analysis for foundation

[longisland]

I had a debate with my colleague on the boundary condition of the foundation in computer modelling. His idea is to assume the foundation to be pinned end. That means no moment is transfered to the pile cap or pad foundation. It also means the pressure exerted on the piles or the pad footing is even through out. I thought the force would only be evened out only if the pad foundation or pile cap is "thick" enough.

Moreover, I don't think a pinned end structure exists in rc buildings. It means the stump is allowed to rotate and CRACK.

comments?

 

[Hariharan]

Boundary condition would depend on the type of foundation
you have. Pin end is conservative for superstructure
moments. It is not appropriate for foundation design and
connection to pedestal. It is best if you can generate
the foundation rotational stiffness and use it as a spring
constant in the foundation nodes. You should use an
upper bound and a lower bound stiffness and take the more
conservative value for design. Sounds complicated, but
it will become routine after a few runs!

 

[Ron]

Obviously you may model either condition and your error will be conservative (pinned). I agree with Hariharan that it is a good idea to model upper and lower bounds, if for no other reason than to present a knowledgeable argument if questioned.

The system you have described would not typically equate to a pinned condition, though it could be designed as such. It is usually considered a fixed condition to more correctly develop consistency in the moment transfer in the structure. RC structures can have some pinned considerations but are usually rigid frames.

 

[ishvaaag]

I bring to your attention the hinges for arches where in X or hourglass reinforcement was used to ensure the hinge behaviour...I think this detail has caused already some deaths and I disfavour it. Be it for lack of confinement or upon yielding of the steel in the hinge which is then absent of any further capacity to restrain shears, I muse some of the failures seen (such one hotel on archs on such hinges on south Spain) can well be blamed partly (movements could also be) on that. Hence, beware.