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RE: bearing on cmu wall

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The compressive stress on the wall can be distributed over an "effective
length" of CMU (refer to 2.1.7 - figure 2.1-15 on page CC-29 illustrates
this well).  The CMU can then be designed to support the vertical load
from the beam as an unreinforced wall (, a reinforced wall
( or empirically (5.4.2).  Note that the empirical method uses
gross area of the wall, and the other two methods use the net area.

The bearing stresses, with any of the methods must be less than 0.25 f'm
(  As with concrete, the bearing area can be increased based on
the ratio of the actual bearing area to the area of wall directly under
the bearing (refer to and figure 2.1-15 on page CC-29)

Hope this helps.

Charles F. Espenlaub, III, P.E.
Martin-Espenlaub Engineering

-----Original Message-----
From: Ken Peoples [mailto:lvtakp(--nospam--at)]
Sent: Monday, May 22, 2000 9:29 AM
To: seaint
Subject: bearing on cmu wall

I am by no means an expert in masonry design so
forgive me for my ignorance here but I have often
found the wording regarding allowable compressive
stress in masonry found in the empirical design
chapter of ACI 530 to be a bit confusing.  The typical
situation that I have is a CMU wall with a beam
bearing on it.  I will have a bearing plate and
specify that the CMU be grouted solid below the
bearing plate.  If I have type N mortar and 1500 psi
prisim strength called out for the CMU work, what
should I be using for the allowable bearing stress? 
Ken Peoples, P. E.
Lehigh Valley Technical Associates

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