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This page is devoted to frequently asked questions (FAQ |
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How are structures with cables analyzed for buckling?
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) related to buckling. |
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Analysis
Why do my hand calculations not match linear-buckling results?
ANSWER: Structural objects should be meshed before running linear-buckling analysis such that the software may accurately capture the instability modes under the specified set of loading conditions.
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What happens analytically when a member reaches buckling capacity during nonlinear buckling analysis?
ANSWER: The analysis process typically experiences convergence problems at the buckling limit.
What is the process for buckling analysis of a structure with cables?
ANSWER: To analyze buckling in a structure with cables, nonlinear analysis should be run to determine the structural stiffness at the end of a nonlinear case. Then run buckling analysis Buckling analysis may then be run, starting at the end of this nonlinear case.
In nonlinear P-Delta Large Displacement analysis, what happens to the solution if a member reaches its buckling capacity?
The analysis will typically run into convergence problems.
Does
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buckling analysis include the effect of shear
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deformation?
ANSWER: Yes, the buckling analysis included includes the effect of shear deformationsdeformation. For models in which shear deformation governgoverns, this may cause keep the calculated buckling factors not to match from matching the theoretical critical load. The user can eliminate the impact influence of shear deformations deformation on the buckling behavior may be eliminated by setting large property modifiers for to shear areas in directions 2 and 3 directions.
Buckling factors
Why
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does lateral-force
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application not reduce the buckling factors
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of a
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cantilevered column?
Expanded question: I modeled a simple cantilever column and determined its buckling load. Then, in a different analysis, I applied lateral load to the column and determined the buckling load at the end of lateral-load analysis. I got Regardless of lateral-load magnitude, the same buckling load (no matter how large is the lateral load). I expected is generated though a smaller buckling load is expected. Am I making a mistake?
Answer: This behavior is expected for the model and loading you have described. For your particular model, the ANSWER: For a cantilevered-column model, linear buckling analysis would yield produce buckling factors independent of the from applied lateral load. This is because the lateral load , in this particular case, lateral load does not affect the geometric stiffness of the structure.
You can still capture the softening of the structure due to applied lateral load. However, you would need to run nonlinear analysis The structural softening which occurs under lateral-load application may still be captured. However, nonlinear analysis must be run with P-Delta and large displacement effects and then plot the applied load against the Large Displacement effect. Lateral load may then be plotted against lateral displacement. The Initially, this relationship will be linear at the beginning, but then the structure will start begin softening at a certain level of the applied load. The plot of the anticipated response is shown below (for a slightly different model of initially crooked column):
Reference: see Internal References
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load. Response of a column with slight initial perturbation is shown in Figure 1:
Figure 1 - Nonlinear buckling evaluation
Reporting
How should internal forces and reactions be interpreted for buckling analysis?
Extended Question: When performing buckling analysis for a cantilevered column, buckling mode shapes result in proportion to applied loading. When an axial load is applied to the column, the resultant axial force is zero for every mode shape, though moment and shear reactions are present. Could you please explain?
ANSWER: The internal forces and reactions reported for buckling load cases correspond to the buckled configuration of the structure. For a vertical cantilever model, the structure buckles laterally, generating internal moments and shears without axial force.
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Why am I getting a negative-stiffness error during P-Delta analysis?
ANSWER: Negative stiffness occurs during P-Delta analysis when structural objects buckle under second-order P-Delta effects. To avoid negative stiffness and buckling, object size should be increased, especially at columns and diagonals.
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