Welded truss joint stiffness

[kcollier]

I am currently involved with analyzing a truss that has welded joints. An analysis was done assuming the traditional purely pinned joints. A separate analysis was done assuming that the joints were pure rigid connections. From the pure rigid joint solution a bottom truss chord fails the shear-moment interaction check. I would like to perform the analysis using a semirigid connection. My question is what rotational stiffness to use in the analysis. Is there any material available dealing with this particular problem?

 

[JAE]

Depends upon the connection type - there's lots of info on WF beam to column joint rotational stiffnesses. For pipe to pipe or tube to tube connections (welded) I'm not so sure there's much of anything.

 

[sdz]

Are you designng a new truss or analysing an existing one?

If you are designing then it's easiest to stick to either pinned or fixed connections. Whichever you use the construction should use connections of type compatible with the design assumptions.

 

[kcollier]

The load rating is being done for an existing bridge. The bridge rates ok using the pure pinned assumption and is very low using the pure rigid joint assumption.

 

[sdz]

Consider what will happen at the location where the shear moment interaction failure is found. Probably some load shedding will occur and the load will redistribute to a safer configuration. This can happen because steel is a ductile material. So unless a local overload could result in a catastrophic failure it should be OK.