Transcript Lean Construction - Swedish College Of Engineering

1
CE-407
Lec-01
Structural Engineering
By
Dr. Attaullah Shah
Swedish College of Engineering and Technology
Wah Cantt.
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.
− 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.
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.
METHODS OF PRESTRESSING IN CONCRETE
PRESTENSIONING & POST- TENSIONING
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.
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
POST - TENSIONING
− WHAT IS POST-TENSIONING?
− Post-tensioning- is a method of reinforcing
(strengthening) concrete or other materials with highstrength 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.
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
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.
This innovative form is
result of post
tensioning.
− 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.
Bridge decks
− 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, posttensioned 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.
POST –TENSIONING METHOD
Method of post-tensioning
Tendons
TENDONS
Wedges tensioned
by jacks
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.
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
 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:
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.
APPLICATIONS
• 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 posttensioning 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 eastwest 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.
•VSL’s 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
Fallingwater’s original setting, furnishings and artwork, the project
was successfully completed in six months.
The lower and upper
terraces cantilever over
the stream below. The
temporary structural steel
shoring was placed
beneath the main level
terrace.
Frank Lloyd Wright's
Fallingwater
Mill Run, Pennsylvania
 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 Institute’s (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 structure’s 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 posttensioning 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. VSL’s 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
Grouting of void using VSL’s specialized vacuum grouting equipment
 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 middepth placement along the geometry of the haunched slab and provide the minimum precompression 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 posttensioning 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
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-inplace 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
−
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, stateof-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 DrakeFluor 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.
−
VSL’s 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 VSL’s 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
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
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" long
30.5" high
52" wide
Weight
560 lbs.
Production Rate
8 gallons per
minute
at 150 psi
−
−
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
31.6 progressing
Pump Type
cavity
Output/Pressure
variable up to 20
gpm, 261 psi
Mix Tank
13.0 CF with
bottom clean out
Mixing Pump
2 x 3 x 6 diffusertype centrifugal
Holding Tank
13.0 paddle
agitating
Drive Power
Air
300 CFM, 100 psi
Physical
Specifications
Dimensions
96" L x 60" W x
63" H
Weight
1800-2800 lbs.
Colloidal Mixer
−
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.
−
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
−
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.
Maximum
Torque
Length
5,590
11.11"
ft./lbs.
(279 mm)
(773 kg/M)
8,000
ft.lbs.
(1,006
kg/M)
12.57"
(319 kg)
Height
Weight
4.49"
(114 kg)
16.75 lbs.
(7.6 kg)
5.09"
(129 kg)
24.95 lbs.
(11.3 kg)
−
T8Z Torque Wrench
−
For applying torque to the anchor bolt
when setting the anchor. Torque
Tensioning charts Williams products
can be found here.
Bolt
Square
Diameter Drive Size
T8Z-04 Torque Multiplier (4:1)
For use with T8Z Torque Wrench. Other
sizes available
Size
GA 186
Square Square Maxim
Drive Drive
um
Input Output Torque
1"
1-1/2"
4,000
(ft. lbs.)
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

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.
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.
T1Z Deep Socket
Corrosion Protection
Methods of Corrosion Protection
Can be
Corrosion Abrasion
Relative
Typical
applied to
Protection Resistance
Cost
Lead Time
Thickness
accessories
Type
(4=best)
(4=highest)
?
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
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 A775 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
Pre-Grouted Bars
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.
− 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
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.
− 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
Strand
components. The end of the steel bar protruding out from the hex Fiber Reinforced
Nylon Cap
End Cap
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
Steel Tube Welded on Flange with
protection at otherwise exposed anchor ends.
Threaded Screw Connections
ScrewOn
PVC Cap
 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.