Lateral Loading for Fall Arrest Gantry Beams 1

[Deener]

Hey guys,
I'm designing a stand alone structure that supports a fall arrest system. It's inside a tractor trailer factory where workers walk atop tankers to perform maintenance. The company needs trolley beams overhead two adjacent bays that the workers can connect to for fall arrest. Top of steel for the trolley beam is about 20' above the floor slab so columns are relatively tall. I'm using a factored vertical arresting load of 16 kN (3.6kip) for design. I'm wondering what kind of lateral loads I should be designing the structure to resist? I'm thinking the lateral load could be caused by the pendulum effect if a worker were to fall from a point where the fall arrest connection isn't directly overhead. I'm currently thinking of taking the horizontal component of the fall arrest load if the worker is swinging with a landyard that's 45 degrees from vertical. This would be about 11.3 kN (2.5 kip). Curious to get others opinions on the magnitude of this design load.
Thanks

 

[straub46]

Fall arrest loads are required to be applied in any direction. Use the 3.6 kips for lateral. I would probably apply them at the same time.

 

[Once20036]

There are lots of threads on fall protection. Here's a recent one asking the same thing.

Fall Peotection - Structural engineering general discussion

For a 5000lb fall protection load, is that also lateral or just vertical? For a person falling over the edge, what amount of eccentricity do you use for torsion on the beam? Thanks

www.eng-tips.com

In my opinion, fall protection loads do not need to be applied in any direction. In this case, it is physically impossible for a worker to fall in a horizontal direction.

 

[dold]

In my opinion, fall protection loads do not need to be applied in any direction. In this case, it is physically impossible for a worker to fall in a horizontal direction.

I'm with Once. There's no reason to apply 3.6k in any direction above say 45 degrees. Some degree of engineering judgement would be easily justifiable.

 

[Deener]

Thanks guys. Really appreciate the responses. I'm proceeding with applying the 3.6 kip vertical and the horizontal component of 3.6 kip at 45 degrees. While I have your attention, what kind of deflection criteria for lateral and vertical would you design for? This not being an occupant comfort or ceiling cracking scenario, I can only think that lateral deflection should avoid P Delta issues. Currently my lateral deflection is about 32 mm (1.25") at the top of the 20' frame. As for vertical deflection criteria, a bouncy beam doesn't present well. Should I stick with span/180?

 

[Lomarandil]

Deflections under fall arrest loading aren't given a hard limit by any code I've seen.

As you note, a few conditions that may limit what you want:

• P-d effects on your structure
• Excessive vertical deflection could reduce the clear fall distance before a worker falls into a hazard below
• Perception (the bouncy beam). I'd agree that L/180 could be appropriate here