huangyhg

cmu shearwaal corner
am inspecting on a project that has one building with 10" cmu exterior shearwalls with verticals of # 6 @ 24".
i am curious about the corners. i observed that the 1st exterior corner to be constructed is actually made of 8" cmu. the mason claims that this is "common industry practice" performed to avoid having to cut a lot of block to keep the mortar joints even.
is this practice something that i should note as a discrepancy and notify the eor about or is this an understood practice?
thanks.
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because of the non-modular size of the wall thickness, it is common to use 8x8x16 units at the corner to maintain modulatity and they use brick or other solid units. the mortar bonding of the solid units and the 8x8x16 units preserves the appearance and the core spacing for proper grouting.
there is frequently a problem where corners got over-built, over-designed, reinforced too much and become out of balance in the entire structure, attracting too much load. this was evident in many buildings i saw after the northridge "rumbler"
dick
dick:
i have not seen this corner detail before in cmu. would you please post a plan detail of the corner construction with the different block sizes? thanks.
mike mccann
mmc engineering
thanks concretemasonry.
mike, don't have a detail on this condition. this is something that the mason is doing because it is "common practice". so what i have is two 10" cmu exterior walls coming together at a 90? corner. the blocks that interlock at the corner are 8" block. this practice is employed for appearance value as it preserves the head joint spacing on the exterior of the walls.
not sure how the practice affects the strength of the wall at the corner. the engineer has 3 # 6 verts at the corners plus # 3 corner bars at 16".
for a good collection of details for masonry, go to the national concrete masonry association (ncma) web site (ncma.org).
one the site, look in the right upper corner area for a box about masonry tek notes. then, click on a state (any state - it makes no real difference since the tek notes are national and local). then, click on a producer (any producer for same reason as previous). look for a tek note index and click on tek 5-9a, which has many corner detailed illustrated. - the are also may tek notes on design, construction and quality control.
in the tek 5-9a, you will find several choices for the 10" corner. the most common are the use of a 10" "l corner" that is made in some areas and the use of a 1 5/8" solid unit that is cut/split to create the "l" and mortared in place. if you look at the detail, the coursing will permit the full mortar bed for the next course, while still maintaining proper appearance on both sides of the wall. - i assume this wall is designed for modular lengths.
a 10" wall is not that common nationally since the material cost and appreciably different, so 12" walls are used used and the 12" l corner is much more common because it is a true modular unit. only the larger/better cmu producers make "l" corners for 4", 6", 8", 10" and 12" units because the common, historical methods of using solids to fill have found to be adequate and approved.
the corner reinforcement is to provide continuity since it is lighter than the main reinforcement of the walls. internationally, i have seen 20 story masonry loadbearing buildings (10 or 15 on a site) using 6" thick block in varying strengths with far less wall steel possibly because of the use of interior walls and poured in place slabs. - when i asked what standard they used, they said "we use yours, but just learned to use it better because it is the most common product to use".
the ncma tek notes on all subjects are very valuable, but are well hidden or not publicized. generally, they are written by professionals that are active in all the codes (ibc, irc, etc.), standards (astm, etc.) and other engineering groups (aci 530, tms).
dick
thanks guy.
mike mccann
mmc engineering

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