Lateral resisting system for flat plate structure 2

[tonycampos88]

I am designing a flat plate parking structure with columns at 20 ft o.c. My problem is to define the lateral force resisting system. I am planning to use the cantilever column approach, does anyone know if this is allowed by the code? Is just that I read that it is not allowed for high seismic zones but I could not find the appropriate section in the code. What other system can I use if I want to maintain the flat plate system (no drop beams)?

 

[slickdeals]

You probably have shear walls around the stair cores in the parking garage. Design them for 100% of lateral loads and the columns strictly as a gravity-only members.

 

[tonycampos88]

I dont have any other lateral elements (no shear walls) it is a one story high structure only

 

[msquared48]

Then you are looking at concrete moment frames - hopefully ordinary or intermediate at worst.

Mike McCann
MMC Engineering

 

[theonlynamenottaken]

Like Mike said, moment frames. You can use strips of slab as your beams, but they won't be the same as your gravity load column strips. Here's a link to the original paper Pecknold did that lays out this analysis technique, and gives recommendations on what strip widths to use.

Link

 

[tonycampos88]

but then the cantilever column system is not allowed? The problem is that I am in SDC D and special moment frames would be required. Thanks for the link

 

[steellion]

ASCE Table 12.2-1 dictates what seismic force-resisting systems you are allowed to use based on SDC and structure height. Moment frames or shear "lite" walls are probably the way to go for your structure based on the information you provided.

 

[msquared48]

tonycampos88:

You can do the pole situation if you use a grade beam system at the foundation for fixity. The connection at the top of the column could be pinned if you want. This is tanamount to an inverted concrete frame with a pinned base. Should not be a code issue.

No worries.

Mike McCann
MMC Engineering

 

[msquared48]

tonycampos88:

You can have an inverted moment frame that would mimic the cantilever column system. All you do is have a grade beam system at the foundation to establish the fixity for the column, and pin the connection at the top of the column. This should be allowable by code.

Mike McCann
MMC Engineering

 

[msquared48]

The above happens when it appears that your first post did not go through... Sorry.

Mike McCann
MMC Engineering

 

[DavidKn]

You are in a seismic zone in which ordinary or intermediate moment frames are not permitted, and you are trying to cantilever the columns to hold up a concrete slab? Why would you expect to be allowed to use a system that is LESS robust than ones that you KNOW are disallowed? The way I read the code, you will need shear walls, or special moment frames, or you will have to change your design so you don't have concrete overhead. (Is it just a roof? Or a slab, like a plaza?) As for "where does it say it is not permitted", the way I read ASCE-7 Seismic provisions, you have to use a system that IS permitted, or prove that the system you are using is just as good as a permitted system. If it's not in the table, you can't use it.