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why do standard modular brick units have 3 holes in them?
2

why do standard modular brick units have 3 holes in them?

why do standard modular brick units have 3 holes in them?

(OP)
I looked on the BIA website and didn't see anything...is it just to save weight?

thanks, just curious

RE: why do standard modular brick units have 3 holes in them?

I think it may have to do with shrink crack control after firing.

Steve Wagner

RE: why do standard modular brick units have 3 holes in them?

Because 4 was too many and 2 was not enough?

Sorry, it probably has to do with the manufacture of these, it may be an extrusion process like for hollowcore slabs.

csd

RE: why do standard modular brick units have 3 holes in them?

'cause it worked 100 years ago when someone had the problem to solve, and we've done it that way ever since (and forgotten why) ?

seriously tho', i think to control shinkage sounds good; different question, how are they formed ? (dowels, cut out after the mound is filled ?)

RE: why do standard modular brick units have 3 holes in them?

It makes the material lighter and allows you to be able to reinforce it.  Brick also comes solid as well.

Don Phillips
http://worthingtonengineering.com

RE: why do standard modular brick units have 3 holes in them?

I've never seen reinforcing put down into one of the brick holes before.

RE: why do standard modular brick units have 3 holes in them?

The holes help the bricks to cool evenly after firing to avoid cracking.  More importantly they allow the mortar to squeeze into them for a doweling effect.  The holes are too small for any reinforcement.

Old clay bricks used shallow depressions top and bottom instead for both reasons.  The shallow depressions were easy for manual casting.  Modern bricks are extruded.

RE: why do standard modular brick units have 3 holes in them?

Saves clay and suits the manufacturing process. The depressions in old bricks are called "frogs".  Did once see someone try to reinforce in the holes, but that was with two hole bricks.  With three holes, don't think they would line up in running bond.

RE: why do standard modular brick units have 3 holes in them?

We have to remember that due to it's minderalogical make-up and microstructure, clay brick is generally much stronger (net area compressive strength than concrete brick of similar dimensions. So even when it's manufactured hollow, clay brick is still pretty strong. Nontheless, there are only so many cells you can have without rendering the brick structurally useless.

ASTM C 652 is the specification for hollow clay brick. A section in this standard deals with requiremens for hollow spaces (cores and cells).

In addition to lighteness and ease of handling, the use of hollow brick cuts down on costs associated with: manufacture (less energy, less material), transportation, construction etc...

As far as reinforcing goes, I am aware of single-wythe(leaf) reinforced clay masonry unit construction (using hollow clay blocks) but not reinforced single-wythe hollow clay brick construction. Has any research ever been done on the latter?

RE: why do standard modular brick units have 3 holes in them?

Using the holes for reinforcement would only ever be advisable for protected (dry) locations.
Even if you could get the bar through the holes the grout could not be relied on to provide adequate cover for durability. Or rather, the grout could be relied on to not provide adequate cover.

RE: why do standard modular brick units have 3 holes in them?

An update from my post above.

What I assumed were hollow clay block because of size, are actually classified as hollow clay brick.

So that means products like interstate brick's 8x8x16 Super Atlas have to comply with ASTM specification for hollow brick, C 652. Table 1 of this standard allows up to a maximum nominal width of 12 inches for Class H60V hollow brick.
http://interstatebrick.paccoast.com/default.jsp?InstRegionProdLineID=65&ProductID=312

This means that some hollow clay brick are indeed manufactured for single wythe/leaf reinforced masonry constrution.

What I'd like to know is how horizontal reinforcement is placed when these large units are used? Is it restricted to joint reinforcing placed in bed joints...or can units be manufactured to look like concrete bond beam blocks...that allow horizontal bars to be placed on the cross webs?

RE: why do standard modular brick units have 3 holes in them?

Henri -

Joint reinforcement is the most common type of reinforcement in the U.S. for clay brick/block. Depending on the size of the units, they can be sawed if some sort of bond beam is required. The most common manufacturing process for clay brick (extruding) does not easily permit shapes with recessed aeas. Concrete masonry is made using a different process (pressing), so units with recessed areas that may accept reinforcing steel are readily available.

In the U.S., much of the larger size clay brick/block has been replaced by 6x4x16 architectural concrete masonry units, but this is still a small portion of the brick market, which is mainly veneer.

In Europe, hollow clay block have commonly been used for many years. There, the size is much different, with 8", 10" or 12" thicknesses common and the units having many cores (4 to 12). These units are basic units used for bearing walls and floor systems and never for an architectural appearance.

There is really no such thing as a "standard" brick, considering the wide range of sizes made - there are only ASTM standards that are the minimums for physical properties and dimensional tolerence. - Almost any size or configuration can be specified.

With proper design, 6" concrete masonry walls are used be used for loadbearing masonry structures over of over 20 stories. All it takes is a good engineer, good specifications and good design codes like ACI 530. To bad all of these sophisticated buildings are common outside the U.S.

RE: why do standard modular brick units have 3 holes in them?

concretemasonry,

What if the clay raw material was blended to produce a low plasticity, dry pressed to produce shapes with recesses, dried (if necessary), and then fired etc? This may be uneconomical prudent for a manufacturer...but can a structurally sound clay bond beam unit be manufactured this way?

RE: why do standard modular brick units have 3 holes in them?

Don't know how to use the edit feature...but the word "prudent" should be struck from the last sentence.

RE: why do standard modular brick units have 3 holes in them?

Some brick are pressed. That is the way frogged brick are made.

Like all ceramics, there is a lot of shrinkage and distortion during the firing (a toilet will shrink an inch or two). If you do not have symetry, you can easily get more distortion, splitting or cracking. I am not an expert on brick manufacturing, but have been involved in the masonry supply inducstry for many years.

P.S. - comparing unit hollow concrete block and brick strengths is like comparing apples and oranges. The orientation of the units and aspect ratios when tested are radically different.. Brick are tested flat (3 5/8" wide x 2 3/8" high) - something like a compression failure, while hollow block are tested with a width typically equal to the height (shear failure). The block minimum strength requirements are minimal (1900 psi on the net area), while I have made and tested hollow block at 8500 psi when I finally found a machine with enough capacity AND a thick enough platten that would not distort. Concrete cylinder testing equipment is not adequate.

RE: why do standard modular brick units have 3 holes in them?

holes in the brick are to save on shipping but the brick with large holes can be useful.if you designed a job that the brick will be layed up fast in height or with not much width to the walls or in a very windy area you may spec the masons to bend the wall ties into the holes. when brick get wet and the sand is wet and your laying the brick on iron the weight will squeeze the joint out causing walls to loosen and fall and if they dont fall bond was broke causing leaks later. if gusts of wind get behind a wall the bricks can come down so placing wall ties into the holes is helpful.

RE: why do standard modular brick units have 3 holes in them?

busyone -

The weight reduction savings on shipping would be negligible since brick are really not bought on price. Usually the key items are meeting specification or appearance.

Bending wall ties has nothing to do with with stability. The specifications control the properties of the mortar, but the masons will change it much quicker than any specification. If you are dealing with wall ties, you have a back-up wall that is already in place.

The configuration of brick is based on the historic performance of the materials and masons.

RE: why do standard modular brick units have 3 holes in them?

wow, in my country, standard bricks can be made with 2 or 4 holes. I think it's just a matter of history.

RE: why do standard modular brick units have 3 holes in them?

Makes it much easier for the bricklayers to put a wall up faster.  Solid brick float and are harder to lay because there are no holes in the middle for the mortar.  So when you place or tap a brick all the mortar has to move to the outside.

RE: why do standard modular brick units have 3 holes in them?

The number of holes in a brick is of no real importance. It makes little difference if there are 3, 4, 6 or 12 cores. The number of cores is determined by the manufacturing process, raw materials and tradition. It is NOT a marketing point or technical issue.

Bricklayers may complain because they have the right to. If solid or concrete brick are being used, the mortar must be mixed differently. ASTM has no real requirements for the amount of water in the mortar when the brick are laid. The key factor in mortar is not really strength, but workability, which relates to the product (material, shape and configuration) being used. ASTM recommends to use the weakest mortar possible to carry the load.

I know of a company that made concrete brick without either "frogs" or cores, so they were genuine "floaters" because of the shape and low initial rate of absorption of the concrete. The contractors complained until the price was reduced $0.005 per brick and then there were to complaints.

Masonry is very forgiving and is often based on habits - that is why it is the most common material for residential (one and multiple story buildings) wall construction in the developed world.

RE: why do standard modular brick units have 3 holes in them?

The BIA link below elucidates some of the issues we have been discussing.
http://www.brickinfo.org/BIA/technotes/t41.htm

Bond beam units described by concretemasonry...where slots are cut at jobsite are shown in Fig 2. The slots can also be made at the plant..and is done after units have been fired.

RE: why do standard modular brick units have 3 holes in them?

The coring size will differ depending on the manf., but the cores serve 2 purposes. First is it allows even firing on the clay mass. The face shell (distance from the edge of the core to the face of the brick) is about 3/4". The distance between each core will be roughly about 3/4" (that dimension will differ depending on the manf.) Having a balanced clay mass evens out the temp. of the brick during firing and avoids a "banana" configuration that results in uneven firing.

The 2nd reason is it reduces the weight of the unit, taking less clay to make and saving costs (and less cost to ship).

The 3/4" dia. cored hole is too small for reinf, that's why there is "clay block" as I call it...or Hollow Clay Masonry. There are a few plants in North America that make these types of units...Interstate Brick (Utah), Mutual Materials (Washington state), Summit Brick (Colorado), Carolina Brick (North Carolina) and a Canadian company called IXL.

RE: why do standard modular brick units have 3 holes in them?

There were questions on Hollow Clay brick and the use of bond beams. I was Interstate Brick's Tech Manager and the only way a bond beam could be created was by the mason...where he rips along the length of the brick (flush to each inside face of the face shell and the upper half of the unit's height). This creates a tab that can be popped out with the tap of a hammer.

If a kerf were to be cut into the brick before firing, it would cause the unit to crack up. The clay mass needs to stay as balanced as possible (as rectangular as possible) for the unit not to crack up or turn into a "banana". The other reason why this can't be done is the manner of the extrusion process. Its much like a tube of toothpaste...where the brick comes extruded out in 8ft slugs. You can blade or kerf anything in that slug as long as it is continuous and to the slug (visulaize a tube of toothpaste and as you extrude it out, sticking a knife blade to it to create a cont. slot...the same holds true with brick manf.).

After the slug is cut, it goes onto a belt table and where wire blades (like a cheese cutter) cut it into the individual unit sizes. It is only at this step that a bond beam could only be cut or created and the orientation is just to impossible for any machine to get to.   

With that said, Interstate did develop an open-ended unit that created kerf's during extrusion (and before the unit goes into the kiln) on the end face shell that could be popped out by a mason. This allows for full head joint construction by having an open end face (i.e., the orientation is an "A" shape).   

RE: why do standard modular brick units have 3 holes in them?

Seems to me that whatever the original reason, and there are a lot of good ones posted here, the holes, whatever the number, also serve to increase the bond and shear force between the brick and mortar by creating small vertical plugs of mortar into the brick.  

Mike McCann
McCann Engineering

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