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Risa 3D - Rigid Links

Risa 3D - Rigid Links

Risa 3D - Rigid Links

For a situation with grillage beam assembly with several beams sitting cross wise on a carrier beam I have used rigid links connected between the centroid of the shapes to model the behavior. At the node that ties to the carrier beam I have released all moments as my initial attempt without releasing the moments in the rigid link introduced too much stiffness. The beams are simply bolted to each other, flange to flange. Does anyone have any additional insight to model this behavior?

At the top of the grillage there are plates welded continuously to the upper member. For this case I have used rigid links with out any releases to model the composite action. Seems to give overall accurate behavior although this method requires some work outside of Risa to check the composite section properties of the stiffened plate composed of wide flanges welded to the underside of the plate.

RE: Risa 3D - Rigid Links

Risa Help Document

"The two beams are each modeled at their correct centerline elevations. Both the top and bottom members need to have a joint at the point of intersection. The distance between the joints would be half the depth of the top beam plus half the depth of the bottom beam. The method to model this is to connect joint A to joint B is with a rigid link. The member end releases at the A or B end can be used to control which degrees of freedom get transferred between the beams. For example, if Beam A is free to pivot over Beam B then you would apply a Pin end release to the top of the rigid link, and a Fixed end release to the bottom of the rigid link. Don't pin both ends of the rigid link though, because then there can be no shear transfer between the beams. See Rigid Links in the Modeling Tips section to learn how to create rigid links."

The help file answered my question, I just need to investigate if it matters which end of the rigid link is has the moments released and which remains fixed.

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