Fall Protection on Platform

[pafabeng]

We are being asked by a client to design a platform for access to a piece of equipment, but are also being asked to ensure that it can handle the dynamic load of a person falling onto the platform. The platform is approximately 4' below the finished floor from which a person could potentially be falling. Has anyone dealt with this before? It seems a rudimentary take would be to simply determine the force by F=ma. Is that an oversimplification? I know the stiffness of the platform they are falling on could also be a factor. Thanks.

 

[TLHS]

Realistically, if you're designing it to a reasonable area load this isn't really going to be an issue I don't think. say it's a 4x4 platform at 100psf. You've got 1600lbf and a 1.6 factor. So ultimate capacity is 2560lbf. That's 10 or more times a person's weight. Also, steel equipment platforms are generally governed by practical detailing more than strength unless you've got to really push on supporting it off of the equipment or something. The reserve strength is generally huge.

So I'd go the other way. Back calculate the capacity you have for a reasonable design and see if you can easily justify it. Then back calculate how much deceleration distance you'd need to hit it and see if you feel good, with the understanding that a person falling from four feet will have a pretty good crumply zone from their legs unless they get tossed off head first.

 

[canwesteng]

F=ma is the static force, where a is g. To calculate the force from a person landing on it, you need to know how fast they decelerate (you don't) or over what distance they decelerate (you could guess). I'd do what TLHS suggest and compare to a fall arrest force from OSHA.

 

[Lutfi]

OSHA and now ASCE 7 part 4.6.5 has provisions as the fall protection forces. ASCE 7 requires 3100 pounds live load. Keep in mind, if I recall correctly, when designing for these forces, you can use the ultimate strength.

 

[XR250]

I can't imagine this being an issue on any reasonably designed platform. Many cardboard boxes could take that. I mean, if it was 20 ft, that might be a different story.

 

[human909]

Seems like a bit of box ticking exercise. It is most justifiable to use fall protection prescribed loads. They'll never get reached (in these circumstances but it is most justifiable). Though if you have to allow for yielding and plastic deformation with ultimate tensile strength as your maximum.

I use a similar approach with explosion forces for structures and vessels.