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FW: Masonry Design

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For anyone interested, I have received the following comment regarding
my question on masonry design from Dr. James Colville.  I understand
that he is the committee chair for ACI530 and a prof at U of Maryland
(Thanks to John Jones for the suggestion to contact Dr. Colville):

Ed Marshall

I have received your question. As an aside, Dr. Brown is at Clemson
University not Ga. Tech, though he is currently on sabbattical leave and
in Australia.

Though I cannot give an "official" answer to your question, it is my
that you would use the average value of the unit strength in using the
strength table in the Specifications. This table tends to give
results anyway in comparison to prism testing, and since prism testing
based on tests of 3 units, I am sure that this is what can also be used
the unit strength approach, that is, the average value from 3 specimens.

I hope this is helpful to you.

Jim Colville


I don't know the answer to your question but there is a professor at
Tech who is on ACI530.  I believe his name is Russell Brown.  When ACI's
travelling road and pony show came to Birmingham this topic was touched
by Dr. Brown but I don't remember what was decided.

He could probably answer the question and if he doesn't all you have to
is drive across town and bug him at his office until he does.  :-y

John Jones


-----Original Message-----
From: Ed Marshall [mailto:elmarshall(--nospam--at)]
Sent: Wednesday, August 12, 1998 8:32 AM
To: seaint(--nospam--at)
Subject: Masonry Design

I have a question regarding the determination of the design compressive
strength of masonry using the unit method rather than the prism test
method (assuming all necessary special inspections are done).

When using standard ASTM C 90, Type 1, Grade N, hollow load bearing
concrete masonry units with type S mortar, do you use the value of 1900
psi (average minimum net area strength for 3 units) or 1700 psi (minimum
individual unit strength), taken from ASTM C 90 - Table 2, in selecting
the net area compressive strength of masonry (f'm) from ACI 530.1-95,
Table 2 (or Table 21-D, 1994 UBC **) ?  I can't find anywhere in ACI
530.1-95, ACI 530-95, the 1994 UBC, or several textbooks that makes this
clear.  ACI 530.1-95 says that the cmu's are sampled and test in
accordance with ASTM C 140 - but it reports both values.

I'm inclined to think that it was intended that the 3 unit average
strength be used since this corresponds to a line in the table -
yielding f'm = 1500 psi (rather than making everyone interpolated).  If
anyone knows somewhere where this is clarified I would appreciate being
pointed there.

** Both the 1996 BOCA and the 1997 SBC codes refer to ACI 530 for
engineered masonry design.

Ed Marshall, PE
Simons Engineering,