Linear Buckling Analysis

Workshop 7.1 - Goals

-The goal in this workshop is to verify linear buckling results in ANSYS Workbench. Results will be compared to closed form calculations from a handbook.

-Next we will apply an expected load of 10,000 lbf to the model and determine its factor of safety.

-Finally we will verify that the structure will not fail structurally before buckling occurs.

Workshop 7.1 - Assumptions

-The model is a steel pipe that is assumed to be fixed at one end and free at the other with a purely compressive load applied to the free end. Dimensions and properties of the pipe are:

-OD = 4.5 in ID = 3.5 in. E = 30e6 psi, I = 12.7 in^4, L = 120 in.

-In this case we assume the pipe conforms to the following handbook formula where P’ is the critical load:

-For the case of a fixed / free beam the parameter K = 0.25.

Using the formula and data from the previous page we can predict the buckling load will be:

Workshop 7.1 – Project Schematic

1.Double click Static Structural in the Toolbox to create a new system.

2.Drag/drop a “Linear Buckling” system onto the “Solution” cell of the static structural system.

-When the schematic is correctly set up it should appear as shown here.

The “drop target” from the previous page indicates the outcome of the drag and drop operation. Cells A2 thru A4 from system (A) are shared by system (B). Similarly the solution cell A6 is transferred to the system B setup. In fact, the structural solution drives the buckling analysis.

Verify that the Project units are set to “US Customary (lbm, in, s, F, A, lbf, V).

Verify units are set to “Display Values in Project Units”.

3.From the static structural system (A), double click the Engineering Data cell.

4.To match the hand calculations referenced earlier, change the Young’s modulus of the structural steel.

a.Highlight “Engineering Data”.

b.Highlight Structural Steel.

c.Expand “Isotropic Elasticity” and modify Young’s Modulus to 3.0E7 psi.

Note : changing this property from “Engineering Data” does not effect the stored value for Structural Steel in the General Material library. To save a material for future use we would “Export” the properties as a new material to the material library. Since we only need the value for this workshop we will not do that in this case.

5.From the static structural system (A), RMB the Geometry cell and “Import Geometry”. Browse to the file “Pipe.x_t”.

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