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LIFTING MYTHS.

Myths abound because we humans believe what we want to believe!

MYTH

Reason for the myth

THE TRUTH

Discussion

The avoidance myth:


Because it hasn't happened it wont happen”


often expressed as:


I've been doing this for years and never had a problem

Fear of change or cost.

Popular excuse for avoiding the truth and the adoption of standards where this may involve effort, change, perceived cost, inconvenience.


Commonly used by persons who are experienced yet lack knowledge about the engineering systems they use and risks which they take on a daily basis.

Standards are developed to minimise risk by pooling experiences and technical knowledge.


Personal experience by itself is not a good predictor of risk. Accidents happen.

You can lift a 10 tonne load on a 5 tonne hook...but it is illegal.


It is possible to “get away” with illegal practice for years “without problems” but ....if an accident occurs you can expect to go to gaol and more importantly, somebody may be injured or killed.

The anti-competitive myth:


It is unsafe to interchange the Concrete Lifting system components of different suppliers.”

Commercially driven,
Sales Spin”

Usually touted by companies with a dominant market share. Its purpose is to restrain trade – under the guise of “protecting safety”.

AS3850 defines compatibility by performance (not supplier)
Compatible: The coordinated use of two (or more) separate components without compromise to the working load limit (WLL) or utility of either component.”


Interchanging components is permissable when they are designed, manufactured, tested and warranted to be compatible (as defined by AS3850) with complying products made by others.


AS3850 requires all lifting system components to be compatible (regardless of supplier).

It is easy to see through this one!


Engineering products can be functionally compatible without being identical.


Performance standards (e.g. AS3850) make no distinction between whether components are supplied by the same manufacturer or others – it is irrelevant. All products must meet the same performance standard.


It is universally accepted to interchange chains and hooks which comply with the same performance standards...it is nonsense to suggest that it is unsafe for a hook from one supplier to be interchanged with the hook of the supplier of the chain it is used with!


More information...

The horizontal anchor bar myth:


An edge trimmer bar or horizontal bar passed through the eye of an anchor reinforces an anchor for higher loads ”

Custom and practice based on misinformation and lack of knowledge.

It may be cheaper and easier to use a horizontal bar than a properly designed “hanger bar”.

Bars horizontal to the anchor axis provide no additional pullout strength to the anchor.


Only hanger bars or bars which cross the crack vertically are capable of supporting the load.


When the concrete cracks from the bottom of the anchor, the horizontal bar (which is closer to the edge!) offers no increased strength and simply rips out of the top edge.
Generally, the simplest and cheapest way to reinforce anchors is with a properly detailed hanger bar.

Rule of Thumb:
Edge lifting a 150mm thick panel in tension, concrete strength limits the WLL to:
... 2.8tonnes at 15MPa
... 3.6tonnes at 25MPa

Hanger bars are required for all anchors located the the edges of thin panels when lifting loads exceed the WLL for the concrete strength limit state.



More information...

The shrinkage steel myth


Shrinkage steel in panels increases anchor loads”

Cost


It is cheaper to believe that the existing steel in the panel is capable of accepting the liftingloads than to add steel or properly designed hanger bars to the anchor

Shrinkage reinforcing is only designed to resist the stresses developed in the concrete when it shrinks.
Reinforcing to support Lifting loads becomes part of the anchor system and must be specifically designed to comply with the requirements of AS3850 and AS3600 for all strength limit states.
Generally, the simplest and cheapest way to reinforce anchors is with a properly detailed hanger bar.

AS3850 requires anchors to have a design factor of 2.5 against the strength limit state.

This applies to steel added to reinforce anchor lifting loads.


More information...

The anchor with flat outside edges myth:


They grip into the concrete without any bursting forces”

Commercially driven
Sales Spin”
This defies the laws of physics!
Newton's third law of motion says that every action has an an equal and opposite reaction.
And.. It is fundamental property of elastic solids that applied loads are resisted by stresses in all directions i.e. parallel to the direction of the load and at right angles to it.

In the case of concrete anchors the applied force is resisted by tensile and shear stresses in the concrete.

These stresses result in an equivalent “bursting” force in the concrete acting at approximately 45degrees to the anchor axis in all directions around the anchor, no matter what the shape of the anchor.


More information...