Close the Hooks

Science based lifting

Understanding Science based lifting

Is the lifting work on your site based on science, or do you only rely on instincts and luck, as the case is unfortunately often?

Do you know how to calculate tensions formed in the slings, in symmetrical and asymmetrical lifts?

Can you always determine what is the maximum tension allowed in the slings in use?

By reading through the book Close the Hooks, Science based lifting, you learn to master these things. No more insecurities about the lift you’re about to do. You know the facts of the lift exactly.

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The Calculator

With this calculator app you can solve most (if not all) lifting situations you will encounter on your site. You can calculate the following...

Degrees of stress in symmetric lifts
‍Free of charge

Chain shortenings for straight flight of stairs

Centre of gravity in precast wall elements

Get the license Try the free version

What exactly does the calculator do?

This calculator gives correct result only in symmetrical lifts. Symmetrical lift, is a lift where the lifting points are located symmetrically with respect to the center of gravity.

Length of the slings

The length of the chains is measured from the bottom edge of the master link to the bottom edge of the hook's surface.

WLL

If more than one lifting accessory is used for the lift, the WLL value of the weakest accessory is used.

Remember: A chain is only as strong as its weakest link.

Form factor

Different hitching methods give different form factors.

Basic choke hitch 0.8

Straight 1

‍Double choke hitch 1.6

U-lift 2
‍U-choke 2

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SWL

Product of WLL and form factor.

Mass

How much the load to be lifted weighs.

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Legs

Between how many legs is the mass of the load divided. There are typically two or four legs.

ATTENTION! In a four legged lift you typically set as the value of the number of legs to three!
Reason being, that the tension isn't typically distributed evenly between four legs.

If the length differences between legs are big enough, it might be that only two legs carry the entire load.
If you see that this really is the case, then set the value of the number of legs to two.

There are exceptions. If the chains have load distributor plate(s), you may set the value at four. Or if the lift is being done as U-lift, you may also set the value at four.

LP-X & LP-Y

LP = Lifting Point

X = X-axis
Y = Y-axis

LP-X = Distance between lifting points on X-axis
LP-Y = Distance between lifting points on Y-axis

If it is two legged lift only this gets a value. LP-Y is then zero. In this case, the value of the right side is zero.

Degree of stress

How many percent of the maximum capacity of the sling is in use. It is recommended that the lifts are made between 1-80%.

Between 81-100% stronger slings are recommended.

Over 100% values you have overload and changing for stronger slings is necessary!

Beta-angle

The angle of the sling with respect to the vertical.

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Tension

Combined effect of vertical load and beta-angle in the sling.

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You can use this 2D-calculator, when the staircase isn't very big, < 3 t. And has fixed lifting inserts. If the staircase doesn't have fixed lifting inserts, and it is being lifted with spherical head anchors, or especially if it's being lifted with the help of wire rope slings, that are attached to concrete anchors, use 3D-version, cause it also calculates tension.

Length of the slings

The length of the chains is measured from the bottom edge of the master link to the bottom edge of the hook's surface.

LP

If lifting inserts are located at the end of the stairs, you might have to use bit bigger value for the run, then it actually is, usually about 30 mm bigger.

Rise

Rise is the height of one step.

Run

Run is the length of one step.

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Angle of inclination

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Shortening

Shorten the chain so, that the length difference of the chains is according to the shortening.

Check the length difference by measuring, before attaching to the element.

Use this 3D-version for even slightly larger stair elements, weight > 3 t.

‍And if the stair element is lifted with cable loops that are screwed to the concrete anchors, then use this calculator, instead of the 2D-calculator. Because of all lifting accessories, the ones attached to the concrete anchors are the most insecure, so it is especially important with them not to overload them. I recommend using this also when the staircase has spherical head lifting anchor.

Does the chains have load distributor plate?

Yes

No

Length of the slings

The length of the chains is measured from the bottom edge of the master link to the bottom edge of the hook's surface.

WLL

If more than one lifting accessory is used for the lift, the WLL value of the weakest accessory is used.

Remember: A chain is only as strong as its weakest link.

Mass

How much the load to be lifted weighs.

Is there a load distributor plate in the chains?

If the chains don't have load distributor plate to ensure the even distribution of the tension between all four legs, calculator will assume there is only one leg carrying the load in the upper end, and one leg in the lower end.

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LP-length & width

Distance between lifting points lengthwise and widthwise.

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Rise

Rise is the height of one step.

Run

Run is the length of one step.

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Shortening

Shorten the chain so, that the length difference of the chains is according to the shortening.

Check the length difference by measuring, before attaching to the element.

Angle of inclination

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Degree of stress

How many percent of the maximum capacity of the sling is in use. It is recommended that the lifts are made between 1-80%.

Between 81-100% stronger slings are recommended.

Over 100% values you have overload and changing for stronger slings is necessary!

Tension higher

Tension in the slings at the lower end of the stairs, per sling.

Tension lower

Tension in the slings at the lower end of the stairs, per sling.

Beta-angle

The angle of the sling with respect to the vertical.

In this example we're lifting a large, asymmetrical wall element with 10mm LK10 chains. In the left chain, the stress level exceeded 80%, so it would be recommended to lift this element with a stronger chains. For example, with 13mm LK10 chains, with which the stress level on the left would have remained at 53 percent.

Length of the slings

The length of the chains is measured from the bottom edge of the master link to the bottom edge of the hook's surface.

WLL

If more than one lifting accessory is used for the lift, the WLL value of the weakest accessory is used.

Remember: A chain is only as strong as its weakest link.

Mass

How much the load to be lifted weighs.

Width of the element

Measurement from the element's edge to edge

Left lifting insert from the left edge

Measurement from the edge to the middle of the left lifting insert.

Right lifting insert from the right edge

Measurement from the edge to the middle of the right lifting insert.

CoG from the left edge

Measurement from the element's left edge to the middle of the CoG sign.

High left

Height difference, when the left side is higher.
In this case, the value of the right side is zero.

High right

Height difference, when the right side is higher.
In this case, the value of the left side is zero.

Chain to be shortened

This tells you witch chain should be shortened.

Shortening

Shorten the chain so, that the length difference of the chains is according to the shortening.

Check the length difference by measuring, before attaching to the element.

Degree of stress

How many percent of the maximum capacity of the sling is in use. It is recommended that the lifts are made between 1-80%.

Between 81-100% stronger slings are recommended.

Over 100% values you have overload and changing for stronger slings is necessary!

Beta-angle

The angle of the sling with respect to the vertical.

Tension

Combined effect of vertical load and beta-angle in the sling.

Here is an example for spiral staircase. Weight 4.5 tons.

Length of the slings

The length of the chains is measured from the bottom edge of the master link to the bottom edge of the hook's surface.

WLL

If more than one lifting accessory is used for the lift, the WLL value of the weakest accessory is used.

Remember: A chain is only as strong as its weakest link.

Mass

How much the load to be lifted weighs.

CoG-X

Here you put CoG's location on X-axis.

CoG-Y

Here you put CoG's location on Y-axis.

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LP1-X (mm)

Here the location of LP1 on X-axis.

LP1-Y (mm)

Here the location of LP1 on Y-axis

LP1-Z (mm)

Here the location of LP1 on Z-axis

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LP2-X (mm)

Here the location of LP2 on X-axis.

LP2-Y (mm)

Here the location of LP2 on Y-axis

LP2-Z (mm)

Here the location of LP2 on Z-axis

LP3-X (mm)

Here the location of LP3 on X-axis.

LP3-Y (mm)

Here the location of LP3 on Y-axis

LP3-Z (mm)

Here the location of LP3 on Z-axis

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Shortening

Shorten the chain so, that the length difference of the chains is according to the shortening.

Check the length difference by measuring, before attaching to the element.

Beta-angle

The angle of the sling with respect to the vertical.

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Tension

Combined effect of vertical load and beta-angle in the sling.

Degree of stress

How many percent of the maximum capacity of the sling is in use. It is recommended that the lifts are made between 1-80%.

Between 81-100% stronger slings are recommended.

Over 100% values you have overload and changing for stronger slings is necessary!

With this calculator you can find the CoG in evenly thick, homogenous wall elements, and slabs.This gives the location of CoG only on the X-axis. If you need it also on the Y-axis , you need to repeat the process, but looking the element from the perpective of its side.