Thread: Post to beam connection - deck

I am looking for "official" documentation for post to beam connection. I have located 2 that are distributed by a forest products company and another and both state they are based on the IRC.

I would like to find the specific IRC reference.

The deck in question is 50" off the ground, 8' x 12', properly attached to the home, but the 2 - 2x10 beams are bolted to the side of 3 - 4x4 posts with 3/8 bolts.

All references I find show shoulder cuts and 1/2 bolts.

Any specific IRC reference as to the correct attachement would be appreciated.

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Call your local AHJ. They are the "official" agency in charge of permitting deck construction in your area, and should be able to give you the "official" source for the document you seek (if it exists).

I've never agreed with the concept of notching a support column to assist in supporting load-carrying members. Far better to splurge and go with one of the several Simpson Strongtie (steel) brackets available.

Start here:

http://www.awc.org/Publications/DCA/...eckarticle.pdf

http://www.fairfaxcounty.gov/dpwes/p...ks/details.pdf

and as BM suggested:

http://www.strongtie.com/ftp/fliers/F-DECKCODE09.pdf

Where in IL are you Bill? It doesn't sound like you are in the City. Some suburbs have their own requirements, others follow various years of the IRC, and I have heard that others have to some extent adopted variations of the Chicago porch and deck requirements.
As has been mentioned, you should contact your local Muni to see what they go by.

2012 IRC has some new stuff in Chapter 5.

In VA, each county has an approved set of typical deck plans. If you have a deck plan other than "their" typical plan, you must have an engineer sign-off on the plan before the county will approve.

Doesn't mean it is safe, just means it was approved by the county.

In VA, you will see a number of techniques used when building decks. Some better than others.

The IRC likes 6 x 6 columns (posts), not 4 x 4s. The skinny 3/8" bolts are also frowned upon, in favor of 1/2" minimum.

I disagree with the IRC's preference for splicing beams at column locations. Much better and stronger (and less likely to cause splitting by having too many holes near the edges/ends of members) if beams are cantilevered, and spliced at the bending moment inflection points (where the moment is actually zero), approximately 1/3 into an adjacent span.

Bill
I have a PDF on deck construction based on the 2009 IRC.
Can't post it here because it's 33 pages, has illustration and is a pretty decent reference guide.

Send me an email and I'll forward it over to you.

prinspects@yahoo.com

Originally Posted by BridgeMan

The IRC likes 6 x 6 columns (posts), not 4 x 4s. The skinny 3/8" bolts are also frowned upon, in favor of 1/2" minimum.

I disagree with the IRC's preference for splicing beams at column locations. Much better and stronger (and less likely to cause splitting by having too many holes near the edges/ends of members) if beams are cantilevered, and spliced at the bending moment inflection points (where the moment is actually zero), approximately 1/3 into an adjacent span.

The IRC prefers splices of all types over bearing points. Please explain in greater detail why you prefer otherwise. Graphic illustrations would also be helpful for those of us who do not live in a blueprint world.

Originally Posted by BridgeMan

The IRC likes 6 x 6 columns (posts), not 4 x 4s. The skinny 3/8" bolts are also frowned upon, in favor of 1/2" minimum.

I disagree with the IRC's preference for splicing beams at column locations. Much better and stronger (and less likely to cause splitting by having too many holes near the edges/ends of members) if beams are cantilevered, and spliced at the bending moment inflection points (where the moment is actually zero), approximately 1/3 into an adjacent span.

Wood beams are typically considered simply supported when on multiple spans. Its not easy to make moment connections in wood beams. While your method probably would be fine with enough nailing, its simple and conservative to assume simply supported. Also, before the use of computer programs the math was easier too!

The 2009 IRC section R502.6, requires a wood beam to have a minimum of 1-1/2 inches of bearing on wood. Bolts alone are not allowed unless designed by a RDP, architect or engineer.
There's also a Girder span table in the IRC Table R502.5(2) that may be used where you may need 3 inches of bearing for wood on wood for girders.

Some deck builders use 2- 1/2" through bolts to fasten a 2x girder to each side of a 4x4 pt post and install a pt 2x4 under the girder on each side to the footing to support the girder, which will comply with the code for 1-1/2" of bearing.

I believe the 2015 IRC will have a deck framing requirements in the code.

Richard,

If you re-read that section of the code, it states "...the ends of a joist or beam..."

Originally Posted by Aaron Miller

The IRC prefers splices of all types over bearing points. Please explain in greater detail why you prefer otherwise. Graphic illustrations would also be helpful for those of us who do not live in a blueprint world.

Here's as graphic as it's going to get:

Let's consider a typical 4 x 4 column, as that's what most deck builders tend to use (despite the IRC recommendation for using 6 x 6s). Having simple span beams meeting at the center of a notched 4 x 4 means 4 holes will be drilled through the column's stub (the portion extending above the notch), and 2 holes will be drilled in each beam end, to line up with the foregoing stub holes. The beam holes will have barely 1/2" of end clearance parallel to the grain (3.5"/2 = 1.75", then divided by 2 again to center the bolts over the beam's bearing point, = 0.875", from which half the diameter of a 5/8" dia. hole for the 1/2" bolts must be subtracted, or 0.875" - 0.3125" = 0.5625". I'm calling it barely 1/2" because of beam end-cut variations and untrue field-drilling practices (bits not perpendicular to surface, hole wallowing, etc.). For through bolts, resisting parallel to grain loading, the American Institute of Timber Construction likes an end distance (their definition is to hole centerline) to be at least 7 bolt diameters for a tension member, which is what our beam ends actually are, wanting to pull away from each other and the bolts while experiencing live load rotation (caused by mid-span positive loading). Seven bolt diameters is 3-1/2", compared to the 7/8" (0.875") we actually have. And with just 1/2" of "meat" from the end of a member to inside edge of bolt hole is not enough to do much good. Small plugs of wood will pull away from the beam from rotation if vertical loading becomes heavy enough. A similar situation exists for the edge distance at the column stub--having 2 sets of holes sharing common grain lines, with barely 1/2" of clear edge distance, will result in the stub member splitting when loading is heavy enough.

A much stronger connection can be achieved by having beams run continuous over the columns, resulting in just 2 holes in both column stub and beam at each location, slightly staggered off of center to avoid locating them along a single grain line. Why weaken any member by making it look like Swiss cheese when it can easily be avoided?

Originally Posted by BridgeMan

Here's as graphic as it's going to get:

Let's consider a typical 4 x 4 column, as that's what most deck builders tend to use (despite the IRC recommendation for using 6 x 6s). Having simple span beams meeting at the center of a notched 4 x 4 means 4 holes will be drilled through the column's stub (the portion extending above the notch), and 2 holes will be drilled in each beam end, to line up with the foregoing stub holes. The beam holes will have barely 1/2" of end clearance parallel to the grain (3.5"/2 = 1.75", then divided by 2 again to center the bolts over the beam's bearing point, = 0.875", from which half the diameter of a 5/8" dia. hole for the 1/2" bolts must be subtracted, or 0.875" - 0.3125" = 0.5625". I'm calling it barely 1/2" because of beam end-cut variations and untrue field-drilling practices (bits not perpendicular to surface, hole wallowing, etc.). For through bolts, resisting parallel to grain loading, the American Institute of Timber Construction likes an end distance (their definition is to hole centerline) to be at least 7 bolt diameters for a tension member, which is what our beam ends actually are, wanting to pull away from each other and the bolts while experiencing live load rotation (caused by mid-span positive loading). Seven bolt diameters is 3-1/2", compared to the 7/8" (0.875") we actually have. And with just 1/2" of "meat" from the end of a member to inside edge of bolt hole is not enough to do much good. Small plugs of wood will pull away from the beam from rotation if vertical loading becomes heavy enough. A similar situation exists for the edge distance at the column stub--having 2 sets of holes sharing common grain lines, with barely 1/2" of clear edge distance, will result in the stub member splitting when loading is heavy enough.

A much stronger connection can be achieved by having beams run continuous over the columns, resulting in just 2 holes in both column stub and beam at each location, slightly staggered off of center to avoid locating them along a single grain line. Why weaken any member by making it look like Swiss cheese when it can easily be avoided?

Good point.

Bill,

Probably as close as you are going to get is with the 2006 IRC is in section 502.6 dealing with bearing ends of beams and griders and I also like 502.9 that deals with post and beam constuction and positive attachment requirements. Here is GA we will soon adopt (and not soon enough for me) is an entirely new deck code called DCA 6. It is a pamplet/book that deals exclusively with deck construction and will be the best thing to happen to deck codes since the 1996 Wood Forest Products Council recommendations of deck construction. it will actually make these deck builders build a decent deck but will add tons of work for me as it will take years for them to fully abide by the requirements...if they ever do.

It appears that the AITC approves of beams splices over support posts judging from AITC 104-2003 TYPICAL CONSTRUCTION DETAILS:

Originally Posted by Mark Reinmiller

Wood beams are typically considered simply supported when on multiple spans. Its not easy to make moment connections in wood beams. While your method probably would be fine with enough nailing, its simple and conservative to assume simply supported. Also, before the use of computer programs the math was easier too!

I'm no design expert, but I disagree with the first sentence, stating "wood beams are considered simply supported when on multiple spans." Considered by whom, or what code? Allow me to explain with a simple example--just try taking a 20'-long 2 x 4, and support it by placing blocks under it every 4'--do you really think it will act the same (when vertically loaded) as 5 individual, short 2 x 4s? Sorry to break the news to you, but that's not the case--vertical deflections under identical loading, at any point, will be significantly less with the continuous configuration, simply because loads in any span are not only resisted by the member at the point of load, but also by the loads' inverse reaction in alternate spans. Spans on either side of a downward-loaded span will rise up, in effect helping to resist the downward forces. A continuous member only requires approximately 80% of the resisting moment that simple spans do, with the same distance between supports. It's one of the reasons that highway bridges today (steel, concrete or timber) are almost always designed and constructed using continuous spans over multiple supports, rather than simple spans. Better performance at lower cost, because of the smaller net section required of load-carrying members. Also, I believe moment connections for wooden deck beams are readily achievable, using through-bolts to rigidly affix continuous beams to column stubs--little if any rotation or displacement of the connection will occur. Your suggestion for using nails at such connections is not recommended, in practice or by the IRC.

Originally Posted by Aaron Miller

It appears that the AITC approves of beams splices over support posts judging from AITC 104-2003 TYPICAL CONSTRUCTION DETAILS:

And so it is. But do take notice--you are referring to glulam construction details, not something typically incorporated into a wood deck. And, FWIW, the details shown do eliminate the need for multiple holes in close proximity through wood members. And, the IRC Deck Code is also quite happy using galvanized steel brackets for beam-to-post connections, again without the need for multiple holes.

You can spend your deck-building money on pricey brackets*, or just 2 through-bolts, at each beam-to-column connection, if you're willing to "liberally interpret" certain IRC recommendations. While enjoying the benefits of having a stronger finished product.

* Several big box stores that I inquired at locally don't stock same for the IRC-favored 6 x 6 posts, with one stating "they might be available on special order, but we'll have to call around first." Interestingly enough, that same store has been conducting "How To Build A Deck" symposiums for several years now, and the presenter I spoke with a few months ago had never heard of the IRC Prescriptive Deck Construction Guide, or its preference for using 6 x 6 columns.

Can you email me a copy of the pdf file you have?


Joe Vaglica, Professional Engineer

- - - Updated - - -

Can you email me a copy of the pdf file you have?


http://www.joevthepe.com/