What is the Max Load Capacity for 4x4x.188 HSS Square Tubing?

[dontupper]

TL;DR Summary

Looking for some answers, and some easier sources for the info on layman's numbers for HSS Square Tubing strengths.

Hi there,

I am very new to the forum, but the reason I ended up here in the first place, is that I was trying to find some working strengths, specifically on 4"x4"x.188" HSS Square Tubing(A500). I would like to know what the max point load that an 8'L resting on 7'W supports(leaving 6" at each end) could handle before breaking? From that point, I will use the number to get the 5:1 design factor required, and potentially a 10:1, if needed in the future.

Thanks in advance!

 

[berkeman]

Welcome to the PF.

What are you planning to hold up with this metal structure? Just curious...

 

[dontupper]

Well, being the film industry, you never know what you may use each item for. In this particular case, it's a 1T chain motor per HSS sharing the load of a 20'L stick of 16"x16" aluminum box truss with a 20' Alum H-beam underneath for a large movie light to move back and forth on. Max static load for this application would be not more than 700lb(500lbs is more realistic) on each HSS 8'L, but dynamic loads happen when starts and stops of the motors occur.

 

[berkeman]

And what might happen if this structure fails?

 

[dontupper]

The items described would fall at the very least. The worst is easily imagined. The HSS solution is widely used in our industry when more conventional means won't work. However, there never seems to be easy literature for quick reference on the HSS, that regular folks(non structural engineers) can see. The .188" wall thickness seems to be used the most, but .250" is also used. However, it is very hard and heavy to get into the spaces we require them at times, therefore the .188" is preferred as they aren't lifted to their final working positions by machinery, but lifted and held in place by workers until fixed into position. I asked about 7' spacing on the resting points, as that is the most common spread, and allows the most useful reference. Also, I have need for some in a 7' space, so it's a double win.

 

[berkeman]

However, there never seems to be easy literature for quick reference on the HSS, that regular folks(non structural engineers) can see.

It does sound like it is done routinely in your industry, but please keep in mind that we are not allowed to give help or advice on projects that sound dangerous. There are potential liabilities for the PF, and it's hard to provide remote-control 3rd party advice without being on-scene to see the design and understand all of the issues.

This thread will probably be closed soon for those reasons, but I am curious how the insurance companies for your film crews view this ad-hoc procedure for building heavy lifting structures without an on-site professional engineer providing consulting services...

 

[dontupper]

Professional engineers are used all the time, but a lot of things don't require them, as we have the engineer's reports for the studios we film in, and all the gear we use have engineer stamped ratings.

It's easy to know what the weight of an item being lifted is for example, and then use the appropriate design factor to make sure that all components in a lifting system are above the minimum, and never exceed the maximum. When in doubt, we call the engineer.

Also, film sets are temporary, and built for artistic purposes only, but we do need them to be safe to work around. That is why I am curious about the strength of the HSS, as if I buy a 12'L, it doesn't come with a manual showing it's care instructions etc.

I don't ask for someone to be involved in some form of liability in any shape or form, I merely don't quite have the full grasp on all specifics required to calculate the breaking strengths of the HSS sizes.

Simply put, before I was asked specifics, my original and only question was and is, what is the breaking strength of 4"x4"x.188"x8'L HSS square tubing when supported at each end of a 7' span with a single point load in the centre?

 

[berkeman]

Professional engineers are used all the time, but a lot of things don't require them, as we have the engineer's reports for the studios we film in, and all the gear we use have engineer stamped ratings.

It's easy to know what the weight of an item being lifted is for example, and then use the appropriate design factor to make sure that all components in a lifting system are above the minimum, and never exceed the maximum. When in doubt, we call the engineer.

Also, film sets are temporary, and built for artistic purposes only, but we do need them to be safe to work around. That is why I am curious about the strength of the HSS, as if I buy a 12'L, it doesn't come with a manual showing it's care instructions etc.

I don't ask for someone to be involved in some form of liability in any shape or form, I merely don't quite have the full grasp on all specifics required to calculate the breaking strengths of the HSS sizes.

Simply put, before I was asked specifics, my original and only question was and is, what is the breaking strength of 4"x4"x.188"x8'L HSS square tubing when supported at each end of a 7' span with a single point load in the centre?

It does sound like you do have some safety standards and professional design resources in your work, and I'd encourage you not to try to work around them. Understanding them better is a good thing, though.

I think we should be able to answer your general, abstract questions about the strength measures of materials and beams/tubing. We just would not be able to help you with questions like "how long of a span of this tubing can I use and still lift a 700lb load safely?".

I'll page @jrmichler and @Baluncore and others to give you pointers to sources of information about the yield strength numbers for your question.

BTW, square metal tubing does not just "break". There are two initial stages of deformation, and then catastrophic deformation. The first stage can be worrisome, but the last two are bad bad.

 

[jrmichler]

There is more than one calculation involved, plus more information needed.

1) Which grade of A500 tubing? There are four.
2) How "pointy" is the point load? Will it cause local yielding or buckling?
3) Need to check for buckling. This is a different calculation than #2 above.
4) Need to check for yield in bending. This is probably what you are thinking of when you refer to "breaking".
5) Should check for crippling at the end supports.

Your best course of action is to call the engineer. An engineer that does these calculations every day can do the complete analysis in just a few minutes.

 

[dontupper]

To be clear, I am not trying to work around any safety issues at all, and gave a specific example of a possible requirement.

Point loads are typically a 3/8" 7x19 aircraft cable wrapped around the HSS to form a basket for the load to be supported from. Cable is always padded from any sharp edges. Let's assume I don't want catastrophic failure, and that bending and deformation is already bad enough to warrant a serious problem.

So at what point would the before mentioned HSS deform permanently from a generically, non pointy, non sharp load hung from the centre of a 7' span?

Keep in mind, I am going to round the number down, and then divide it by 5 for my appropriate load maximum knowledge, and very much know that the number given is provided as a general answer to a general question only, and should not be plugged into designing a non engineer stamped structure that would put people or property at risk.

 

[berkeman]

Let's assume I don't want catastrophic failure, and that bending and deformation is already bad enough to warrant a serious problem.

Er, what does that mean?

 

[dontupper]

Put simply, it means "obviously I want to avoid anything bad at all, including bending, deforming, breaking, scratching, discolouration, or any other unwanted scenario to occur". Listen, I just wanted some friendly help on a general topic(albeit it involves math so it'll be held in a non general category). I am not looking for the third degree, attitude, or loftiness, but instead was hoping for friendly, professional advice on a myriad of potential physics and engineering topics that may come up in the course of the future. I thought this was a good place to expand my knowledge, but it doesn't seem that way from my stand point.

 

[berkeman]

Put simply, it means "obviously I want to avoid anything bad at all, including bending, deforming, breaking, scratching, discolouration, or any other unwanted scenario to occur". Listen, I just wanted some friendly help on a general topic(albeit it involves math so it'll be held in a non general category). I am not looking for the third degree, attitude, or loftiness, but instead was hoping for friendly, professional advice on a myriad of potential physics and engineering topics that may come up in the course of the future. I thought this was a good place to expand my knowledge, but it doesn't seem that way from my stand point.

Sure. I hope you can appreciate how many new posters we get here who are trying to design structural assemblies that involve life safety ("please help me calculate this beam size for my new balcony..."), and I'm sure you can see the problems for us in those cases.

Your original post (OP) was marginal, but I was trying to understand the context and see if we could help you with your question and not set us up for the balcony collapse scenario type question. It seemed like there was a middle ground that we could both gather on to help your general knowledge without causing a problem with your insurance company.

Please send me a private message (click on my avatar and Start a Conversation) with a link to an agent for your company's insurance company so that I can discuss this with them. It seems like that would be the best way for this thread to go forward, based on your reply...