Strip Foundation Corner Capacity 3

[KootK]

I am curious about the capacity of strip foundations at corner locations. If I have a column point load on a straight section of foundation, then I realize that I can consider that load as distributing out to either side.

Is that the case with a point load applied to the corner of a strip foundation however. I would expect that whole assembly would behave as an eccentrically loaded structure. I would think that the corner would tend to sink and and the foundation segments extending from the corner would be much less effective in resisting the vertical load than they would be for the straight wall situation.

I am currently looking at a location in a structure where there is a 2' jog in the foundation wall. If the point load is applied to the far corner of the jog, how much of the surrounding foundation can I consider as helping to resist the load? Maybe it could be treated like an eccentrically loaded mat foundation with some material missing?

Does anyone have any recommendations or references for this kind of situation? It occurs on virtually every builing so I figure that it must be addressed somewhere.

 

[ishvaaag]

You now can analyze easily a wall (notched or not) plus strip fpundation (even in 3D), say, on compression springs representing the soil.

Before that, situations without notches were analyzed again against subgrade reaction with the help of beam on springs (beam on elstic foundations), or grills if you had the ability.

Iy you were in the risk of the corner or end column disengaging, of course you prevented that by check, it was not the idea to allow such behaviour.

And of course, when the situation allowed many extended -and extend- the foundation beyond corner or end.

 

[haynewp]

It sounds like you have a column point load on top of a basement wall? I modeled a stip ftg corner with a direct point load in PCA mats before and the force did not distribute out well. The stiffness of the ftg just let the corner sink. However, I then took into account the stiffness of the large corner walls that would be transferring the force into the ftg, and it was an extremely different distribution. Before the corner sinks, it will have to bend the walls and take them too. You will still need a certain length of wall/foundation projecting from each leg of the corner for the distribution to take place. This may not be possible in your 2' jog situation.

 

[LPPE]

If you have a point load on a foundation wall, you can look at the foundation wall as a very deep concrete beam (say 8' deep). As long as you reinforce the wall, I think you'll find you are OK. Just like haynewp said.