Shear Key no Flexural Reinforcemnt

[Thoughful]

I am working on getting the flexural capacity of this shear key. However, no flexural reinforcement for the shear key is provided in caltrans standard plan, would it make sense to assume that the section below the NA is already cracked and just determine the capacity based on the compressive part?

 

[KootK]

Interesting. On the occasions that I've used shear keys, I've always reinforced them per the CRSI manual.

...would it make sense to assume that the section below the NA is already cracked and just determine the capacity based on the compressive part?

That doesn't make sense to me if I understand your intent correctly. In an unreinforced cross section, the gig is pretty much up once you develop flexural cracking anywhere. The Caltrans detail seems geared towards creating keys that are twice as wide as they are deep. My guess is that their intent is to create a cross section in the key that would work in flexure as plain concrete. As such, I'd evaluate flexural capacity of the key as plain concrete per the ACI provisions for that. It still makes me a bit nervous to use unreinforced concrete for this but, at the same time, creating a more onerous detail than the Caltrans standard is not likely to win you any extra business.

 

[TLHS]

I would never even consider doing an unreinforced corbel, which is really the same thing. But I guess there's no reason it can't work in theory.

I flipped back to the image to see if there was anything clever happening where vertical load might put a vertical compression force into the key and effectively preload it against moment tension, but it's not in the right place for that.

Plain concrete theoretically gets used in foundations all the time, it just feels weird to use here. I did a quick flip through details and every other one I looked at has at least a bar on the one face.

Not necessarily wrong, but not what I would do.

But yeah, if you crack a section you have no tension capacity, so you can't treat it as though you're resisting moment by doing that. You either need to do plain concrete bending or just decide that you're fine with the load transmittal via inspection based on the ratio by treating it as near support shear or something.

 

[Tomfh]

We reinforce our shear key, but it seem reasonable to have a very stocky unreinforced key. Realistically, how is it going to break off? It’s going to win the fight against the dirt.

 

[KootK]

It’s going to win the fight against the dirt.

Well put. That articulates something that I was "feeling" in my initial response. In many instances, the detailing of the key reinforcement as it ties into the footing element is only sort of legit anyhow.

 

[BridgeSmith]

I would never even consider doing an unreinforced corbel, which is really the same thing.

It’s going to win the fight against the dirt.

That's the difference. Corbels support concrete or steel, not relatively soft soil (sorry, still can't call it 'dirt'; I got rapped on the knuckles once too often by my profs for that).

Rod Smith, P.E., The artist formerly known as HotRod10

 

[KootK]

On the other hand, load is load, regardless of whether it originated from something soft or rigid.

 

[TLHS]

Yeah, the amount of resistance that some methods give you credit for on a shear key is pretty significant.

 

[rapt]

My thought would have been, does a shear key have a "flexural" capacity.

I would however reinforce it for shear.