Whatever "topping" you put over the beam becomes the total beam height.

Sure, but the thing to do is buy the proper InsulDeck with the proper depth instead of adding slab over to make the beams deeper.

Have you ever heard of rebar being called on the top portion of the InsulDeck beam?

Concrete is usually fine in compression (on top), but it needs steel on the bottom for the tension.

Posted By Lbear on 19 May 2014 10:44 PM

I was also told by the engineer that the 4" slab on top of the beam portion plays a vital role in the beam/floor strength during the monolithic pour. Whatever "topping" you put over the beam becomes the total beam height. For example, if you have a 10" InsulDeck form with an 8" beam pocket and pour a 4" slab on top, you really end up with a 12" beam, not an 8" beam. Likewise if you only pour a 2" slab on top, you will end up with only a 10" beam.

True, but it's more complicated than that. In a beam you have the neutral axis where the portion of the beam above is in compression and the portion below in tension. Since concrete has zero tensile strength the rebar provides the tensile strength below the axis. Concrete below the axis adds no strength to the beam except by keeping the rebar in place. You just have to have enough concrete around the rebar to restrain it in the position it needs to be in to provide the greatest strength.

The stiffness and strength of a beam is related to the property called the moment of inertia, or I, which is determined by the cross sectional area and shape of the beam. The farther the area is from the neutral axis the greater the I. It's a cube function. That's why joists and trusses and beams in buildings use an I shape, i.e., "I" beam. That's why a standard 1 x 6 board on edge is twice as stiff as a 2 x 4 on edge. But a 1 x 6 will twist more readily than a 2 x 4 when it's loaded on edge.

Your Insuldeck floor system is a series of T beams side by side. The thicker the slab the higher up the neutral axis.  If you get the neutral axis too high then there is the possibility of the vertical leg bending, or twisting, sideways when there is a heavy load on the beam. And the thicker slab automatically adds load. The thickness of the vertical section, the depth of the beam, and the thickness of the slab all interplay with each other. It's possible that a 2" thick slab may actually give you a stiffer and stronger floor than a 4" slab will. One would have to do detailed calculations to know for sure. You might actually be better off to have deeper beams spaced farther apart with a thinner slab on top. It's not a simple 12 is stronger than 10 situation.

Posted By FBBP on 19 May 2014 11:20 PM

Does the engineer not call for ties or stirrups along the beams tying the top and bottom bars together?
••• Whatever "topping" you put over the beam becomes the total beam height.••• Exactly right. Bigger distance between tension and compression.

NO stirrups or ties that I can see. In the "Joist Reinforcing Schedule" is shows nothing in the "Stirrups" column. It mentions "splices" but nothing about ties.

Posted By dmaceld on 19 May 2014 11:51 PM

 It's possible that a 2" thick slab may actually give you a stiffer and stronger floor than a 4" slab will. One would have to do detailed calculations to know for sure. You might actually be better off to have deeper beams spaced farther apart with a thinner slab on top. It's not a simple 12 is stronger than 10 situation.

The InsulDeck beam spacing is locked in at 24" since that is how the forms are designed. As you mentioned, the only variable one can change is the depth of the beam by choosing different form thickness.

I was told that a 2" slab on top of the InsulDeck would NOT be enough to prevent significant cracks and support structural weight on the 24" spans between the I-Beams. One would also have a very difficult time installing #4 rebar @ 12" o.c. on top of rebar chairs and trying to cover that with only 2" of concrete. No contractor I talked to would go less than 3" but most wanted 4" in order to have a finished floor that they could warranty.

My total floor thickness is 14" (from bottom to top):
2" EP
8" Deep I-Beam Pocket @ 5" wide
4" Slab

No contractor I talked to would go less than 3" but most wanted 4" in order to have a finished floor that they could warranty.

I think your problem might have been that you wanted the InsulDeck surface to go outside. It's difficult to protect the reinforcing steel from outside corrosion when the slab is only 2" or 3". Is that what they were reacting to?

Other than that, they might owe you an explanation as to why they thought they had to re-engineer a system that has worked fine for quite a while now.

anyone needing the latest design manual email me at
insuldeckflorida at aol dot com

anyone needing the latest design manual email me at
insuldeckflorida at aol dot com

Has there been a revision in the last 6 or 7 years?

Posted By ICFHybrid on 20 May 2014 08:51 AM

I think your problem might have been that you wanted the InsulDeck surface to go outside. It's difficult to protect the reinforcing steel from outside corrosion when the slab is only 2" or 3". Is that what they were reacting to?

Other than that, they might owe you an explanation as to why they thought they had to re-engineer a system that has worked fine for quite a while now.

As with any profession, you will get differing opinions. Engineers will disagree with other engineers and InsulDeck is in the business of selling stay-in-place forms and will always tell you to consult with an engineer. The span tables are general "rules of thumb" with a safety factor built in. The tables are based on a "pinned" install and not on a "locked" install.

Nothing was really "re-engineered" and the engineers who use InsulDeck forms just use a software program that is used to determine beam design. I have seen the program and it shows the "T Beams" but of course doesn't show the EPS form work because the program is a commercial based concrete beam program.

As a matter of fact I had two separate engineers recommend the 8" beam pocket with the 4" slab.

Posted By Lbear on 20 May 2014 12:01 AM

Posted By FBBP on 19 May 2014 11:20 PM

Does the engineer not call for ties or stirrups along the beams tying the top and bottom bars together?
••• Whatever "topping" you put over the beam becomes the total beam height.••• Exactly right. Bigger distance between tension and compression.

NO stirrups or ties that I can see. In the "Joist Reinforcing Schedule" is shows nothing in the "Stirrups" column. It mentions "splices" but nothing about ties.

For my Amdeck, I had over 5,000 stirrups.

icfhybrid
yes, about 2 years ago.....

Posted By ICFHybrid on 20 May 2014 10:20 AM
Has there been a revision in the last 6 or 7 years?

Yes, they revised it because it was overly engineered and they wanted to loosen it a bit but as it stands now, the span tables and charts are based on a very conservative approach. There is probably a 25% margin of safety factored in.

If you look at the old vs new span charts, they increased the span capabilities by a few feet.

Posted By ba_icf on 20 May 2014 12:04 PM

For my Amdeck, I had over 5,000 stirrups.

Are you serious? What kind of structure are we talking about here?

Posted By Lbear on 20 May 2014 04:46 PM

Posted By ba_icf on 20 May 2014 12:04 PM

For my Amdeck, I had over 5,000 stirrups.

Are you serious? What kind of structure are we talking about here?

It is just a standard floor.  At least, there is nothing special about it.  I think our maximum span is less than 25'.  I basically have the exterior footings and we put in 2 more footings, so that the spans were about equivalent.

I think my floor thickness is between 4-5".  The plan was 4" minimum, and because we used no threshold showers, we needed to have that 1" lower than the floor, so that necessitated the 5" slab in most places.  I am pretty sure the slab is pretty thick. 

I didn't get to see the pour because we were away on vacation for 2 weeks when the radiant and floor pour occurred.  I saw lots of the rebar and stirrups being added.

I guess I could check on my plans to see the exact floor thickness.  I know the area around my crawlspace access holes are about 16" tall.  I guess I could measure and then I would know for sure.

Posted By ba_icf on 20 May 2014 05:12 PM

It is just a standard floor.  At least, there is nothing special about it.  I think our maximum span is less than 25'. 

A 25' span and 5,000 stirrups? Wow, either that figure is way off or whoever engineered it went completely insane on the reinforcement. I don't even know how it is possible to fit 5,000 stirrups on a 25' span floor. There is not even enough room to fit them. The cost would be insane.

Something is askew here...

Do you have any pics of the project or finished floor?

Posted By Lbear on 20 May 2014 05:54 PM

Posted By ba_icf on 20 May 2014 05:12 PM

It is just a standard floor.  At least, there is nothing special about it.  I think our maximum span is less than 25'. 

A 25' span and 5,000 stirrups? Wow, either that figure is way off or whoever engineered it went completely insane on the reinforcement. I don't even know how it is possible to fit 5,000 stirrups on a 25' span floor. There is not even enough room to fit them. The cost would be insane.

Something is askew here...

Do you have any pics of the project or finished floor?

I have a 3000+ sq ft amdeck floor.  i am not sure how the 25' span is related to the number of stirrups.

Posted By ba_icf on 20 May 2014 07:05 PM

Posted By Lbear on 20 May 2014 05:54 PM

Posted By ba_icf on 20 May 2014 05:12 PM

It is just a standard floor.  At least, there is nothing special about it.  I think our maximum span is less than 25'. 

A 25' span and 5,000 stirrups? Wow, either that figure is way off or whoever engineered it went completely insane on the reinforcement. I don't even know how it is possible to fit 5,000 stirrups on a 25' span floor. There is not even enough room to fit them. The cost would be insane.

Something is askew here...

Do you have any pics of the project or finished floor?

I have a 3000+ sq ft amdeck floor.  i am not sure how the 25' span is related to the number of stirrups.

Do you mine me asking aprox price of the amdeck floor, do you have any break down? 

Posted By krom on 20 May 2014 09:08 PM

Posted By ba_icf on 20 May 2014 07:05 PM

Posted By Lbear on 20 May 2014 05:54 PM

Posted By ba_icf on 20 May 2014 05:12 PM

It is just a standard floor.  At least, there is nothing special about it.  I think our maximum span is less than 25'. 

A 25' span and 5,000 stirrups? Wow, either that figure is way off or whoever engineered it went completely insane on the reinforcement. I don't even know how it is possible to fit 5,000 stirrups on a 25' span floor. There is not even enough room to fit them. The cost would be insane.

Something is askew here...

Do you have any pics of the project or finished floor?

I have a 3000+ sq ft amdeck floor.  i am not sure how the 25' span is related to the number of stirrups.

Do you mine me asking aprox price of the amdeck floor, do you have any break down? 

unfortunately, I don't have a price breakdown.  Originally, I was trying to be an owner/builder, but the task seemed to be too big.  I did manage to get some amdeck quotes from different contractors, but not with my current contractor.  I was getting bids in the $60k range for 3,000 sq ft.  I think we in northern california are always paying higher than other people.  I presume my current contractor was in that general vincinity, but I am not sure.  My contractor gave me a total cost with all of the things included.  Other contractors gave me a more detailed breakdown of their costs, but my current contractor's total price was competitive, they were local, i have been to 3 of his current homes.  i have talked with his current and former clients, so in the end, i didn't ask for a detailed bid.

we have just completed the texture on the walls, and they might have started painting the walls today.  based on my contract, it hasn't been an issue without having the detailed information of each subcontractor. 

i am sorry that i couldn't be more helpful

If you look at the old vs new span charts, they increased the span capabilities by a few feet.

Well, sounds like my InsulDeck floor is extra, extra strong.

Posted By ICFHybrid on 20 May 2014 11:11 PM

Well, sounds like my InsulDeck floor is extra, extra strong.

On a 14' span a 5" high joist plus a 3" slab over with two #4 bars at the bottom is more than stout. Did you use the InsulDeck tables or is this what the engineer called for?

What was the psi of the concrete and what type of reinforcement did you use on the 3" slab?

I think the architect used the tables as a starting point. We re-engineered it all for maximum seismic resistance. The concrete was specified to be 3000 psi minimum, but with extra doses of fly ash, it was coming in much higher. The slab was reinforced with #3 bar at 18" OC. One thing we had which I haven't really seen elsewhere were the edge ties. There was a remarkable amount of right angle steel connecting slabs and verticals and footings and verticals.