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VABS, A Unique Tool for Modeling Composite Beams

Wenbin Yu's picture

I am glad to introduce VABS, a unique software tool for modeling of composite structures having one dimension much larger than the other two dimensions such as helicopter rotor blades, wind turbine blades, HALE wings, and bridges.


Despite this simple geometry, these slender components could be made out of virtually any material and have very complex internal construction such as modern rotor blades having skins made of hundreds of composite layers, web and D-spar made of active materials and a core filled with foam materials. The efficient, high-fidelity cross-sectional analysis tool, VABS, is capable of realistic modeling of initially curved and twisted anisotropic beams with arbitrary sectional topology and materials. Relative to 3D analyses, two to three orders of magnitude in computing time can be saved using VABS, with little loss of accuracy. VABS  is currently used extensively in the rotorcraft industry. Researchers from other industry also begin to use VABS.


The unique features of the VABS methodology are: (1) use of the variational asymptotic method (VAM) as the mathematical foundation for dimensional reduction, incorporating both mathematical rigor and engineering simplicity; (2) absence of ad hoc kinematic assumptions, common in other approaches; (3) decoupling of the original 3D nonlinear problem into two sets of analyses: 2D, linear, cross-sectional analysis and 1D, nonlinear global beam analysis. This allows the global beam analysis to formulate exactly and intrinsically as a general 1D continuum over the reference line and confines all approximations to the cross-sectional analysis, the accuracy of which is guaranteed to be the best by VAM.

Please for more details on VABS.



Wenbin Yu


I would like to ask the following question regarding VABS.


   Is VABS capable of accurately predicting transverse shear and  normal stress across the thickness of laminated composite  beam without integrating the equilibrium equations?.





Wenbin Yu's picture

Dear Subramanian,

Thanks for your interest. Yes VABS can accurately predict transverse shear and normal stresses without integrating the equilibrium equations. We did a 20-layer example. VABS calculates almost the same results as ANSYS using 3D elements. Please refer to the following paper for more details.

Yu, W. and Hodges, D. H.: "Generalized Timoshenko Theory of the Variational Asymptotic Beam Sectional Analysis, " Journal of the American Helicopter Society, vol. 50, no. 1, 2005, pp. 46-55. (pdf)


Dear Ben,

    Your website says "either too simple (CLPT) or too complex (higher order layerwise theories). ........................... thepredictability is not guranteed  because".  This seems to be incorrect. I have developed a set of simple and highly accurate higher oder shear deformation theories for the analysis of laminated composite structures.



Wenbin Yu's picture




Again, I appreciate your comment. The sentence you pointed out states that
based on a priori assumptions a whole spectrum of models can be developed
ranging from the very simple one, Classical Lamination Theory (CLT), to very
complex ones, Higher-Order Layerwise Theories (HOLT). It does not say that
there are no models having better accuracy than CLT and simpler than HOLT. Of
course there are some models in between such as first-order shear-deformation
theory, higher-order shear deformation theory, zigzag theories. This discussion
is more relevant to VAPAS, a sister code of VABS. We have compared our code with
a zigzag-based model in ref. [1], the results of which support the sentence you
pointed out. We have plans to compare with the Generalized Unified Formulation
of Prof. Luciano Demasi at SDSU in the near future. If you are interested, I will
be very glad to collaborate with you to test the performance of either VABS or
VAPAS against your models.



[1] Yu, W.; Kim, J. S.; Hodges, D. H.; and Cho, M.: "Assessment of Two
Reissner-Mindlin Type Models for Composite Laminated Plates," Aerospace
Science and Technology
, vol. 12, no. 5, 2008, pp. 408-417. (pdf)

Dear Dr.Bin,

Thanks a lot for your clarifications. Currently I am doing research in the field of  higher order shear deformation  theories, I am unable to share my results with you.




If your desire is to have the transverse stresses a priori and without the integration of the indefinite equilibrium equations you can use a mixed vartiational statement such as Reissner's.

Wenbin Yu's picture


Nice to see you have also signed up for Imechanica. How is your new job? Must be very busy!



Nice to see you too. The new job makes me busy...but who is not busy?

Wenbin Yu's picture



If you are interested, you can request VABS through

The limited version, VABS Lite, is free and the full version can be evaluated for free for three months.



attash3099's picture


please answer me,in 2D analysis of cross section,meshed cross section analysisi of abaqus is better or vabs?wich one,have better result at warpping?(in and out warping)

please answer me with reson,or test,or camparsion analysis witheen abaqus and vabs?

Wenbin Yu's picture

I am not familar with ABAQUS and do not have access to this software at this moment. However, you are welcome to request VABS to compare for yourself. I am pretty confident that VABS will be better. I will appreciate if you can share your conclusion with us.  I am not coming to this site very often. If somebody want a quicker reponse, please send me an email.

Wenbin Yu's picture

A student just made a chart for comparing the sectional capability of ABAQUS and VABS. Please refer to for more details.


If you are interested in the assessment of VAPAS via GUF, I and professor Yu published a conference article on the subject:


L. Demasi, Yu W., “
Assess the Accuracy of the Variational Asymptotic Plate and Shell Analysis
(VAPAS) Using the Generalized Unified Formulation (GUF)
”, Presented at
the 50th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics & Materials
Conference, Palm Springs, California, 4-7 May 2009





If you are interesting in learning more about this powerful technique you can see the following references:


1 ) Generalized Unified Formulation applied to displacement-based theories for composire structures  (Advanced Shear Order Deformation Theories, Zig Zag Theories and Layerwise Theories; note that an infinite number of theories is included in the GUF framework and all these formulations can be generated from SIX invariant  1 X 1 arrays):  

L. Demasi, An Invariant
Model for any Composite Plate Theory and FEM Applications: the Generalized
Unified Formulation
, Presented at the 50th AIAA/ASME/ASCE/AHS/ASC
Structures, Structural Dynamics & Materials Conference, Palm Springs,
California, 4-7 May 2009.


2) Generalized Unified Formulation applied to the mixed theories based on Reissner's Mixed Variational Theorem (RMVT)  (formulation in which all the mixed theories are generated from 13 invariant 1X1 arrays): 

L. Demasi6 mixed plate theories based on the
Generalized Unified Formulation. Part I: Governing Equations
Structures, Vol. 87, (2009), 1-11.

3) Generalized Unified Formulation applied to  RMVT-based Layerwise theories for composite structures: 

L. Demasi, 6 mixed plate theories based on the
Generalized Unified Formulation. Part II: Layerwise theories
Structures, Vol. 87, (2009), 12-22


4)  Generalized Unified Formulation applied to RMVT-based Advanced Mixed High Order Shear Deformation theories and quasi-layerwise theories:

L. Demasi, 6 mixed plate theories based on the
Generalized Unified Formulation. Part III: Advanced Mixed High Order Shear
Deformation Theories
Composite Structures, Vol. 87, (2009), 183-194


5) Generalized Unified Formulation applied to RMVT-based Zig-Zag theories:

 L. Demasi, 6 mixed plate theories based on the
Generalized Unified Formulation. Part IV: Zig-Zag Theories
Structures, Vol. 87, (2009), 195-205


6) RMVT-based theories and their numerical performances compared against the elasticity solution:

 L. Demasi, 6 mixed plate theories based on the
Generalized Unified Formulation. Part V: Results
Composite Structures,
Composite Structures, Vol. 88, (2009), 1-16.


If you are interested in a PhD opportunity on these and other topics please contact me at the following address 






Respected Professor,

I know i am bit late to add to this discussion but Please reply if possible as i am knew to VAM and really want to learn.

While going through your papers (''Asymptotic construction of Reissner-like composite plate theory with accurate strain recovery'' and few others) ,I noticed that you ususally do some transformation into reissner model although in the Neoclassical plate theory by Hodges ("Application of the Variational-Asymptotical Method to Laminated Composite Plates") they included the shear strain in the 3-D strain term itself ,In the similar manner 3-D elasticity formulation is done in a paper by Peereswera of inter-laminar stresses in composite honeycomb sandwich panels under mechanical loading using Variational Asymptotic Method) 

So i just want to understand are these two different theories or the same ,if same then why do we need to go through transformation part. 

also some links in above discussion doesn't work any more if possible plase provide updated links.

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