# \*ERROR in add\_sm\_st: coefficient should be 0 **URL:** \ **Category:** General Questions\ **Tags:** results\ **Created:** [December 2, 2025, 6:16pm UTC](https://prepomax.discourse.group/t/error-in-add-sm-st-coefficient-should-be-0/3114 "2025-12-02T18:16:19Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![FEANOOB](https://avatars.discourse-cdn.com/v4/letter/f/b5a626/32.png) [@FEANOOB](https://prepomax.discourse.group/u/FEANOOB)\ **Post date:** [December 2, 2025, 6:16pm UTC](https://prepomax.discourse.group/t/error-in-add-sm-st-coefficient-should-be-0/3114/1 "2025-12-02T18:16:19Z")
Hello All, I am trying to evaluate web buckling in the deep beam shown here. I have two compound parts, the deep beam with stiffeners and a smaller beam that applies equal forces on both sides to contact the top flange of the deep beam and develop buckling and stress in the web. I am using a reference point at each end of the small beam, tied to the outline of the end face, and applying a boundary condition at those reference points that restrains all degrees of freedom except translation in the Z direction. I have tried several approaches but I still cannot get the analysis to run properly. I ran a frequency analysis and it completed without issues, and the mode shapes appear reasonable. Let me know if you need more details. ![image](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/3/36e46fcd53e385fa8b8cf50591985c77398f933d.jpeg) I have attached the model below as well. Thanks for any help/suggestions > **[Web\_Buckling.pmx](https://drive.google.com/file/d/1ODwvkG8noMKTKdZ8YrttKSKgbZnEm1sy/view?usp=sharing)** > > Google Drive file. ---
**Author:** ![Matej](https://avatars.discourse-cdn.com/v4/letter/m/a698b9/32.png) [@Matej](https://prepomax.discourse.group/u/Matej)\ **Post date:** [December 2, 2025, 7:31pm UTC](https://prepomax.discourse.group/t/error-in-add-sm-st-coefficient-should-be-0/3114/2 "2025-12-02T19:31:05Z")
I did not test your model, but using rigid connections and shell elements in Caclulix is not advisable. From your description, I think you can easily replace them with boundary conditions. It should help to remove one possible cause of problems. ---
**Author:** ![ANYS](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/anys/32/7737_2.png) [@ANYS](https://prepomax.discourse.group/u/ANYS)\ **Post date:** [December 2, 2025, 7:50pm UTC](https://prepomax.discourse.group/t/error-in-add-sm-st-coefficient-should-be-0/3114/3 "2025-12-02T19:50:38Z")
If you are planning to perfom some initial test to check Prepomax response and the model itself is not much important, I would suggest you to follow the document rcm-2017-4-ar-1.pdf that can be downloaded freely after registration in the CTICM webpage. > **[Notre librairie | CTICM](https://www.cticm.com/notre-librairie/?fwp_search=l%E2%80%99Int%C3%A9raction%20)** > > Un entrepôt géant d’information pour tous les acteurs de la construction métallique.   Pour télécharger librement les ressources gratuites, vous devez être connecté. L’inscription est rapide et gratuite.   Retrouvez ensuite vos produits... ![imagen](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/9/9cc7bac0df088dc1ab1a453679cdf119a31c248b.png) Your section looks like very familiar and there you can find some guidance and the reference solution for this kind of problem. It can help you to achieve the right set up for future projects. ![imagen](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/2/217741bd2a9cef71b581a45add4432be4a640495.jpeg) ---
**Author:** ![synt](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/synt/32/4658_2.png) [@synt](https://prepomax.discourse.group/u/synt)\ **Post date:** [December 2, 2025, 8:02pm UTC](https://prepomax.discourse.group/t/error-in-add-sm-st-coefficient-should-be-0/3114/4 "2025-12-02T20:02:34Z")
your model is unstable probably, trying to add torsional w/o rotational restraint at both ends of reference point may solve the problem. \*edited (add similar problem examples from my previous test) ![2020-02-19 01_15_17-Window](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/a/a49c10cf86c0aa72e77df1b769294cbd501295c3.png) ---
**Author:** ![Gunnar](https://avatars.discourse-cdn.com/v4/letter/g/ed655f/32.png) [@Gunnar](https://prepomax.discourse.group/u/Gunnar)\ **Post date:** [December 2, 2025, 8:09pm UTC](https://prepomax.discourse.group/t/error-in-add-sm-st-coefficient-should-be-0/3114/5 "2025-12-02T20:09:50Z")
It works for me if i change the contact method to node to surface. ---
**Author:** ![FEANOOB](https://avatars.discourse-cdn.com/v4/letter/f/b5a626/32.png) [@FEANOOB](https://prepomax.discourse.group/u/FEANOOB)\ **Post date:** [December 2, 2025, 8:24pm UTC](https://prepomax.discourse.group/t/error-in-add-sm-st-coefficient-should-be-0/3114/6 "2025-12-02T20:24:41Z")
This works perfectly @Gunnar , THANK YOU! Can you please elaborate on the difference between both methods and why it makes a difference ? ---
**Author:** ![FEANOOB](https://avatars.discourse-cdn.com/v4/letter/f/b5a626/32.png) [@FEANOOB](https://prepomax.discourse.group/u/FEANOOB)\ **Post date:** [December 2, 2025, 8:26pm UTC](https://prepomax.discourse.group/t/error-in-add-sm-st-coefficient-should-be-0/3114/7 "2025-12-02T20:26:00Z")
Thanks @Matej , I eliminated the rigid connections and changed for boundary conditions and applied my load as a traction load and that worked as well. Thank you! ---
**Author:** ![FEANOOB](https://avatars.discourse-cdn.com/v4/letter/f/b5a626/32.png) [@FEANOOB](https://prepomax.discourse.group/u/FEANOOB)\ **Post date:** [December 2, 2025, 8:26pm UTC](https://prepomax.discourse.group/t/error-in-add-sm-st-coefficient-should-be-0/3114/8 "2025-12-02T20:26:37Z")
@ANYS These are some great references for what exactly I am doing here. Appreciate you sharing 🙂 ---
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [December 2, 2025, 11:25pm UTC](https://prepomax.discourse.group/t/error-in-add-sm-st-coefficient-should-be-0/3114/9 "2025-12-02T23:25:22Z")
This error usually means there’s an overconstraint in the model - some constraints (rigid bidy, tie, contact, BCs) overlap. > [@Matej](#): > > using rigid connections and shell elements in Caclulix is not advisable And unfortunately, not possible with CalculiX 2.23. > [@FEANOOB](#): > > Can you please elaborate on the difference between both methods and why it makes a difference ? It’s described in detail in CalculiX User’s Manual, but in short words, node to surface contact acts between a slave node and a master face while surface to surface contact acts between a slave face (its integration point) and a master face. The latter is preferred in most cases and leads to more uniform contact pressure distribution and less strict master-slave relationship. ![IMG_9501](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/0/0ee79bac93010958df113c885a1491b0cfe362c5.jpeg) ![IMG_9502](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/4/41056784c5b06024d26ee9b57175a3f221b73175.jpeg) ---
**Author:** ![FEANOOB](https://avatars.discourse-cdn.com/v4/letter/f/b5a626/32.png) [@FEANOOB](https://prepomax.discourse.group/u/FEANOOB)\ **Post date:** [December 3, 2025, 1:34am UTC](https://prepomax.discourse.group/t/error-in-add-sm-st-coefficient-should-be-0/3114/10 "2025-12-03T01:34:50Z")
Thanks for your reply @FEAnalyst and for the great explanation. ---
**Author:** ![synt](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/synt/32/4658_2.png) [@synt](https://prepomax.discourse.group/u/synt)\ **Post date:** [December 3, 2025, 5:08am UTC](https://prepomax.discourse.group/t/error-in-add-sm-st-coefficient-should-be-0/3114/11 "2025-12-03T05:08:24Z")
i’m not open or even running the models attached, it’s shell element contact problems. Many knots generated there at intersection and may conflict with penalty contacts, separated the flange and web’s part and reconnect with tie constraints to eliminate this condition. ---
**Author:** ![Matej](https://avatars.discourse-cdn.com/v4/letter/m/a698b9/32.png) [@Matej](https://prepomax.discourse.group/u/Matej)\ **Post date:** [December 3, 2025, 9:23am UTC](https://prepomax.discourse.group/t/error-in-add-sm-st-coefficient-should-be-0/3114/12 "2025-12-03T09:23:30Z")
> [@FEAnalyst](#): > > And unfortunately, not possible with CalculiX 2.23. This is news to me. Is this no longer supported? ---
**Author:** ![FEAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/feanalyst/32/688_2.png) [@FEAnalyst](https://prepomax.discourse.group/u/FEAnalyst)\ **Post date:** [December 3, 2025, 9:29am UTC](https://prepomax.discourse.group/t/error-in-add-sm-st-coefficient-should-be-0/3114/13 "2025-12-03T09:29:05Z")
Yeah, unfortunately: [Rigid body cannot be used with shells at all in ccx 2.23 · Issue #134 · Dhondtguido/CalculiX · GitHub](https://github.com/Dhondtguido/CalculiX/issues/134) But I asked Guido about this and he said he would check if using rigid body constraints with shells can be allowed for linear analyses.