2 Heavy Point Loads

[Johnrmd]

I have 2 heavy point loads of 15kips each for a bay that is 30.5'x30.5' for a 9in slab that is on the 9level and I was trying to figure out how many reshore floors i need to have. It is for a exterior platform that is being supported by 2 post for at the edge of the building slab, the platform is 8' wide the post are right below the point loads, each floor below is also 9" slab and also 40psf live load Does any one have a solution I could look at for the problem. Thanks for your input.

 

[Howlyn2]

Johnrmd can you elaborate what you mean by reshore floors? Are you suggesting how far to chase the load? What's your ultimate goal? Typically I have chased loads far enough into the building until I have met IEBC 402 exemptions for gravity & lateral loads (5% & 10% respectively) in order to insure the supporting structure further in the building is adequate.

 

[Enable]

I'm also a tad confused at the configuration of the loads / structure. I think a quick sketch would help.

But in general you need to look at ACI 347 - Guide for Shoring/Reshoring of Concrete in Multistory Buildings. In particular, navigate your way to the so-called "simplified method", which addresses usual assumptions in reshoring design. The skinny of it is you assume each floor takes load proportional to its stiffness / design load. Now, you do have to take care here as that assumes a UDL over the effected area which even with full slabs being supported isn't exactly true. It's definitely not true for point loads. Though this is the starting point for any reshoring design scheme you are considering.

So having said that, the point load case I would be very careful relying on the same assumptions as the simplified method. You are only engaging a localized area of the structure and you need to pay attention to the bar layout in that area (e.g. are you putting negative moment where the slab wasn't designed for it).

I might be inclined to take the load directly to the vertical load path of the structure. Meaning, prop the load down with some 25 kip PERI props onto a distributing beam that is blocked at its ends overtop of columns below. If that's not possible (usually not because columns have a tendency to continue damn you continuous load path!), then same idea but use shelf angles installed into the columns to rest the beam onto. 15 kips wouldn't be difficult to resolve that way.

CWB (W47.1) Div 1 Fabricator
Temporary Works Design

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