Finally an interesting question

[nashe]

I hope this one is interesting one. I have an existing 80 feet long wall as one side of exist bldg. The wall is there so it should have adequate footing etc. The height of wall is 40 feet. 20 feet of which is below grade. In the top 20 feet portion I am creating an 40 feet wide opening. So traditional lintel and then end columns. Now at the top of wall or bottom of new columns the load will be concentrated and higher but as it goes down to existing footings 20 feet deep, probably it will distribute itself say at an angle 30 to 45. So footing should feel no additional load. Do we have any ref for distribution of this kind point load arrangement.

 

[Lion06]

Since you are creating an opening in the wall, is there any way you can create a bond beam at the bottom of the opening?

 

[UcfSE]

The ACI 318 and 530 both limit the effective width of the wall to be used for compression. I would not go any further than this width for your width of footing to resist that concentrated load.

 

[JAE]

UcfSE - I think that the ACI requirements certainly apply to the design of the wall itself. I would limit it to the 4t or whatever the width is.

But for the foundation design, I don't think that the ACI requirements apply at all. They are directed at the CMU or concrete wall calculations for strength, stability, reinforcing, etc.

The true behavior of the wall, in spreading out the load, is due more to an analysis of the wall behavior, not a code requirement. The presence of control joints might affect this spread of load but in truth, the load is spread out, and the footings only see the distributed load.

 

[UcfSE]

Correct, they don't apply to the foundation, so all I gave was an opinion .

If the effective part of the wall is more heavily reinforced however, particularly for cmu such as having a series of grouted cells, then that part of the wall I would expect to be more stiff and hence attract more load than just spreading it out evenly across a uniform wall. I believe this would cause the footing to "see" more of a concentrated load.

Either way it's isn't codified and seems to be left to our judgment for the foundation. It's interesting to see all the ways the same thing can be done different and each one be justified somehow.

 

[ironmon]

I would agree that concentrated load down to footing atop a 20 ft wall should "spread out" and not be a "bearing" concern. This is a judgement call.

I agree that the location of control/construction joints will limit the load spreading.

I would make sure that this is not a shear wall, and or that the remaining 40 feet is adequate. Also you should consider component and cladding wind loads. How will they be transmitted to the superstructure at each end of this large opening?