How to Calculate Partial Fixity Spring Constant?

[garnereng]

I am using STAAD.Pro 2003 to model a truss type structure consisting of welded square and rectangular tubular shapes using beam elements.

A typical connection might be a 1.25x1.25x.125 wall tube welded to a 2x2x.25 wall tube. A fully fixed connection is probably overstating the true condition as there will be some rotation at the connection joint due to the flexibility of the side wall of the 2x2x.25 wall tube that smaller tube is welded into.

My dilemma is in how to calculate an appropriate value of partial fixity (either a percentage of full fixity or a spring constant for the connection) to be used in my STAAD beam element analysis of the structure.

Any help would be most appreciated.

 

[trainguy]

Check out Packer And Henderson - Design Guide for Hollow Structural Section Connections (Canadian Inst. of Steel Constr.)- the truss design chapter.

This text elaborates on required assumptions to use when designing trusses, and how to lay out the connections.

tg

 

[lippie]

You can use partial moment releases in STAAD.Pro. Under Releases, you can specify MPX, MPY or MPZ as a percentage of full fixity (50%, 80%, etc.). This is called a semi-rigid connection. Much easier than defining a spring.