Unrestrained Basement Wall 1

[pioneer09]

Looking to see if anyone has some tips/ideas to design the unrestrained basement wall as seen in the attachment. My initial design was a retaining wall. Like a typical project in the design-build field, the contractor thinks this is nuts and way overdesigned. Per the usual, they did not have this amount of concrete figured in their contract and are super concerned about cost. After talking to their concrete subcontractor (due to lack of belief in the engineers design), the subcontractor believes (2) pilasters extending 4' into the soil as denoted in red will be sufficient to brace this wall. I took this approach and looked at the wall spanning as a continuous beam and used the pilasters as supports. The force at these pilasters becomes very large and to prevent overturning and sliding the 4' length will not work. I assumed this would be the case and the length required becomes extreme and I will hear major push back from the contractor.

I have thought of other possible scenarios that may work:

1. Span wall the 36' between cross walls (unrealistic due to reinforcing and depth needed)
2. Place steel beams on the outside of the wall and somehow tie to the basement wall (beam would span horizontally to cross walls.)

I know my design is not dictated by the contractor that had overlooked this when bidding, however I want to give the most efficient and cost effective solution possible. I am at somewhat of a lost on this. Any ideas would be greatly appreciated.

Thanks

 

[pioneer09]

CBSE,

Did not give that design guide a thought. Have used it before, but wasn't thinking of this project as a tank.

I fully agree with your point. There are so many ways to strengthen this wall, but in the end cost is the key factor and I am with you that small amounts of concrete and excavation outweigh non-traditional design methods that the contractor is not familiar with.



In the end, I believe it is our clients lack of knowledge with this irregular style basement that has led to the issues I am having trying to meet his criteria. The individual keeps resorting back to the saying, "not in my budget." We have all been in this situation I am sure and all it does is make design professionals look like we are being over conservative in design. This is by far not the case and I hope that clients like this come to this realization. Obviously, we are all design professionals and we strive to be contractor friendly while also providing a viable engineered solution. As we continue to move forward in our professions, I hope all of us can continue with this notion.

Reverting back to the original unrestrained basement wall, our customer has finally agreed to my design of a retaining wall after pointing out to him the costs associated with different design approaches we have presented.

I am very appreciative to all that have contributed to this discussion.

Thanks

 

[oldestguy]

Pioneer:

Do you think that maybe asking the client to view this thread and the comments might help a little?

 

[pioneer09]

oldestguy,

Great thought. I know there have been some comments from this client about talk in his office to use a engineering firm from a different city to get a second opinion. Which means hoping for a better solution (cheaper). Maybe this can portray to him that I am not "incompetent" and looking out for not only myself but his reputation as a quality contractor in the long run.

 

[JLNJ]

Maybe you talk your contractor into a reinforced CMU wall full height.

 

[HouseBoy]

Any pilaster or counter-fort strategy will place great demand (requirement for) substantial footing size and cost.

I think the "cheapest" solution will be to run a couple of steel "wind columns" full height (as you mentioned).
If they could live with the 4 ft high pilasters, the full height wind columns might not be too much more intrusive.

Agree with the others, 36 feet is too far and they definitely will have a problem if something is not done to brace the wall.

About the "not in the budget...." situation - perhaps the owner would be open to the notion that the extra cost is a legitimate extra. IF the contractor had included it originally, his number would have been higher and they would have had to pay for it anyway. Only counter argument is if his price (without it) was compared against someone who did have it in their budget. From the sound of things, nobody had it in their budget.

Seems to me that whoever gets the savings could also get the risk and in that case, they deserve to know what that risk vs.benefit is.

Just a thought.