raft foundation help 1

[wrxsti]

hi engtips fam


i am interested in doing raft design without having the spread the pressure along whole raft

i was exploring some flexible raft design procedures and i came across the one below

asking some clarification on the pic below

by number 1. does he mean that the balancing mmoment is coming from ta simiilarly loaded wall/column on the opposite side
?to satisfy using this methodology.


number 2 . now makes it seem like a portion of the slab is resisting the unbalanced moment
my interpretation is that the bearing pressure reaction ifs trying to lift up the slab and the weight of the slab x lever arom around o will create the balancing moment


looking forward for your input
thanks in advvance

 

[BAretired]

1. That seems to be what he is saying, but there is no justification given, and I don't think it is a necessary condition, and often not a typical condition.

2. The author does not say what he thinks is reasonable for a length of slab, but I think M=wL^2/2 would be one method of finding L required (w being the dead weight of slab).

I don't think the pressure would be uniform over the length B, but that would require an analysis of a beam on elastic foundation, which is not for the faint of heart. Also, B=(P+wL)/p_a seems to be more precise than his formula, it seems to me. I assume p_a is the allowable soil pressure.

BA

 

[wrxsti]

thanks BA

 

[BAretired]

You are welcome, wrxsti.

BA