flat slab - column moment frame (no beams or walls)

[AskTooMuch]

To those who have done flat slab and column only buildings (no beams or walls), where slab and column act as moment frame, if I need to put a new hole in the column strip (cutting the rebars), how do I check this and what is the best way to compensate that cut rebars along the column strip.

 

[AskTooMuch]

If anyone got a book or reference recommendaion of flat slab - column (no beams or shear wall) buildings, please post here.

 

[hokie66]

That was essentially the system employed in the apartment building which just collapsed in Miami, flat plate with very little in the way of shear walls, so not many of us will be in favor.

 

[SteynvW]

Agree with hokie, unless you have a thick slab like a waffle slab creating moment frames with a flat slab
and column should be avoided.

 

[AskTooMuch]

This is existing that I'm just checking. It's also just 4 columns and 1 slab supporting 1 equipment that we'll be replacing. I just need a good book as a reference specially how to check the lateral loads. I downloaded in ACI, equivalent beam for flat slab but I feel it's lacking information. It was just 9 pages.

 

[tckieu]

 

[hetgen]

It depends on the size of the hole. A small sleeve, say 200mm dia, could be justified by verifying the excess capacity of the column strip, but if you are cutting a large section of the column strip then you have to do a full FEM analysis of the structure to gauge the force distribution.

A reasonably thick flat plate and column frame structure can be used as a lateral resisting system, but it is limited to 1-5 story buildings located in low seismic and wind hazard areas. These limits are not codified, it is just that you can't make it work beyond that.

I don't believe the building that collapsed in Miami is employing this system, if that is the case then it is substantially underdesigned and should not be inferred as a case in point to discredit the system. Lateral resisting systems for flat plate structures are used all over the world and are acceptable according to many design standards.

 

[w-streng]

What are the spans, column sizes and height, slab thickness, hole size required and approximate position on plan and the weight and position of the machine/ry.

 

[AskTooMuch]

hetgen, do you have a good book/reference recommendation for this system. I've downloaded a few technical papers but you may have other suggestion specially a good book.

 

[Settingsun]

CIRIA Report 110 covers flat slabs to the former British Standard. It mostly covers gravity loading on the assumption that something else will carry lateral loading in most buildings, but does provide some comment on unbraced frames.

 

[KootK]

There are a few papers available on this, as you mentioned, but I'd be surprised to see you find a book covering the method in any detail. As others have mentioned, it's not a method currently held in high esteem.

Considering what the parts and pieces would be doing in the frame that you've described, restricting the new penetrations to the middle third of the column strip span might be a reasonable place to start. And, if that doesn't sink your gravity load carrying capacity, you may well be okay.