Shear in Slab with Concentrated Load 1

[sclee21]

I have a situation where a two way slab supported by walls along each side is subject to a 16 kip vehicle load. When this load is close to the edge of the slab there is a high shear stress at the face of the support. Does the code address the width of the slab cross section that should be considered to resist shear? If I assume a 12-inch wide cross section I get a 20-inch thick slab. 18-inch wide cross section I get a 14-inch thick slab, 24-inch wide cross section I get a 12-inch thick slab.

 

[msquared48]

Assuming a 12" square for punching shear, and depending on the strength of your concrete, it seems like something in the range of a 4" to 6" slab should be able to handle that.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[sclee21]

I would agree for punching shear.

I am checking the beam shear at the support wall.

Looking at it like a simply supported beam with a large concentrated load near the face of the support, would you not need to check the beam shear?

My question is what to assume for bw in 2XSQRT(f'c)XbwXd??

 

[ATSE]

Width for beam action shear (1-way) in a 2-way slab system should not be less than the column strip. True for walls or columns. However, for walls all 4 sides, beam shear will always be conservative.

 

[csd72]

I would spread it out at a 45 degree line each side and check the shear on that width.

 

[sclee21]

csd72,

"I would spread it out at a 45 degree line each side and check the shear on that width."

This is basically what I have done in the past. I was hoping someone could point me in the direction of a code requirement that backs it up.

ATSE,

I would not think the entire width of the wall could be considered. It would seem that the shear in the slab would be equal to the reaction that the slab is putting on the wall which would be much higher at the location of the load than 5 feet away.

 

[cap4000]

I did this problem using Westergaard's formula a while ago. The shear load as I recall was reduced by 55% close to the wall. If you have Ram Advanse you can model it as a shell or plate to verify this large reduction.

 

[LOKSTR]

sclee21,

See the attached file for calculating slab width for concentrated load.

 

[Ron]

Check AASHTO design criteria. This is similar to a bridge slab near the supports. I believe the early criteria were 24"+some percentage of the span.