Thru bolts in existing concrete column

[cmoran]

Hello all I am looking for some guidance on thru bolts in an existing concrete column (see attached pdf for clarification.)

I have pretty high loads when factored around 350 kips to be exact and using 1 1/2" bolts in double shear I can get the bolts to work for the shear. However, right now I am looking at Appendix D with my current cover and I am having all kinds of trouble getting it to work.

Has anyone else run into a situation similar to this? Any help would be greatly appreciated.

Thanks

 

[slickdeals]

I don't think ACI Appendix D applies in your case. For good measure, I would epoxy inject the hole after the through bolts are installed in place, prior to placing the plates and bolting.

 

[ron9876]

Need to be sure that bearing stresses are ok.

 

[RHTPE]

123 kips / 8 bolts = 15.4 kips single shear left side.

Assuming bolts are securely tightened, you will have confinement of the cover concrete around the holes. Which could enhance the bearing strength of the bolt against the concrete at the bottom.

I think slick's suggestion of epoxy in the holes before attaching plates is a good idea, assuming it has the appropriate compressive strength and will not flow under extended high load.


Ralph
Structures Consulting
Northeast USA

 

[port125]

I have a question regarding this question.

How can you develop the full shear capacity of the bolts?
What mechanism allows the load to transfer from the bolt into the column?

I did a real basic bearing check that i think shows the bending of the bolt will be exceeded before the full 15 kips will be able to transfer into the column. (See attached)

Is there something in the concrete code that allows this connection to work?

As a note I have (very) limited experiance with steel to concrete connections. but quite a bit with steel to steel.

 

[ron9876]

port125 that is similar to the approach that I have used in the past to analyze this type of condition. I assume about a 1-1.5" bearing length. If bearing stresses work then check for bolt bending. Haven't ever seen anything written about tests or research on this condition.

If you can get epoxy to fill the opening so much the better. I have required it in the past but not so comfortable that the contractor will take the proper steps required to completely fill the void.

 

[SLTA]

Do you know for sure where the rebar is in the column? They're often heavily reinforced, and you'd want to make sure you don't hit that.

 

[cmoran]

Thanks all for the comments so far. I'll try to answer some of the questions that came up...

slta - I know where the vertical/horizontal reinf in the columns is and as long as it was built somewhat close to the existing drawings it shouldn't be a problem.

port/ron - I hadn't check bearing yet but what is your thought process that the bolt only bears 1-1.5"?

 

[ron9876]

cmoran it was an educated guess/assumption. When the bolt deflects due to bending it will try to concentrate the reaction at the edge of the concrete. The concrete will likely be overstressed and will crush/deform locally. No doubt the real answer depends on the bolt diameter, bolt length and the magnitude of the load.