Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

CONC - Footing Design

[Subject Prev][Subject Next][Thread Prev][Thread Next]
I have a couple of footing design questions that I would like to have some opionions on. 
When designing an isolated footing that is located several feet below grade and has a 
substaintial lateral force from wind or seismic that causes overturning, do other 

a) assume the soil cannot take any uplift and reduce the effective bearing area 
accordingly  (this means no top footing rebar is required for strength).


b) assume the soil above the footing does bear against the top of the footing and design 
the top footing steel accordingly.  Also, does this mean that the bearing pressure on 
top of the footing gets combined with the self-weight of the soil above the footing for 
determining the moments and shears in the top of the footing?  

Furthermore, when using ultimate strength design, do you usually apply the load factors 
before determining the net bearing pressure or after by simply using a average load 
factor times the net service bearing pressure.  If option a) is used, applying the load 
factors before of after determining the bearing pressure can make a big difference.

Also, has anyone seen a reference that discusses how to handle bi-direction shears when 
they are applied to a pier or column at the same time (e.g., how is the total shear 
strength of the pier or column compared to the total applied shears?).

Mark Ahlskog, PE