Beam Construction Joint

[MacGruber22]

CIP concrete garage repairs. Full column replacement and enlargement at upper 2 levels. Additionally, a beam (62 ft span) being replaced full-depth (by 8 ft long) at column. Contractor wanted a construction joint 2-ft from the enlarged column face to cast the columns and the 2-ft extension prior to repairing the remainder of the beam. I wanted to pocket the column enlargement and cast the beam repair into that pocket - however, the contractor protested. From that, I released repair details which included 2#4 inclined stirrups (single piece per double legged stirrup) across the construction joint. My shear-friction calcs indicated that I needed 2#3 bars - I am using #4 bars because of what is already on-site.

However, if you look at the photo, they provided 2-piece stirrups with a non-standard 90-deg hook around the btm. bars. Needless to say, I was miffed that they didn't contact me to let me know that they were having trouble placing the specified single stirrup piece. So, the million $$ question - do I make them chip it out and chip a new pocket in the recently cast column (or) do I rationalize this somehow?

"It is imperative Cunth doesn't get his hands on those codes."

 

[KootK]

Three problems for me:

1) the hooks that you mentioned.

2) the inclined shear friction bars appear to be almost parallel to the construction joint, rendering them ineffective.

3) the pour joint surface is pretty rough.

Are you sure that you need the inclined bars? In these situations, I usually find that the top steel alone is sufficient for shear friction.

If the top steel is sufficient for shear friction, I'd just have the beam chipped back until I had a clean surface to pour against. If not, I'd chip back to the column face plus a nominal bearing ledge.




I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[MacGruber22]

2) A bit of a bad angle to see. I measured it - I asked for 20-deg and got 20-deg
3) I know - they used plastic bags to plug up the first cast. Horrible.

The tension bars at both the +/- regions of these beams do not properly resist the code-required loads. Since those top bars are already at or above capacity, there is no net As req/As prov to use as such. Basically, the whole garage hasn't been designed properly, and it is evident by the a level of cracking that does not appear to be solely related to bad construction.

Your last suggestion is what I am leaning to.

"It is imperative Cunth doesn't get his hands on those codes."

 

[KootK]

Since those top bars are already at or above capacity, there is no net As req/As prov to use as such.

This is where you've got a bit of room to run if you like. You can double dip with bars that are both shear friction reinforcement and flexural steel. Basically, no matter what the flexural demand, you can use 100% of your top steel as flexural reinforcement.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[MacGruber22]

Basically, no matter what the flexural demand, you can use 100% of your top steel as flexural reinforcement.

I don't follow. Are you taking the double-dipping from this commentary below?

R22.9.4.6 Tension across the shear plane may be caused by restraint of deformations due to temperature change, creep, and shrinkage. Where moment acts on a shear plane, the flexural compression and tension forces are in equilibrium and do not change the resultant compression Avf f acting across the shear plane or the shear-friction resistance. It is therefore not necessary to provide additional reinforcement to resist the flexural tension stresses, unless the required flexural tension reinforcement exceeds the amount of shear-transfer reinforcement provided in the flexural tension zone (Mattock et al.1975).

"It is imperative Cunth doesn't get his hands on those codes."

 

[KootK]

That's exactly it MacGruber.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[MacGruber22]

OK - I will have to digest the theory of that a bit. Much appreciated. I have 4#9 top, so that is way more than required for shear friction. It is always nice to dispose of preconceived conservatism.

"It is imperative Cunth doesn't get his hands on those codes."

 

[TXStructural]

Using the #9 top bars only works if they are fully developed on both sides of the cols joint, which I'm not sure can happen if the end extending into the column is as short as it would appear. But it is hard to tell what exactly is going on in there.

I would probably just roughen the surface of the incline to get a reasonable magnitude of roughness and go with it. Although, I don't exactly follow about the inclined stirrups that are nearly parallels the joint. It may increase shear in the new beam, but the weak plane is the cold joint. Again, they need to be properly embedded on both sides of the joint, so I'm not sure how that was planned to work with them so nearly vertical.

 

[MacGruber22]

TX:

I know that the top bars are developed into the column for sure. I measured them prior to the column full-section repair. The other direction, I do not know as we have no existing drawings.

I don't exactly follow about the inclined stirrups that are nearly parallels the joint.

They are not "nearly parallel" - the photo is a bit misleading in that regard. I have the angle I need. Please read my initial response to Kootk. The whole issue is with the contractor's (bad) decision to change by single piece stirrup to 2-pieces.

I ended up leaving the inclined stirrups as is, roughened the surface to CSP#6, and called it a (frustrating) day.



"It is imperative Cunth doesn't get his hands on those codes."

 

[TXStructural]

Single leg stirrups are fine. There is nothing magical about closed stirrups unless you have torsion. In the photos they appear to have 180 degree hooks and should be ok. As you can tell, repairs are generally much easier with two-piece stirrups since they can't cut long bars or squeeze them together to get a 360 degree stirrup around them. I had a few sketchy repair contractors on jobs, but I also had one or two excellent ones. And I had one truly phenomenal contractor who earned every penny and then some. He made me look like a rockstar on one very complex job as well as on the little ones.

 

[MacGruber22]

I agree that single legged stirrups are fine, if they are developed top and bottom. They may appear to have 180 degree hooks, but they are merely very short 90 degree ones. I asked them to bend those hooks into 180, but they refused. I probably should have posted a better photo.

These guys aren't horrible; I am disappointing they deviated from my details without consulting me.



"It is imperative Cunth doesn't get his hands on those codes."

 

[TXStructural]

These guys aren't horrible; I am disappointing they deviated from my details without consulting me.

Welcome to repair work. <wink> or maybe that should be "welcome to construction"?