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LEAP Bridge Steel: Member Forces - Mx, My, Mz, & Mz Lat? / Flange Lateral Moment ?

Derrek Day
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Hi,

I've modeled a 5 span curved steel bridge with 4 Continuous girders.  Taking a look at the Member Forces along each girder for DL and LL, I have some questions about the reported lateral moments.

Dead Load:

  • What is the Mz lat.  load moment?  I would expect an My moment for "lateral moment",  why is this not the case?  
  • Is it about the global z axis or local girder axis?   
  • Does Mz Lat. need to be incorporated into global beam bending loads  (ie, Mz + Mz Lat.)?
Dead Load Final - Final - Self Weight Slab
POI Loc. (ft) Span Fraction Fx (kip) Fy (kip) Fz (kip) Mx (kip-ft) My (kip-ft) Mz (kip-ft) Mz Lat. (kip-ft)
0.0000 1.0000 0.00 64.86 0.00 10.16 0.00 -8.50 43.14
13.3566 1.1000 0.00 52.97 0.00 1.35 0.00 778.64 43.14
26.7132 1.2000 0.00 29.47 0.00 0.99 0.00 1313.50 40.44

 Live Load Results: 

  • Similar to above,   what is the "Flange lateral moment" and what axis is the moment about?
  • Is it about the local girder y axis?   
  • What is difference of positive and negative
POI Loc. (ft) Span Fraction Max. neg. moment Mz (kip-ft) Max. pos. moment Mz (kip-ft) Max. neg. shear Fy (kip) Max. pos. shear Fy (kip) Flange lateral moment neg. (kip-ft) Flange lateral moment pos. (kip-ft)
0.00 1.000 -34.75 101.88 -60.65 114.35 26.257 -109.104
13.36 1.100 -96.56 1256.15 -8.52 94.19 26.257 -109.104
26.71 1.200 -140.17 1946.72 -17.59 56.57 24.613 -102.277
40.07 1.300 -170.24 2248.85 -29.95 37.16 12.306 -93.745
53.43 1.400 -217.87 2315.55 -38.48 27.50 5.633 -75.875

 Thanks,

Derrek

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    Hi Derrek,

    Dead Load: Mz Lat is the lateral flange bending moment and it is with respect to flange's local axis. Therefore, it should not be combined with global girder moment, Mz.

    Live Load: Similarly, Flange Lateral Moment is the lateral flange bending moment. Depending on the location and application of the live load, it may be a negative or positive (similar to global girder live load results).

    Thanks,

    Burak

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  • 0 Offline

    Hi Derrek,

    Dead Load: Mz Lat is the lateral flange bending moment and it is with respect to flange's local axis. Therefore, it should not be combined with global girder moment, Mz.

    Live Load: Similarly, Flange Lateral Moment is the lateral flange bending moment. Depending on the location and application of the live load, it may be a negative or positive (similar to global girder live load results).

    Thanks,

    Burak

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