STAAD RC Building: Fixed or Pinned Support ba sa Superstructure Base?
Nalilito ako sa proper support assumption sa STAAD kapag separate ang model ng superstructure and substructure for an RC building.
For a typical monolithic RC column na continuous papunta sa pedestal/footing, dapat ba fixed or pinned ang support sa base ng superstructure column before i-transfer ang reactions sa substructure/foundation model?
Ang understanding ko kasi, mas reasonable ang fixed support since continuous ang RC column papunta sa substructure/footing, so capable siya mag-transfer ng axial, shear, and moment reactions. Meanwhile, ang pinned support forces base moment = 0.
Nalilito ako kasi may nakita akong TikTok comment from someone claiming to have a master’s degree in structural engineering saying na dapat daw pinned, kasi shallow footing/soil is not perfectly fixed and can rotate. Parang may kulang or mali sa advice, kasi gets ko naman na hindi perfectly fixed ang footing/soil, pero hindi rin ibig sabihin na true pinned na agad yung RC column-footing connection. If pinned ang gagamitin, mawawala yung base moment sa superstructure reaction, so baka hindi ma-transfer nang tama yung moment demand sa foundation/substructure model.
Gets ko naman na ang actual behavior is probably partial fixity, and mas refined kung gagamit ng soil/rotational springs if may available soil stiffness data. Pero for practical STAAD modeling of a low-rise RC building, ano ang mas defensible assumption: fixed, pinned, or spring support?
Also, good practice ba na i-run both fixed and pinned as sensitivity checks?