beam pocket in block foundation?

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Old 06-10-13, 09:57 AM
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beam pocket in block foundation?

OK this sound like a dumb question but I'm planning a built-up beam (3X2X12") for the first floor joists in my addition (18X18'), with 2 columns on footing supporting the beam, which would rest in pockets on either end. I see that creating pockets in a poured foundation is easy enough -- whats the approach to beam pockets for a block foundation? I live in N NJ and the foundation will be a crawlspace. ghx!
 
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Old 06-10-13, 12:46 PM
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Knock out the block (fulls & halves) next to the pocket and 4" under the elevation of the bottom of the beam to allow a 4x8x16 solid block to be placed for bearing. To close off the outside of the opening make sure the beam length is not so long it does not allow you the replace the exterior with an 4" block(preferred) or a 2" thick solid block with a 8x16 face.

Dick
 

Last edited by Concretemasonry; 06-10-13 at 12:47 PM. Reason: spelling/fat fingers
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Old 06-10-13, 04:30 PM
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Dick... don't the hollow blocks under the pocket have to be completely slugged with concrete to support a load bearing beam?
 
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Old 06-10-13, 05:02 PM
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Not necessarily.

The masonry quickly spreads out the load at about a 45 degree angle and a 4" thick solid will immediately increase the bearing width. Obviously, filling the cores is better, but in may not be practical based on the information provides.

Since it is a 1 story addition (18x18), the loads on the column end would normally be about half of the loads on the interior columns inside the basement.

It is probably a 8" or 12" block wall holding up some 2x framing.

Dick
 
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Old 06-11-13, 06:48 AM
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Correct; the load-path 'fans out' at approximately 45 deg. from the point of application.
But you still have to be careful that the localized stress in the wall of the block immediately under the solid bearing block is not excessive if the voids are not concreted.
 
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Old 06-11-13, 11:46 AM
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gentlemen thank you for the input. and I've tried to keep up with the dialogue and learning a lot! let me add a little more detail; I should have been clearer in my original post. I'm planning a 2-story, 18X18' addition. the built-up beam requiring the pockets would be 6X12", supporting 2X10" lapped joists above for the first floor. Below the beam there would be two posts equally spaced on footings in the crawlspace. An interior bearing wall directly above the beam would support the 2nd floor joists. Everything 16" o.c. I understand the recommended approach of using solid block under the beam for load bearing, and filling the cores as well to add strength which should be OK. Here's the wrinkle -- on the side connecting to the existing structure, the beam (perpendicular to the existing wall) would sit adjacent to the opening to the existing basement -- a break in that wall. If I understand the solution below correctly, using a 16" solid block beneath the beam would put the opening to the basement at least 8" distant from the beam? But of greater concern is the load path comment below -- if the opening is 8" away from the beam, then there's not a full length wall for the load to spread out at the 45 degree angle described. Is there a means of additional support for that end of the beam i.e. another post and footing adjacent to the wall? Apologies if my lack of experience is showing; and really appreciate the help!
 
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Old 06-11-13, 01:09 PM
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If you are attempting a 650 sf two story addition (double the loads), you need professional structural advise by someone that can look at what is really there. DIYing 100% can be foolish and using help where necessary may be needed.

The extra 8" longer span does not add appreciable load to the end of the wall since it also adds to the more highly loaded columns and footing that are probably not sized efficiently. It is "dirt cheap" to make form changes and the concrete amount different. Fortunately, concrete is the most forgiving material when it comes to shear and compression.

Contrary to the apparently obviously up/down path of loads, when you distribute them outward, they push laterally and a little post does little. The old "Boy Scout" or wood butcher approach would be to add a column to the end of wall and hope it is the right height since if it was to high, it would end up taking more load.

How do you expect to get a permit for and obvious addition?

Dick
 
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Old 06-12-13, 08:25 AM
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completely agree some professional help is in order on a project of this scale! and when you say how will I get a permit -- if you mean w/o an engineer doing the drawings, well, the wonderful (some might say scary!) thing about where I live -- in bergen county NJ -- is that the owner can act as his own architect and engineer, do his own drawings and sign them. but I'm not a fool don't get me wrong. my plan is to get the design as thought-out as possible, do some pencils, and get the counsel of a professional before submitting. and thats where this board comes in -- to be able to get advice and feedback as I develop the design will save a great deal of time and effort and allow me to have something much tighter to ultimately review. so again thanks, and appreciate the patience with questions that may sound naive.
 
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Old 06-13-13, 11:02 AM
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G.R.
If I am reading you correctly, is this your situation? If that's the case, the load-path on the left will of course be interrupted by the door.

However, the load imparted by the end of the beam on to the concrete pad will be relatively low. This is because the beam is continuous over three spans, which means that the load on the pad will be less than one-half the load on the adjacent span(this is the 'continuity effect' of beams).
The critical part is generally the shell of the block immediately below your bearing block, and your SE will do a check on that.
To do the full check, he will also evaluate the stress in the wall at a lower level (our code requires a check at 0.4xheight below the bearing block).
Fwiw my guess is that if the wall is concreted, you will be OK; if it's still hollow, depending on your loads, the SE might pay safe and suggest an additional column near to the wall.
 
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Old 06-13-13, 04:52 PM
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DIY is a challenge in your case... as you are under both "I" codes; New Jersey Building Codes

Remember to leave a 1/2" air space around the wood beam in a masonry pocket, solid blocking every 8' of joists and above each bearing, ties to shear walls, etc.; Chapter 23 - Wood

International Residential Code for One- and Two-Family Dwellings

Gary
 
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Old 06-18-13, 07:18 AM
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thanks again for the replies! tonyG appreciate the drawing to clarify -- apologies I did not provide one myself! and yes you have it exactly right. if concreting the wall is a solution that seems simple enough -- but to your point I will have it checked out by an SE. I also saw somewhere that pilasters are sometimes used in block walls just for this purpose using special block? I'm not sure if thats a better solution or not though. and Gary it does get tricky in jersey. but the town engineer and inspector are really good and reasonable guys. I think its all how you approach them! again thanks.
 
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Old 06-18-13, 08:53 AM
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Piers supporting beam too!

A followup if I may to my earlier questions on beam pockets etc. For the piers supporting the beam, I've seen metal columns, 6X6 posts, even block piers used. Is there a preferred way, or is it simply builders' preference? I understand loads and what's above might make a difference of course but from what I've seen these seem to be used interchangeably. As to the footings, again that seems to be done different ways. a simple 2'X2"X1' pad at there same depth as the foundation footings? For reference, again the details on my job are: 18X18' 2-story addition; crawlspace foundation with about 48" of clearance; 6X12' beam supported by the foundation on the ends and two piers in between spaced equally. thanks again -- wonderful place here!
 
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Old 06-18-13, 12:58 PM
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As you said, the SE will take full structural liability for the project. To compare your 40# floor joists load with the footings on a deck, 40#; pp.13, Table 4; http://www.awc.org/Publications/DCA/DCA6/DCA6-09.pdf

Gary
 
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