Column base plate retrofit
Column base plate retrofit
(OP)
I have a PEMB steel building that the contractor did not order a special inspection. The building is 100% complete and the lack of special inspection only came up after the contractor went to the city to get their CO. We have since found out that the installed anchor bolts were only embedded half as deep as the plans required. I need to increase the size of the existing base plate to accomodate the new bolts we will be epoxying into the footing. The added portions of base plate will be the same depth as the original base plate and will run parallel with the column web. I originally thought to support the new sections of base plate with gusset plates perpendicular to the column web. A second option would be to overlay the existing base plate with plate that is the thickness I need and weld it to the column flanges and web (I could even remove the existing nuts and bolt this new plate to the existing plate in addition to the welding). Have others done similar retrofits? If so, is there some input you could provide as to why or why not one of these solutions would be acceptable? Obviously better ideas are definitley welcome.






RE: Column base plate retrofit
I have a pretty good idea of what you are thinking, but would like to see a sketch before commenting
Ram
RE: Column base plate retrofit
Blodgett's book should give you some ideas.
RE: Column base plate retrofit
A sketch is attached. ToadJones, I think I follow what you are saying, can you elaborate a little more? Maybe a sketch too?
RE: Column base plate retrofit
My idea is likely overkill for your application and it might add fixity to the base that was not part of the original design of the building or foundation.
I don't think I like the idea in your sketch. The weld will be in the worst possible spot and doing a full pen weld against the foundation will be next to impossible.
One idea might be to weld angles in against the web of the column and extend them out to catch the new anchors. Blodgett's book calls them "hold down angles".
RE: Column base plate retrofit
RE: Column base plate retrofit
This is a PEMB, only uplift forces, no moment. I was only trying to show where my new bolts needed to be. If I added to the base plate, I would provide stiffeners perpendicular to the web so the weld wouldn't be trying to resist moment. However, increased fixity at the base is also a concern. I could overlay a plate over the existing baseplate and extend the new plate out to the new bolts. If I am understanding you correctly, then I think this would be similar to the angles that you mentioned. I don't have Blodgett's book, so I was hoping you could provide a sketch to make sure I am picturing it correctly.
RE: Column base plate retrofit
RE: Column base plate retrofit
RE: Column base plate retrofit
RE: Column base plate retrofit
RE: Column base plate retrofit
RE: Column base plate retrofit
RE: Column base plate retrofit
You're right. The plate should be fully bearing on the slab or grout. I really like ToadJones' fix too. In fact I have already moved forward with sizing the angles.
RE: Column base plate retrofit
RE: Column base plate retrofit
RE: Column base plate retrofit
Not sure what the net benefit/penalty of that would be for your design if you are considering the combined tensile capacity of the new and old anchors, especially if the adhesive anchor spacing will still be pushing the cantilever distance out.