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Re: Truss end connections

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Is there really any difference in how the forces are transferred between 
a braced building frame (i.e., a vertical truss) and a built-up 
horizontal framing member that we call a truss? The actual forces and the 
pattern of force transfer may vary, but as long as the connection 
configuration is similar and equilibrium is satisfied, I think the 
Uniform Force Method is equally applicable. In the end, the whole idea 
behind the UF Method is to select the gusset geometry so that the brace 
force and the gusset edge forces intersect at or near a single point in 
space, thereby eliminating or minimizing (respectively) the 
eccentricities (and resulting moments) on the gusset edges.


Todd Hill wrote:
> I am currently involved in checking heavy long span truss connections.
> The trusses in question frame into column flanges.  The detailer's
> engineer is using the Uniform Force Method to resolve the forces at this
> connection.  His mathematical method is correct but my question is whether
> the Uniform Force Method is a valid analytical method for this
> application.  AISC Volume II Connections only uses Uniform force Method
> analysis in regard to vertical bracing applications.  Does it matter how
> the axial force originates?  For example: In the vertical brace case,
> compression in the horizontal member is a result of that member being
> compressed between 2 columns.  This compression strut in effect will bear
> against the column.  Compression in the top chord of a truss on the other
> hand is a result of internal stresses and will in effect result in the top
> chord of the truss to shorten.  This  would seem to result in the
> compression chord to want to pull away from the column.  I guess my
> question is if the uniform force method is applicable to the truss end
> condition, does the horizontal component at the gusset/column interface
> have to be resolved somehow at the top chords connection at the column.
> (Reference fig.7-50 page 7-108 AISC Volune II Connections-ASD 9th ed.)
> I've always resolved the forces similar to the methods shown on page 7-60
> of the above referenced manual.
> Any information would be greatly appreciated.
> Todd Hill, PE