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RE: FEMA 350

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Kipp,

Ze will equal Zx in the LRFD manual for rolled shapes except for RBS and
if the Plastic Hinge is located in an area where reinforcing, cover
plates, or haunches occur.

This is most common in RBS, where you are cutting away some of the
flange. To calculated the Ze (also called ZsubRBS later in the book),
you need to calc it manually. Here is the equation for an I shape:

Z = bf * tf * (d-tf) + 0.25 * tw * (d - 2tf)^2

Where bf= flange width ; tf = flange thickness ; tw = web thickness ; d
= beam depth

Use the new bf values for your modified flange width.



Hth,
-gm
 

-----Original Message-----
From: Kipp.A.Martin(--nospam--at)us.mwhglobal.com
[mailto:Kipp.A.Martin(--nospam--at)us.mwhglobal.com] 
Sent: Tuesday, December 02, 2003 12:04 PM
To: seaint(--nospam--at)seaint.org
Subject: FEMA 350

One of my engineers is working on a project that needs to meet the
requirements of FEMA 350.  We are slowly working our way through the
requirements, but came upon a question that we couldn't figure out.  On
page 3-6, in equation 3-1, there is a term Ze (Z sub e).  This is
defined
as the effective plastic modulus for the beam at the location of the
plastic hinge.  How do I determine Ze?  Is it the Z that is given in the
LRFD manual? Or does it need to be decreased (or increased) by some
factor?
I've looked in the LRFD manual, but I can't find an equation that
defines
how to determine Ze.

--Kipp Martin, SE
  MWH Americas
  Portland, Oregon




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