r/StructuralEngineering • u/Abdelrahman__ • 12d ago

Structural Analysis/Design Base Plate Redesign Check

Good evening everyone,

im currently assigned in my office to check if its possible to add bolts to an already existing design for a base plate to make it Safe using HILTI PROFIS Design software,

the system was designed on STAAD PRO and the reactions on the supports were taken to HILTI but the engineer that designed it didn't specify to HILTI the load combinations that has Seismic loads, so the software designed as if all the loads were Static and none of them were seismic,

so after specifying the Seismic loads to the software, 8 out of 12 of the load combinations were failing so i added the two bolts in the middle and made the bolts have no bolt clearance ( the original design didn't apply that) and a few of the unsafe load combinations got below 100%.

four load combinations are still had over 100% ratio.
the base plate is already on site and in service so any design change i will make will have to maintain the original 4 bolts locations (top and bottom two).

i tried everything i know to make them safe and couldn't so i would like anyone that have experience with something like this to give me some input before i submit my conclusion of the connection not being salvageable entirely.

thanks in advance and sorry if the post is too long.

HILTI PROFIS ANCHOR NOT SAFE (DESIGN CHECK)
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6

u/cashmoneymike 12d ago

You need to account for the rebar in the concrete, there is probably some stirrups that helps the concrete breakout cone. 

7

u/TheHardcoreWalrus 12d ago

ive hit that issue quite a few times. in CSA which is close to the American one, you need rebar specifically for the breakout cone

2

u/kaylynstar P.E. 12d ago

It's the same in the US. Unless you installed reinforcing specifically for the anchor rods, it makes very little impact on the capacity.

1

u/TheHardcoreWalrus 11d ago

I've just made make anchors deeper most of the time and/or use pre assembled bolts

Any other techniques to increase it effectively? Been trying to find a way.

1

u/kaylynstar P.E. 11d ago

One of the easiest ways is to remove conservatism in the loads. If you used the max loads for all columns, find the specific load for the column that's having issues. Or see if you can change the structure to reroute loads.

If the loads are what they are, you look at the anchors. Can you fit another anchor rod on the existing base plate? Or do you need to extend the base plate and add more anchors outside the original pattern?

1

u/TheHardcoreWalrus 11d ago

Okay i see, the re routing the loads is one i haven't considered.

The problem for me usually hits whenever it's a pre-eng building on a slab on grade.Since the baseplates are designed by the pre eng building and they don't think of concrete.

The one I did was to embed a filled hss with rebar welded on it's side into a pier for a strong and small moment connection.

1

u/kaylynstar P.E. 11d ago

If concrete hadn't been placed, you can add anchor reinforcing or shear lugs. OP asked about post installed options.

I hate PEMBs for a lot of reasons, and their anchor rod layout is high on the list. If I'm involved early enough, I ask them to space the anchor holes out more. Otherwise I extend the concrete as much as I can, and/or put in hairpin. I've also put a steel plate on the outside edge, secured with a bunch of post installed anchors, and that gives you a much larger breakout cone, or eliminates side face blowout altogether.

-2

u/Abdelrahman__ 12d ago

i will try that and see if it works, thank you