VABS force/moment derivative terms

  1. Meryem Nisa Ataç

       While I am working on VABS, I get confused about when we should include derivative terms since there is no example problem provided in example files. I get internal forces/moments from GEBT and put them into the VABS input file. Even if the load is distributed, as far as I know, GEBT does not give derivative terms of forces/moments. Does it mean we should not only put internal forces obtained by GEBT but also the derivatives of them (by performing hand calculations) when we have distributed load?

       I would appreciate it if you could help me handling this error.

       Kind regards..

  2. Aref Fahadan Hajipour

    Hi friend..

    I need VABS . I search it but i can't find it's codes . Can you send me yours?! .. I will be grateful ..

    My E_mail:

     Kind regards..

  3. AnalySwift LLC

    Hello Araf,

    Thank your or your interest in VABS.  You may request the VABS code from or access it online through the following links below.

    1. Request to join the VABS group at  Here you will be asked for some very basic export information to join the group and access the software (also below, if more convenient to reply directly):
      • Names of engineer(s) evaluating VABS
      • Organization name 
      • Physical address of organization where VABS will be used
      • Type of entity (private, government, public, military)
      • Nature of business (what does your organization do?)
      • Number of years organization has been in business
      • Specific end use of VABS (what will you use VABS for?)
      • Civilian or Military Use (or both)?
      • Should we also send PreVABS (preprocessor to VABS, which is not yet part of the cdmHUB)?
    2. Once approved, launch VABS from the following link:
  4. Wenbin Yu

    Nisa, the derivatives for distributed forces/moments are applied loads. They are given. You can evaluate them by hand. They are different from those obtained by GEBT, those are internally force/moment resultants.

  5. Meryem Nisa Ataç

    Thank you Prof. Yu. I am going to prepare a simple input file for it.

    Kind regards...

  6. Meryem Nisa Ataç

    For example, beam in the attached file, we have uniform distributed load f. As far as I understand when we want to solve this problem, we can use F1 M1 M2 M3 F2 F3 (let’s say large_F) or f1 f2 f3 m1 m2 m3 (let’s say small_f).

    (I use the same notations in the VABS-manual.)

    Large_Fs are the internal loads applied in the cross-section. They can be obtained from GEBT by writing the external loads in the input file. This is how I perform my analyses.

    What about small_fs? As I understand from what you said, they are the external loads; but I do not get the logic behind the giving external loads in the cross-section since in VABS we do not define the whole model. If they are the external loads, are they calculated by f1=f*x (x=location of the cross-section we are interested)? If no, how should we calculate these small_fs?

    At the end, large_Fs and small_fs give the same stress output, right?

      Thank you..

    beam model

  7. Wenbin Yu

    Internal forces/moments will be the major contributors. Small f/m and their derivatives are also needed to recover stresses but not major contributor. You need to read the recovery theory about VABS to find out why. Briefly, when I transform to Timoshenko model, we need to use 1D equilibrium equation, that introduce f/m into the VABS formulation.