Tek-Tips is the largest IT community on the Internet today!
Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!
-
Congratulations cowski on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!
why do standard modular brick units have 3 holes in them? 2
- Thread starter hippo11
- Start date
'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 ?)
seriously tho', i think to control shinkage sounds good; different question, how are they formed ? (dowels, cut out after the mound is filled ?)
DonPhillips
Structural
It makes the material lighter and allows you to be able to reinforce it. Brick also comes solid as well.
Don Phillips
Don Phillips
-
1
- #7
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.
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.
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.
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?
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?
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.
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.
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.
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?
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.
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?
-
1
- #12
concretemasonry
Structural
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.
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.
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?
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?
concretemasonry
Structural
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.
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.
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.
concretemasonry
Structural
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.
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.
concretemasonry
Structural
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.
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.
- Status
Similar threads
- Locked
- Question
- Locked
- Question