MDX Software - FAQ #12<BR><BR>

What is 
the procedure for determining governing forces in cross frame members?<BR>
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<BR>
<UL>There generally are about twelve combinations of moment and shear on both 
  ends of the frame which are involved in producing governing effects. (See bracing output table "Summary of Analyses - Girder i.")  For each 
  one of these combinations the frame is detached from the pin connections on 
  the side where the shear and moment are applied. The connection plate is 
  assumed to act as a vertical member of the frame between the detached 
  connections. The applied moment is resolved into a force couple of oppositely 
  directed horizontal forces acting on the detached nodes. Half the shear is 
  applied as a vertical force to each of the detached nodes if there is a diagonal connected to each node.  The entire shear is applied if only one diagonal is connected. If the resulting frame is determinate (Types A, B, C), a determinate analysis of the truss produces member forces. If not (Type E), an indeterminate analysis of an indeterminate pin ended truss is used.  </UL>

<UL>
If wind is applied as a lateral load on the bottom flange of the girder connected 
  to the frame a compression/tension force, determined according to the specification, 
  is superimposed on the bottom chord. A summary table of member forces for each 
  of the separate analyses is tabulated at the end of the bracing output. 
  Governing tension and compression forces from this table are used for design 
  and rating of the cross frame members. </UL>