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Shear in Reinforced Concrete Walls 1

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crunkcrete

Structural
Aug 24, 2006
2
I am designing a below grade sump that is 37'-0" by 24'-0" in plan. The controlling wall height is 40'-0". I am analyzing the walls use plate bending theory to get some relief on moment and shear from cantilevered design. What is the concrete shear strength if I am using plate theory as the design basis? Is it 2fc^0.2 or 4fc^0.5? I am not sure if when using plate theory the wall can be considered to fail by one way or punching shear. Or am I totally off base all together?? Do to the wall span and depth shear is controlling and I am trying to minimize wall thickness.
 
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For most of our designs, we've used 2(sqrt(f'c)). However, read through the commentary in ACI 318, section 11.3.2.1. Specifically, ACI provides for axial compression (which aids the concrete shear strength) in equation 11-4 (ACI 318-99), so for shear across a horizontal plane, where your sump wall adds axial force to the plane, you may be able to justify a higher value of Vc.

The two way shear values (4(sqrt(f'c)) from later on in chapter 11 could be considered, but I have always noted that finite element analyses tend to produce much smaller values than those done by hand using more crude analysis methods, so I've always tended to the conservative side.

 
In the design of such structures, we use 2(sqrt(f`c)). The effect of axial force is negligible. To reduce the design shear force, calculate shear at a distance d away from the base mat or corners. For the shear at the interface, use shear friction and dowel to the adjoining slab.
 
To CRUNKCRETE:
Application of concrete shear investigation in wall design may have allowable strengths as a funtion of 2f'c^.5 and thickness 'h' near wall ends at location 2 to 3 times 'h'.
Consider mid wall allowables of 4f'c^.5 at 1/3rd wall span locations.
 
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