help with severly corroded A bolt and Base plate 1

[delagina]

I have an abandoned existing steel structure. They want to use it now plus add new level above.

My biggest concern is the A. bolt.

I plan to just add 4 new Hilti bolts outside column shaft and neglect the capacity of existing A bolt.

All base plate A bolts have similar corrosion.

Will this work? Any other recommendation what i should put in my drawing regarding existing corroded A bolt and Base plate.

 

[delagina]

I meant ALL columns' base plate and A bolt are corroded.

 

[slickdeals]

That looks like a heavy-duty moment connection. Probably with lapped reinforcing to the anchor bolts. Gut feeling tells me that adding 4 new anchor bolts without any supplementary reinforcing ain't going to cut it. Do the numbers.

 

[joeHSE]

I agree with slickdeals. You'll probably need to rework at least stiffeners (and maybe the baseplate too) for each column. I would imagine at least as many post-installed anchors as there are anchor rods and you may need to run plates down the sides of the pier with additional post-installed anchors depending on the loads.

 

[delagina]

i plan to re-analyze it as pinned instead of fixed. and just retrofit superstructure/connection if it fails.

 

[slickdeals]

1. Don't check strength alone. Drift limits might supersede. 2. Don't forget P-delta in your analysis.
3. Follow the load path completely (as in redistribution of forces based on your pinned base assumption)

I presume you will have to bring the building up to today's codes, which might mean a complete re-analysis based on today's wind and seismic provisions.

 

[paddingtongreen]

I agree with slick and joe that that is a heavy moment connection. You say you plan to add four Hilti bolts to each, Is this a preliminary proposal or is it based on an analysis? if on analysis, are you considering the base to be fixed or pinned?

To use a Hilti, you will have to drill a large enough hole in the baseplate to allow access for the concrete drill/core borer, and then use a thick washer plate on top of the baseplate to cover the oversize hole. Is there enough room left for legal edge distances?

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[delagina]

yes, there is enough edge distance. i plan to re-analyze it as pinned.

or is it better to still analyze it as fixed and add plate on the sides of pedestal and put horizontal A bolts?

 

[joeHSE]

I don't know what your scope is but to avoid a complete re-analysis as slick brought up you may be better off dealing with base plate mods.

 

[delagina]

my scope is to design the whole thing. i have already designed some equipment platform structures.

 

[paddingtongreen]

If you use horizontal anchor bolts, they must be low enough on the pier to allow rebar development above them. I can't see how much is available from the photo.

If it were me, I would try to see if the modified structure would work with a pinned base, and if so, how much uplift on the bolts; and if not, how to remake the moment connection. If I needed a moment connection I would consider removing existing boot and Anchor bolts and welding on a new boot to carry over the new bolt positions you marked. I would do this before I considered the horizontal bolt modification, but that is just my preference.

Work your analysis first and then see how to get what you need from the foundation, when you have that information the problem might go away.


Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[delagina]

ok thanks. i'll bump this thread later. for now i'll run it as pinned.