Civil Engineering/foundation

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QUESTION: what is the main difference between pinned support and fixed support in footing ?
which one i should use while making 3d model in staad.pro

dowel bent toward center
dowel bent toward cent  
ANSWER: Dear Kavi

Pinned or fixed supports are those you use details to provide them. In fact , in ordinary structures we dont have pinned connection. Theoritically, references give a central oriented bent reinforcement detail in RC column or pedestals where the cross point of rods is located on the column (pedestal) and foundation interface. I have seldom seen this detail being applied but it is credible.



In industrial steel structures like bridges or so you can see pinned connection very frequently.

In ordinary steel buildings you can follow other detail than the pedestal I said before. You can provide the bas plate with 2 dowel being aligned in one direction leaving the other direction with a moment free connection. With the base plate you can arrange to have a total pinned connection with the dowel connected in the center of the base plate.

Regards
BEH



---------- FOLLOW-UP ----------

QUESTION: if we use fixed support in foundation how the stress will be distributed in the soil ? and same for pinned support also ?

ANSWER: Dear Kavi

distribution of vertical loading combined with moment will be a trapezoidal shape i.e. rectangular ( for vertical loading)  + triangular ( for moment ) . For pinned support you have vertical loading which is distributed uniformly ( rectangular pattern).

Regards
BEH

---------- FOLLOW-UP ----------

QUESTION: what is a pressure bulb ? why it is created sir ?

Answer
Dear Kavi

Pressure bulb is the effective block of soil resisting under loading.
Theoretically it is the zone in a loaded soil mass that is bounded by a selected stress isobar. This idea gives an image of the mass of soil which is effective provided that you consider a certain level of stress as the boundary of failure of the mass.

In fact engineers use the trapezoidal pattern as the pressure bulb which is a sophisticated approach toward soil behavior.

Regards
BEH

Civil Engineering

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Babak Esmailzadeh Hakimi

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