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Different results

Question:

Hi,

We got different results after analysis:

1) about 20 MPa



2) about 16 MPa



Please let me know why stress results of same analysis are different.

Thaks

Regards





Answer:


In the time history analysis by the nonlinear direct integration method of midas Civil, there is a way to reflect the static analysis result by gravity load as the initial condition of the dynamic analysis, 1) to perform a non-linear static analysis for gravity and perform a continuous time history analysis, 2) to enter the static analysis result for gravity load as the initial cross-sectional force to reflect the time history analysis results.

When entering static analysis results as initial cross-sectional forces, the linear time history analysis can simply combine the initial cross-sectional forces with the time history analysis results. However, the nonlinear time history analysis does not ensure consistency between the load conditions that are performed consecutively unless the initial cross-sectional forces are taken into account in determining the status of the non-linear elements. In addition, the cross-sectional forces generated by the member is caused by the external force applied, so if the initial cross-section forces are reflected in the equilibrium equation into the member internal forces, equilibrium condition is not established. midas Civil performs a non-linear time history analysis by obtaining hypothetical deformation for the initial cross-sectional forces and considering the condition of non-linear element.


Therefore, if you perform nonlinear analysis for the initial loads as shown below, 

and select 'Initial Load (Global Control)',

you can get the accurate stress results of fiber section as shown below. Revised file is attached here for your reference.


Regards,
DK Lee
Technical Manager

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Creation date: 10/6/2020 12:43 AM (dklee@midasit.com)      Updated: 10/6/2020 10:16 AM (dklee@midasit.com)
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original file revised.mcb
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sforzo normale.mcb
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