huangyhg

masonry block
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?
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what code are you using?
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.
should have included: international 2000, but i haven't found anyone who can interpret masonry codes from that format.
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.
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
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.
although not req'd by aci, i would probably limit h/t to about 25.
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.
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.
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.

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