Stack Bond CMU Design

[StructuralEd]

Are there any special structural considerations/restrictions/requirements in the design of stack bond cmu walls. We will be having both perimeter backup walls for lateral support of brick veneers as well as interior partitions.

 

[haynewp]

1) Corbelling won't work over openings.

2) Check your code to make sure shearwalls can be constructed as stacked bond if in seismic area.

3) I am not sure if the wall will act like a T beam for out of plane bending or not (partially filled and reinforced cells). In fact, I know some engineers that will only use stacked bond walls if they are solid grouted in all cells.

I have tried to search out information on stacked bond walls in structural applications before and was not real successful.

 

[minorchord2000]

there is a good masonry reference textbook which talks about stack bond masonry

Design of Masonry Structures
Narenda Taly

 

[UcfSE]

Joint reinforcement becomes more important. I would either place vertical bars no more than 16 inches o.c. or a bond beam no more than 4'-0" o.c. As mentioned, you may have issues if you're in a seismic region that restricts stacked bond in shear walls.

 

[concretemasonry]

It is always preferred to use running bond for masonry because of the load distribution advantages. Most codes and standards state the block shall be laid in running bond unless otherwise required.

The definition of running bond requires that head joints in successive courses of masonry are horizontally offset at least one-quarter the length of the units. Anything other than this is considered "stack bond". It is possible to lay units without the head joints vertically aligned and still be considered stack bond.

There are specific corner units ("L" shaped) made to provide runing bond for 6", 10" and 12" thick walls in addition to the typical 8x8x16 corner units.

It is not necessary to stack bond the masonry units that are reinforced. There are many units that provide adequate core alignment in the common reinforced wall thicknesses (6", 8" & 12"). Because of the alignment, it is not necessary to grout a wall solid, which is an ineffective method of increasing strength. If this is a reasonable size project you could get much higher block strengths as required.

There also may be a cost increase for stack bond if the wall is exposed.

The ACI 530 commentaries are very valuable.

Dick

 

[StructuralEd]

We have no shearwalls; primarily backup walls and partitions.

 

[rgerk]

See if you can find a CMU with a center score in it. That way you can stack it in running bond but have the look of stack bond.

 

[concretemasonry]

If the stack bond appearance is an architectural concern, you can still get most units scored to give you an 8x8 pattern.

Often, two faces scored are cheaper (labor cost) in back-up construction since a bad face can be turned toward the cavity, since it costs more to throw away or patch a chipped block than it costs.

Dick

 

[lkjh345]

See 2.3.3.3 of ACI 530-5 Building Code Requirements for Masonry Structures for limitations on effective compressive widths per bar when have stacked bond with bond beams greater than 4'-0" (vertically) apart.

See Also Paragraphs 1.11 for mimnimum area of horizontal steel.

 

[StructuralEd]

Thanks all.