Minimum thickness for shear in concrete
Minimum thickness for shear in concrete
(OP)
Can anyone point me to a minimum thickness in ACI 318 for shear? Client wants a 3" thick edge that vehicles will drive over, I feel this is too thin regardless of the load but can't find the reference.
Maine EIT, Civil/Structural.






RE: Minimum thickness for shear in concrete
I don't know of a code specified minimum for shear. You could run an edge column style punching shear check on the tire contact area to get a required thickness. As a traffic surface, durability requirements may put your rebar near mid-depth which won't help shear any.
All that being said, there are precast double tees in many garages with 4" flanges. That is often made possible by sketchy assumptions regarding load sharing between adjacent tees however.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Minimum thickness for shear in concrete
It's actually a recessed concrete cover, but they wanted to recess it in a less than optimal way. Outdoors, level with grade, fire truck access but not highway loads or super frequent traffic. Obviously the channel will help "armor" the edges but I'm concerned that the whole thing will crack at the base of the 3" stub with repeated traffic assuming the grade is slightly lower than the top of the 3" stub.
It's probably fine but I still seem to recall 4" being the magical "you shall not pass" number for thickness.
Maine EIT, Civil/Structural.
RE: Minimum thickness for shear in concrete
I'd push for six inches so that I could get two layers of vertical rebar in there somehow. I realize that kind of overkill isn't likely to fly in the precast world however. You'll have one layer of centred vertical steel I imagine, making "d" for your shear calculation 1.5".
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Minimum thickness for shear in concrete
RE: Minimum thickness for shear in concrete
RE: Minimum thickness for shear in concrete
Kootk: Yeah, I described it poorly. Yes, we expect a lateral load as the wheel has to "climb" over the lip assuming the grade becomes lower than the top of the corner. We would like at least 4", then it meets the minimum requirement for walls per ACI.
Oh well, I guess I'll run the numbers as best we can for 3" and see if my boss approves it.
Maine EIT, Civil/Structural.
RE: Minimum thickness for shear in concrete
Maine EIT, Civil/Structural.
RE: Minimum thickness for shear in concrete
Still seems like a crap detail to me.
Maine EIT, Civil/Structural.
RE: Minimum thickness for shear in concrete
I would agree that it's a "crap" detail.
How does one obtain reliable "interlock" between the headed studs and whatever minimal reinforcing exists in the 3" wide portion of the wall?
I can imagine a heavy vehicle moving right to left on your detail having to hit the brakes hard and snapping the 3" wide portion off.
Ralph
Structures Consulting
Northeast USA
RE: Minimum thickness for shear in concrete
Maine EIT, Civil/Structural.
RE: Minimum thickness for shear in concrete
A706 bars I hope.
Ralph
Structures Consulting
Northeast USA
RE: Minimum thickness for shear in concrete
Maine EIT, Civil/Structural.
RE: Minimum thickness for shear in concrete
I got involved in a lawsuit over brittle A615 bars. Seems the "wheelbarrow" contractor was tack welding intersections rather than tying them. So I took a bunch of short #4 bars to a certified welder and had him do a number of sample welds - some using the AWS standard for A615, some without. The ones done without could be snapped by hand-bending. The ones done with the proper preheat did not. The best rebar fabricator that I know uses A706 exclusively for all of their prefabricated cages. One of their specialties is prefabricated cages for tunnels & precasters.
Ralph
Structures Consulting
Northeast USA
RE: Minimum thickness for shear in concrete
Anyway, back to studying for the SE exam and my whiskey.
Maine EIT, Civil/Structural.
RE: Minimum thickness for shear in concrete
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Minimum thickness for shear in concrete
Maine EIT, Civil/Structural.