What If I Need To Drive A High Access Machine On To My Stage Lift?

What If I Need To Drive A High Access Machine On To My Stage Lift?

What If I Need To Drive A High Access Machine On To My Stage Lift

This question comes up quite regularly, and most recently was asked in relation to a theatre wanting to use a recently acquired Haulotte Star 10 mast lift on their forestage lift. This machine weighs in at nearly 3 tonnes, and the question was whether the stage lift floor is rated to take the machine.

The lift has rating signs that say “Floor Loading 7.5kPa UDL”, “Point Load 4.5kN”, & “WLL 6,000kg”. Official sounding, by the book and correct as these signs are, they still left the operator asking “so does this mean I can drive a 3 tonne machine onto the lift or not?”

In this article, we’ll try to de-mystify the interpretation of those floor load ratings.

The first thing to consider is that a motorised stage lift is two things – it is a machine for raising and lowering loads, and when it is parked, it is a floor that forms part of a building. This means that it must serve two masters, and be rated both as a machine that complies with the Standards and Regulations covering plant and machinery, and it must also be rated as any floor in a building is rated, to structural engineering Standards and to the Building Code of Australia (BCA).

When the stage lift is raising and lowering loads, then it must be rated for the maximum load that it can safely raise and lower. The traditional term for this was SWL – the Safe Working Load.

The term SWL is now not officially sanctioned (apparently this term was deemed to be risky, as it implied that the only thing needed to be “safe” was to not exceed the Safe Working Load) and the preferred term now is either Working Load Limit (WLL) or Rated Capacity.

When the stage lift is parked, it becomes part of the floor that it is adjacent to and must be rated for exactly the same loads as the floor it is now part of. These ratings are the Uniform Distributed Load (UDL) and the Point Load.

The UDL (“area loading”) describes the maximum average load per square metre that can be placed over the entire surface of the floor. This loading is used to design the sub floor structure – the columns, beams and bearers that hold the floor up. It is permissible to exceed the average loading per square metre when applying large localised loads (point loads) so long as you leave sufficient unloaded area around this localised loading to bring the average back down to the rated UDL.

The Point Load is used to design the floor itself – the joists and floor sheeting. If you exceed this rating, you run the risk of bending or breaking joists and cracking the floor sheeting – not a good look if you’re 10m up in the air in a high reach machine that just went through the floor.

The Building Code of Australia states that floors must be designed to safely withstand the loading conditions set out in AS1170.1 – Structural Design Actions. This standard defines the design loads for a stage floor (Table 3.1, Row C5) as a Uniformly Distributed Load of 7.5kPa (765kg/m2), and a Point Load of 4.5kN (459kg) applied over an area of 0.01m2 (0.1m x 0.1m).

So, can we drive the Star 10 lift on to our stage floor?

The lifter will cover an area 1m x 1.2m and weighs 3,000kg, so at first glance you would think this exceeds the UDL rating. If, however, you place the lift in the centre of an imaginary 4m2 area, and add no more load in this 4m2, then the average loading over that 4m2 is now less than 7.5kPa.

The lifter has 4 wheels, each with a “footprint” of about 0.15m x 0.15m (0.0225m2) and imposing a load of approximately 750kg. This equates to a point load of 3.3kN per 0.01m2 – less than 4.5kN. If the footprint of each wheel was smaller, then you could still drive it on to the lift floor, but you would need to place spreaders under each wheel to make the footprint of the load larger.

And finally, the lifter weighs 3 tonnes, which is less than the WLL of 6 tonnes, so you can even raise and lower the lifter on the stage lift (with the basket safely retracted of course).

 

Jands Staging provide articles to the "Staging What If" section in CX Magazine. If you have any questions regarding this article then please comment below or email info@jands.com.au

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Richard

Hi, the Star 10 are rated at 1737daN per wheel as per the decals and manual. Would this exceed the 4.5kN?

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