# Cantilevered Beam



## darcar (Dec 13, 2012)

Take a look at this picture and tell me if you see an issue OR what what point cutting the end of a cantilevered beam becomes an issue.In this particular case a ouble 2x12 beam was angle cut at the end for appearance, but only 4" was left before the angle took off.Additionally the spacing of the joists are at 24" OC instead of the more common 16"OC.This particular builder takes the minimum code and pushes that as much as he tyhinks he can get away with it.Outside of consulting an Enginerd, I don't feel comfortable making the determination on each deck. I'm not the designer.Thanks for your input.Fire away!

View attachment 1743


View attachment 1743


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## darcar (Dec 13, 2012)

bad picture... try this onesorry...

View attachment 622


View attachment 622


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## RLGA (Dec 13, 2012)

Looks fine to me.  In a cantilever it is the top of the beam/joist that is most critical, which is in tension; and the depth is important where the moment force is greatest, which is back at the point where the cantilever begins.

Picture a shelf bracket that is larger at the point where it connects to the wall and tapers down towards the edge of a shelf.


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## brudgers (Dec 13, 2012)

It's not cantilevered. It's overhanging.


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## RLGA (Dec 13, 2012)

brudgers, you're correct, the condition is overhanging.  However, the principles are nearly identical, except that the overhanging portion benefits from the loading on rest of the beam, and vice versa, thus minimizing the moment force.  This allows a smaller depth in the beam/joist.


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## mjesse (Dec 13, 2012)

Dar raises a good question though. At what point does the beam no longer work as designed. Obviously can't start the angle cut at 0", what about 1" down, 2" down, etc?


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## Darren Emery (Dec 13, 2012)

mjesse said:
			
		

> Dar raises a good question though. At what point does the beam no longer work as designed. Obviously can't start the angle cut at 0", what about 1" down, 2" down, etc?


Seems to me that you could start the angle cut at whatever depth would work for a beam without the angle cut.  So, if 4" of depth were required to carry this overhanging load, then the angle should not start before 4".  I've had concern with this condition in the past, and unfortunately, it has resulted in a judgement call each time.  Is the inspector "comfortable" with the condition?  Not a great yard stick, but the only one we have without perscriptive language from the code, or PE involvement.


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## brudgers (Dec 13, 2012)

I'd be concerned about the fasteners in the end grain.


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## rleibowitz (Dec 13, 2012)

The load on that joist is about one half the distance to the next joist mutiplied by half the joist length times thetotal load. In-other-words, not much of a load on that end of the beam. I'd be more concerned with the post seemingly screwed into the face of the band.


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## DRP (Dec 13, 2012)

I'm kind of concerned about how the spread beam is connected to the post.


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## Yankee (Dec 14, 2012)

I need a short course in "spread beam" ???


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## DRP (Dec 14, 2012)

I'm guessing the girder is hanging just on bolts at the post, figure 9 in DCA6 vs the approved figs 4&8


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## Glenn (Dec 14, 2012)

DRP said:
			
		

> I'm kind of concerned about how the spread beam is connected to the post.


Yeah, the first thing I see are two single member beams that appear to be screwed to the side of the support post from both sides.  Big problem.  Not worried about the angle cut in the least.

Deck construction is a mess of confusion in this country.


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## Rio (Dec 14, 2012)

brudgers said:
			
		

> It's not cantilevered. It's overhanging.


But isn't it the case that in construction we use the term cantilever for this situation?

The below is from the 2010 CRC:

*2.2. Floors shall not cantilever past the exterior*

*walls.*

If I'm not mistaken they are referring to a floor overhanging the exterior wall.  There's many more examples in the building codes where an overhanging situation is referred to as a cantilever or am I missing something?


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## Pcinspector1 (Dec 14, 2012)

Ok with the deco cantilever end design, but I feel about the same as Glenn and Bill Cower in regards to the single beam attachment, Cower does not look happy!

Fear that's two single beams attached to the outside of the post, probably not notched?

pc1


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## Rio (Dec 14, 2012)

Here's another example from the 2010 CRC:

*4. For wood-frame construction, a continuous*

*rim joist is connected to ends*

*of all cantilever joists. When spliced,*

*the rim joists shall be ..............*


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## brudgers (Dec 14, 2012)

Rio said:
			
		

> But isn't it the case that in construction we use the term cantilever for this situation?  The below is from the 2010 CRC:  *2.2. Floors shall not cantilever past the exterior walls.*  If I'm not mistaken they are referring to a floor overhanging the exterior wall.  There's many more examples in the building codes where an overhanging situation is referred to as a cantilever or am I missing something?


  "Cantilever" when applied to beams has a specific technical meaning including bearing conditions and equations to determine code compliance.


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## darcar (Dec 14, 2012)

addressing the seemingly insuficient fastening method of the beam to post...

The fasteners used are ledger locks (generic term - each manufacturer has its own brand name). We see these more and more often in place of lag bolts. There are two on each beam into the post.

And as far as the screws into the end grain of the joists, that has been common place ever since I was building decks 20+ years ago. Do you require hangers there also?


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## DRP (Dec 14, 2012)

Hanging on ledgerlocks, lags, bolts... where are you seeing the minimum bearing being met in that? Which member of that beam is taking almost the entire load?

The rail needs to be able to take 200 lbs in any direction, the infill pickets #50/sf.

DCA6 is worth looking at.


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## Pcinspector1 (Dec 14, 2012)

DRP,

Would a Simpson DJT14Z be an easy solution to the OP issue?

pc1


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## Pcinspector1 (Dec 14, 2012)

Ledgerloks have their place but they're being missused. Contractors can't tell me the length, spacing nor the quanity it takes to fasten a deck ledger, I find myself doing a lot of new product reading lately. Don't even mention CSST!

pc1


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## darcar (Dec 14, 2012)

I take it back... there are three of the ledger locks thru each beam into post.

I have a call into our local Simpson Strong Tie supplier to see how he suggets we approach ledger locks in beam to post application. How many per etc. similar to their requirements for leaqdger lock spacing at the ledger.


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## Glenn (Dec 15, 2012)

In a side bolted beam the weak member in the connection is the wood, not the bolt.  That is likely the case with the structural screws as well, depending on span of the beams.  You won't find any information on that connection from the structural screw manufacturers.


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## Francis Vineyard (Dec 15, 2012)

Must use through bolts with nuts to secure guard post; lag and other screws are subject to withdrawal.

Not to mention CSST, Simpson strong may have something patent pending; this is may save your day in this instance; Deck Rail Post To Rim Board

Francis


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## Glenn (Dec 15, 2012)

Francis Vineyard said:
			
		

> Not to mention CSST, Simpson strong may have something patent pending; this is may save your day in this instance; Deck Rail Post To Rim BoardFrancis


That is from FastenMaster by OMG, not Simpson.

It is a very good product.


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## ICE (Dec 16, 2012)

brudgers said:
			
		

> "Cantilever" when applied to beams has a specific technical meaning including bearing conditions and equations to determine code compliance.









Another cantilever


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## darcar (Dec 17, 2012)

Francis Vineyard said:
			
		

> Must use through bolts with nuts to secure guard post; lag and other screws are subject to withdrawal.Francis[/font]


How is a screw subject to withdraw? A straight shank nail I can see withraw issues but not a screw...


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## Francis Vineyard (Dec 17, 2012)

darcar said:
			
		

> How is a screw subject to withdraw? A straight shank nail I can see withraw issues but not a screw...


“The lag screw connection detail _failed by withdrawal__ of the threaded portion_ from the band joist at an average ultimate load of 178 pounds.”

“For the bolted deck rail post assembly shown in Figure 2, the connections failed at an average load of 237 pounds - barely surpassing the code required design load with almost no safety factor for the service life of the assembly.”

STRUCTUREmag - Structural Engineering Magazine, Tradeshow: Tested Guardrail Post Connections for Residential Decks

Francis


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## darcar (Dec 17, 2012)

Francis Vineyard said:
			
		

> “The lag screw connection detail _failed by withdrawal__ of the threaded portion_ from the band joist at an average ultimate load of 178 pounds.”“For the bolted deck rail post assembly shown in Figure 2, the connections failed at an average load of 237 pounds - barely surpassing the code required design load with almost no safety factor for the service life of the assembly.”
> 
> STRUCTUREmag - Structural Engineering Magazine, Tradeshow: Tested Guardrail Post Connections for Residential Decks
> 
> Francis


I'm not the one building to meet minimum code but the arguement will be even though it "barely surpassed the code minimum", it still does meet minimum. I wish I could enforce my standards but cannot unless I'm paying for it


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## facade3a (Sep 23, 2015)

I am new here. Can I ask;

3 story frame house. First story CMU wall. I want to cantilever 2nd & 3rd floor 4' making building width 32'. Back span 18' Conforming code is IRC which has table for cantilever roof & a wall, not roof and story. If I double up 2nd floor floor joists 2x12 every one of them, is that adequate to support roof load 3rd floor load and 2nd floor load?


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## cda (Sep 23, 2015)

welcome welcome

sorry not an engineer so cannot answer your question, but stay tuned and you should get some answers.

Answer Might be that you need a strucural engineer to look at it.


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## steveray (Sep 23, 2015)

It would be wise to contact a design professional as there are a lot more things to look at than the joist sizes....


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## Francis Vineyard (Sep 23, 2015)

cda is correct in accordance with section R301.1.3


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## Rick18071 (Sep 25, 2015)

Back to the deck. Don't you make them put blocking between the joists at the beam when there is a cantilever? See table R502.3.3(2)e


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## Francis Vineyard (Sep 25, 2015)

Rick18071 said:
			
		

> Back to the deck. Don't you make them put blocking between the joists at the beam when there is a cantilever? See table R502.3.3(2)e


Yes, however the table is for balconies.  For decks see 2015 IRC;

R507.5.1 Lateral restraint at supports. Joist ends and

bearing locations shall be provided with lateral restraint to

prevent rotation. Where lateral restraint is provided by

joist hangers or blocking between joists, their depth shall

equal not less than 60 percent of the joist depth. Where lateral

restraint is provided by rim joists, they shall be

secured to the end of each joist with a minimum of (3)10d

(3-inch x 0.128-inch) nails or (3)#10x3 inch (76 mm) long

wood screws.

OR  (2009 IRC)

R502.7 Lateral restraint at supports. Joists shall be supported

laterally at the ends by full-depth solid blocking not less than 2

inches (51 mm) nominal in thickness; or by attachment to a

full-depth header, band or rim joist, or to an adjoining stud or shall

be otherwise provided with lateral support to prevent rotation.


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## Rick18071 (Sep 28, 2015)

What's the difference between a deck and a exterior balcony?


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## cda (Sep 28, 2015)

About ten feet In height ???


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## Francis Vineyard (Sep 28, 2015)

Good question.  In reference to the above sections balconies; the interior floor joist extend or cantilever beyond the exterior wall.  Decks generally have the floor assemblies attached to the exterior wall if not free standing.


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## JBI (Sep 28, 2015)

Rio said:
			
		

> But isn't it the case that in construction we use the term cantilever for this situation?The below is from the 2010 CRC:
> 
> *2.2. Floors shall not cantilever past the exterior*
> 
> ...


The deck joists are cantilevered. The deck beam is overhanging.


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## Francis Vineyard (Sep 28, 2015)

John that CRC section more than likely applies to seismic design category E.

Roofs overhangs are in the IRC. Additionally the term overhang is frequently used in the AWC Wood Deck Construction Guide.

For cantilever beams see IRC 2015 R507.6.

Suppose we all use these terms interchangeably as with beams, girders and headers.

Contradicting my earlier reply how can a balcony be self-supporting?

*R311.5.1 Attachment. *Exterior landings, decks, balconies,

stairs and similar facilities shall be positively

anchored to the primary structure to resist both vertical

and lateral forces or shall be designed to be self-supporting.


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