Column Anchorage of a Multistory Buckling Restrained Brace Building

[MALV]

Hello,
Code requires that columns and their anchorages to be designed for the maximum brace force of the BRBs. The problem is that with heavy loaded buildings in high seismic areas like California, these brace sizes are getting very large, and with multiple stories of them the anchorage is seemingly impossible with standard anchor bolts. For example, the 4 story building I'm working on is coming up with an uplift of 7000 kips at the columns, which is going to require 20 grade 105 2 1/2" diameter anchor bolts. My question is how are buildings with more stories able to make their column anchorages work with such high brace forces that need to be designed for?

 

[r13]

Assume your calculation is correct, either your building is too light, or the aspect ratio (L or B vs H)is not adequate. Please provide more essential information if you want meaningful feedbacks.

 

[MALV]

I think the problem with the building is that only two bays of braces are allowed per side of the building, which led to BRBs with core area sizes of 40 in^2 on the lower two level. I guess my question should instead be, other than typical anchorage connections with bolts, what alternatives are there for resisting large uplifts in columns?

 

[KootK]

Weld a billion nelson studs to the bottom of your columns and extend them deep into your foundations? Seriously, I've seen this.

 

[Agent666]

Yeah as Kootk noted, plunge columns feed centrally into piles seems to be the norm here.

One other option I've seen used is very thick baseplate with crap load of welded bars vertically into the foundation, with a short stub with column splice above the footing level. Sometimes a horizontal collector beam is cast into the footing to also deal with the shear out of the bracing.

 

[Agent666]

Just worked out what 7000kips is in kN (31000kN). Holy hell.

With that level of uplift I think you've either got something going on wrong in your calculations on a 4 storey building or you have the most inefficient arrangement of bracing on the planet. With the right placement, number and width of braced bays and efficient sizing of the BRB utilising some moderate level of ductility the uplift should be relatively minimal I would have thought.

 

[r13]

I am in line with Agent666's response. Double check your cal and arrangement. What kind of brace system was used?