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# Re: welded truss design assumptions

• To: seaint(--nospam--at)seaint.org
• Subject: Re: welded truss design assumptions
• From: Nacionales Alex <acnacionales(--nospam--at)yahoo.com>
• Date: Wed, 11 Sep 2002 02:02:16 -0700 (PDT)

I used to design trusses assuming pinned connections and design for axial compression and tension only.But using software like RISA2D, I assumed also fixed connections and design members for combined axial and bending and assuming k=1. I found that the latter results to  heavier members which is on the safe side and that RISA is very fast and fun to use.

Alex C. Nacionales C.E.

Chung-Soo Doo wrote:

I agree with Warren. The forces in the diagonal member shall be resisted by the strength of the member. We have member capacity of bending, axial, and shear. It is not a big problem if the truss is properly modeled and analyzed. However, the calculation of k-value is very complicated since we need to calculate the stiffness of top and bottom chord. Fortunately, we usually use much stiffer members for those members and the relative nodal displacement is very minor. It make me assume to be k = 1.
However, if the top and bottom chord has about same or less bending stiffness, then you need to calculate the relative stiffness and adjust your axial capacity by calculated k-value.

Chung-Soo Doo

"Foy, Warren" wrote:

I usually analyze the webs as having fixed ends to design for the moment induced, but design with a k=1 for axial loads.
-----Original Message-----
From: Ken Peoples [mailto:kspeoples(--nospam--at)lvta.net]
Sent: Tuesday, September 10, 2002 4:48 PM
To: Seaint
Subject: welded truss design assumptions

I am reviewing someone elses truss design and question one of his assumptions.  When we do trusses, we typically assume that the web members are pinned and that these members only carry axial load - even if the connections are welded.  The truss that I am reviewing was designed with all of the members assumed to be fixed ends.  It is a typical WT top and bottom chord truss with angle webs.  No special connections - just gussets in line with the WT webs and welds on one leg of the angles.  Just curious what the general concensus is out there.Thanks in advance.Ken  Kenneth S. Peoples, P. E.
Lehigh Valley Technical Associates
Northampton, PA 18067-9039
Phone: (610) 262-6345
Fax: (610) 262-8188
e-mail: kpeoples(--nospam--at)lvta.net
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