retaining wall

[GoddyMgwasa]

Im just to design a propped retaining wall. My superior wants one face reinforcements but I think that is not propper as propped retaining wall experience both positive and negative moment. I preffer putting reinforcements at both faces, near and far face. Please advice!

 

[DaveAtkins]

Is this a basement wall, or a cantilever retaining wall laterally supported at the top? If it is a basement wall (pinned top and bottom) it can be designed as unreinforced.

DaveAtkins

 

[hokie66]

I think Dave means a basement wall can be reinforced only on the inside face. I agree, but in practice, I usually provide some reinforcement in the outside face near the bottom to deal with whatever fixity may occur.

 

[AlmostPE]

If you are not retaining that much load, just use one layer of reinforcement (in the middle) and use about 8 to 10" of concrete. If that doesnt work then you might need to do 2 layers. Depends on how long and how tall the wall is.

 

[concretemasonry]

Basement block walls can also be unreinforced. - It depends on geometry and materials. - See IRC

 

[Lion06]

ACI stipulates that you must use reinforcement on both faces if the thickness of the wall is greater than or equal to 10".

 

[DaveAtkins]

No, I meant basement walls can be unreinforced (as long as the numbers check out). I know this is done all the time in residential work, and I think it is OK for commercial or industrial work as well (but I am not near my ACI Code right now). Unless the Chapter on Structural Plain Concrete specifically excludes basement walls, it can be done.

DaveAtkins

 

[Lion06]

I agree. It seemed like it needed to be reinforced and that's what I was basing the statement on.

 

[GoddyMgwasa]

thanks all for valuable information.
DaveAtirks the wall is cantilever and lateral supported at top. The height of which is about 2.5m high. It retains a lot of backfill soil.

 

[SteveMort]

Florahaule, if the wall is laterally braced at the top, it is not a cantilevered retaining wall; it is a simply supported "basement" wall and can likely be designed as an unreinforced concrete wall. If it is not braced at the top or does not have resistance on the opposing side of the building (such as a walkout basement), it should be designed as a cantilevered retaining wall with reinforcement on the tension face only (as your superior is suggesting). The design is dependent on several factors including the soil density and its properties like its angle of internal friction. These properties determine the horizontal soil pressure acting on the wall. As a guideline, I suggest the following reinforcement for a 2.5 m high cantilevered retaining wall, soil density of 130 pcf, angle of internal friction of 35 degrees, no slope to the backfill, no surcharge on the soil, concrete compressive strength of 3000 psi, re-bar yield strength of 60,000 psi: Wall stem is 8", the heel extends 1'-10" from the face of the wall and there is 8'-0" of backfill over it, the toe extends 1'-8" from the face the wall, the base is 12" thick, the vertical bars on the tension face of the wall are #4@9" or #5@12", horizontal longitudinal bars in the stem are #4@12", horizontal bars in the top of the footing (heel)are #4@9" or #5@12" in the short direction and 6#4 logitudinally, diagonal bars that just about intersect the vertical stem bars and the horizontal heel bars are #4@9" or #5@12". The CRSI Design Handbook has excellent design examples and tables. I hope this helps. GREETINGS TO DAVE ATKINS! I WORKED WITH YOU IN MADISON WISCONSIN IN THE EARLY 1990'S!

 

[GoddyMgwasa]

Thanks SteveMort, I agree with you, its not a cantiliver wall because its supported at the top. If you look at my original question I called the wall as 'Propped retaining wall' because it has been propped at the top and it retains earth material.
Im asking why should I just reinforce one face while the nature of the bending moment shows there is positive and negative moments along the wall and there is also a point of zero moment. The bending moment needs 2 face reinforcements.

 

[PEinc]

If the wall facing is relatively thin, one mat of steel will make it hard , if not impossible, to insert a concrete chute or concrete pump hose down into the form. I use 12 inch minimum facing with 2 mats of steel for permanent tiedback walls.

 

[msquared48]

Florahaule:

I do not understand the existance of any negative moment here if it is truly a basement wall - all that type of wall sees is positive moment with the steel on the side away from the soil. The only circumstance that would produce any negative moment on a "basement wall" here is if the wall retained enough earth above the level of support of the wall diaphragm, or prop level, as you put it, to generate a negative moment.

So...Does the earth extend above the "prop"?

Also, if the wall is 10" thick or greater, I would install two mats of steel anyway, using minimum steel requirements and distribution per ACI where appropriate.

Mike McCann
McCann Engineering

 

[haynewp]

I think you might have made a computer model of the wall with a support at the top and a support at the basement slab level some distance above the top of the footing, thereby creating double curvature in the wall?