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[GEN/Result]Displacement Appears Normally, but Experiencing Excessive Natural Frequency

Question

The displacements due to static analysis are coming out fine, but the natural frequency of the structure is too large. What should I do?

 

Answer

The natural frequency of a structure is directly proportional to its mass and inversely proportional to its stiffness. If the displacement caused by the static analysis is normal, the structure has entered too much mass.

For example, consider the structure below, where the maximum displacement due to gravity loads is 1.2 mm, but the natural frequency for the first mode, as shown in Image-3, is 78 seconds.

Upon inspecting the material assigned to the floor slab, it's evident that the weight density has been set to 5.0 x 10^5 times the normal value, as shown in Figure 2. By correcting the material properties to match a C30 concrete mix, as shown in Image-4, the first mode's natural frequency becomes a more reasonable 0.14 seconds, indicating a proper solution.

[Image-1] Deformation of a structure by a Dead Load

[Image-2] Input Material Data

[Image-3] The structure's natural frequency (If W.D. : 1*106)

[Image-4] The structure's natural frequency (If W.D. : 23.54)

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