Are there limits to the types of composite beams sections for which VABS can calculate accurate Vlasov torsion and warping constants?

  1. Hart Honickman

    I recently used VABS/PreVABS to carry out a parametric study of a specific type of built-up hybrid composite beam. For the most part, the beam is a simple laminated bar having a quasi-rectangular cross-section; however, there are some additional components in the cross-section that cause it to behave differently than just a simple laminate. I can’t go into too much detail regarding the beam’s construction architecture or material composition, but I can say that it tends to behave somewhat like a closed rectangular box section, despite the fact that it is in fact a solid prismatic bar.

    I was able to reconcile most of the VABS results with my own analytical calculations and empirical test data (bending stiffnesses, torsional stiffnesses, transverse shear stiffnesses, etc.), and I have good confidence in most of these results. However, for some configurations of the beam section, I found the Vlasov warping constants from VABS to be significantly larger than I would have expected (approximately five times larger than I would have expected for some of the beam configurations), and in some special cases, I found the Saint-Venant torsional stiffness values from VABS to be quite high as well (higher than my analytical calculations, as well as empirical test data).

    I recently read the article: W. Yu, D. H. Hodgesb, V.V. Volovoib, and E.D. Fuchs, “A generalized Vlasov theory for composite beams”, Thin-Walled Structures, 43(9):1493–1511, 2005, doi:10.1016/j.tws.2005.02.003. That article indicated that the VABS generalized Vlasov theory should not be used for closed sections. As such, I am wondering if this explains why my Vlasov analysis results seem to be erroneously high as well. As I said, the section that I am studying is a solid bar; however, due to its material composition and construction architecture, it behaves very much like a closed rectangular box section. Is it possible that the Saint-Venant torsional stiffness of such a section would be over-predicted by VABS as well?

    Thanks in advance for your help with this.

  2. Wenbin Yu

    Torsional stiffness of such section should be ok. The Vlasov term is not carefully validated for closed section. If you have concern, feel free to send us your model and we can verify it for you. 

  3. Hart Honickman

    Thanks for your response. Unfortunately, I am unable to share the technical data at this time, but it is good to know that there may be a known scientific basis for the discrepancy that I am seeing.

    To be clear, are there some cases in which VABS gives accurate Vlasov terms for closed sections, or is it generally unreliable for such geometries (other than closed sections that have a negligible closed area)?

  4. Wenbin Yu

    In principle, it should work. We just need a case that it will not work for us to debug the theory and the code. ---- Emailed forum response from