fatigue moment
fatigue moment
(OP)
can someone walk me through the steps for calculating fatigue moment for a simple span bridge, span 80', rolled section, service load on one beam: 625 plf DL, 425 plf LL.
thanks
code is AASHTO 2002, using LFD
thanks
code is AASHTO 2002, using LFD





RE: fatigue moment
RE: fatigue moment
take unfactored moment and shear from the live load only, increase it by 1.15 for dynamic load allowance then multiply by 0.75 for the fatigue load factor.
also: above dead load should be 890 plf
RE: fatigue moment
In the old days, I was expected to use the values from my "normal" analysis to check fatigue. But because I think there is now a fatigue truck, I don't think you can just use that straight forward approach anymore.
On the other hand, I believe your approach would be conservative, but likely not economical.
I haven't designed a bridge to the new LRFD code so I may not have my facts straight on this.
Good luck.
RE: fatigue moment
RE: fatigue moment
Article 3.6.1.4.1 then states that "... the fatigue load shall be ONE design truck ...". Does this mean that for the design of a transverse member (e.g. cross girder), fatigue truck is applied only in one lane, although there may be multiple lanes available? (My interpretation is that it is not necessary to apply fatigue truck in multiple lanes.)
Thanks!
-ok
www.bridgeart.net
RE: fatigue moment
Perhaps you should get a copy of "A Fatigue Primer for Strucutral Engieers" by the National Steel Bridge Alliance. It contains examples for various types of bridge fatigue calculations.
bridgeart - I've done it the same way for floorbeams; one truck positioned to give the maximum load.