# FW: through-truss without top chord bracing

• To: "Seaint (E-mail)" <seaint(--nospam--at)seaint.org>
• Subject: FW: through-truss without top chord bracing
• From: "LaCount, Curt" <Curt.LaCount(--nospam--at)jacobs.com>
• Date: Tue, 12 Feb 2002 10:40:01 -0500
```Everyone,

Take a look at the new LRFD 3rd edition, which contains a new section on
bracing.  Bracing design is comprised of two components; strength and
stiffness.  The 2% rule will provide strength, but with the problem at hand,
the stiffness of the bracing might be the tougher nut to crack.

Curt La Count
Jacobs Engineering
Portland, OR

-----Original Message-----
From: Matthew Stuart [mailto:m.stuart(--nospam--at)aespj.com]
Sent: Tuesday, February 12, 2002 4:19 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: through-truss without top chord bracing

Dr. Yura's bracing research has shown that the 2% rule-of-thumb is
conservative. Obviously you would use 2% of the maximum top chord axial
force at the midspan of the truss to design all of the web members providing
even more redundancy.

-----Original Message-----
From: Majid Sarraf [mailto:msarraf(--nospam--at)unl.edu]
Sent: Monday, February 11, 2002 10:45 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: through-truss without top chord bracing

Ken,

I suggest that you look at Timoshenko and Gere's Theory of Elastic
Stability, pages 111 and 112.

I do not believe that using 2% of axial load applied as lateral load for the
design of top chord is a conservative assumption.  Axial force in the top
chord varies from 0 at the ends to its maximum at the mid-span where the
stability against out-of-plane buckling of the entire top chord can be
provided only through bending stiffness of the web components and rotational
restraint of the floor beams.

Majid Sarraf, Ph.D.
Senior Bridge Engineer
Imbsen and Associates Inc.
Sacramento, CA

======================================================================================
NOTICE - This message may contain confidential and privileged information that is for the sole use of the intended recipient.  Any viewing, copying or distribution of, or reliance on this message is strictly prohibited.  If you have received this message in error, please notify us immediately by replying to the message and deleting it from your computer.

==============================================================================

******* ****** ******* ******** ******* ******* ******* ***
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp
*
*   This email was sent to you via Structural Engineers
*   Association of Southern California (SEAOSC) server. To
*   subscribe (no fee) or UnSubscribe, please go to:
*
*   http://www.seaint.org/sealist1.asp
*
*   Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you
*   send to the list is public domain and may be re-posted