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Old 07-03-2012, 04:59 PM   #1
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Handrail strength? Garden stair needs hand rail


According to wikipedia, the appropriate hand rail strength is 50 plf (pounds linear foot) with an active load of 200 plf. That makes sense, about the weight of a person.

However, I can't find any calculators to tell me the span or wood I'd need to do this.

We're putting a handrail along our front walk as we re-do the steps - we have eighty steps (yes, that's right, our house is about three stories up from the street), so a handrail isn't just something I can put off.

I don't think I need balustrade because it's not a sheer cliff, but a long hillside covered in ferns and other garden features.

However, I can't figure out how many supports I really need, and I'd hate to have to re-do this.

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Old 07-03-2012, 05:27 PM   #2
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Handrail strength? Garden stair needs hand rail


What's the handrail going to be attached to?

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Old 07-03-2012, 05:42 PM   #3
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Handrail strength? Garden stair needs hand rail


The ground! I'm using http://www.strongtie.com/products/co...rs/ezfence.asp modified with steel eye bolts that tie to anchors under the stair treads. (I'm mimicking a patented anchoring product that's much more expensive: http://www.geogrid.com/sleeve-it.html )

The posts are 4x4 equivalent and the handrail is not designed to code, being a redwood branch segment (which is also a 4x4 equivalent, stronger than cedar, but weaker than doug fir) which is historically correct for my neighborhood. Full round pieces are incredibly rigid.

I know where I can get tables for doug fir and cedar, but trying to get linear foot and smaller piece of lumber is beyond what I know.

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Old 07-03-2012, 06:25 PM   #4
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Handrail strength? Garden stair needs hand rail


The simplest way to design a handrail would be to assume a point load at mid span between two supports. A load of 200 lbs seems reasonable, although there may be code requirements I am not aware of. Designing a rail based on distributed load makes little sense, since the rail will not likely see distributed loading. Distributed loading would be more applicable to a guard rail over a tourist attraction, for example, where many people might simultaneously lean on the rail.

For a simple garden rail, you would probably be OK designing for a midspan load of 200 lbs. Treat the rail as a simply supported beam with a midspan point load, figure the maximum stress based on the shape of the rail and the clear span, then calculate the factor of safety against bending failure. You need to know the maximum allowable extreme fiber stress for the species of wood you are using.
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Old 07-03-2012, 10:09 PM   #5
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Handrail strength? Garden stair needs hand rail


How would I do that, however?

http://www.awc.org/calculators/span/...rcalcstyle.asp

Seems sorta like what I want, but I'm not sure how to convert its answer (square feet) into linear feet.

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Old 07-04-2012, 12:13 AM   #6
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Handrail strength? Garden stair needs hand rail


Quote:
Originally Posted by CKentavr View Post
........Full round pieces are incredibly rigid...........
Full round handrail is fine but don't get carried away with strength through mass at the expense of a comfortable profile especially with all those steps. For a full round profile I'd try to keep it under a 3" diameter. When you're old and grey you'll appreciate it.

Remember this is a handrail, not a guardrail.
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Old 07-04-2012, 02:30 AM   #7
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When I'm old and grey I'll sell the house to someone who can go up three stories with the groceries.

It's beautiful living in the trees, but I'm not insane.
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Old 07-04-2012, 10:45 AM   #8
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Handrail strength? Garden stair needs hand rail


CK, Before you get old and grey think about any of your guests or relatives that may be,
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Old 07-05-2012, 05:17 PM   #9
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Handrail strength? Garden stair needs hand rail


Well... It's not going to be sculpted oak, it's a handrail, yes, but it's made out of local materials.

I'm just trying to figure out the calculations for pounds per linear foot or single point load instead of pounds per square foot evenly distributed.

I know the material I'm using is very strong as softwood goes, I just don't know which formula to use.
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Old 07-05-2012, 06:19 PM   #10
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Handrail strength? Garden stair needs hand rail


Since I am a registered professional engineer, it would be unethical under the terms of my license for me to perform design work without a site visit and a contract. Sorry, that's the law. However, you are free to do your own design.

You need to look up the formulas for maximum fiber bending stress for a point load applied at the midpoint of your handrail. You have already determined you want to use 200 lbs for the point load. You also need to determine the moment of inertia of the rail, which will depend on the shape you select. You also need to determine the distance from the centroid of the shape to the edge. You also need to know the allowable extreme fiber bending strength of the wood you select. If this seems complicated, it is a bit, but that is how you do it. Unfortunately the particular structural problem you are seeking to solve does not have a simple solution that you can find in a code book, so you need to actually do the mathematics. Or find someone to do it for you, who is permitted to do so under the law. Or just install the rail and don't worry about it.
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Old 07-05-2012, 09:32 PM   #11
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Handrail strength? Garden stair needs hand rail


IF I understsnd you correctly you are not actually looking for calculations for the handrail but for the guard.

That is you need direction on installing or designing an acceptable guard that includes the posts, rails, balusters (not desired) and handrail?

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Old 07-10-2012, 06:26 PM   #12
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Handrail strength? Garden stair needs hand rail


Quote:
Originally Posted by Daniel Holzman View Post
Since I am a registered professional engineer, it would be unethical under the terms of my license for me to perform design work without a site visit and a contract. Sorry, that's the law. However, you are free to do your own design.
Then why reply? To puff up engineers and make them sound intolerable? Your answer is uninformative at best, and downright insulting to your profession at worst. You didn't even provide the formula in which these variables would be inserted, so it is yet to be a mathematics problem.

I know my material, and have formulas to determine the proper weight load if spread across two or more members, however, there doesn't seem to be any that do the same for a single member. It's not like I'm using an unusual material like a plastic or metal or composite; I'm using a simple redwood rail similar in performance to a 2x4 on edge.

-Crissa

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Old 07-10-2012, 06:45 PM   #13
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Handrail strength? Garden stair needs hand rail


I told you exactly how to solve the problem, and I explained why I am unable to perform the calculations for you. I don't get why you are so pissed off over that, but so be it.

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