING STRETCHED BY JACKS
9
POST - TENSIONING
  • WHAT IS POST-TENSIONING?
  • Post-tensioning- is a method of reinforcing
    (strengthening) concrete or other materials with
    high-strength steel strands called tendons.
  • Post-tensioning allows construction that would
    otherwise be impossible due to either site
    constraints or architectural requirements.
  • Requires specialized knowledge and expertise to
    fabricate, assemble and install.
  • After adequate curing of concrete, reinforcing
    tendons (placed in side the voids of the
    structure) are tensioned/stretched by jacks on
    the sides grouts filled with appropriate mix.
  • Applications a) Structural members beams,
    bridge-deck panels, Roof Slabs, Concrete Silos
    Etc.

10
BENEFITS
  • Concrete is very strong in compression but weak
    in tension
  • This deflection will cause the bottom of the beam
    to elongate slightly cause cracking.
  • Steel reinforcing bars (rebar) are typically
    embedded in the concrete as tensile
    reinforcement to limit the crack widths.
  • Rebar is what is called passive reinforcement
    however it does not carry any force until the
    concrete has already deflected enough to crack.
  • Post-tensioning tendons, on the other hand, are
    considered active reinforcing.
  • Because it is prestressed, the steel is effective
    as reinforcement even though the concrete may not
    be cracked . Post-tensioned structures can be
    designed to have minimal deflection and
    cracking, even under full load.

Post Tensioned Structure
11
ADVANTAGES/APPLICATIONS
  • Post-tensioning allows longer clear spans,
    thinner slabs, fewer beams and more slender,
    dramatic elements.
  • Thinner slabs mean less concrete is required.
    It means a lower overall building height for the
    same floor-to-floor height.
  • Post-tensioning can thus allow a significant
    reduction in building weight versus a
    conventional concrete building with the same
    number of floors reducing the foundation load
    and can be a major advantage in seismic areas.
  • A lower building height can also translate to
    considerable savings in mechanical systems and
    façade costs.
  • Another advantage of post-tensioning is that
    beams and slabs can be continuous, i.e. a single
    beam can run continuously from one end of the
    building to the other.
  • Reduces occurrence of cracks - Freezing thawing
    durability is higher than non pre-stressed
    concrete.

This innovative form is result of post tensioning.
Bridge decks
12
  • Post-tensioning is the system of choice for
    parking structures since it allows a high degree
    of flexibility in the column layout, span lengths
    and ramp configurations.
  • In areas where there are expansive clays or soils
    with low bearing capacity, post-tensioned
    slabs-on-ground and mat foundations reduce
    problems with cracking and differential
    settlement.
  • Post-tensioning allows bridges to be built to
    very demanding geometry requirements, including
    complex curves, and significant grade changes.
  • Post-tensioning also allows extremely long span
    bridges to be constructed without the use
    of temporary intermediate supports. This
    minimizes the impact on the environment and
    avoids disruption to water or road traffic below.
  • In stadiums, post-tensioning allows long clear
    spans and very creative architecture.
    Post-tensioning can also be used to produce
    virtually crack-free concrete for water-tanks.
  • The high tensile strength precision of
    placement gives maximum efficiency in size
    weight of structural members.
  • Applications of various prestressed techniques
    enable quick assembly of standard units such as
    bridge members, building frames, bridge decks
    providing cost-time savings.

13
POST TENSIONING METHOD
14
Method of post-tensioning
Wedges tensioned by jacks
Tendons
TENDONS
15
PRESTRESSED CONCRETE
  • Prestressed concrete, invented by Eugene
    Frevssinet in 1928 is a method for overcoming
    concrete's natural weakness in tension . It can
    be used to produce beams,floors or bridges with a
    longer span than is practical with ordinary
    reinforced concrete. It can be accomplished in
    three ways pre-tensioned concrete, and bonded or
    unbonded.
  • Pre-tensioned concrete
  • Pre-tensioned concrete is cast around already
    tensioned tendons.
  • This method produces a good bond between the
    tendon and concrete, which both protects the
    tendon from corrosion and allows for direct
    transfer of tension.
  • The cured concrete adheres and bonds to the bars
    and when the tension is released it is
    transferred to the concrete as compression by
    static friction.
  • However, it requires stout anchoring points
    between which the tendon is to be stretched and
    the tendons are usually in a straight line.
  • Thus, most pre-tensioned concrete elements are
    prefabricated in a factory and must be
    transported to the construction site, which
    limits their size.
  • Pre-tensioned elements may be balcony elements,
    lintels , floor slabs, beams or foundation piles.

16
  • Bonded post-tensioned concrete
  • Bonded post-tensioned concrete is the descriptive
    term for a method of applying compression after
    pouring concrete and the curing process (in
    situ).
  • The concrete is cast around a plastic, steel or
    aluminium curved duct, to follow the area where
    otherwise tension would occur in the concrete
    element.
  • A set of tendons are fished through the duct and
    the concrete is poured. Once the concrete has
    hardened, the tendons are tensioned by hydraulic
    jacks.
  • When the tendons have stretched sufficiently,
    according to the design specifications they are
    wedged in position and maintain tension after
    the jacks are removed, transferring pressure to
    the concrete.
  • The duct is then grouted to protect the tendons
    from corrosion. This method is commonly used to
    create monolithic slabs for house construction in
    locations where expansive soils create problems
    for the typical perimeter foundation.
  • All stresses from seasonal expansion and
    contraction of the underlying soil are taken into
    the entire tensioned slab, which supports the
    building without significant flexure.
    Post-stressing is also used in the construction
    of various bridges.
  • The advantages of this system over unbonded
    post-tensioning are

DECK STEEL LAYING
17
  • Large reduction in traditional reinforcement
    requirements as tendons cannot destress in
    accidents.
  • Tendons can be easily 'weaved' allowing a more
    efficient design approach.
  • Higher ultimate strength due to bond generated
    between the strand and concrete.
  • No long term issues with maintaining the
    integrity of the anchor/dead end.
  • Unbonded post-tensioned concrete
  • Unbonded post-tensioned concrete differs from
    bonded post-tensioning by providing each
    individual cable permanent freedom of movement
    relative to the concrete.
  • To achieve this, each individual tendon is
    coated with a grease (generally lithium based)
    and covered by a plastic sheathing formed in an
    extrusion process.
  • The transfer of tension to the concrete is
    achieved by the steel cable acting against steel
    anchors in the perimeter of the slab.
  • The main disadvantage over bonded post-tensioning
    is the fact that a cable can destress itself and
    burst out of the slab if damaged (such as during
    repair on the slab). The advantages of this
    system over bonded post-tensioning are

18
External Prestressing
  • This refers to the case where prestressing
    tendons are placed outside the concrete section
    and the prestressing force is transferred to a
    structural member through end anchorages or
    deviators. Advantages of external prestressing
    include the possibility of monitoring and
    replacing tendons, ease in concreting and hence
    better concrete quality and the use of narrower
    webs. External prestressing is being increasingly
    used in the construction of new bridges and is a
    primary method for the strengthening and
    rehabilitation of existing structures.
  • At NUS, a three-year project on the application
    of external prestressing in structural
    strengthening has been completed, and this has
    resulted in design charts being developed for
    such applications.  Works were also carried out
    on the use of fibre-reinforced polymer (FRP)
    reinforcement as external tendons in both simply
    supported and continuous beams.

19
APPLICATIONS
The lower and upper terraces cantilever over the
stream below. The temporary structural steel
shoring was placed beneath the main level terrace.
  • Fallingwater is comprised of a series of
    concrete cantilever trays 30-ft. above a
    waterfall. Previous efforts failed to permanently
    address excessive deflections of the cantilever
    and repair the cracks. After a thorough design
    review, the owner and engineer selected an
    external post-tensioning solution for its
    durability, aesthetics and structural
    unobtrusiveness.
  • Construction plans called for strengthening of
    three support girders spanning in the north-south
    direction with multistrand post-tensioning
    tendons consisting of multiple 0.5 diameter
    strands.
  • Thirteen strand tendons were placed on each side
    of two girders. One 10-strand tendon was placed
    on the western side of the third girder (access
    on the eastern side of this girder was not
    available). Eight monostrand tendons, 0.6
    diameter, were slated for the east-west
    direction.
  • The monostrand tendons were stressed in the
    east-west direction and then the multistrand
    tendons were stressed in the north-south
    direction and grouted with a high quality,
    low-bleed cementitious grout mixture.
  • VSLs scope of work also included welding steel
    cover plates, attaching structural steel
    channels, injecting epoxy grout, doweling
    reinforced cast in place concrete blocks and the
    installation of near surface mounted carbon fiber
    rods. Challenged with maintaining Fallingwaters
    original setting, furnishings and artwork, the
    project was successfully completed in six months.

Frank Lloyd Wright's Fallingwater Mill Run,
Pennsylvania
20
  • Cline Avenue Bridge Gary, Indiana
  • The Cline Avenue Bridge (SR 912) is a
    predominately cast-in-place post-tensioned
    structure located in Gary, Indiana. The bridge
    mainline is over 6,000 LF, has two adjacent
    segments nearly 35 feet wide each, and contains
    four connecting ramps. An inspection and analysis
    team was assembled to perform a thorough
    investigation of the bridge. The team
    concentrated on the existing post-tensioning
    system and interior and exterior concrete cracks.
    The engineer retained VSL to assist with the
    inspection of the tendons.
  • VSL approached the Cline Avenue project with a
    guideline that outlines a statistically sound
    method of sampling the tendons. A statistical
    sample pool (which consisted of the mainline
    structure and the ramps) was defined by
    referencing the American National Standard
    Institutes (ANSI) guideline Sampling Procedures
    and Tables for Inspection by Attributes as
    published by the American Society for Quality
    Control (1993).
  • The probable void locations throughout the
    structures mainline segments and ramps were
    initially identified by VSL to appropriately
    distribute the sampling population. Such areas
    consisted of high points, areas approaching and
    leaving the high points, and couplers.
  • Using non-destructive Ground Penetrating Radar
    (GPR) and field layout drawings, VSL located
    existing post-tensioning tendons. Once the layout
    was performed, specific tendons throughout the
    bridge and ramp structures were sampled by
    drilling into the duct and exposing the tendon
    for visual inspection. The use of a borescope
    allowed for detailed visual inspection of the
    tendon and also captured video footage to share
    with the owner and the engineer. After review of
    each inspection, VSL placed epoxy in the
    borescope hole to protect the tendons from air
    and moisture intrusion. When voids were
    encountered, the project team observed and
    documented the condition of the strand based on
    the PCI Journal guideline, Evaluation of Degree
    of Rusting on Prestressed Concrete Strand. VSL
    used vacuum grouting technology to fill the void,
    thereby protecting the previously exposed strand.
  • The tendon inspection data was analyzed with
    other findings (such as crack survey findings) to
    determine what type of rehabilitation was
    required. VSLs goal to establish a statistically
    sound sample of physically inspected tendons that
    provided valid data as to the current state of
    the existing PT system was accomplished

21
Grouting of void using VSLs specialized vacuum grouting equipment
22
  • 85th Street Bridge Valley Center, Kansas
  • The 85th Street North Bridge is a seven span
    post-tensioned haunched slab bridge with a
    typical span of 26 meters for the middle five
    spans, and 20 meters at the ends. This 170 meter
    long bridge accommodates two lanes of traffic
    reaching over the Wichita Valley Center Floodway.
    VSL post-tensioning systems utilized for this
    project include 5-19 longitudinal tendons as well
    as 6-4 transverse tendons.
  • Post-tensioned haunched slab bridges are noted
    for ease of construction. Once the geometry of
    the bridge falsework has been obtained,
    prefabricated spacer frames are set into place.
    The spacer frames serve as templates for
    profiling the longitudinal post-tensioning
    tendons and aid in the placement of the remaining
    conventional reinforcement. Transverse tendons
    maintain mid-depth placement along the geometry
    of the haunched slab and provide the minimum
    pre-compression over the length of the structure.
  • The fi nished product has several advantages over
    conventionally reinforced concrete. Dead loads
    are balanced by the use of longitudinal
    post-tensioning reducing the sustained loading
    and associated creep. Corrosion resistance is
    increased due to the encapsulation of the
    post-tensioning reinforcement. Through the use of
    transverse post-tensioning, added compression
    improves the longevity of the structure by adding
    resistance to de-icing methods such as salt and
    magnesium chloride. Post-tensioned haunched slab
    bridges allow for a larger span to depth ratio
    than that of conventionally reinforced haunched
    slab bridges. The labor and material savings on
    mild reinforcement is another clear advantage to
    using post-tensioning for this application.

Overlooking the 85th Street Bridge prior to
concrete placement
23
  • Colorado Convention Center Expansion Denver,
    Colorado
  • The Colorado Convention Center Expansion project
    is a 1.4 million square foot expansion of the
    existing facility. This was a multi-level
    project, which included a 1,000-car attached
    parking garage.
  • The garage above the street was constructed
    using precast tees and columns with a
    cast-in-place topping slab. In order to maintain
    regular spacing for the columns in the precast
    section of the garage and still maintain an
    unobstructed path for the road and light rail,
    large post-tensioned transfer girders were
    required to support several of the columns above.
    The transfer girders allowed for the placement of
    columns required for the precast design despite
    the restricted column locations at the street
    level.
  • Post-tensioning the transfer girders resulted in
    smaller dimensions than a conventional reinforced
    concrete design, an important factor given the
    girders are over 7 feet high and up to 7 feet
    wide and a larger section would not fit within
    the space constraints of the building. The
    girders could not be stressed until after the
    precast garage was fully erected and the topping
    slab poured on the truck dock. Temporary columns
    were placed under the girders to support the load
    until stressing.
  • The effective post-tensioning force required for
    the beams ranged from 2176 to 5457 kips. A
    multistrand bonded system was installed

24
  • The Seward Silo project involved the
    post-tensioning of three interconnected ash silos
    that are part of the Seward Re-Powering Project
    in Seward, Pennsylvania. The overall project
    involved the construction of a new,
    state-of-the-art 208 MW power plant designed to
    burn low-grade coal that can not be burned in
    ordinary coal plants. This is a design-build
    project with Drake-Fluor Daniel as the
    owner/construction manager until the completed
    plant is turned over to Reliant Energy, the
    ultimate owner.
  • T.E. Ibberson Company was contracted to build
    three 187-6 tall, interconnected, in-line
    silos two 82-4 diameter fly ash silos and one
    64-8 diameter bed ash silo. The silos were
    built using the slip-form method of construction
    and are believed to be the first interconnected
    silos in the world built using post-tensioning as
    the primary circumferential reinforcement.
  • VSLs work was performed from November 2003
    through February 2004, during the second coldest
    winter on record locally. Significant snowfall
    and subzero temperatures made progress
    challenging, yet with a strong focus on safety,
    both cold-related and otherwise, the job was
    completed with no incidents. The job required
    close coordination between the various trades
    working in close proximity and constant
    communication between parties working above and
    below VSLs work locations to phase the work to
    avoid having personnel under an active work zone.
  • The strand installation, stressing and grouting
    operations were completed successfully, with
    cold-weather grouting made possible through a
    variety of heating methods.

Seward Silo
25
THE BICYCLE WHEEL
  • Bicycle wheel as we know it today - each is
    associated with an application of prestressing to
    a structural system.
  • The first and most obvious is the tensioned
    spokes - the rider's weight is carried from the
    forks to the ground not by hanging off the top
    spokes, but by reducing the pretension in the
    lower spokes - only a couple of spokes are
    carrying the load at any one time.
  • The second is the pneumatic tyre, where the
    compressive load is carried to the ground by
    reducing the tension in the sidewall. The air
    pressure in the tyre does not change when the
    load is applied.
  • The final prestressing system is the tyre cord,
    which is shorter than the perimeter of the rim.
    The cord is thus in tension, holding the tyre on
    the rim, which enables the pretension in the
    sidewalls to be reacted

26
EQUIPMENTS -
  • T6Z-08 Air Powered Grout Pump
  • Pumps cement grout only, no sand. 32 Gallon
    Mixing Tank. Mixes up to 2 sacks of material at
    once and allows for grout to be pumped during
    mixing or mixed without pumping.

Approximate size 50" long30.5" high52" wide
Weight 560 lbs.
Production Rate 8 gallons per minuteat 150 psi
27
  • Colloidal Grout Plant
  • The heavy duty, high volume Colloidal Grout Plant
    is favored for precision post-tension grouting.
    The unit features a high speed shear mixer that
    thoroughly wets each particle and discharges the
    mixed material into a 13 cubic foot capacity
    agitating holding tank. A direct coupled
    progressing cavity pump delivers slurries at a
    rate of up to 20 gpm and pressures of up to 261
    psi. The unit easily mixes and pumps slurries of
    Portland cement, fly ash, bentonite, and lime
    flour. All controls are conveniently located on
    the operator platform for easy one-man control.

Pump Pump Type 31.6 progressing cavity
Pump Output/Pressure variable up to 20 gpm, 261 psi
Colloidal Mixer Mix Tank 13.0 CF with bottom clean out
Colloidal Mixer Mixing Pump 2 x 3 x 6 diffuser-type centrifugal
Colloidal Mixer Holding Tank 13.0 paddle agitating
Drive Power Air 300 CFM, 100 psi
Physical Specifications Dimensions 96" L x 60" W x 63" H
Physical Specifications Weight 1800-2800 lbs.
28
  • T7Z Hydraulic Jacks
  • Used for testing and pre-stressing anchor bolts.
    Available with up to 5-1/8" center hole. Unit
    comes with ram, pump, gauge, hoses, jack stand,
    high strength coupling, high strength test rod,
    plate, hex nut and knocker wrench. Calibrations
    are available upon request.
  • Note Jack pull rods should have a higher
    capacity than the anchor rod.

29
  • T80 Post-Tensioning Jacks
  • With the T80 series the enclosed bearing housing
    contains a geared socket drive to tighten the
    bolt hex nut during tensioning. Test jack housing
    will accommodate up to a 9 deep pocket.

T80 Post-Tensioning Jacks
30
  • T8Z-18 Hydraulic Torque Wrench
  • The hydraulic torque wrench is used for
    tensioning anchors in tight fitting locations
    where it would be difficult to use an hydraulic
    jack. The wrench is also recommended for use when
    setting the large diameter Spin-Lock anchors. The
    torque wrenches are light weight and can achieve
    a maximum of 8,000 ft-lbs. Torque Tensioning
    charts Williams products can be found here.

MaximumTorque Length Height Weight
5,590 ft./lbs.(773 kg/M) 11.11"(279 mm) 4.49"(114 kg) 16.75 lbs.(7.6 kg)
8,000 ft.lbs.(1,006 kg/M) 12.57"(319 kg) 5.09"(129 kg) 24.95 lbs.(11.3 kg)
31
  • T8Z Torque Wrench
  • For applying torque to the anchor bolt when
    setting the anchor. Torque Tensioning charts
    Williams products can be found here.

BoltDiameter SquareDrive Size Capacity(ft. lbs.)
1/2"-1" 3/4" 0-500
1/2"-1" 3/4" 0-600
1-1/8"-2" 1" 0-1,000
T8Z-04 Torque Multiplier (41) For use with T8Z
Torque Wrench. Other sizes available
Size Square DriveInput Square DriveOutput MaximumTorque
GA 186 1" 1-1/2" 4,000 (ft. lbs.)
32
  • T1Z T2Z Long Fitting Tool Adapters
  • For driving hex nuts and setting tools, typically
    with our Spin-Lock anchor systems. Works with
    torque wrench or impact gun.Available with 1" or
    1-1/2" square drive. Please specify square drive
    for compatability with your equipment.

T1Z Deep Socket
2Z Regular Socket
K3F-26 Long Fitting Wrench Adapter For applying
torque to recessed anchor nuts that are under
tension when using hydraulic jacks. Available in
all anchor sizes.
33
Corrosion Protection
Methods of Corrosion Protection
Corrosion Protection Type Abrasion Resistance (4best) Typical Thickness Relative Cost (4highest) Lead Time Can be applied to accessories?
Hot Dip Galvanizing 4 3-4 mils 2 2-4 weeks yes
Epoxy Coating 1 7-12 mils 1 2-3 weeks yes
Pre-Grouted Bars 3 2", 3" or 4"tubing 3 2 weeks no
Extruded Polyethylene Coating 2 23-25 mils 1 2-4 weeks no
Corrosion Inhibiting Compound 2 N.A. 2 2-4 weeks yes
34
Methods of Corrosion Protection
  • Epoxy Coating
  • Fusion bonded epoxy coating of steel bars to
    help prevent corrosion has been successfully
    employed in many applications because of the
    chemical stability of epoxy resins. Epoxy coated
    bars and fasteners should be done in accordance
    with ASTM A-775 or ASTM 934. Coating thickness is
    generally specified between 7 to 12 mils. Epoxy
    coated bars and components are subject to damage
    if dragged on the ground or mishandled. Heavy
    plates and nuts are often galvanized even though
    the bar may be epoxy coated since they are
    difficult to protect against abrasion in the
    field. Epoxy coating patch kits are often used in
    the field for repairing nicked or scratched epoxy
    surfaces.

Cement Grout filled corrugated polyethylene
tubing is often used to provide an additional
barrier against corrosion attack in highly
aggressive soils. These anchors are often
referred to as MCP or Multiple Corrosion
Protection anchors. The steel bars are wrapped
with an internal centralizer then placed inside
of the polyethylene tube where they are then
factory pre-grouted. When specifying couplings
with MCP ground anchors, verify coupling
locations with a Williams representative.
Pre-Grouted Bars
35
  • Hot Dip Galvanizing
  • Zinc serves as a sacrificial metal corroding
    preferentially to the steel. Galvanized bars have
    excellent bond characteristics to grout or
    concrete and do not require as much care in
    handling as epoxy coated bars. However,
    galvanization of anchor rods is more expensive
    than epoxy coating and often has greater lead
    time. Hot dip galvanizing bars and fasteners
    should be done in accordance with ASTM A-153.
    Typical galvanized coating thickness for steel
    bars and components is between 3 and 4 mils. 150
    KSI high strength steel bars should always be
    mechanically cleaned (never acid washed) to avoid
    problems associated with hydrogen embrittlement.

Extruded Polyethylene
Williams strand tendons contain an extruded high
density polyethylene sheathing around each
individual strand in the free-stressing portion
of the anchorage. The sheathing is minimum 60
mils thick and applied once the 7-wire strand has
been coated with a corrosion inhibiting compound.
Extruded polyethylene sheathing provides a
moisture tight barrier for corrosion protection
and allows the strand to elongate freely
throughout the free-stressing length during the
prestressing operation
36
Corrosion Inhibiting Wax or Grease with Sheath
  • Williams corrosion inhibiting compounds can be
    placed in the free stressing sleeves, in the end
    caps, or in the trumpet areas. Often bars are
    greased/waxed and PVC is slipped over the
    greased/waxed bar prior to shipping. Each are of
    an organic compound with either a grease or wax
    base. They provide the appropriate polar moisture
    displacement and have corrosion inhibiting
    additives with self-healing properties. They can
    be pumped or applied manually. Corrosion
    inhibiting compounds stay permanently viscous,
    chemically stable and non-reactive with the
    prestressing steel, duct materials or grout. Both
    compounds meet PTI standards for Corrosion
    Inhibiting Coating.

Coal Tar Epoxy
Coal tar epoxy has shown to be abrasion resistant, economical and durable. This product when specified should meet or exceed the requirements of (a) Corp of Engineers C-200, C200a and (b) AWWA C-210-92 for exterior. Typically the thickness is between 8 and 24 mils. Make sure that the surfaces of the bar are clean and dry before coating.
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  • Heat Shrink Tubing
  • Heat Shrink Tubing provides a corrosion protected
    seal when connecting smooth or corrugated
    segments.

Epoxy Coating Patch Kits
Epoxy Coating Patch Kits are available upon
request.
Anchor Head Protection
The most important section of a ground anchor that needs adequate corrosion protection is the portion of the anchor exposed to air/oxygen. This is typically defined as the "anchor head", which generally consists of a steel bearing plate, a hex nut and washer for a bar system, or a wedge plate and wedges for a strand system. For permanent ground anchors it is best to galvanize the hex nut and plates even if the bar is epoxy coated. Galvanized components, if scratched during shipping, are less likely to cause corrosion concerns than scratched epoxy coated components. The end of the steel bar protruding out from the hex nut is often protected by the use of a plastic or steel end cap packed with grease or cement grout. Williams offers several different types of PVC and metal end caps to provide corrosion protection at otherwise exposed anchor ends.
Screw-OnPVC Cap
Fiber Reinforced Nylon Cap
StrandEnd Cap
Steel Tube Welded on Flange with Threaded Screw
Connections
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  • Field Splice for Bars
  • Continuous corrosion protection can even be
    accomplished for the MCP Pregrouted anchors
    manufactured from Williams Form Engineering. To
    achieve the equivalent levels of corrosion
    protection the coupled sections of bar anchors
    can be wrapped in a grease impregnated tape that
    is further protected with heat shrink sleeving.
    This scheme is acceptable by most governing
    agencies and is specified in the PTI
    Recommendations for Prestresed Rock and Soil
    Anchors.
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