# Calculix Bolt Pretension **URL:** \ **Category:** Uncategorized\ **Created:** [December 19, 2024, 9:06am UTC](https://calculix.discourse.group/t/calculix-bolt-pretension/2527 "2024-12-19T09:06:16Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![ademyilmaz](https://avatars.discourse-cdn.com/v4/letter/a/eb8c5e/32.png) [@ademyilmaz](https://calculix.discourse.group/u/ademyilmaz)\ **Post date:** [December 19, 2024, 9:06am UTC](https://calculix.discourse.group/t/calculix-bolt-pretension/2527/1 "2024-12-19T09:06:16Z")
Hello, I am trying to do a 2D bolt analysis in Calculix. The analysis has 2 steps. In the first step, I give preload using a pre-tension element. In the second step, I give the temperature of the entire node. But I expect is a decrease in preload in the second step, I read the reaction forces, but contrary to what I expected, an increase in preload occurs. The step part is as follows. Can you help me ? \*PRE-TENSION SECTION,ELEMENT=852,NODE=1052,NONLINEAR 0.,1.,0. \*INITIAL CONDITIONS,TYPE=TEMPERATURE NALL,22 \*Step, Nlgeom \*Static \*Cload 1052,1,640000 \*Node file,output=2D RF, U \*El file,output=2D S, E \*NODE PRINT,NSET=Ncoup1,TOTALS=YES RF \*NODE PRINT,NSET=Ncoup2,TOTALS=YES RF \*End step \*Step, Nlgeom \*Static \*Boundary,FIXED 1052,1,1 \*TEMPERATURE,OP=NEW NALL,300. \*Node file,output=2D RF, U \*El file,output=2D S, E \*NODE PRINT,NSET=Ncoup1,TOTALS=YES RF \*NODE PRINT,NSET=Ncoup2,TOTALS=YES RF \*End step ---
**Author:** ![ademyilmaz](https://avatars.discourse-cdn.com/v4/letter/a/eb8c5e/32.png) [@ademyilmaz](https://calculix.discourse.group/u/ademyilmaz)\ **Post date:** [December 19, 2024, 9:08am UTC](https://calculix.discourse.group/t/calculix-bolt-pretension/2527/2 "2024-12-19T09:08:49Z")
For a better explanation, I am trying to set up the example given below with 2 flanges as 2d. The bolt connects the flanges. The preload value I read in the first step is correct. If I do not give additional temperature, the preload remains the same in the second step and is protected. [https://www.feacluster.com/CalculiX/ccx\_2.18/doc/ccx/input\_deck\_viewer.php?input\_deck=pret3](https://www.feacluster.com/CalculiX/ccx_2.18/doc/ccx/input_deck_viewer.php?input_deck=pret3) ---
**Author:** ![jbr](https://avatars.discourse-cdn.com/v4/letter/j/ecccb3/32.png) [@jbr](https://calculix.discourse.group/u/jbr)\ **Post date:** [December 19, 2024, 3:31pm UTC](https://calculix.discourse.group/t/calculix-bolt-pretension/2527/3 "2024-12-19T15:31:47Z")
> [@ademyilmaz](#): > > I give the temperature of the entire node. But I expect is a decrease in preload in the second step, I read the reaction forces, but contrary to what I expected, an increase in preload occurs. The step part is as follows. Can you help me ? Why are you expecting a decrease in bolt load with an increase in temperature? Expansion would simply increase your bolt load… ---
**Author:** ![ademyilmaz](https://avatars.discourse-cdn.com/v4/letter/a/eb8c5e/32.png) [@ademyilmaz](https://calculix.discourse.group/u/ademyilmaz)\ **Post date:** [December 20, 2024, 8:49am UTC](https://calculix.discourse.group/t/calculix-bolt-pretension/2527/4 "2024-12-20T08:49:42Z")
You are wrong, I installed the same model in Ansys. Preload should decrease due to temperature effect. ---
**Author:** ![jbr](https://avatars.discourse-cdn.com/v4/letter/j/ecccb3/32.png) [@jbr](https://calculix.discourse.group/u/jbr)\ **Post date:** [December 20, 2024, 2:17pm UTC](https://calculix.discourse.group/t/calculix-bolt-pretension/2527/5 "2024-12-20T14:17:20Z")
> [@ademyilmaz](#): > > You are wrong, I installed the same model in Ansys. Sure, I could be wrong. However, your statement lacks clarity and seems to overlook basic principles of thermal expansion. Simply stating that it works in Ansys isn’t a valid explanation. When you apply `*INITIAL CONDITIONS, TYPE=TEMPERATURE, NALL, 22` and then `*TEMPERATURE, OP=NEW, NALL, 300`, you are effectively raising the temperature, which causes the material to expand. In a bolted joint, this typically increases preload unless other factors—such as differential thermal expansion between the bolt and the surrounding material—are at play. What specific boundary conditions, material properties, or thermal expansion coefficients have you used in your Ansys model? These can significantly influence the results and might explain why you’re observing a decrease in preload. > [@ademyilmaz](#): > > Preload should decrease due to temperature effect. Have you also compared your Ansys results with a hand calculation or a simplified analytical model? That might help clarify whether the preload should decrease or increase. If you have stress/strain plots or reaction force outputs to support your claim, please share them. Otherwise, your response remains conjecture unsupported by fundamental principles.