Modelling of Elements Below Grade

[notpasible]

Greetings!

I am quite confused as to whether elements below grade (i.e. ground beams, columns extending to footings, tie beams, etc.) should be modelled in ETABS/STAAD. I have seen quite a few people consider these elements in their models (making the base of the model coincide with the top of the footing), while others prefer to do the opposite (base coincides with the ground floor level).

So, my questions are:
1. Should these underground elements be modelled, analyzed, and designed separately?
2. What should the modelling approach be when it comes to buildings with basements? And to high-rise structures?
3. What are the pros and cons of modelling or not modelling these elements?

Your insights into this topic are very much appreciated.

 

[MegaStructures]

I think this depends on how stiff the element under the ground is. If you have the possibility for significant deflection of the element I would model it, if there is 10’ of concrete around a column under grade I would set a BC at grade and call it a day

“Any idiot can build a bridge that stands, but it takes an engineer to build a bridge that barely stands.”