Net Area - CMU

[humanengr]

ACI 530-13 makes use of net area (An) and gross Area:
1) Is it correct that An = full CMU Cross-Sectional Area if the blocks are fully grouted?
2) If the blocks are not fully grouted, how is An calculated? Wouldn't you need to
subtract the area of the open cells from the gross area? I have been unable to
locate where such dimensions can be found.
(In case you haven't noticed, I do very little CMU design work).
thank you,

 

[KootK]

1) Is it correct that An = full CMU Cross-Sectional Area if the blocks are fully grouted?

Yup

Wouldn't you need to subtract the area of the open cells from the gross area?

Yup

I have been unable to locate where such dimensions can be found.

Link

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[msquared48]

Amrhein Table B-3a has equivalent solid thicknesses with associated weights for grouted masonry.

Mike McCann, PE, SE (WA)

 

[concretemasonry]

Keep in mind that there is no such thing as a "standard" CMU. - The ASTM specification for concrete masonry units provides some minimum dimensions (face shell, webs) and minimum web thickness per linear foot. By, definition, any cmu with greater that 75% solid is classified as a solid unit for code applications. - This is determined by the ASTM C140 procedures that have nothing to do with grout or mortar.

With these parameters, a multitude of different units can and are being made. I worked for a major supplier that had a library of over 1000 different mold configurations for 8" "standard" units alone and a smaller number of shapes in 3", 4", 6", 10", 12", 14" and 16" cmus. - Yes, there are producers, engineers and contractors want the 16"x8x16 units with different core arrangements. Keep in mind that the bonding of the courses can have an effect, depending on the core arrangement. - A 2 common 2 core 8x8x16 CMU when laid in running bond does not provide the opportunity to use full bedding and have the cores align for a clear, unobstructed vertical core for grouting, and grouting will be more difficult. - An 8x8x16 unit with open ends, 2 webs(one core) at 8" o.c. provides the idea unit for full mortar bedding

Multiply that by the number of different densities (lightweight, medium weight and normal weight there are many more units available.

Jim Amrhein's information is very good for the area he represented as far as local availability and production. Unfortunately there are other market areas that have different needs and practices.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[Antnyt23]

NCMA TEK 14-1B may be helpful.

http://www.masoncontractors.org/tech-notes/

 

[humanengr]

Sorry, I was away for a while. Thank you all for the information. If I understood you correctly, the specific manufacturer
data should be used to determine CMU properties, net areas, etc.
Thanks much!