Deck-railing post connection 3

[CEmonkee]

I'm designing a deck with the following specs:

Height: > 30" above ground

Material: Western Red Cedar (No. 2)
Fb = 575 psi
Fv = 65 psi
Fc (perp) = 350 psi
Fc (parallel) = 825 psi
E = 1.1E6 psi

Joist size: 2x6

I need to come up with a detail for the deck-railing post connection that meets the load requirement in the IRC (R301.5) of 200 lbs.

I have looked at using a Simpson Strong-Tie HD2AHDG deck post connector, however this requires a 2x8 joist size. I also looked at using a DeckLok bracket system. I didn’t see anything on their website (

http://www.deck-lok.com)

regarding joist size requirement (or type of wood).

Does anyone have any experience with the DeckLok brackets, or do you have any suggestions for a detail I could use for the post connection that will meet the code requirement?

Thanks for your help!

 

[PSlem]

If the deck is ~30" I would just extend all posts down to the ground. Other choice is decrease post spacing.

 

[Ron]

Set your posts on the outside band rather than onto the deck. If you do this, you will only need to bolt the post through the outside band with 4 carriage bolts and you will develop the lateral resistance in the post.

Keep in mind that you are using a low strength wood. It has low pull-through, pull-out, and flexural strength as compared to others.

 

[CEmonkee]

Thanks for your replies!

PSlem - the deck is about 4' off the ground. Part of the deck has an overhang (about 2' beyond the beam line), so extending the railing posts to the ground would not be an option on that side of the deck (the railing posts could be right next to the posts supporting the beam, depending on where the rail posts lined up).

Ron - by my calcs a 200 lb load at the top of a 36" railing post will result in a load at the rail attachment to the band joist of approximately 2000 lbs. It's my understanding that carriage bolts are typically used in nonstructural and minor structural applications - I don't think they would be able to handle that high of a load...

 

[Ron]

CEmonkee...for a 4-bolt pattern, that works out to be 1000 lbs. per bolt from the force couple. A 1/2" dia. carriage bolt will easily handle a 1000 lb. load. (that's 5000 psi on a 30+ ksi material.)

I'd be more concerned about the bending in the wood.

 

[hokie66]

Don't forget the connection of the joists to the trimming beam. And also blocking with connections to take the load into the floor where the railing is parallel to the joists.

 

[racookpe1978]

What are the remaining deck dimensions?

I build (as a sideline) the steel posts and wrought iron rails for decks and stairs and interior raling, and anchoring the posts is ALWAYS a struggle. Particularly at stairs where I cannot anchor around a corner as a lateral brace.

For this application, the "standard" OSHA 200 lbf sideways force is actually on the rail as a whole, not on just one post. Your rails (the upper and middle rail) will transmit that 200 lbf load sideways to the post in question and two (at least!) adjacent posts IF the connecting rails are rigid. You should NOT splice your horizontal rails do they DO carry that load, and each rail should be attached "firmly" to each post. (The catalogs you have are great, use them with the screws provided - nails will work loose. Bolts are better. Carriage bolts works OK, but I prefer to use galv oversized washers under the carriage head, rather than let the bolthead sink into the wood. They don't spin if carriage bolt and washer are both galvanized.)

Two 1/2" galvanized bolts in each post are sufficient: this is an outdoors deck and you don't have a finicky homeowner who wants all of her bolts and welds and fasteners to be "invisible" and "never to rust"! (That's "hard" - to say the least.)

Your deck boards extend a good distance away from your beams underneath.

I'd run one 2x6 (or better yet two invisible) beams under the edge fastened to each deck board. Then at each post, use a 3x3x1/4 angle thats cut two boards "long" to clamp the vertical post from underneath to the runner(s) under the deck board. The post load then is supported by several deck boards, and prevented from twisting out by the bolt through the angle iron and the second bolts through the runner beam.

 

[Ron]

racookpe....the 200 lb lateral load is to be applied anywhere along the rail, thus when applied at one post, the load is not shared by another post. If applied 1/2 way between two posts, yes, it is shared, but that's not what the code requires.

Further, there is a requirement for 50 lb/lf applied in any direction along the top rail. For post spacings of 48 inches, it is the same as the 200 lb. lateral load. If the spacing exceeds 48 inches, the load on the post goes up.

 

[kslee1000]

Agree with Ron.

 

[PSlem]

If you had a continuous 2x6 cedar top rail, the section is 1.5(5.5)^2/6 = 7.56 so M = 7.56 x 575 = 4350 = PL/4 for L = 96", P = 181#. So a single post does not have to carry 200# alone.

 

[racookpe1978]

Thank you for the review.

 

[kslee1000]

the 200# requirement is accounting the effect of person lean on the rail, the leaning force can be centered at one post, causees it to fail before others would catch on.

 

[CEmonkee]

Thanks everyone for your comments/suggestions. Quick question - I have seen a max railing post spacing of 6' listed in some places. Can anyone tell me where that requirement is specified in the IRC or IBC?

Thanks!

 

[Ron]

I don't know of a limitation on spacing. It is dictated by the capacity of the system to resist the required loading.

 

[CTW]

Maybe this helps.

http://www.structuremag.org/article.aspx?articleID=303

 

[BAretired]

Great link, CTW. Now the question is, how literally should we take the code requirement of 200# in any direction? As pointed out in the article, if a tree falls onto the railing from the outside, the force is pushing inward. The connection was not tested for that condition.

My vote is to forget about a force pushing inward as it is not likely to ever occur. And if it does occur from a tree falling, 200# is nowhere near enough anyway.

Best regards,

BA

 

[Ron]

BAretired...I agree. I analyze railings for two different manufacturing clients. One of them actually only fastens (against my advice!)to resist outward load, since that is the critical one for railing.

The 200 lb requirement is a lateral load requirement. The 50 lb/ft is to be applied in any direction.

 

[kslee1000]

Ron:

I think the downward push (200#) on rails should also be considered. How often we see people sitting on the rail, and/or standing on the mid-rail to post for photo-op, and to gain better views. This phenomenon is most prevalent in touring areas, parks, schools.... Any thoughts/advise on that?

 

[kslee1000]

Also, a word of friendly warning, pay extra attention to railing design whenever the area it encloses would have crowd gathering, especially college age kids. It's not rare to become a headline news in the papers.

 

[kslee1000]

After said that, I agree it is too much to ask designers to come up solutions for those situations, however, we have at least to treat the code requirements as the absolute minimum, not the other way around.