Raft/ mat foundation design
Raft/ mat foundation design
(OP)
I would like that any experienced practicing structural engineer may please describe the steps involved and method of designing of raft or mat foundation, describing any useful hints and valuable information.






RE: Raft/ mat foundation design
If you design this by hand, you must assume the mat is infinitely rigid. First, you calculate the soil bearing pressure at all four corners of the mat (check these against the allowable soil bearing pressure). Then, using factored soil bearing pressures, design the concrete mat as a two way flat slab.
DaveAtkins
RE: Raft/ mat foundation design
RE: Raft/ mat foundation design
i wonder what one will use as spring constant for bearing pressure.. i am assuming one will use rigid approach to get the spring constant.. then finite element??
what the heck is the finite element good for if the bearing pressure was computed using rigid approach..
RE: Raft/ mat foundation design
RE: Raft/ mat foundation design
RE: Raft/ mat foundation design
RE: Raft/ mat foundation design
DaveAtkins
RE: Raft/ mat foundation design
then apply it to the plates and design the footing as FEM..
hmmm...
RE: Raft/ mat foundation design
DaveAtkins
RE: Raft/ mat foundation design
i thought the bearing pressure is the one that you should use for FEM as soil spring value for computer program..
i guess other engineers here will agree with me?
RE: Raft/ mat foundation design
RE: Raft/ mat foundation design
RE: Raft/ mat foundation design
Alternatively is it acceptable under any code or rules to assume that the bearing pressure under neath the foundation is uniform regardless of wether the load is eccentric or concentric.
RE: Raft/ mat foundation design
Old CA SE
RE: Raft/ mat foundation design
RE: Raft/ mat foundation design
Not true. The bearing pressure under the mat will NOT be uniform unless the loads are concentric. This is true whether you use FEM or design by hand. Find the bearing pressure correctly, and design for that.
DaveAtkins
RE: Raft/ mat foundation design
RE: Raft/ mat foundation design
h
RE: Raft/ mat foundation design
RE: Raft/ mat foundation design
The max pressure typically occurs at an edge in a ridgid foundation...and then that pressure decreases as a triangle load so spans are loaded differently...could this cause a greater moment than the max load?....maybe it could...
RE: Raft/ mat foundation design
You said "determine if you are inside the Kern limit, and design for P and M appropriately."
what happens if you are NOT inside the kern limits?
RE: Raft/ mat foundation design
RE: Raft/ mat foundation design
RE: Raft/ mat foundation design
RE: Raft/ mat foundation design
The reason that it wouldn't apply, in my opinion, is if there is relative vertical movement of columns the stresses developed due to the differential movement won't be accounted for. I guess if you feel that the mat is stiff enough to resist relative movement (which is the assumption that I apply for say a 5' thick shearwall pilecap) then maybe it would be okay. I think if you have say 4' thick areas under columns and 8"-12" thick between columns that there may be differential movement.
RE: Raft/ mat foundation design
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RE: Raft/ mat foundation design
RE: Raft/ mat foundation design