Column fixing to Existing Slab - Uplift

[raligt]

We have a fairly tall steel frame building bearing on to an existing 600mm thick RC slab. At the braced bays however the uplift is quite excessive and i am struggling to get a decent number of Resin Anchor fixings to work (i am using the Hilti Profis design and it is asking for 16no. M30s).

My uplift force is 900kN with 300kN shear force.

is there any alternative solution I can look at?

 

[human909]

Have you considered increasing the number of braced bays? Spreading the load to multiple points is always a good idea.

 

[GeorgeTheCivilEngineer]

At 900kN you'd need around 6sqm of 600mm thick concrete to resist that uplift. I would suggest that the anchors potentially not the only limiting factor here.

 

[KootK]

is there any alternative solution I can look at?

A 600 mm thick slab is thick enough that you can provide discrete beam elements within the slab volume. I would detail a pair of orthogonal beams beneath your columns similar to how shear head reinforcement is sometimes provided to address punching shear. If you design the stirrups etc of the faux beams properly, you should be able to use reinforced concrete design principles rather than anchorage principles to resist your uplift. This will have the added advantage of being a more ductile uplift resistance mechanism.

 

[structSU10]

Do the new frames align with columns below? Any chance you can provide rebar that can be developed with the existing column verticals to transfer the uplift? look into hilt HIT-RE 500 V3. the profis tool allow you to look into developing rebar with epoxy.

maybe the base of the steel column gets cast into concrete where you can transfer the force from that new concrete encasement to the epoxied bars that are developed with the existing bars?

 

[Retrograde]

Core through the existing slab so you can through-bolt with threaded rods and washer plates on the soffit.

 

[KootK]

I just now clued into the fact that this is an existing structure. I retract my proposed solution which was intended for a new build situation. Must. Read. More better.

 

[milkshakelake]

That is a really massive uplift. It seems like a lot of anchors, but to me, it doesn't seem like enough. Sometimes, the design is just the design. Maybe use a giant steel base plate to spread the anchors more efficiently.

I'd look into AISC Design Guide 5 - Low and Medium Rise Buildings to get an idea of how to add just a little bit more steel but efficiently reduce the force. They have a creative solution in there.