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Re: AASHTO Plate Girders

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Thanks a lot for your prompt response Tom!
The above is a design example from the NSBA.  Page 8, section 4.1 uses the table I referenced.  They use L = max span length, as did I.  I don't see anything that defines L in the AASHTO table.  Can you help me out by pointing to a part of the code that I may use to document your proposed L?
Also,  if I'm reading the table correctly, the formula I used specifically states "depth of I-beam portion of composite I-beam".  I take this to mean the outside dimension of flange to flange.
Again,  thanks for the response Tom.  If you or others can help with the additional issues above I'd appreciate it!

On Feb 5, 2008 11:48 AM, Cummings, Thomas J. <tcummings(--nospam--at)> wrote:



The depths indicated in the table are the total structure depth, including the deck slab and haunches. Also, the span length "L" is taken as the distance between dead load points of contraflexure for continuous spans. These two criteria should reduce your girder depths to near the 6ft. deep section.


Good luck with the design.  Hope this helps.





Thomas J. Cummings, PE

Manager - Bridge Design Practice

Gannett Fleming Engineers and Architects, P.C.

One Penn Plaza, Suite 2222

250 West 34th Street

New York, NY 10119

P:  (212) 967-9833 Ext. 5244

F:  (212) 268-6684

E:  tcummings(--nospam--at)


From: g r [mailto:gr7070(--nospam--at)]
Sent: Tuesday, February 05, 2008 12:34 PM
To: seaint(--nospam--at)
Subject: AASHTO Plate Girders


I'm taking over a past dormant project that has a bridge where 3 of the 26 spans are continuous steel plate girders.  Only layouts have been completed (and approved), but they show a plate girder section of 6' deep - that's the girder depth.


The spans are 200'-280'-200'.


I'm not very experienced with steel plate girder design.


Article Optional Criteria for Span-to-Depth Ratios contains a Table  This table provides a minimum recommended steel girder depth of 0.027L.


0.027 * 280 = 7.56'


That's much greater than the current 6'.


So how worthwhile is the value in this table.  That's a stark difference.  Did the original producers of the layout just have no idea what they were doing?


Thanks in advance for any comments or helpful criticisms!