linear static analysis & buckling analysis

[nzaem1992]

i am very confuse ... if i use inventor simulation for make ? .. what is difference between buckling analysis & linear static analysis ??

[John_Holtz · Accepted solution]

Hi @nzaem1992 

First, Inventor Stress Analysis does not perform a buckling analysis, does it? You can perform a buckling analysis in Inventor Nastran though.

The differences are as follows:

• Linear stress calculates stress and displacement due to the applied loads. It does not give any indication if the model will buckle or not.
• Buckling calculates how much load is required to cause the model to buckle.

For a model like your tower, I would think that you need to check both. You will use the stress results to decide if they are above the allowable (according to whatever building code you are using for the structure). The building code may not include a buckling check. Since buckling can occur at loads (and therefore stresses) that are lower than the allowable, the structure should be checked for buckling.

[nzaem1992]

sir .. i am new in nastran analysis .. the result of nastran give me eigenvalues .. i know eigenvalues  multiplied to force

give me critical buckling load ,, i have more forces not just one force .. my second question .. how can i ensure my model not fail by buckling ,,, thank you 

[John_Holtz]

Hi @nzaem1992 

Your first question is not a question. Your statement is correct: the eigenvalue multiplies all of the loads in the model: gravity, different forces, and so on. If there is a load that does not change in reality (like gravity), then you can use the procedure described in the Simulation Mechanical documentation for Critical Buckling Load:

---

Include constant loads

Critical buckling scales all applied loads by the calculated buckling multiplier. In some situations, you might want to scale the live loads (like pressure) while other loads (like gravity) are not scaled. Use the following procedure if the constant loads are significant and must be included.

1. Estimate what the buckling multiplier will be, either from experience, doing a hand calculation, or running the analysis. Call it the last buckling multiplier.
2. Change the constant loads to the quantity (constant load/last buckling multiplier) and leave the live loads at their rated value.
3. Run the buckling analysis.
4. If the result of the new buckling calculation gives the same buckling multiplier, then the solution is okay. The constant loads at the buckling result is (constant load/last buckling multiplier)*(new buckling multiplier) = constant load, and the variable load that causes buckling is (variable load)*(new buckling multiplier).
5. If the result of the new buckling calculation gives a different buckling multiplier, replace the last buckling multiplier with the new value. Repeat steps 2 through 5.

Since critical buckling is an eigenvalue solution, the displacement results show the buckling mode shape. The magnitude of the displacements is meaningless. Likewise, there are no stress or strain results from a critical buckling analysis.

---

See this post for the answer to your second question 😁. https://forums.autodesk.com/t5/inventor-nastran-forum/buckling-analysis/td-p/9486515