Grillage Model In Plane Deformation

[EngJoe]

I'm fairly new here to the forum but so far it's been pretty useful. Here is a question that I have:

I've been reading up on grillage modelling of bridge decks. From what I understand, the grillage model has three degrees of freedom; out of plane translation, and rotation about both in-plane axis. Is it possible to use a grillage model for in plane deformations caused by forces such as thermal expansion/contraction by adding some additional degrees of freedom on my grillage elements? If I model my support conditions correctly for in plane deformations, would the grillage model predict in-plane deformations correctly?

Any help would be great. Thank you.

 

[IDS]

It depends on the software you are using. If it is a pure grillage program then the in plane actions won't be included in the analysis, but if you are using a general purpose frame analysis or FEA program then you can set up the analysis as a space frame and everything will be included.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[EngJoe]

Thanks for the reply Doug. My question was not really whether the in plane deformation will be calculated or not by the model. My question was more to the theory and accuracy of the grillage model when it comes to in-plane deformations. From the literature I've read it seems like a grillage model is never used for in-plane deformations. But none of the text I've read explains the theory as to why not.

I'm thinking the in-plane deformations of a grillage model are inaccurate compared to a full 3D FE model because the stiffness of the plate being modeled as a grillage along the in-plane surface is not correctly modeled by just longitudinal and transverse members?

Any other thoughts?

 

[IDS]

I'm thinking the in-plane deformations of a grillage model are inaccurate compared to a full 3D FE model because the stiffness of the plate being modeled as a grillage along the in-plane surface is not correctly modeled by just longitudinal and transverse members?

Yes, in fact a grillage model won't have any output of in-plane deformations, or any provision for input of in plane forces or deflections. If it is a true grillage these things do not appear in the analysis.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/