NAAMM Design of Railings with guardrail and post having different material 1

[Orsted]

Hi,

I would like to ask if there are tests/articles that provide a concrete result for the statement below.

From NAAMM Stair Manual (AMP 510-92) page 5-26.

This is just my curiosity on the topic.

Thanks for help.

 

[Orsted]

Btw I've tried AMP 521-12 for Pipe Railing System Manual and below is it's statement so I figure it's not actually indeterminate but just different from using pipe as material?

Thanks,

 

[BAretired]

I would like to ask if there are tests/articles that provide a concrete result for the statement below.

I doubt it. It looks like a conservative assumption which one could override with calculations to justify a different distribution.

BA

 

[JStephen]

I think they mean "cannot be determined with this procedure", not necessarily a determinate/indeterminate structure.
But I do find myself thinking that just assuming all posts were the weaker of the two ought to be conservative. I'll have to give that some thought.

 

[Orsted]

Thanks for the responses and I agree with the both of you on this

Does the load reduction factor of railings only work for pipes? or any material (like tubes or flat bars) as long as it's section, grade and material is the same?

Thanks,

 

[Once20036]

To me, this procedure is about the stiffness.
When everything is the same stiffness (material) the posts share the loads in accordance with the publication.
If you start making something stiffer, their tests are no longer valid and they take the conservative stance that you need to apply 100% of the load.

Out of curiousity, what is your situation that justifies changing the strength of your posts?

 

[Orsted]

what is your situation that justifies changing the strength of your posts?

Regarding pipes as member size, mostly due to spacing of the posts.

 

[dhengr]

Orsted:
Their simplified methods, rules of thumb, prescriptive methods for handrail (guardrail) design are likely in error when you start changing post spacing around too. Why not actually analyze and design the darn thing and be done with it. Usually, when you consider the loading requirements for these designs, you will find that uniform post spacing and no changes in handrail or post sizes, stiffnesses and strengths (constant sizes) are the easiest to deal with.

 

[Orsted]

I'm not really designing anything railing related right now. I'm just curious if it works when the material size isn't Pipe/Round Tube since it's from AMP 510-92.

 

[dhengr]

Orsted:
I don’t have the books or stds. which you are looking at, so I don’t know exactly what either one says about the process of design. Generally speaking, the analysis and design process is essentially the same for all materials, knowing the load criteria, railing height and post spacing. But, of course, each construction material has its own connection detail issues, strengths and the like, which must be considered in the process. Knowing very little about what you are doing in the way of engineering design, and then using some rules of thumb or prescriptive methods can actually be fairly dangerous in terms of safety and a satisfactory design outcome.

 

[Ron]

Agree with dhengr....railings are life safety concerns and their design should not be left to rules of thumb and old tabulated data for tests that might not be applicable to individual conditions. I've designed numerous railing systems and while load sharing does occur, post spacing, top rail stiffness, and post attachment are significant variables.


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[JLNJ]

I agree with Ron that there are many factors in play and many of those work against posts sharing the load.

If you have an end post with a "P" loop, the point load can be applied beyond the last post. No sharing going on there. Especially in a run with just two or three posts.