Load Rating of a structure

[Vish S]

Hello All,
I have a structure(attached - everything is L2x2x3/16") which is used for tie-offs during maintainence. I am required to find the load rating of the structure as some feel its unsafe for tie-offs.
My thought process is to find the find the tensile strength of the structure but not sure how much welding adds strength to it.
The industry standard is that for one person the structure should be rated for 5000lbs & if there's two then 10000lbs. Our company goes with only one.
Any pointers on how to proceed here?
Thanks,

 

[Greenalleycat]

With all due respect mate, this is a relatively simple task
If you've got this little idea on how to progress then I suggest you find someone in real life to oversee or do the work for you and learn from/with them

The broad steps for tackling the task are:

Firstly to draw a picture to represent the structure then apply your loading to it so you understand the problem
The 5000lb point load (which seems a bit excessive tbh) - which directions does it apply?
You may end up with 3 different load directions (up/down, in plane/along the frame, transverse to the frame)
You then need to evaluate the structure's ability to handle that - I expect this to be primarily moment governed for the members, but I would also check global deflections to make sure they're not OTT (the 5000lbs load is HUGE though relative to a person's weight - so I would apply a more realistc loading to simulate deflection under use, not ultimate conditions)
You then work you through the connections, foundations, etc

 

[TRAK.Structural]

This looks suspect at best for fall protection. I suggest you find an Engineer with experience running these calculations to check this out.

 

[Greenalleycat]

We do a lot of fall protection work and I agree with you TRAK
The saving grace is probably that the '5000lbs' design load (which will completely write that structure off IMO) doesn't really exist
Energy dissipation in the ropes combined with (hopefully) ductile behaviour of the steel will likely save someone...unless it deflects so much that they hit the ground anyway as they have too much slack in their system

 

[Vish S]

This looks suspect at best for fall protection. I suggest you find an Engineer with experience running these calculations to check this out.

Trying to do that within the company. As of now its just me and my supervisor - he has put his hands up on this so I am on my own.

 

[Geoff13]

Many good answers already, so I take a different direction.

Here's some quick gut check questions I ask myself when looking at fall protection anchor points.

• What location would you be willing to hang your car off? My answer would be nowhere in those pictures. Handrail is required to support 200 lbs, and this looks flimsy enough to have trouble with that small load.
• What location would you be willing to tie-off to yourself and intentionally fall off? If I won't tie-off to something why would I tell others it's suitable?

As stated above, your company need to hire an experienced fall protection engineer.

 

[SWComposites]

1) the part is not likely to fail in pure tension; its going to fail by buckling or bending of those thin members, or fail by breaking the welds
2) the part is not adequate for a 5000 lb load; bad by inspection, no analysis required
3) if you want/need to bother with an analysis, start by drawing a sketch of the part, then for each possible load location and direction, apply the loads and draw a free body diagram and work out the loads/stresses in each member of the part.

 

[JStephen]

I agree with the above.
I can't tell how this is attached to the concrete below. It's possible you could put a loop around one leg or the other and show it's adequate for that load. Although, based on the construction above, that seems rather unlikely.
It might be possible to fabricate a hook assembly that fits over the top of the wall.
I think here are a number of anchor points that could be installed on the top or side of that wall, also. You'll still have some analysis to do to show that they are good for that load.

 

[phamENG]

@Vish S , I've run enough of these to know that what you have in those pictures will not pass. Period. You've got a flat bar bending about its weak axis. I could probably create a plastic hinge in it by leaning on it, much less falling off of that platform while strapped to it.

I mean no disrespect to you - I'm sure that, like most of us, you're a good engineer when working within your specialty. I also think it's good to expand your horizons and learn new things. But people's lives are literally on the line with this one. Hire a specialist consultant to come in and design a new fall arrest system. The workers at your company deserve as much. And as for management - make them realize that whatever fee the designer charges will be recouped 100x as soon as there is an accident.