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composite bridge plate girder design - unbraced

composite bridge plate girder design - unbraced

composite bridge plate girder design - unbraced

(OP)
1) LRF Design: For the unbraced length of plate girder between the cross-bracing, you use the two end moments, k, omega etc. to get the Mult based on lateral torsonal buckling mode.  Which Mf do you compare to?  The higher end or the middle?  I would think it is more appropriate to use the moment in the middle zone of the unbraced length where the buckling will start, rather than the higher moment at one end (in the +M area where the moment is single curvature and increasing from one end to the other)?  My Lu is very long in this case (due to the bridge type) so the one end moment is much higher than the middle portion.

2) Also, if you have field splice in mid portion of the long Lu where the section changes, what is the simple way of assessing the Mu for the Lu?  Some kind of weighted average of the section properties?

RE: composite bridge plate girder design - unbraced

Which specification are you working out of? If it's the AASHTO LRFD Bridge Design specs, please give a section reference. If you are using another spec, you will need to define the variables you refer to for me to be sure I understand the question.

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