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[hemalmistry]

For buildings with basement/podium
Can we say that
(1) If basements are connected with tower, foundation depth includes basement height provided that backstay effect considered. Stability checks can be performed at podium (backstay diaphragm) level and not at foundation level.
(2) If basements are separated from tower with seismic joint, foundation depth does not include basement height.
According to chinese code JGJ 6-2011 (Technical code for tall building Raft foundations and box foundations), consideration of basement as embedded  part of building depends on combination of following factors:
(1) Type of foundation (Raft, piled raft, box, piled box)
(2) Structural system of tower (frame, frame+shear wall, shear wall etc.)
(3) No. of basements (single or multi)
(4) Relative lateral stiffness of basement floors.
(5) Distance between basement wall and main exterior structural wall of tower.

Regards
hemal

[alpa_sheth]

Hemal:

To answer your query,
If extended basements are separated from the tower by seismic joint, the foundation depth still includes basement. Its just that there is no backstay effect.

Hope I have understood your query and responded.

regards,
Alpa