CMU Lintel With Standard Unit Turned Vertical 1

[bldgdesign]

Has anyone seen CMU lintels constructed with a unit that looks like a standard block turned vertical. Do they make a lintel block that is 8" wide, 16" deep (vertical), and 8" long (parallel to wall)? Structural details call for a 16" lintel over a large window opening. There are four courses above the window and the contractor has installed two courses of 16" deep units in stack bond. If I was designing a 16" deep lintel then I would expect an 8" lintel block with a standard block laid on top in running bond and all grouted together at the same time...forming a 16" deep lintel.

Does the fact that these units are laid stack bond rather than running bond matter for a lintel? I couldn't find anything in ACI or IBC that reduces the strength of the lintel because it is stack bond.

 

[UcfSE]

See the Rinker Contractors Guide, page 55, T105. Note this is a large download, about 35.2MB.

The block you are thinking of are made, but I've never used them vertically for beams. When I was in masonry (before engineering) we used these block as "pipe" block to get around in-wall plumbing. That didn't always work out because these block have pretty thick walls.

 

[concretemasonry]

The 16" high block you described is usually readily available in many areas. I was in an area where it was available in 6", 8", 10", 12", and 16" wall thicknesses.

If you need a 16" deep lintel, it can be made using a normal 8" high bond beam/lintel unit with a course of other units above that could have the top of the webs sawed out for top steel, if necessary.

The fact that they are in stack bond should not be a major problem since it (the 16" high lintel) is a reinforced member. Care should be take to makes sure the bottom of the lintel over an opening is properly shored prior to and shortly after grouting. Make sure grout (8" to 1" slump) is used and not concrete or mortar for filling.

The solution of using 2 different units in separate courses is a common solution where the masonry is exposed and the mortar joint pattern must be preserved.

Dick

 

[miecz]

I'm imagining the CMU voids made two long horizontal tubes. I have to wonder how they got the tubes grouted solid, without an air space at the top of the tube.

 

[concretemasonry]

Depending where you are, there are commonly available units that are made for the cores of the units turned vertically to create a large "U" shaped lintel that is 8", 10" or 12" thick, 8" length along the wall and 16" high if the designer wants a single unit 16" high.

There are thousands of different sizes, shapes and configurations of CMUs meeting ASTM C90 specs made. All it takes a prudent call to a local supplier/contractor which units are available, preferred and used locally. - You have local differences depending on the amount of seismic activity.

If there are four courses of masonry above the opening and there may not be a need for a 16" high units for a small opening because of the arch action of masonry - see ACI 530.

 

[jike]

In our area, they are often refered to as "horse collars". As concretemasonry said they are commonly available in the US.

My only caution would be if the masonry will be left exposed, get the architect to make the decision on whether this will be an acceptable appearance.

 

[csd72]

Are you sure it is not a U block?

I would be concerned about how they would compact the grout in a standard block on its side.

 

[concretemasonry]

csd72 -

The terms for lintels, U-block, bond beams, etc. vary geographically. A single manufacturer may make as many as 6 or 8 different shape units for a single wall thickness. Very often, the units have knock-out sections (webs, ends) that can be removed to facilitate placement, reinforcement or grouting.

You do not compact masonry grout. It is not like concrete. Grout should be between 8" and 11" slump, in contrast to the 3" to 5" for concrete.

You pour or pump grout at a high moisture content to make sure you get complete filling and bonding between the CMU, steel and grout. The excess moisture is absorbed by the block, creating a good bond.

This is in contrast to concrete that is placed in non-absorblive forms that must the removed and trap the excess water in the concrete.

As the moisture in grout is absorbed, the grout compacts and the water in the units provides a ideal curing condition.

The strength of grout is not really as critical as most people think once you really look at it. Ideally, it is approximately the same strength as the gross compressive strength of the units. Very often, there are limits on the maximum strength. This is particulary important when you are looking at prism test results.

See ACI 530 and the comments.