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RE: AASHTO Load Combination

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Your are applying the load combination factors correctly.
That said, iIn the 16th or 17th edition of the AASHTO Standard Specifications for Bridge Construction,
    1)  See Article 3.5 (Overload Provisions) for the applicability of the Group 1A combination.
    2)  Also review Article 3.8 (Impact) to determine when you also need to include the impact factor to the Live Load.
BTW, the current AASHTO code is LRFD which has a different live load and different load combination factors.  You may need to check whether or not your project permits you to use the older code.
David Finley
M. David Finley, P.E., P.A.
2086 SW Main Boulevard - Suite 111
Lake City, FL  32025
-----Original Message-----
From: Rich Lewis [mailto:seaint04(--nospam--at)]
Sent: Friday, October 27, 2006 12:24 PM
To: seaint(--nospam--at)
Subject: AASHTO Load Combination

I rarely do any DOT work so I am not familiar with the AASHTO standards. 


I am working on a simple spread footing design for a bridge pier.  I’m looking at the load combinations on Table 3.22.1.A.  As I understand this I use these load factors with Equation 3-10.  I have a question concerning LFD combinations I & IA.  I see them as follows:


Group I – (1.3*1.0)Dead + (1.3*1.67)Live = 1.3Dead + 2.17Live

Group IA – (1.3*1.0)Dead + (1.3*2.20)Live = 1.3Dead + 2.86Live


Am I interpreting this correctly?  Do I have a live load factor of 2.86?