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RE: STRUCTURAL STEEL: Large Pipe Column?

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Yes, Amy. This is from the AASHTO "Standard Specifications for Structural
Supports for Highway Signs, Luminaires and Traffic Signals," Fourth Edition
(2001), which IIRC you have.

Please note that in this case I'm designing a CANTILEVER STRUCTURE (i.e.
single column). There is apparently some research ongoing to determine
fatigue design parameters for "bridge type" structures, but the current
edition of the AASHTO Specification doesn't address such structures.

In the Commentary in Section 11: Fatigue Design, there is the following

"Square cross-sections have been much more prone to fatigue problems than
round cross-sections."

In the past, the Houston District of TxDOT has designed cantilever sign
supports using square tubes. I do not know what their record of performance
has been but I do note that they no longer allow such designs.


William L. Polhemus, Jr. P.E.
Polhemus Engineering Company
Katy, TX, USA
Phone (281) 492-2251
FAX (281) 492-8203
email bill(--nospam--at)

-----Original Message-----
From: Amy Ellis [mailto:EllisAL(--nospam--at)]
Sent: Thursday, February 28, 2002 1:12 PM
To: seaint(--nospam--at)
Cc: Greg Creamer; Darrell Thompson; vkimm(--nospam--at)
Subject: RE: STRUCTURAL STEEL: Large Pipe Column?


I am working on a project for the new Terminal out at DFW Airport.  DFW
specifies HSS 16x16 tubes for all overhead signs.  I was wondering about
your statement regarding not using rectangular tubes in the state of Texas
due to fatigue.  Could you elaborate on this point or let me know where to
look to find out more information.

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