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Modelling of Bowstring Truss Joint

Modelling of Bowstring Truss Joint

Modelling of Bowstring Truss Joint


Got a problem where the bottom chord of the truss is two members, and the splice is staggered at two different panel points.

Is there any option in Risa 3D to account for two identical members of the same truss member type framing into a joint, one discontinuous and one continuous?

Since this is a Bowstring truss with inherent design flaws due to the age of construction, specifically secondary stresses due to member moments and connection eccentricities, that were not considered in the original design, modeling this type of joint correctly becomes necessary.

I could run it both ways and bracket a solution, but that ewould not tell me what the stresses really are.

Thanks in advance for any feedback, Josh.

Mike McCann
MMC Engineering

RE: Modelling of Bowstring Truss Joint


I believe that you can put to members on top of one another in 3D space - connected to the same joints, yet they will behave as though independent members.

The program only "knows" that each member creates a force-displacement relationship between nodes.

RE: Modelling of Bowstring Truss Joint

Yeah, I think you could put the members on top of each other. Just be careful about doing a "model merge" after that. The program could look at those members as duplicates and try to merge them together.

I might prefer to model the bottom chord slightly differently (especially if this were to be a double angle chord). I might define one double angle member on the right side of the right most splice then I'd use a different double angle member on the left side of the left most splice. The member in between the two splices could then be a third member with some custom defined properties.

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