Correct understanding of tensile reinforcement in cantilever wall? 5

[SoiloftheMonth]

Looking to see if the cantilever walls that I have drawn in the attached pdf correctly show which reinforcement is under tension. #7?

attached pdf

-SOM

 

[hokie66]

1. Cantilever walls are not "hinged at stem". They must be rigidly connected to the footing.

2. The vertical reinforcement in a cantilever wall is in tension on the side with the earth load.

3. You have shown all of the vertical bars incorrectly in the footing. The bars must go to the opposite side of the joint, in the case of footing, to the bottom.

4. There must be bars in the top of the footing to resist the moment, and these bars must be developed and anchored on the opposite side of the wall.

Your understanding is sorely lacking. Are you a student?

 

[BAretired]

#7 is wrong!

Also, you can't bend the tension bars from the wall into the top of footing the way you show typically. The bars will pull out of the concrete at the bend.

I suggest you get the CRSI Design Handbook which shows details of retaining walls.



BA

 

[BridgeSmith]

BA, #7 is detailed incorrectly, but as hokie66 pointed out, so are all the others. It will have very little bending capacity, even compared to the other configurations.

At the risk of indulging foolishness, I'll weigh in on the diagrams: Equilibrium dictates that all the configurations with lateral loading must have resisting loads, which means some portion of the bottom steel will be in tension in all configurations except No. 1, so the only ones that could be considered correct would be No. 2 and No. 5. No. 5 would only be correct if the vertical load is large and the lateral load is small, otherwise the bottom of the right end of the footing would be in compression.

 

[SoiloftheMonth]

Thanks hokie, BA, and HotRod. Working to understand some reinforced concrete wall design, thinking about these fictitious walls and hoping to find where my thinking is wrong.

updated the previously attached pdf

1. I updated the steel to show it only extending to the lower mat. No bends or hooks considered right now.

2. For 7 I was thinking of a case where the vertical steel was placed by error on the wrong side of the wall, perhaps it was detailed as 6. When this incorrectly built wall is loaded would the vertical steel in 7 then still pickup some tension, however much less than 6? Then when built, depending on the lateral load, the wall may very well topple right over?

3. re:hokie's 1, is the connection at the stem fixed, such that it will develop x, y, and moment reactions?

4. re:hokie's 4, I cannot figure where the moment comes from that would require structural steel in the top of the footing. In the footing I imagine compression in the top face due to the reaction of the subgrade (2,5). When the footing is subjected to the subgrade reaction isn't the footing bending in a smiley face shape, tension at bottom of beam and compression at top?

5. If you load both sides of the stem with earth or have liquid containment (earth retained on one side, water on the other) does case 8 apply? ie vertical steel still only in theory needed on the side with the higher lateral loading?

6. with the exception of 2 and 5 which have subgrade drawn, I was thinking of these fictitious walls as somehow magically weightless. So 1 has no tension or compression, just magically floating in space... Number 3 has no footer tension because there is, magically, no subgrade reaction force. By my thinking at least...

 

[dik]

As above, but, your tension reinforcement should extend to the bottom (far side, Hokie#3) and should be bent the other way so the compressive load is acting on it.

Dik

 

[ukbridge]

This is a good example showing how an RC retaining wall should be properly detailed.

 

[JoelTXCive]

This is still a work in progress, but I made diagrams showing each loading that a normal cantilevered retaining wall is subjected to; and then I showed the related steel reinforcement associated with that loading.

There is Stem Loading, Toe Loading, Heel Loading, and Temperature & Shrinkage.

See attached....It might help

 

[BridgeSmith]

"I was thinking of these fictitious walls as somehow magically weightless."

What do you hope to learn by drawing structures that only work in a fairytale world where equilibrium doesn't apply? If you want to understand the mechanics, it has to follow the laws of physics.

If all you're trying to do is identify the tension and compression faces, apply the bending moments, and draw the deformed shape of the walls. The faces that are stretched (convex) are in tension and the ones that are shrunk (concave) are in compression.

 

[SoiloftheMonth]

"I was thinking of these fictitious walls as somehow magically weightless."

What do you hope to learn by drawing structures that only work in a fairytale world where equilibrium doesn't apply? If you want to understand the mechanics, it has to follow the laws of physics.

If all you're trying to do is identify the tension and compression faces, apply the bending moments, and draw the deformed shape of the walls. The faces that are stretched (convex) are in tension and the ones that are shrunk (concave) are in compression.

good point. I can see how this could be dangerous, leave out crucial information and I could arrive at the wrong conclusion.


I don't mean to ignore equilibrium here rather I aim to take on my misunderstanding in small steps, ignoring certain concepts at first. In statics we ignored the weight of the beam at first, soon we added a uniformly distributed load to each problem.
-SOM

 

[BridgeSmith]

SOM, what you're asking here is covered thoroughly in Mechanics of Materials and first semester Structural Analysis. You should review your textbooks, assuming you have completed those classes. If you haven't completed them yet, just be patient and you should have a grasp of the concepts when you have.

Btw, even in a Statics course, equilibrium is never ignored, it is the central theme.