House floor post on exterior foundation wall 1

[magicming]

Hi there,

I saw it a couple of residential houses design drawings. The designer used steel beams (like W10x45, W12x50, even W14x90) for the second floor load and one end of beam was supported by steel column (HSS 4"x4"x1/4"). However, the column was placed at the exterior foundation wall. I am roughly guessing the load on column might be 20,000 lbs or higher. The foundation wall was 10" thick and the footing was 16"wide and 8" deep. And there was no extra reinforcement in the foundation wall. My question is that is it safe to design like this? I am in Toronto, the house I saw is a two floor residential building with a nine foot height basement. I don't see that often so I think it is bold to do so. Or maybe my experience is not sufficient enough coz I am into residential design for a year. If this is safe, it will be very helpful to do many designs with aesthetic interior.

 

[a_urbs]

If you're asking someone to comment on whether a design is safe based on the limited information you gave, I doubt you will find any takers. It holds no water without having access to the bigger picture.

However, I find as a general trend, more steel is finding its way into homes, especially the higher-end ones so it doesn't surprise me that you're seeing that.

 

[magicming]

Thanks for your reply, @a_urbs. I know the information is limited here. If you need more information please let me know. I can give so we can have further discuss. And yes you are right, this is a high end house, worth more than 6 million.

I want to initial the discussion that the steel post is supported on foundation wall. I know usually wood posts, especially built-up posts are used and they usually not undertaking too much load. For the steel column I mentioned in this design, the load is pretty high. So such a high point load on a foundation wall, is it safe to be supported by the regular foundation wall, not a thickened one or reinforced one.

The main reason I ask this question is that if it is good to design like this, I would definitely do such design to reduce the exposed columns in the middle of an open space.

 

[SWComposites]

You can’t just eyeball design the foundation. You have to actually run an analysis. How do you know what is inside the foundations you have seen?

 

[magicming]

Thanks for your reply, @SWComposites. I didn't eyeball the foundation. I have the design drawings. That triggers my deep interest.

 

[a_urbs]

Ming,

Asking the forum if this is "good" or "safe" is a bit asinine. How do you know it's not safe? Maybe this residential foundation wall is using 80 MPa concrete, I don't know.

Is it nice to free up the floor plan by bearing on the foundation wall when possible? Sure, architects would love that. But, as you mentioned sometimes the load coming down on a column or post is too high, then it needs another solution.

Like I said, without the bigger picture, this is moot.

 

[a_urbs]

I just saw your other comment, if you have the drawings, try to redesign it yourself if you're so curious, see what you get.

 

[magicming]

Thanks, @a_urbs. Very appreciate your suggestions. As I have the drawings, I do have the intention to run all the calculations myself to see how does it look.

 

[XR250]

The foundation wall will potentially spread the load out at 45 deg so you may have 18 ft. of footing engaged.

 

[phamENG]

Where are you getting the 20kips? Just because it's steel? That doesn't mean much. Steel is often used to control deflection in a shallower depth, so the loading may not be all that high. Then again, it might be.

In general, I would say a steel column sitting on a 16" wide and 8" thick, unreinforced footing would be very suspect, so you're certainly right to question it. But how tall is the foundation wall? Are we talking a 24" stem wall, or a 12' basement wall?

Be sure to post the results of your analysis so a real discussion can take place.

Also - there's no reason to double post in the wood forum. Anyone who would see it there has already seen it here.

 

[LittleInch]

Sounds like a 9 foot high wall 10" thick which sits on a pretty weedy looking foundation 16" wide and 8" deep.

no idea what the wall is made of...

Of course a drawing or sketch would not have us all guessing all of this.....

Some sort of bearing pad or similar would seem like a good idea, even if not required from calculations or regulations, but then we don't know that either...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[phamENG]

Where are you guys getting 9' for the foundation wall? Am I blind?

 

[jjl317]

8th sentence in the original post?

 

[LittleInch]

", the house I saw is a two floor residential building with a nine foot height basement. "

So we are working on the basis that the column sits on top of this wall which then sits on the foundations.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[JAE]

Seems like I'd not be concerned with the footing as the 9 ft. basement wall would probably distribute this away over a long stretch of footing.

But the local bearing on the concrete wall would demand a closer look-see as most residential concrete walls in my neck of the woods aren't reinforced properly at all.
Almost to the point where you're looking at ACI plain concrete provisions.

 

[phamENG]

aha! I am, in fact, blind. thanks, everyone.

 

[jayrod12]

If I'm understanding his description though, the steel beam doesn't sit on the foundation wall. It sits directly on the footing, just inside of the foundation wall. So you can't count on the wall spreading the load out like we normally would.

 

[JAE]

jayrod12 - I think, though, that if the footing and wall are adequately connected via reinforcing, the two will only deflect in unison, forcing the load to spread out.

If the footing doesn't bend/deflect more-so than the wall, then load will spread out significantly.

If the column load forces the footing to settle and "tear away" from the wall above then yes, very high localized soil stresses.

 

[magicming]

Thanks for all your inputs. It is really a great chance to discuss with you all here.

1. To allow you all see clearer the design, I attached one section of the structural drawing from basement to second floor. P6:HSS 4"x4"x1/4" column, B17 = W10 X 45, B18 =W10 X 54, B19 =W12 X 50, B20 = W12 X 58, B21 = W14 X 90, B22 = W14 X 76,
2. Also a correction, the footing is 26" wide x 8" deep, not 16" as I mentioned in the first place. The concrete used for footing and foundation wall is 20 MPa.
3. The steel post on foundation wall are mostly in the un excavated footing/foundation walls, but there are two posts sitting on foundation walls that one side is soil and the other side is basement.


@XR250, not sure what is the degree of angel the designer used.
@phamENG, I get the 20kips by rough estimating the load above, including the load of one section wall from the second floor (second floor has smaller footprint and the exterior walls are on these steel beams), the roof load, tributary area. Of course, my estimation may be wrong coz I didn't detailed the calculations.
@LittleInch, more information is added. And I also think it may be better idea to increase the size of foundation wall where the column sits, but the design doesn't have that.
@JAE, I get your point that point load my crash/crack the concrete on top of foundation wall, so I did a rough calculation, for a 6" plate at the bottom of steel column, the concrete contact surface can stand over 100kips of load for a 20MPa (2900psi) concrete. So that shouldn't be an issue. And your concern is mine as well, if the footing doesn't bend, high concentrated load would occur, so it seems wiser to increase the thickness of foundation wall where the steel column sits, forming a pilaster shape concrete column to support the steel post.
@jayrod12, The steel post sits right on top of the foundation wall, not the footing.

 

[jayrod12]

From those clippings, it appears the posts sit on top of your foundation wall? If so, the wall will spread the load out quite significantly as indicated by other posters above.