Stirrups

[PUEngineer]

I'm working on a fairly large concrete wide-module framed building in the US. Falls under the IBC and it's a SDC A structure. For typical interior beams of substantial width, including lateral beams, why would one use stirrups with 90 degree hooks rather than just using stirrups with 135 degree hooks? There will be plenty of spandrel beams where this 135 degree hook ends would be required anyway. So, it just seems keeping one kind is simpler. I'm only talking about the bottom U shaped piece in a two piece stirrup, not the cap piece.

 

[hokie66]

Some might consider the 90 degree hooks simpler to bend and to place, but the development of 135 degree hooks is superior. The 135 degree hooks also limit the chance of insufficient cover if the hook bending is not quite right.

 

[DST148]

Agree with hokie66. Per ACI 318-11 Commentary, larger bar sizes with 90 degree hooks tend to pop out under high load.

@PUEngineer> In beams of substantial width, normally what maximum lateral distance between the vertical legs you allow?
Not sure, but some codes restrict distance to about 0.75 times effective depth.

 

[precast78]

If you have a small enough x-section, sometimes 90 degree bend wont give you enough development.

 

[msquared48]

Sometimes it's easier to place the stirrups with a 90 degree hook at one end and a 135 at the other end rather than than one with two 135's.

Mike McCann
MMC Engineering

 

[PUEngineer]

@hokie: I'd agree, they are simpler, but from a cost perspective, it seems that extra 45 degrees would add very little. Trying to figure out if that cost is worth the consistency in the field is the root of my question.

@DST: It's a #4 stirrup we're talking about here. I'm trying to keep things consistent in the project. All spandrel beams will have two piece stirrups with the main 'U' bar having 135 degree hook ends. So, it seems simpler to just make that a consistent approach. I usually think about adding legs when the beam width gets over 30".

@msquared: I assume you're talking about the cap in a two piece stirrup. I'm strictly questioning the bottom 'U' piece in a two piece stirrup. Let me know if I'm wrong.

 

[msquared48]

Yes, or column stirrups in two pieces where the stirrups are needed only nominally at best.

Mike McCann
MMC Engineering

 

[hokie66]

I don't think there is a cost difference. The 135 degree hooks give better anchorage, and they also give the consistency you want, so use them.