Concrete Questions?

[jk96]

I'm in the need to build to build some additional explosive storage magazines and have some questions on concrete spans. The two current magazines I've built are as follows

1. 12'x20'. All poured concrete, walls, floor, and ceiling at 8" thick.
2. 14'x24' Concrete floor and ceiling at 8" thick. Walls were concrete block - dry stacked with surface bond.

My question is in regards to the concrete roof. Minimum thickness to meet ATF spec is 8" thick. I would like to make a larger magazine than in the past, preferably 20'x32' but 16'x32 would work as well. What I'm not sure about is how far I can safely clear span the concrete roof at 8" thick and the amount of rebar required to do it.

Below is a picture of the 14'x24' magazine we built a few years ago using block.


Jeremy

 

[Egon]

You may need a qualified person to design the roof structure.

And also the pour Framing/Supports.

You may want to look into precast flooring slabs and use them for the roof.

 

[jk96]

You may need a qualified person to design the roof structure.

And also the pour Framing/Supports.

You may want to look into precast flooring slabs and use them for the roof.

I'm well aware an expert can handle this but what would be the fun in that?

I still have access to the oak timbers and posts I used to support the roof during the pour on the first two buildings. I can frame up and handle the roof framing/supports, just curious about the stength of concrete over an open span. I don't need a detailed analysis, just hoping for a few people on TBN who could tell me "yes, you can span that distance with a rebar grid every X amount on center and be well within tolerance" or "no - your pushing toward an unsafe limit"

The concrete roof will not be carrying a load, only needs to support its own weight. Also - precaset would not work because it needs to be 8" solid concrete to meet spec.

Jeremy

 

[dodge man]

I work for an engineering company and you are getting into structural engineer teritory. One thing I can tell you, most of the reinforcement should go towards the bottom of the concrete in the roof, but check with an expert.

 

[Cat_Driver]

Please look into adding either stainless steel fibers of plain fibers the batch mill would add it to the truck before it arrives.

You will not believe how much stronger it makes the concrete.

I won't pour a fence post without fibers.


Steel Concrete Fibers Xorex Crack Contro - Propex Concrete Systems

Enduro Macro Micro Synthetic Concrete Fi - Propex Concrete Systems

 

[jk96]

I work for an engineering company and you are getting into structural engineer teritory. One thing I can tell you, most of the reinforcement should go towards the bottom of the concrete in the roof, but check with an expert.

The first two buildings we did (12x20 & 14x24) were poured 8" thick with a rebar grid of 12" on center and placed 3" from bottom. These were poured 4 years ago and to-date there is not a single crack in the roof structure. I may just stick with the 14' span and increase the length of the building. This only places the inside span with 8" walls at just over 12'.

 

[Egon]

With only 8 inches it gets pretty hard to be able to place the re-bar where it is supposed to be and do much good for the bending moment stresses.

You might want to form a deeper?? beam sections spaced?? for the proper support. Also should know what size re-bar??? you will use for the stresses.

Guesses do work up to a certain point! but then gravity takes over.

 

[6sunset6]

I have no idea what you are using the magazines for. I worked in hydrogen furnace buildings and they were built so if there was an explosion blast panels would let go. This prevented concrete from flying around the parking lot.
Of course in a small structure it would probably allow thiefs to get in so not what you would want. Just a thought.

 

[jk96]

I have no idea what you are using the magazines for. I worked in hydrogen furnace buildings and they were built so if there was an explosion blast panels would let go. This prevented concrete from flying around the parking lot.
Of course in a small structure it would probably allow thiefs to get in so not what you would want. Just a thought.

I own a fireworks display company. Aerial FX - Spectacular fireworks displays & 1.3g fireworks supplier The magazine is for the storage of high explosives (i.e. salute/concussion type shells) and must be a minimum of 8" thick to meet bullet resistant requirements for storage.

Here's a link to some pictures of some of our past shows. http://www.aerialfx.com/AFX Show Photos/

Jeremy

 

[WVBill]

Just curious but isn't there a limit to the size of magazine? I'd think that a bunch of smaller magazines would be safer than one big one. Maybe not more convenient, but safer.

 

[tommu56]

There might be a volume restriction as to the amount of material you have in a single bunker and if you have a "problem" multiple bunkers might save you some product.

At the old Hagley powder works every thing was solid 3 sided with a blow off roof and 1 wall. its an awesome tour if your in the area.

Hagley Museum and Library: Welcome!

tom

 

[jk96]

Just curious but isn't there a limit to the size of magazine? I'd think that a bunch of smaller magazines would be safer than one big one. Maybe not more convenient, but safer.

10,000 lbs of pyrotechnic material per location - shells are figured by 50% of gross weight and multi-shot cake items by 25% of gross weight to get the estimated pyro comp weight. So basically 20,000 lbs total weight for shells or 40,000 lbs total weight for multi-shot cakes per location. Seperation distance is 200 feet between magazines.

 

[crashz]

There is no quick and dirty way to assume this. I'm a civil engineer by education and trade and there is no way that I or any of my collegues would respond with a "rule of thumb" answer to this. I'm not trying to be a jerk here, its just that there are to many unkowns given the information in your posts.

As a building structure, don't you need a building permit? And to obtain the building permit, won't you need sealed plans by an architect or engineer? A single story structure that you describe can easily be designed reasonably by a local engineering firm. Modern structural and concrete design software makes it fairly quick. Probably gonna cost around 5-10% of your total construction cost to do it, and may even save you on overall costs. Would definately remove some laibility off of your shoulders.

 

[dfkrug]

What I'm not sure about is how far I can safely clear span the concrete roof at 8" thick and the amount of rebar required to do it.

I designed this concrete roof last year. It is 8" thick with dual #5s at the
bottom of each "beam", both ways. The foam blocks are there to reduce
weight. I simplified the design to be a bunch of parallel T-shaped beams,
8" wide at the top and 4" wide at the bottom. The span is 20' both ways.
For max strength the bottom bars are 1" from the bottom form. Shoring
was done with 2x4s on end 18" OC both ways.

 

[jk96]

I think I found what I was looking for.

Slab Designer

 

[hitekcountry]

I designed this concrete roof last year. It is 8" thick with dual #5s at the
bottom of each "beam", both ways. The foam blocks are there to reduce
weight. I simplified the design to be a bunch of parallel T-shaped beams,
8" wide at the top and 4" wide at the bottom. The span is 20' both ways.
For max strength the bottom bars are 1" from the bottom form. Shoring
was done with 2x4s on end 18" OC both ways.

Very nice!!!

 

[Egon]

For max strength the bottom bars are 1" from the bottom form.

What coverage does the rebar require to meet your codes?

 

[dfkrug]

What coverage does the rebar require to meet your codes?

As I recall from the ACI 318, you can have as little as 3/4" of cover over
the bars, if the concrete is not exposed to soil, as in the outside wall of
a basement. This is an inside ceiling, so the 3/4" would apply, though
I specced 1", knowing the installers would not be very careful.