Anchor for concrete footing

[jaypack]

I have been asked to determine a way to repair or replace the anchors on a concrete footing supporting a steel frame for a coal car shaker. The existing anchors have broken at the top of the base plate due to corrosion. I have been told that the entire concrete footing will have to be replaced. I was also asked if drilled anchors for hardened concrete would be acceptable.
There are two anchors, both have broken and both are embedded in the concrete footing.
Is there a procedure for repairing anchors without replacing the entire concrete footing.

 

[SlideRuleEra]

I have made repairs similar to what you describe. For a railcar unloader the concrete foundations are probably quite thick. If the concrete is sound, you may be able to core drill (core diameter maybe 3 or 4 times the existing bolt diameter) at the location of the existing anchor bolts to remove what's left of the embedded portion of the bolt. Then grout a new anchor bolt (inside the cored hole) in the exact same location.

If the existing concrete is not sound enough for this procedure, a new foundation is probably in order anyway.

Best Wishes

 

[Lutfi]

I agree and have done what SlideRuleEra done as well. I like to add some additional options and pointers:

1. Use stainless steel or HDG anchors on the new installation.

2. If you concrete is sound and cannot core drill the existing anchor, try to drill new hole and use adhesive (epoxy type anchors). They work great as well. You must evaluate your edge distances and anchor placement and what type of loads the AB is carrying (shear, tensile or combination).

Good luck

 

[jaypack]

Thank you for your reply. The concrete footing is only 14 square inches and I will have to look at edge distances and whether there is enough to core drill.

Thank you again.

 

[Lutfi]

Well, if it is only 14 inches and this sounds small to me. I like to use minimum of 18 inches square footing. This way you can have decent base plate layout, 0.75-1 inch grout with 45-inch miter (this adds up 1.5 to 2 inches to the base plate foot print). You also need some minimum cover for the anchor bolt that will act as an edge distance. It may be easier to just shore the column and replace the footing.

Keep in mind, I do not have the full picture of what is all around the footing and potential interferences.

Good luck

 

[SlideRuleEra]

jaypack - I agree with Lutfi, this sounds like an unusually small size for an industrial footing. Is it really a footing, bearing directly on soil? Or is it a concrete pier sitting on and tied (with rebar) to a much larger concrete base mat?

 

[jaypack]

Thanks again for your responses. I believe this footing was put in place in 1951. I agree that this is small for a concrete footing. The frame of the coal shaker is W10x21. The base plate is 12x12".

 

[CSEllc]

That is a small footing even for 1951 standards. Based on my experiences, engineers in those days were a little more liberal with concrete sizes, partly due to working stress method used in concrete design and partly due to being more conservative than most are today.

I think you should look into it a little more. IAs SlideRuleEra stated, it might be a concrete pier not a footing.

Regardless, if the concrete and base plate are sound, you might want to try cleaning the base plate and welding bent plates or angles (with the vertical leg pointing down) and re-fasten the base to the pier/footing on its sides. When you layout the new bolts, be sure to chek that they don't cross or align to minimize interfence. I wouold use (2) bolts in each section of angle or bent plate.

Good luck

 

[jaypack]

CSEIIc

You are correct. I apoligize for the word mix. I am calling it a footing but the correct name is pier (14"x14") which is then attached to a footing 4-feet underground that is 6'x6'x15".

Again, I appreciate your responses.

 

[Lutfi]

Now this makes much more sense! Never mind the mistakes, I typed 45-inch in lieu of 45 degree. The new bi-focal glasses are not as good as I thought.