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Re:FEMA 310 - Handbook for the Seismic Evaluation of Buildings - A Prestandard.

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Edward Gonzalez,

Thank you for your October 22, 1998 response to my posting to the SEAOSC List
Server concerning FEMA 310.

You were correct to question the "reasonableness" of a 36" thick by 25 ft.
long by 30 ft. reinforced concrete shear wall.  I used FEMA 310, Section
4.2.4.5.1, Eq. (4-12) and Table 4-4, page 4-17, m = 2.5, "Shear walls
controlled by shear."  I used a Qce shear stress equal to 2.5*2500^0.5 = 125
psi, which resulted in a 36" thick reinforced concrete shear wall.  

FEMA 273, Table 6-20, Footnote 1, ".....and the maximum shear stress must be
less than or equal to 6*fc^0.5, otherwise the shear shall be considered to be
a force-controlled action."  Using the maximum shear stress equal to
6*2500^0.5 = 300 psi, the thickness of the shear wall can reduced to 14".

However, there is still the problem of how to deal with the overturning
forces.  In your email message you mentioned the application of FEMA 310, Eq
(4-9) and Eq. (4-10).  Application  of  Eq. (4-9) with a value of "CJ" = 2.75,
and the provisions of FEMA 310, Section 4.2.4.3.4 results in a tensile force =
71 kips and a compressive force = 538 kips at the ends of the 14" thick by 25
foot long reinforced concrete shear walls.  FEMA 310 states Eq. (4-9) shall be
used when the forces contributing to QUF are delivered by yielding components
of the seismic framing system.

Application of  Eq. (4-10) with a value of "C" = 1.1,  and the provisions of
FEMA 310, Section 4.2.4.3.4. results in a tensile force = 527 kips and a
compressive  force = 995 kips at the ends of the 14" thick by 25 foot long
reinforced concrete shear walls.  FEMA 3110 states Eq. (4-10) shall be used
for all other evaluations.

FEMA 310, Section4.2.4.3.2, Force-Controlled Actions, provides for a Method 1:
"Force-controlled actions, QUF, shall be calculated as the sum of the forces
due to gravity and the maximum force that can be delivered by deformation-
controlled actions."  FEMA 310 in the Side-bar on page 4-7 does not provide
any guidance concerning whether a reinforced concrete diaphrapm (which occurs
in the sample building) is a "deformation controlled" or a "force-controlled"
action.  Therefore, Method 1 was not used in the sample building example.

Thank you again for taking the time to respond to my FEMA 310 inquiry.  It is
difficult to "peer review" your own work.


Frank E. McClure    FEMCCLURE(--nospam--at)aol.com  October 23,1998.