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RC Wall Under Strength for Shear
- Thread starter Ericson66
- Start date
Probably need some more information. In plane or out of plane shear? Shear in the wall itself or in the connection between wall and slab/foundation? A sketch showing the layout and information on existing reinforcing would also be beneficial.
- Thread starter
- #4
Is it actually showing signs of shear failure or is that just what your calculations are showing? Don't create a problem if there isn't one.
At 1 meter thick, this is a pretty hefty wall and should require appropriate engineering care.
1. Sharpen your pencil and recheck your analysis
2. Hire geotechnical engineer to provide you with actual active soil pressures based on borings.
3. Extend toe of wall and add concrete buttresses
4. Jet grout behind wall to relieve active earth pressure (hire geotech)
5. Excavate part of backfill behind wall and fill with low density foam backfill (hire geotech)
6. Drill and install tiebacks partial way up the wall (hire geotech). This will change the behavior of the wall.
Just some random ideas to answer a question with very little information.
At 1 meter thick, this is a pretty hefty wall and should require appropriate engineering care.
1. Sharpen your pencil and recheck your analysis
2. Hire geotechnical engineer to provide you with actual active soil pressures based on borings.
3. Extend toe of wall and add concrete buttresses
4. Jet grout behind wall to relieve active earth pressure (hire geotech)
5. Excavate part of backfill behind wall and fill with low density foam backfill (hire geotech)
6. Drill and install tiebacks partial way up the wall (hire geotech). This will change the behavior of the wall.
Just some random ideas to answer a question with very little information.
Something seems fishy. Assuming 4 ksi concrete with no supplemental shear reinforcing.... you should have over 30 kips/ft of capacity. Even at 30ft tall with 40 pcf backfill and 1.35 load multiplier, I'm only getting 24 kip/ft demand. How tall is your wall!? Do you have a rail load surcharge adjacent to it? Are you accounting for earthquake effects?
- Thread starter
- #8
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- #9
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- #11
HTURKAK
Structural
- Jul 22, 2017
- 3,366
I will suggest RC concrete overlay . The exterior surface of the wall will be chipped and bonded anchors installed .The height of overlay could be 2-3 m . In past, we used this method against punching shear.Although the picture attached is for slab strengthening, similar analogy can be used for wall.
- Thread starter
- #13
Any one with experience with this product as a solution to shear problem Shear design of externally bonded FRP systems??
Erison,
This is a critical issue, please pay attention.
I've evaluated the wall using the following parameters.
- Density of soil = 125 pcf
- At rest pressure coefficient, Ko = 0.5
The resulting shear at the wall base, V = 131 k/per ft of wall, which is far exceeding the concrete shear capacity,Vu Vn = 44 k/ft.
The reason to use at rest pressure coefficient is that it is essentially a propped cantilever beam, for which active earth pressure may not develop. Another things potentially causing problems are ground water, and surcharge at the ground level. I don't think FRP strengthening is able to make up the deficit in strength. Also, I suggest to check the deflection at the top of the wall, which may not satisfy the service criteria.
This is a critical issue, please pay attention.
I've evaluated the wall using the following parameters.
- Density of soil = 125 pcf
- At rest pressure coefficient, Ko = 0.5
The resulting shear at the wall base, V = 131 k/per ft of wall, which is far exceeding the concrete shear capacity,
The reason to use at rest pressure coefficient is that it is essentially a propped cantilever beam, for which active earth pressure may not develop. Another things potentially causing problems are ground water, and surcharge at the ground level. I don't think FRP strengthening is able to make up the deficit in strength. Also, I suggest to check the deflection at the top of the wall, which may not satisfy the service criteria.
- Thread starter
- #15
Given the proportions of the structure, I would expect that some reduction of the demand at the base can be achieved by considering two way behavior of the walls.
Are you considering that?
The buttress walls sounds like a good idea and may still be needed at the middle zone but some reduction seems likely if the walls have two way action (i.e they are spanning horizontally and vertically).
Are you considering that?
The buttress walls sounds like a good idea and may still be needed at the middle zone but some reduction seems likely if the walls have two way action (i.e they are spanning horizontally and vertically).
If it is information you can share, I would be very interested to know how this situation came about. Is this a design issue? If so, what was the root cause? How was it discovered? I would think there are multiple 'lessons learned' here for the Engineer of Record and his/her employer.
BridgeSmith
Structural
retired13 said:
Per the OP's sketch, Ko = .37
Rod Smith, P.E., The artist formerly known as HotRod10
I'm not entirely convinced there's an issue here.
Did you look at this as a cantilevered retaining wall? I'm guessing so, since doing it otherwise would give you a higher shear at the middle floor slab. Though you didn't say how it's failing in shear. Are you worried about diagonal shear cracking or a shear friction failure?
It seems to me that this should be looked at more as a braced cut in terms of analyzing the geotechnical side of things. Structurally, I would look at the stress distribution through it as if it were a tube with slender walls separated by plates. I think the scale works reasonably well for that. I think you'll find that it's capable of a lot more that it seems when you bring all three dimensions into play.
How is it reinforced? There's bound to be a lot of rebar in that wall - probably on both faces. If so, only part of it will be engaged in resisting flexural tension and the rest can be looked at for shear friction resistance (tension in the shear friction bars + applied dead load will be the normal force for the equation).
Did you look at this as a cantilevered retaining wall? I'm guessing so, since doing it otherwise would give you a higher shear at the middle floor slab. Though you didn't say how it's failing in shear. Are you worried about diagonal shear cracking or a shear friction failure?
It seems to me that this should be looked at more as a braced cut in terms of analyzing the geotechnical side of things. Structurally, I would look at the stress distribution through it as if it were a tube with slender walls separated by plates. I think the scale works reasonably well for that. I think you'll find that it's capable of a lot more that it seems when you bring all three dimensions into play.
How is it reinforced? There's bound to be a lot of rebar in that wall - probably on both faces. If so, only part of it will be engaged in resisting flexural tension and the rest can be looked at for shear friction resistance (tension in the shear friction bars + applied dead load will be the normal force for the equation).
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