Thru bolt loaded in single shear in concrete
Thru bolt loaded in single shear in concrete
(OP)
If you have a thru bolt loaded in single shear bearing on a hole in a concrete member, is there any test data or evidence that can show that the stress distribution in the hole is parabolic instead of triangular?





RE: Thru bolt loaded in single shear in concrete
Just like most other things in structural engineering, we greatly simplify the load distribution, provided there is enough ductility for the connectors and base material to reach "design strength" without fracturing.
Just curious - what is the reason to sharpen the pencil for this condition? Usually, this type of connection is over-designed, and for good reason.
RE: Thru bolt loaded in single shear in concrete
The pencil sharpening is because we are pushing the envelope here. Usually, we are able to cast in a steel pipe thru which the bolt would be inserted. This, of course, increases the bearing area to the concrete considerably. This time, however, it is direct bolt-to-concrete bearing, so we have essentially line bearing right at the outside edge of the hole. That, coupled with a required phi factor of 0.65 in bearing, is really making it difficult to meet the required load. That's why I was looking for some justification for a parabolic distribution so I could use an average stress of 2/3 f'c instead of the 1/2 f'c for a triangle.
But, thanks for your input.
RE: Thru bolt loaded in single shear in concrete
The other engineer's lawyer asked him what would happen to the stresses if the outside edge were to crush and were to redistribute the stresses in the concrete. He replied that he wasn't able to produce that type of model... but that the concrete had crushed.
He was presented with data from a 3D FEM model that I had written showing the redistribution. Maximum stress could be established. Client lost, but, had fun in the process.
Until redistribution from yielding/crushing the stresses can be quite high and there was little difference with a tiny air gap around the rebar. I suspect a bolt would be the same.
Dik
RE: Thru bolt loaded in single shear in concrete
I am convinced that a stress redistribution takes place in cases like this, but have never been able to formally prove it.
Logic tells me this: unless there is a punching shear failure due to the lack of enough concrete wall thickness, then the outer edge of the hole will most certainly start to crush when the f'c stress is exceeded. But, since the load is still present, it then has to go somewhere else, and that would be to crawl inward along the bolt until equilibrium is finally met. If you could plot that path, my guess is that it would look very much like a parabola.
But, just being an ordinary engineer and not a PhD college professor, what do I know?
RE: Thru bolt loaded in single shear in concrete
It was a different time, and, I was a bit different.
Dik