Concrete Wall Shear at Slab Intersection

[TWG84]

Hello,

I am fairly new to concrete design and am trying to determine a way to increase allowable shear resistance in a concrete wall at the intersection of a slab. I am currently dealing with a cantilevered, laterally loaded, wall that has a slab that provides lateral restraint to the wall. My main question is there any way to increase the shear capacity of the wall at the slab intersection without thickening the wall? Any help would be much appreciated.

TWG84

 

[TWG84]

JAE, Do i not have to account for an increase in shear at the slab intersection (assuming the slab is bracing my wall @ 2ft from the top of footing). I was using that assumption and looking at the wall as a single span w/ cantilever. I was assuming a fix condition at the foundation and a support @ 2ft from the foundation (slab). From that analysis i agree with your 23 k/ft (that you mention above) as the shear approaches the slab, however at the slab would the shear not increase due to the slab acting as some type of brace/support?

BA. i apologize for an earlier confusion on my previous sketch. The wood wall above I have spanning between the columns so I wasn't accounting for any direct interaction with the concrete wall. I understand that in carrying the loads from the wood wall to the columns would interfere with the behavior of my columns. There is some shear that my wall is having to resist, but I am not having any problems with them resisting the shear that I am transferring to the columns. For my wood wall I am using LVL beams with plywood sheathing on ea. side. Because I am distributing the load to the columns, I have my columns to be @ the 10ft center to center, to keep from developing too much shear in my wood members. As the load gets to approximately 2ft above the concrete wall the load distribution begins to decrease as it carries further up the wall.

I have attached another sketch to hopefully provide more clarification of the section that I am looking at. Please note that the Columns are not shown in this section. This section is only showing the wood and concrete wall with how I laid out my pressure distribution on the wall. Thanks for all of your help so far.

 

[TWG84]

I also plan to look into the yield line analysis. I have not every looked into this theory. Does anyone have a any good references?

 

[BAretired]

TWG84,

Your information comes in bits and pieces, each contradicting the previous one. You must learn to start thinking like a structural engineer. I don't mean that as a criticism as we all had to start somewhere. It takes time and until you are able to do that, you are going to need supervision from a qualified engineer, which you don't appear to be getting now.

The first thing you need to do is to develop a conceptual framing arrangement for the entire structure. Before doing a lot of calculations, you may wish to discuss it with your boss and get his input. Or you may find that your first idea didn't work after doing a few calculations. It is far better to spend time developing a workable concept than to get bogged down in detail.

Forget about yield line theory for now. It may have been applicable to your first sketch, but no longer makes much sense. Focus instead on how you are going to frame these storage bins from foundation to roof.

Regarding your latest sketch:

1. What is the elevation of exterior grade?

2. What happens at top of columns 33' above the wall? Are the columns tied by beams across the 40' bay or are they just flapping in the breeze?

3. Do you have a tentative Roof Framing Plan?

4. Why is top of footing 2'-0" below top of slab? Would it be better to cast the slab directly over the footings?

BA

 

[TWG84]

BA,

Thanks for all of your input. I do not take any of this as criticism as I am merely trying to fully understand and know that what I am designing is structurally adequate plus the qualified engineer that I am under is not of much help. To answer your questions:

1. Elevation of existing grade will match finish floor elevation

2. The columns will be tied together each direction by glulam members.

3. I have a Roof Framing Plan laid out based on my column locations and spacing. The plan consist of what is described in 2 above. Also I have a steep slop on my roof. Roof slope on one side if 4/12 and a 12/12 on the other side.

4. the wall on the right side of the sketch is an exterior wall, therefore I have it 2ft below finish floor in order to achieve the minimal frost depth. being that the other footing is interior it could be raised up to cast the slab directly over the footing.

Thanks,

 

[BAretired]

It is a very unusual structure to say the least. You appear to be relying on 24"x24" cast-in-place concrete columns spaced at 10'-0" centers to resist lateral pressure from the wood wall above Elev. 114'-0" but it is not clear what provisions will be made to handle the column reactions at roof level. The cost of casting those columns to a height of nearly fifty feet is not trivial and I suspect they are not deep enough to do the job without excessive deflection.

What governed the wall cutoff level of 114'-0"? Why not use a consistent framing system with wood wall framing between columns all the way from bottom to top and avoid those messy cantilevered walls. From an erection standpoint, it would be simpler and cheaper to use glulam or structural steel columns.

That is my first reaction, but others may have different opinions.



BA

 

[BAretired]

Correction: Elev. 114' should read Elev. 112' in the previous post.

BA