Location of vertical steel in basement and garage walls

[Lake06]

I have two questions regarding the location of the vertical steel. The first is where should the vertical steel be located in a house foundation wall for an 8 foot high basement wall with an unbalanced backfill height of 7 feet? The 2nd question is where should the vertical steel be located for a garage wall with equal fill located on both sides of the wall. Both walls will be 10” thick concrete and the garage wall is only 4 feet high above the footing. I have read different views on this issue and would like some clarification.

 

[hokie66]

Put the steel near the tension face. If no tension, it can be centred or distributed to each face.

 

[msquared48]

Agree with Hokie. Read ACI 318-05 14.3.4.

Mike McCann
MMC Engineering

 

[MiketheEngineer]

Also look at IBC prescriptive comments. Don't often show any vertical steel - with which I disagree.

 

[Lake06]

Mike,

I live in NYS and checked the NYS Building code. According to table 1805.5(5) there is no vertical steel required for a 8 foot high wall, 9.5 inches thick, PSF =30, with a 7 foot unbalanced backfill height. According to the code this table is based on grade 60 steel and 2,500PSI concrete. I'm confused, after reading the ACI 318-05 14.3.4 code this information conflicts each other. Why would the NYS code be less than the ACI code? Here is the link to table 1805.5(5)

http://publicecodes.citation.com/st/ny/st/b200v10/st_ny_st_b200v10_18_sec005_par029.htm

 

[SkiisAndBikes]

In Canada, 'regular', residential basement foundation walls are unreinforced for wall thickness of 8" with a maximum wall height of 8'-2" and a maximum retained soil height not exceeding 7'-6" as per the prescriptive tables of the Code.

Whenever the foundation walls exceed 8'-2" they are engineered and reinforcing steel is normally specified on the tension face. If a garage wall is backfilled on both sides, normally it is not reinforced, however, in the unusual case it is, I usually specify the rebar down the centre of the wall.

 

[msquared48]

Lake06:

Read 14.2.7, then turn to 22.2.2(c). Point being that unreinforced IS allowed in the ACI code... If you have the commentary too, read the section on 22.2.2 and 22.2.3.

However, that does not mean that I, as a registered professional engineer in a highly seismic zone, would ever design anything without resteel. Not even residences... Nothing.

Mike McCann
MMC Engineering

 

[Lake06]

Msquared48,

Thank you for the section references to the ACI 318 Code. I typically see on plans and in the field for 10” thick walls for 8 foot high house foundations, in our low seismic area of NYS, vertical steel #4 or #5 at 48” O.C. ACI code 318 for min reinforcement and min reinforcement due to flexural members requires more steel than this. Are these designs based on plain concrete with common building practices are to supplement the plain concrete with #4’s or #5’s at 48”O.C for temperature requirements?

 

[msquared48]

Probably for a small measure of limited crack control.

Mike McCann
MMC Engineering

 

[hokie66]

The vertical steel is probably because the designer doesn't believe in using plain concrete in walls. Neither do I.

Vertical steel in this case doesn't have a lot to do with crack control...the cracks due to restraint shrinkage would be vertical, so the control reinforcement would be horizontal.