MDX Software - FAQ #15<BR><BR> 

Why can't I match any of the values listed in the governing shear and moment 
tables in the girder output with the three tables shown separately for the 
AASHTO truck, AASHTO lane, and defined truck?<BR>
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<BR>
<UL>The system analysis program will load each lane separately with (1) AASHTO 
  truck, (2) AASHTO uniform lane load, and (3) the nonstandard truck (if one is 
  used), if ASD or LFD loading is used. Governing effects of these three 
  loadings are retained. It then sorts governing effects of all lanes and 
  arrives at a total effect from a comparison of lane effect combinations considering the lane multiple presence factors. Thus 
  it is possible to have a mix of all three types contributing to total 
  governing effects. (If the condition CONSISTENT LANE LOADING is used in system 
  analysis input data, governing effects will consist either of all uniform lane 
  loading or all truck loading. This is less conservative than if a mix of 
  loading types is permitted.) 
<br>
<br>
  LRFD uses HL93 loading where lane loading is 
  overlaid with either the design or tandem trucks, whichever governs, in 
  addition to a possible permit truck. Using LRFD multipresence factors a similar mix for governing effects would involve these three types of truck. Girder output tables will show separate 
  tables for (1) governing effects, (2) standard truck effects, (3) uniform lane 
  effects, and (4) nonstandard truck effects. These last three show values as if 
  the type in that table were the only one applied in all lanes. <BR><BR></UL>