Basement Wall Design 2

[pmour]

I am looking for some references/codes/guides that would be available for the design of basement walls as plates with fixed end supports rather than as a retaining wall. While constructing residential basements, I had built walls with a very minimal longitudnal steel. I had gone out to a consultant recently that returned a basement wall design which I believe is far overdesigned as a retaining wall.

 

[jike]

For walls which are free at the top (such as at a stair or elevator on an outside wall or an areawell), I calc. those using a FEM program. It gives very reasonable answers in a minute or two.

There are also numerous charts available in "Rectangular Concrete Tanks" by PCA. Years ago, I used a book that had similar charts. I think it was a book called "Moments and Reactions for Rectangular Plates". I think that it was written in the UK.

 

[bylar]

Try National Concrete Masonry Association TEK brochures
15-1A and 15-2A Will give you tables for the basement wall up to 16 feet high. Determine your soil pressure and check the tables and see how it comparew with what you got. If you use IBC read

Table 1610.1 (c) For relatively rigid walls, as when braced by floors, the design lateral soil load shall be increased for sand and gravel type soils to 60 pounds per square foot per foot of depth. Basement walls extended not more than 8 feet below grade and supporting flexible floor systems are not considered as being relatively rigid walls.

 

[MiketheEngineer]

Try

http://www.Archoneng.com.

Check Wincrete.exe They have very nice program modules for the engineer - about $40 eac

 

[EG]

Hey all. I am a consulting engineer who used to do elementry structural analysis for my father's firm while in college. I built my first home last year and caught the structural engineering bug big time. I have been hitting the books very hard, constantly harrassing other area structural engineers and builders, reading Eng-Tip forums daily, and have now engineered 4 simple homes, always careful to stay within my conservative comfort zone. Anyways, I have spent a lot of time studying up on the basement wall issue. I have focused on Hillerborg's strip method for slabs. There is a specific application for slabs supported along three edges and unsupported along the forth, with a distributed load that increases linearly from zero along the free edge to a maximum at the opposite supported edge (bottom of wall). I haven't been able to find any references that account for the vertical loadings coming down to the top of the wall relative to the above, but simply use those loads for wall stability, etc... Thanks for your time and I look forward to hearing more about this subject as I have been constantly thinking about the same problem.

 

[archeng59]

I generally do not design basement walls as cantilever retaining walls because they are restrained at the top by the upper floor slab when the building is completed. However, the wall needs to be temporarily braced during construction until the upper slab construction is complete. the upper slab must be designed to resist the horizontal shear from the wall. designing the wall to span vertically typically results in a more economical design than as a cantilever retaining wall. the horizontal reinforcing must meet the requirements of ACI 318 section 14.3

 

[structural01]

I am assuming you are talking about concrete reinforcing basement wall.

There is a good example on how to design basement wall for reinforce or nonreinforce basement wall in ACI 318-99 commentary.

Good luck.

Structural01

 

[archeng59]

structural01, are you talking about the "PCA Notes on ACI 318-99"?

 

[structural01]

Yes. I meant to say PCA notes.

 

[bjb]

I agree with archeng59. I design basement walls to span vertically, as long as they can be braced by the floor. Except at the corners, they behave as one-way slabs in the vertical direction.

With residential basements, I have seen lots of failures of walls (designed/built by others). The main reasons have been no reinforcing in the wall, inadequate connection between the top of the wall and the floor system, and substandard backfill resulting in large horizontal forces.

I recommend that you always provide vertical and horizontal reinforcing so that the wall has strength when it cracks, even if you can make things work on paper without reinforcing. The 2000 IBC allows unreinforced basement walls, but I strongly recommend against it. Vertical rebar greatly increases the bending strength, and you're covered if the wall cracks. If something happens to an unreinforced wall and you get a horizontal crack, the wall has failed. Fixing it costs way more than providing some rebar during construction. Unfortunately, in my area it is common not to reinforce residential basement walls. The contractor for the last failed wall that I designed a repair for indicated he would now start putting in some vertical rebar. Horizontal rebar is a good idea for crack control and to tie the wall together.

Also, the connection between the top of wall and the wall is a major source of failures. The minimum code requirement of a 1/2" bolt spaced not more than 6 feet apart usually doesn't work. Again, this is for residential basement walls with wood floor framing.