FALL ARREST LOAD (ASCE and OSHA) 6

[nameSrp]

I have a question about fall arrest load as per ASCE and OSHA.

Why does the fall arrest load need to be 13.8 kN? Is it too much for a human's weight?
Can I use only 1 or 2 kN for a human's weight? (I have to design a fall arrest system on a metal sheet roof top, and it seems impossible to use 13.8 kN as the fall arrest load)

Thank you in advance.

 

[Once20036]

I would consider using the extraordinary event load combination.
In most existing (and many new) buildings we are trying to make things work reasonably and not find a reason to needlessly spend the Owner's money.

I agree with making things work reasonably, but IBC requires 3,100lb fall protection load in section 1607 (which is the live load section) and therefore requires a 1.6 live load factor for LRFD designs.
Calling this an extraordinary load implies the use of a 1.0 load factor which would put you 40% lower than the minimum requirement.

 

[Once20036]

Great video on the testing of those anchors. I had never considered that they`d come apart like that.
With that in mind, the plate that Human909 shared clearly shows a lot of locations where similar deformation could be expected.

 

[dik]

You're down under, so I suspect G is a little lower...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

I did a building about 50 years back and the guy cleaning the caissons was attached to a rope at the top. Safety wasn't so much of an issue, back then. The caisson was about 40' deep and his rope was about 80'... oh, well... any drop more than about 10' or so, the safety equipment, unless you have an absorber, the equipment will likely kill you.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Luceid]

Jumps back to the beginning, but here's a guy dropping some weight (I'm assuming around the weight of a person) just four feet and how the fall weight scales in such a short distance, part of some training demonstration:

https://www.youtube.com/shorts/Y77Ns0dmO-Q

 

[dik]

Great clip Luceid... maybe 10' is excessive... thanks.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[human909]

Great clip Luceid... maybe 10' is excessive... thanks.

It isn't the distance that matters in this case it is the fall factor. AKA the length of lanyard/length of fall. Had that demonstation been completed with a 100' lanyard then the force would have been the largely the same.

This is why we have energy absorbers. That said what the demonstrator there is saying about damage to the person is a BS in the case of 4' as the person becomes the energy absorber and would drastically reduce the overall force.

Like I've said I've fallen over 4' on a stiff lanyard; mild bruising. I've also fallen over 25 feet but with a good energy absorber in the system; no big shock at all. Both in my recreation but both uses similar equipment with similar but different ratings and standards.

Jumps back to the beginning, but here's a guy dropping some weight (I'm assuming around the weight of a person) just four feet and how the fall weight scales in such a short distance, part of some training demonstration:

A good video to get the message across to some users. A bad video because half the message is exaggerated and incorrect. The force is incorrect in the case of a soft squishy human and also claiming the person will see the force 3 or 4 times is simple BS.

 

[Luceid]

Yeah human, wasn't relying too heavily on the nitty gritty here at all, just gets my head to start understanding the idea

 

[human909]

Yeah human, wasn't relying too heavily on the nitty gritty here at all, just gets my head to start understanding the idea

Sorry. I was being a bit pedantic wasn't I.

I agree. The video is short and effective at getting the idea of the high impact of falls without energy absorbers.

 

[JSgam]

I just wanted to mention a few things I haven't seen mentioned in any of the fall protection related threads:

1) OSHA calls for 5,000 lbs per anchor point, OR the anchorage to be designed by a Qualified Person (see OSHA definition) that maintains a factor of safety of 2. This can be less than 5,000 lbs.
2) Horizontal lifelines call for a mandatory use of this Qualified Person's design and supervision as these systems can easily exert more than 5,000 lbs on an anchorage.
3) ANSI Z359.6 provides load combinations (both ASD and LRFD) for fall protection systems. They are very similar to the ASCE load combinations, but they take into account "Active Loads" which are your fall arrest/travel restraint loads.
4) OSHA typically refers to ANSI for their rulemaking decisions.

Just throwing this out there.

 

[dik]

One of the few areas of engineering that I don't try to skimp on are life safety issues... they are in the came category as columns and cantilevers...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[NorthCivil]

@human909

I find these suspect, because as you mentioned, you are claiming 8 rivets through 0.5mm steel sheet will take 15kN of load in any direction.

it might do this, installed perfectly, in the laboratory. How about 5 years on? once the rivets and the 0.5mm base sheet have been saturated in moisture and airborne salts for 5 years. these long run roofing products often have 50+ year lifespans, left in service well past the point significant corrosion has started.

i wouldnt trust my life to 8 rivets through a 0.5mm steel roof sheet with an expected life of 50+ years.

see the video above my bones206. the weakest link in the system is the base sheet the assembly connects to.

the weakest link of the assembly is the connection to solid structure... this is against the most basic principles ive learned in structural engineering (weaker members, stronger connections)

 

[human909]

@human909

I find these suspect, because as you mentioned, you are claiming 8 rivets through 0.5mm steel sheet will take 15kN of load in any direction.

This is THE leading manufacture in Australia of working at height safety anchors and Australia has some of the most stringent OH&S rules in the world. I don't currently have reason to doubt the manufacturer.

it might do this, installed perfectly, in the laboratory. How about 5 years on? once the rivets and the 0.5mm base sheet have been saturated in moisture and airborne salts for 5 years. these long run roofing products often have 50+ year lifespans, left in service well past the point significant corrosion has started.

If this was a big issue then it would have been discovered by now. Testing and inspection of anchors is mandatory.

i wouldnt trust my life to 8 rivets through a 0.5mm steel roof sheet with an expected life of 50+ years.

I would. I'd inspect the connection and any less experienced user should read the inspection plate on when it was last assessed.

see the video above my bones206. the weakest link in the system is the base sheet the assembly connects to.

Completely different system. The moment created by that design is severe.

 

[dik]

I thought it was really quite elegant, and wanted one for myself, and was a little disappointed it didn't come in 22kN .

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik