Masonry Block 3

[Alpharetta]

There is a formula to height of masonry block wall, ratio of Block width dimension; i.e. 4" block, maximum 6' height. I've forgotten the formula and can't find note within my reference materials for maximum height of 6",8", 12". Can you help?

 

[haynewp]

What code are you using?

 

[CSEllc]

The used to be a limit on the height of masonry. I believe the limit was h/20.

Undfer the "new" masonry codes, that provision was basically removed. However, most people still use it.

 

[Alpharetta]

Should have included: International 2000, but I haven't found anyone who can interpret masonry codes from that format.

 

[haynewp]

Well it references ACI530-99 and it does not have a specific h/t for engineered design of masonry walls. There are h/r equations that take into account the slenderness of the wall. However, there are h/t limitations for columns.

If you are really concerned about P-delta effects on the wall, you could try the UBC slender wall design method and see what you get, Enercalc has it.

 

[TFL]

THE EMPIRICAL DESIGN PROVISIONS OF ACI 530-02 HAVE THE h/T PROVISIONS. TABLE 5.5.1

THEY ARE VERY USEFUL AS A GUIDEINE EVEN FOR ENGINEERED DESIGNS

 

[haynewp]

You're going to be pretty limited by the emperical h/t values. For an 8" block, you are only allowed to go to 12' high for partially filled units in a bearing wall.

 

[haynewp]

Although not req'd by ACI, I would probably limit h/t to about 25.

 

[CSEllc]

The "old" NCMA Masonry Code (circa 1970,now longer referenced), limited the height of unreinforced load bearing masonry walls to a h/t ratio of 20. (8" block limited to 13'-4"). Columns where limited to an h/t ratio of 25, based on the least dimension...minimun dimension for a column was also 12".

Reinforced masonry walls under the NCMA Code were limited to h/t of 36, unless "evidence by a qulaified person showing the wall met all the other requirements".

As I previously ststed, the MJSC no longer limits the height of the "engineered" walls. Walls are designed based on the h/r ratio, where r is the radius of gyration = sq. root of (I/A).

If you are "designing" a masonry walls based on the EMPIRICAL DESIGN methodilogy of Chapter 5, the h/t ratiuoa are still used. The h/t ratios are different than the "old" NCMA limits but not significantly. The "new" h't ratios classify the walls as bearing or non-bearing walls, interior or exterior.

 

[pricklyPete]

There is a book called "Masonry Design Manual" whose 2nd addition was published around 1972. On the first page of the first chapter it gives a table for maximum ratio of unsupported height to thickness. For reinforced hollow unit masonry bearing walls, it give h/t of 25. It also gives h/t ratios for nonbearing walls for combinations of exterior/interior and reinforced/unreinforced. Apparently this table comes out of the 1970 UBC.

It is interesting that they give and h/t ratio of 20 for an unreinforced nonbearing exterior wall. If you were to engineer a wall like this, particularly with a small dead load to reduce the tension bending stresses, it would never work out under most wind loadings.

 

[Alpharetta]

Thank you. It has been several years since I've dealt with masonry partitions and didn't have a comfort level with the new codes. Apparently, same people that write the tax code wrote revisions for the building code.

 

[3dboy]

be careful how you apply those h/t ratios they are different according to bearing/non-bearing, exterior/interior. Forget the empirical stuff you can get much better values by using the engineered approach.

 

[boo1]

check

http://www.ncma.org/etek/homefrm_map.cfm?spdm=cemexusa.com