Modeling errors

A very common modeling error

In the first picture:

Vertical section in a model of a building modeled using ETABS program, the ground floor column is characterized by a double height, meaning that it is not connected to the slab of the first floor, but continues directly to the second floor. It is not actually connected to anything at this level, which led to a distortion of the shape of the moment diagram of the column and considering that the length of the column is only its length from the ground to the first floor and not its total length.
In the second picture:
A shell diaphragm was added to the model with the point diaphragm cancelled.. Therefore, the column was not connected at the level of the first floor with an imaginary link, and therefore the shape of the moment diagram was correct and the length of the column is its total length from the ground to the level of the second floor
The result :
The point diaphram may be one of the reasons for the emergence of unexpected errors in the modeling and consequently in the results.. We noticed how there was a fundamental difference in the behavior of the column and the design results due to the use of the point diaphram in connecting all columns, even the unconnected to something
I recommend shell diaphragm
Or strict attention while using the point diaphragm
The pictures are from an engineer’s question

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