Caged Ladder Design

[mastruc]

Hey all, I've got a question about how ladders in an industrial setting are typically analyzed. In verifying a proposed stationary 16' ladder that uses 2-1/2"x3/8" flat bar for the stringers and 3/4" pipe for the rungs, I'm not entirely sure how these are generally modeled. My first instinct is to treat the Lx as the full length of the ladder, the Ly as the distance between treads, and the tread-to-stringer connection as fixed (in verifying the stringers) and pinned (in verifying the treads). Also, I'm not entirely sure about how to account for the proposed connection, in which the stringer has a hole drilled through it, through which the rung partially penetrates and is all-round welded on the inside of the hole. Is there a generally accepted procedure for modeling those perforations?

 

[TLHS]

For the most part you don't redesign these. Look at your local OHS requirements and they normally either have a required detail or refer to a standard that includes details and/or a design basis. Your client may also have their own standards.

ANSI-A14 is pretty commonly accepted. PIP has a good standard ladder too.

This is very much a 'don't reinvent the wheel' scenario.

 

[JStephen]

Similar issues have come up with guard rails in some recent posts.

There are in fact some standards that give minimum member size, spacing, etc, and also minimum design load, and it can be difficult to make the two jive.

Wherever you get your design loads from, note if they are allowable loads or "must not fail under this load" or what. It may require using plastic moment, etc., to match the minimum member sizes to the design loads.

Check if rungs need to be non-skid or not. If so, possibly use weldable rebar. If you're using "pipe", check if structural tubing of the desired size is available- it may have a higher yield point that helps on the design.

 

[TLHS]

US OSHA just straight up copied the requirements from the ANSI ladder. If that's your jurisdiction, you should cross check once because a couple of dimensional requirements apparently changed in ANSI after they copied them over, so they aren't quite the same anymore. I believe loads are all the same still. So the intent is in the ANSI standard. It has both design loads *and* sizes of members that meet those loads. If you really want to back check to figure out what kinds of loads they are, you could do that, but I'd just go ahead and use the required sizes.

Making something on your own is significantly more likely to cause you problems than following a standard that's safely and successfully been in use for decades.