Precast Lifters Safety is not an accident. It is the ... · Using Clutches with Lifters Since the...
Transcript of Precast Lifters Safety is not an accident. It is the ... · Using Clutches with Lifters Since the...
Driver & Crane Operator Training Program
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Precast Lifters
Safety is not an accident. It is the responsibility of all employees to ensure
we all go home as healthy as when we arrived for work.
Even though you may not be part of the production team we feel it is
important that you understand the principles behind the use of lifters in our
products.
This Section on Lifter Safety is designed to provide Users with a better
understanding of the use of lifters and how recognize potential hoisting
problems and how to safely attach to and use them.
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Lifters
Key points covered in this section:
1. Basic knowledge on the concept of
lifters.
2. Lifters have higher capacity if they
are reinforced. That Oldcastle
Precast requires all lifters be
reinforced with rebar.
3. Problems with 4-way lift gear and
insert placement.
4. Problems with cable lifters, ‘A’
anchors, and other types of lifters.
5. Affects of lift gear chain angles on
increasing the loads.
6. Handling issues with Center of
Gravity (CG) being offset.
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Lifter Rating
• Just because a lifter uses a "4 Ton" lifting clutch, does not mean it will lift
4 Tons!
• The lifter label typically refers to the lift clutch system – not the lifter’s capacity.
• Here are some "4 Ton" lifter types:
The "4 Ton" lifters shown vary in their lifting
capacity. Below are Capacity Ratings from the Lifter
Manual:
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Lifter Rating
Below are Capacity Ratings from the Lifter Manual:
Anchor Type Tension Rating at 3500 PSI
4 Ton Spread Anchor (#79113) 2670 Lbs. = (1.34 Tons) Not 4 Tons!
4 Ton Plate Anchor (#79044) 4732 Lbs. = (2.37 Tons) Not 4 Tons!
4 Ton Plate Anchor w/rebar (#79044) 8000 Lbs. = (4 Tons)
4 Ton Tech Anchor (#79544) 4305 Lbs. = (2.15 Tons) Not 4 Tons!
Which lifter has the FULL rated capacity of the lifting clutch at 3500 PSI?
Only the 4 Ton Plate Anchor, with the additional rebar reinforcement, is
rated at full capacity of 4 Tons.
Consequently, many lift insert manufacturers have revised the name of the inserts for example from a "4 Ton" lift insert to a "4T" insert. Regardless, it is critical to know the actual allowed capacity or rating of the lift insert being used within the precast product
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The capacity of a lifter may be
increased by using reinforcement
around the lifter. The ‘Plate Anchor’
and ‘Flat Foot Anchors’ are examples
of lifters that this rule applies to.
This is easy to do by making #4 x 18”
leg rebar ‘hairpins’ that can be tied to the anchor…
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IMPORTANT NOTE:
Precast requires lifters on the unformed (top) surfaces prior to casting to be tied-in to reinforcing, or attached to the forms
regardless of the manufacturer’s requirements. This ensures the lifter
is in the correct position, and the lifter is not dislodged by contacting
concrete, rebar or a vibrator.
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Center of Gravity of Loads
Many products have holes, or can be made as irregular shapes. These
changes will affect the Center of Gravity (CG) of the product.
The CG will always be a point directly under the hook when the product is
lifted.
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For a symmetrical product (the same on both sides) this is always in the
center of the product.
Examples of symmetrical products, which has a CG target directly under the
hook:
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If the product has an offset hole, it will have an off center CG:
In order to pick this product in a level manner, the lifters need to be moved,
or the length of the chains adjusted. Engineering will determine the location
of lifters.
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In order to pick this product in a level manner, the lifters need to be moved,
or the length of the chains adjusted. Engineering will determine the location
of lifters.
In this case the lifters will be moved to allow this bridge to pick level, and
give equal load on the lifters.
Many times the most severe load on a lift insert or lifting device will occur during product movement out of a form or product tipping in the yard. The specific inserts used for this purpose need to be designed for that special loading.
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Rolling blocks and cables, or spreader bars, can also be used to equalize the
load to the lifters. This pick also requires “rolling blocks” to equalize the
loads on the lifters….
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Using Clutches with Lifters
Since the majority of the lifters we install in our concrete products are
recessed, clutches are utilized to provide a “link” between the sling and the
lifter.
Example of using clutches with lifters installed on the top of the product.
• Clutch Example
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Using Clutches with Lifters
• Points for lifters to be
installed on top of product
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Using Clutches with Lifters
• Close-up of installed lifter.
Ensure there are no visible
severe cracks or defects in
the concrete around the
lifter that would cause you
to doubt the strength.
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Using Clutches with Lifters
• Attaching clutch to lifter as
a “link” between the lifter
and the sling.
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4 Way Chain Sling Picks
Many products are handled using 4 lifters and a 4-way chain or cable sling. It
is critical to get each leg of the 4 way pick to pick equal load. If a lifter is
misplaced it will only have 2 legs of the 4 way picking the product:
All employees need to be able to
recognize when a 4 way pick has
2 legs loose, and must stop lifting
the product until the lifting is equalized.
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One way to solve this is to use the
correct lift gear. The 4-way sling
shown below has a large hook eye,
with 2 smaller eyes holding the chain.
The smaller eyes will correct for slight
errors (about 1”) in the placement of
lifters.
The Production Manager will make
sure your plant has this type of lift
gear.
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Here is an example of using the 4-way chain sling, with proper tension being
equalized on all four legs.
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4 Way Chain Sling Picks
Having chains at a small Sling Angle will increase the load on the lift gear
and the lifter.
Here is a chart showing the Tension on the lift gear and the lifter, as the angle
decreases:
Many precast plant production policies normally specify a 60 degree, or
greater, sling angle. As shown in the table above, this increases the load on
the lifters and chain by 16% from a straight vertical lift. (Tip: If your sling
leg is long enough when laid down to reach pick point A to B then the
horizontal angle will be at least 60 degrees).
A 30 degree angle will increase the tension by 2 times the load on the lifter, and lift gear.
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4 Way Chain Sling Picks
If the lift gear has sling angles less than 60 degrees, STOP and consult with
engineering to determine if the additional load has been accounted for.
Here is an example
of using the 4-way chain
sling, with at least a
60 degree horizontal sling
angle being utilized.
(you can see he could
easily touch from pick
point "A" to pick point "B"with a single leg of the
sling).
A B
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Using 4 Way Chain Slings
Many of the loads we produce and deliver will require the use of a 4 way
chain sling to place them at the site. Here are some basic steps for safe
hoisting using these systems.
• Install the clutches on each of the
4 lifters. Ensure they are locked
into place correctly.
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Using 4 Way Chain Slings
Safely and slowly position the crane
hook and 4 way slings directly over
the center of gravity of the load.
Provide enough slack in the slings
for proper attachment to the
clutches.
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Using 4 Way Chain Slings
• Lay out the slings in proper
position to be attached to the
clutches.
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Using 4 Way Chain Slings
• Ensure the hooks on the
slings are facing outward and
the locking mechanism on
the hooks is closed.
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Most rigging problems with lifters can be solved by following:
• Check sling angles are 60 degrees or greater
• Check tension is equal on lift gear legs of a 4 way
• Make sure your lifters account for offset Center of Gravity
• Visually check the lifter and concrete around it for any signs of failure or
severe issues that would cause you to doubt the strength prior to elevating
the load.
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Safe lifts are everyone's responsibility! Follow your company policy and
procedure for the correct use of rigging and attachment to lifters at all times.