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Amy, for design of sign supports using AASHTO's "Standard Specification for
Structural Supports for Highway Sings, Luminaires and Traffic Signals" 1994
Edition, you must use ASD, period. There is really no "cross-over"

Now, that's not to say that LRFD design couldn't work; from what I've been
able to determine for myself, the design equations, etc., for steel design
in the AASHTO Standard are pretty much equivalent to those in AISC ASD Ninth
Edition spec. But I am willing to wager that your design calcs, etc., are
going to have to be "checked" by TxDOT--at least that's been my experience
designing such supports for Houston METRO--and TxDOT is not even willing to
look at LRFD stuff.

One particular problem with design of sign supports, etc., using this AASHTO
Specification, is that they are trying to "bridge the gap," pun intended,
between the world of AISC design and AASHTO's own bridge design
specifications. The design equations, etc., as I've said, boil down to AISC
ASD, but the "flavor" of the spec, the way loads are treated, the standard
units used, etc., are very familiar to the bridge designer who uses AASHTO's
ASD bridge spec. It looks to me like AASHTO is stricken with the "Not
Invented Here" syndrome.

Now, I have just ordered the 2001 edition of the AASHTO "Signs"
specification, but I haven't yet received it. It could be that they have
updated it to conform to LRFD, since that is the way the AASHTO has been
pushing to go for some time, at least for bridge design (their First Edition
LRFD Bridge Design spec was published in '94). If you can get a copy of that
(can be ordered here:
) then that might be your best bet.

Otherwise, I'd be glad to let you know how things stand when I get mine.


-----Original Message-----
From: Amy Ellis [mailto:EllisAL(--nospam--at)]
Sent: Thursday, October 25, 2001 10:10 AM
To: seaint(--nospam--at)
Subject: LRFD and AASHTO

I am a recent graduate and would typically use LRFD in designing.  My boss
typically uses ASD.  I am just doing simple sign structures for DFW Airport
but the question has come up, how does LRFD fit in with AASHTO?
Specifically we are looking at the different load combinations and which
factors to apply.  If anybody has any ideas please respond directly to me.

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