Box section deflection calc - another one

[thoward]

Sorry for another box section calc, but there seems to be a lot of knowledge on here.
I've got a single centre fixing of 1350kg rating , and I need to spead it a very short distance to two mounting clamps that are on a curtain track that has a 500kg rating for each clamp.

I don't need the full 1000kg of the two clamps, but just to future proof anything else hanging I'd like to go a bit overkill just in case anyone else hangs something else on it later.
I have 25x50x3mm box and 60x60x4mm I could use ... I'd like to use the smaller if I can just so it's closed to the ceiling.

(there are two of these fixings, one at each end of the track)

As this is entertainment it could do with a 4/1 factor of safety so I'm thinking I'll have to use something like the 60x60x4mm and label it low, but not sure how low, or if I'll even get away with the 50x25x3mm on edge once it's de-rated by a factor of 4/1 or similar.

 

[tigdlo]

I use the information here, https://eurocodeapplied.com/design/en1993 with this calculator, https://optimalbeam.com/beam-calculator.php

I have no idea if either are correct though.

 

[Rrobson]

This is a product that is going to be lifting? Or carrying weight?
I doubt a simple deflection calculation is going to be acceptable for this. You will need a proper calculation of the weight carrying capacity of the beam, which would need certifying by a regulated body and more than likely testing to confirm it meets the required standard. It would then need identifying with an ID number and WLL.

The consideration here is if it failed, and caused harm, who signed off the design and put it to use? Negligence is no excuse and fines plus prison time is well documented.

Although, I don’t know this industry so i may be misinformed here, but in the industry I work in you can’t just cobble come thing together and use it for lifting or carrying weight, it needs to be a certified item which is subject to regular testing / inspection and be designed for it’s intended purpose.

 

[Erie Fred]

Did you try beamboy for the box tube ?
flat stock on edge ?
don't go down that road.....

 

[atomant48]

How are you applying the loads/attaching the clamps ?

 

[jenki]

https://www.robindejongh.com/ His you Tube video's are very informative and may provide the info you need.
However I would echo Rrobson above if this is for use in any form of Public location then for you own safety get it properly designed and suitably signed off by someone who is certified and fully insured.

 

[thoward]

It's attached to an inspected lifting point, the clamps are inspected, it's attached with a rated inspected shackle to an eye on the beam. The two clamps at the outer edge are bolted, M12 10.9 tensile, which is what's spec'd by the clamp. I just need to spread the beam from a central point 200mm each way as I don't have two mounting points spaced 340mm apart on the beam and that's how far the mountings are spaced - I'd usually use a round sling and shackle to the beam but I don't want to lose that much head height if possible.

I could do it in Unistrut to keep it rated but I assumed a piece of 60x60x4mm box would have a higher rating than a 400mm piece of unistrut

 

[Agroshield]

I could do it in Unistrut to keep it rated but I assumed a piece of 60x60x4mm box would have a higher rating than a 400mm piece of unistrut

No piece of box section in the world has an intrinsic 'rating' as such. It will have physical and geometric properties that will determine its deflection when a load is applied to it. That is the physics. The 'politics' or the 'rules' of the particular design code to which the object is subject will determine whether that deflection is acceptable.

What you could do as a comparative exercise is look at the acceptable bending moment for a piece of unistrut and see how close your actual applied moment is to that figure. You can also compare the I value of the unistrut to the I value of the box section.

 

[carbonarc]

Assuming the steel sections have not been overloaded to cause them to yield and are Grade 43 steel. Both will be capable of supporting the loading identified. Using the 50x25 3mm thick section the maximum bending stress is around 170N/mm2. When the maximum design bending stress is taken as 275N/mm2 then the 50x25 section safety factor is 1.6.
Using the 60x60 4mm thick section the maximum bending stress is around 54N/mm2. When this is compared to a design bending stress of 275N/mm2 the 60x60 section has a safety factor of 5. I hope this helps.

 

[Jelly_Sheffield]

Although, I don’t know this industry so i may be misinformed here, but in the industry I work in you can’t just cobble come thing together and use it for lifting or carrying weight, it needs to be a certified item which is subject to regular testing / inspection and be designed for it’s intended purpose.

Based on what's been said, it needs to comply with BS EN 17206:2020 I think it does differ in key ways from the conventional lifting and structural regs, but PUWER and LOLER still apply if it's going to be classed a piece of lifting equipment.

Without access to the aforementioned standard it's possible that in an entertainment context it can be classified as part of the temporary structure, and signed off based on compliance with the guidance in the associated code of practice.

Either way, I would ensure that it's approved by someone "Suitably Qualified and Experienced" (which in an entertainment rigging context, may not be satisfied by using a structural engineer or certified software tool, unless they/it have sufficient knowledge of the specific application).

 

[Agroshield]

When this is compared to a design bending stress of 275N/mm2 the 60x60 section has a safety factor of 5

A stress-based analysis is only one very small part of an overall 'fitness-for-purpose' calculation.

As above, there are limits on maximum deflection which more often than not establish the allowed load.

If it were a fluctuating load, the stress limits are very different due to having to consider fatigue failure.

With a thin-walled section it is also necessary to check things like local bearing.

What I am saying is that any analysis you present is in danger of being misapplied if it does not acknowledge up front the simplifying assumptions behind it and locate what is presented in its proper place in a comprehensive scheme.

EN 17206 (108 pages) available here. Enjoy:

https://riglab.org/wp-content/uploads/2023/07/en17206-2020.pdf