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RE: Unusual Joist Designation

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A gentleman, scholar, and list participant is D. Matthew Stuart.   Mr. Stuart wrote a series of articles in Structures Magazine on open web joists in a series called Antiquated Structural Systems in 2009. 
Back in the old days, joist designations would have the first 2 digits as the joist depth and the following 2 digits would be a chord designation.  But I looked at what I had for Bethlehem joists and they did not track well with what you have indicated for weights.  Example: The 48L18 Bethlehem joists weighed 61 pounds per foot.  As opposed to the 52 pounds per foot that you have indicated. 

Regards, Harold Sprague


Date: Wed, 14 Apr 2010 11:09:55 -0400
Subject: Unusual Joist Designation
From: avakiener(--nospam--at)
To: seaint(--nospam--at)
CC: avakiener(--nospam--at)

Fellow Listers,

I am reviewing an existing building from 1955 with long span joist roof framing.  I am unfamiliar with the joist designations that were used.  They are:

#5620 - Wt 63#/LF
#5420 - Wt 63#/LF
#5219 - Wt 57#/LF
#5018 - Wt 52#/LF
#4818 - Wt 52#/LF
#4616 - Wt 45#/LF
#4215 - Wt 41#/LF
#3814 - Wt 36#/LF

The joists have clear spans ranging from 88 feet to 58 feet.  I am assuming that the first two digits of the designation are the depth of the joist in inches.  I am also assuming that the Wt is the weight of the joist in question.

I would like to know the capacity of the joists to ascertain whether they are strong enough to withstand the weight of a new roof that the architect wants to add.  Does anyone know where I could find load tables for joists with these designations.  Any help would be greatly appreciated.

Please respond directly to me as I am in digest mode.

Adam Vakiener, P.E.
Structural Engineer
Southern A & E, LLC
7951 Troon Circle
Austell, Georgia 30168
phone - (770) 819-7777, ext. 144
fax - (770) 819-7770

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