Elevated lazer tag platform

[YoungGunner]

Client wants us to engineer an elevated platform for a lazer tag arena. The floor will be W-shapes with steel decking and plywood sheathing on top and HSS columns supporting. The existing slab is 6" thick, unsure if it is reinforced. I'm trying to limit the number of columns used in the LFRS to avoid cutting out the slab and pour spot footings. However, preliminary design is revealing that that R=1.25 is requiring massive footings. I'm looking for insight if there are a few ways of helping the situation, and also asking for clarification on some design aspects.
1) Another LFRS system I could explore outside of ordinary cantilever columns?
2) This will have obstacles built on it - do I need to include that as dead load in seismic weight if those obstacles aren't designed to resist seismic forces? We are designing the platform for 100psf, more than plenty to handle vertical weight. Follow up to that - do I need to design whatever they put on top to not fall over?
3) Any good thoughts on resisting the overturning moment at the base? Currently getting spot footings 78" wide NOT including partition dead load. Moment is on the magnitude of 18kip-ft ASD.

 

[TLHS]

Can you not turn the decking into a diaphragm and put some moment frames on the perimeter?

 

[YoungGunner]

I was originally doing cantilever columns on the perimeter and still using the deck as a diaphragm. Avoiding moment frames because they need very very small members to get head heights. The floor will be W6s @ 6' O.C. and dropped below that will be W8s. I guess in hindsight the W8s wouldn't be an issue for moment frames if ordinary, but that does pose an interesting connection.

 

[GC_Hopi]

1) A braced lateral system is another option depending on how much open space is needed below the platform.
2) I would consider the obstacles as partitions. Take a look into how the code handles partitions. Heads up: it confusing.
3) See #1, switch to a brace system.

You will need to look into vibration of the floor too.

 

[TLHS]

If you see a big cost savings that justifies a loss in flexibility, they might also be able to incorporate bracing into their obstacles. Chevron bracing could get hidden in a plywood arch, X-bracing could have a crawl through and some windows to shoot through. I'm sure there's something you could do with knee braces to make that moment connection, as well.

You could also hide a lateral system in the ramps in at least one of the two directions.

 

[YoungGunner]

You will need to look into vibration of the floor too.

I was wondering about that, but considering that this will be people running around, not in sync, is there a concern for how they feel the floor will feel? Static deflection under an extreme 100psf live load wouldn't be sufficient to overcome that?

 

[Aesur]

I would see if you would work with the owner on the following options:
1. Braced frames, as others have said, try to incorporate into the features of the structure, ideally walls as you don't want a brace hitting someone in the head.
2. Moment frames, depending on your location, you could look at using "steel not specifically detailed for seismic" with an R of 3 but a lot less seismic moment frame detailing. This is how PEMB manufacturers typically do it in low seismic country.
3. I'm assuming there are obstructions in there somewhere, can they be shear walls by chance?

 

[GC_Hopi]

Maybe "need" was a little strong. I would "consider" it. I have seen how the kids treat these laser tag areas. Its like a mini indoor track and field arena. They are running circles and jumping. As far as the static deflection with 100 psf being stiff enough, that is outside of my expertise to just make a judgement call without looking at some numbers.

Edit: AISC design guide 11 is a reference for vibration of steel framed structures.