Multiple Course CMU Lintel Construction 2

[BadgerPE]

Hey all,

I have never designed a multiple course CMU lintel before without just using 16" U-shaped blocks. What is the typical way to construct a simply supported lintel with say 3 courses required? Would you first place a set of 8" U-shaped blocks with reinforcing, place two more courses of standard blocks above, and grout the whole thing solid? What about continuous lintel? Would you knock out the webbing of the standard blocks to place top reinforcing where needed? If anyone has a sketch or a standard detail they are willing to share, it would be greatly appreciated!

 

[structSU10]

why not use structural steel? could use 3 angles beneath the CMU, a WF with a plate on the bottom, channels with a plate on the bottom, etc. Otherwise just design it for the required strength and see how you would have to detail it. It probably depends on how your wythes are connected and such.

 

[kylesito]

structSU10, would this option be available if he was trying to design a higher ASCE 7 R value wall...like a special reinforced wall? I believe the requirements for those walls state you have to continue the horizontal reinforcing beyond all openings to tie the wall together. If you use steel lintels (or precast for that matter), you can't make this happen.

I could be wrong. Just stands out in my mind as one of the reasons I haven't been able to use non-masonry lintels in the past.

Crackerjack...sorry, I am not able to answer your question. But I will be following the answers!




PE, SE
Eastern United States

"If a builder builds a house for someone, and does not construct it properly, and the house which he built falls in and kills its owner, then that builder shall be put to death!"
~Code of Hammurabi

 

[ron9876]

Normally use a precast concrete lintel with beam block over the lintel.

 

[Michel60]

Good morning CJ,
In my practice I've only done fully grouted masonry and all lintels at openings would be constructed pretty much as you describe. A lintel or inverted bond-beam block at the bottom and another a bond-beam course at the top. Horizontal reinforcing provided according to the demand in bending and vertical reinforcing based upon beam shear (hooks may be required on the ends of the vertical bars for anchorage). For lintels with large tributary areas/spans out-of-plane bending may need to be considered too.

regards,
Michel

 

[spats]

The the attached page is extracted from a block shapes catalog. #86 is an open bottom bond beam block with web knock-outs. #87 is a restricted bond beam block. Either can be used to reinforce the upper course, with a normal U bond beam block (#85) at the bottom. Quite frankly, I've never used/specified the restricted block, but I specify the open bottom block all the time.

 

[ron9876]

spats that approach would certainly work but it requires shoring. Why not a precast unit that is self supporting during construction unless the span gets long then they only require single post shores.

 

[BadgerPE]

Spats and Michel,

If I need a lintel that is 32" deep, the bottom course would be a U-shaped block (#85 in Spats' document). Assuming the wall extends higher than the required 32" lintel, would you just use standard blocks for the three courses above the U-shaped block and then grout the entire 32" solid? Or would you use one of the flow-through type blocks for the (3) upper courses of the lintel?

 

[spats]

ron9876,

That's true... I'm just not a big fan of precast lintels, because I've never really found a satisfactory way of specifying them. Cast-Crete, for one, has a too complicated naming convention for specifying. I worry about them just pulling something convenient off the shelf. Specifying gravity loads, lateral wind loads and uplift loads is too complicated. How do you specify?

 

[spats]

Crackjack47,

Yes you can use standard block in the three courses above and fill solid. The only problem I see is if they forget to fill the upper blocks. Even if you don't need top bars, I usually put them in to remind the contractor that the whole thing is the lintel. 32" is a pretty deep lintel... have you checked shear? The top bars also provide mechanical anchorage to help develop the vertical shear reinforcement, which needs to be hooked around the top and bottom bars as stated by Michael60.

 

[Michel60]

Construction lay-up in between would not need to be more than std block with the bond courses at normal spacing for horizontal steel in deeper lintels. I would have a reinforced bond course at the top of the lintel too. In seismic applications you end up with lots of horizontal reinforcing so the bond courses are pretty frequent (16"c-c not at all uncommon). So that tends to keep things pretty well tied together. And yes it does mean having centering/shoring in place until you get grouted and have enough strength to support self-weight and construction loads.

regards,
Michel

 

[BadgerPE]

Yes I checked shear. It wouldn't using Mu/(Vudv)=1, but when I solved Mu/(Vudv) at all locations on the lintel it passes. I am still thinking about using steel on this particular lintel though.

 

[azcats]

In this (Phoenix) area, it seems that masonry lintels are the most common. I only specified steel lintels when we couldn't justify a masonry lintel. Although I haven't done any masonry design in a few years.

If I had to guess, I'd say that the masons around here prefer not to involve another trade when they can fairly quickly build up wood shoring to support most lintel construction. I remember one or two contractors who would use something like a Powers Steel lintels in lieu of shoring but still construct them as masonry lintels.

http://powerssteel.com/lintels/index.html

As for the block, I often saw the masons cut out one of the end shells of a typical 8x8x16 to gain the requirement that no air gaps remained in solid grouted lintels. Or an open bottomed bond beam block with one end removed where there was horizontal reinforcing.

 

[BadgerPE]

Is it fairly easy to install vertical shear reinforcing in an 8" lintel or is it a complete PITA?

 

[Michel60]

Not sure about "PITA" but you do yourself a favor by keeping the vert bar sizes smaller in the lintel and reducing spacing if necessary. #4 hairpins usually no problem in 8" block....at least I've never had any problem marking it on the detail!

regards,
mk

 

[hokie66]

Agree with Michel60, spats, et.al., in using masonry for the whole thing. Use block shapes as required. Why restrict yourself to "standard" blocks when there are a lot of standard shapes?

Precast lintels and steel lintels in block walls cause too much discontinuity for my liking.

 

[ron9876]

I call out Castcrete precast lintel bottoms for all masonry beams/lintels and require a submittal for review for any alternates. The Castcrete manual provides design info for the various span/depth conditions. In my area if I called out full depth masonry beams/lintels the contractors would think I was crazy. Difference in parts of the country I suppose. By the way I am not a Castcrete representative.

hokie66 they have a slot for vertical reinforcement placement at the ends.

 

[dik]

They often sawcut the top block web down 2" or so and carefully remove it with a hammer! and, if they are really good, they don't sawcut it...

Dik

 

[concretemasonry]

The advantage for a 32" high CMU lintel is that does not require advance ordering, delivery time, a setting problem with an appearance that is compatible with the rest of the structure from both a structural and appearance standpoint.

Also, if the structure uses pigmented or split architectural units, it is easy to satisfy the architectural or appearance requirements using units that may normally be on the job.

Every location of the country has preferred shapes that are made to satisfy local preferences and needs, especially in seismic controlled areas. There are many variations in what people think are standard units and one mold manufacture has a file of over 1500 different variation of just 8x8x16 CMUs and a dead file of molds not ordered in last few years.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[hokie66]

ron9876,
Thanks, but I was talking about horizontal continuity.