# Issue with Tie Constraint on Shells **URL:** \ **Category:** General Questions\ **Created:** [February 10, 2024, 12:29am UTC](https://prepomax.discourse.group/t/issue-with-tie-constraint-on-shells/1493 "2024-02-10T00:29:20Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![DIYAnalyst](https://yyz2.discourse-cdn.com/free1/user_avatar/prepomax.discourse.group/diyanalyst/32/2682_2.png) [@DIYAnalyst](https://prepomax.discourse.group/u/DIYAnalyst)\ **Post date:** [February 10, 2024, 12:29am UTC](https://prepomax.discourse.group/t/issue-with-tie-constraint-on-shells/1493/1 "2024-02-10T00:29:20Z")
Hi, I’m relatively new to FEA in general and very new to PrePoMax, Calculix and Salome. I’ve been working on a ground-mounted solar panel fixture, but am having repeatable issues using tie constraints between different shell components. I’ve created tie constraints both manually and with “search contact pairs”, but the issue occurs with both where the tie constraint is seemingly ignored and the vertical column detaches from the fixture. The issue I’m repeatedly facing is shown below: ![image](https://global.discourse-cdn.com/free1/uploads/prepomax/original/2X/1/1e6415145c8cc2597190d83fc6675f0fb8ea108a.jpeg) Being a new user I’m not able to upload my pmx file, but can send it other ways if needed. I’m using PrePoMax 2.0.3 Dev, but it also occurs on the stable release. Mesh was made in Salome. Any ideas? Thanks, ---
**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:** [February 10, 2024, 7:47am UTC](https://prepomax.discourse.group/t/issue-with-tie-constraint-on-shells/1493/2 "2024-02-10T07:47:41Z")
maybe change the tolerance or moving column part to half of flange thickness can solve the problem. ---
**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:** [February 10, 2024, 8:25am UTC](https://prepomax.discourse.group/t/issue-with-tie-constraint-on-shells/1493/3 "2024-02-10T08:25:53Z")
It’s sometimes better to use compound parts. But if you want to use tie constraints, make sure that adjustment is enabled and that tolerance is properly set. ---
**Author:** ![AleksanderS](https://avatars.discourse-cdn.com/v4/letter/a/ebca7d/32.png) [@AleksanderS](https://prepomax.discourse.group/u/AleksanderS)\ **Post date:** [March 18, 2025, 10:34am UTC](https://prepomax.discourse.group/t/issue-with-tie-constraint-on-shells/1493/4 "2025-03-18T10:34:29Z")
How do you use compound parts correctly? Do these need to me merged in CAD, the Geometry step of PrePoMax or at the FE Model step of PrePoMax? ---
**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:** [March 18, 2025, 11:02am UTC](https://prepomax.discourse.group/t/issue-with-tie-constraint-on-shells/1493/5 "2025-03-18T11:02:59Z")
You don’t have to merge in CAD, you can import separate parts, select them, right-click and choose _Create Compound Part_ in the _Geometry_ tab. ---
**Author:** ![Matej](https://avatars.discourse-cdn.com/v4/letter/m/a698b9/32.png) [@Matej](https://prepomax.discourse.group/u/Matej)\ **Post date:** [March 18, 2025, 1:23pm UTC](https://prepomax.discourse.group/t/issue-with-tie-constraint-on-shells/1493/6 "2025-03-18T13:23:50Z")
You create compound parts only if you need them. You need them if you want to split a body into separate but connected bodies. Usually, this is used to apply different materials or to be able to perform structured mesh. If you have separate parts from the design and would like to model them as connected, you can merge them in CAD or create a compound. In this case, there is no difference. ---
**Author:** ![AleksanderS](https://avatars.discourse-cdn.com/v4/letter/a/ebca7d/32.png) [@AleksanderS](https://prepomax.discourse.group/u/AleksanderS)\ **Post date:** [March 18, 2025, 1:32pm UTC](https://prepomax.discourse.group/t/issue-with-tie-constraint-on-shells/1493/7 "2025-03-18T13:32:36Z")
I have now used to create a compound out of three shells. However they dont stay together. Any ideas? ---
**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:** [March 18, 2025, 1:34pm UTC](https://prepomax.discourse.group/t/issue-with-tie-constraint-on-shells/1493/8 "2025-03-18T13:34:23Z")
Depending on how the parts are connected, compound creation may fail to merge them: [Deformation in 2 or more bodies - #10 by Matej](https://prepomax.discourse.group/t/deformation-in-2-or-more-bodies/524/10) ---
**Author:** ![Matej](https://avatars.discourse-cdn.com/v4/letter/m/a698b9/32.png) [@Matej](https://prepomax.discourse.group/u/Matej)\ **Post date:** [March 18, 2025, 4:59pm UTC](https://prepomax.discourse.group/t/issue-with-tie-constraint-on-shells/1493/9 "2025-03-18T16:59:25Z")
For shells, the only real scenario in which the compound is needed is a non-manifold geometry. In other scenarios, a CAD merge is a better solution.