I'm a dummy, can some let me know if I can change larger diameter rebar with 2 piece bundles? 1

[Terrysteen]

Looking for information if I can replace larger diameter rebar with 2 smaller diameter pieces? I am building 5 - 2 story villas in Indonesia and my Architect is missing???
Anyways the beam and column plan call for 12-14- and 16-mm rebar. In the 40-40 step columns have 12-16 mm rebar and 50 -45 beams with 12-14mm rebar. Columns 1st step is 3.3 meters and the longest beam is 5 meters.
The reason I would like to use a bundle is pricing of material. Going rate for a 10mm, 6 meter bar is $7.00, a 14mm, 6 meter bar is $18.50.
If I could bundle a 10 and 6 mm bar to replace a 14mm ,I could potentially save %25 of my steel costs. There will be no lapping in the beams and the columns will be properly lapped for the second-floor step-up. There is no issue with spacing for cement flow, labor is cheap and easy to do multiple tie spacing's.
Thanks in advance for your answers, even more so if its positive!! Price of steel is going up! Cheers, Terry

 

[CANPRO]

Terry, you should be more concerned about the missing engineer, not the architect.

A 10mm bar + 6mm bar is only 70% of the area of a 14mm bar - easy to see why this saves you 25%. You should stick with the plan until advised otherwise by a design professional.

 

[Terrysteen]

Thanks Canpro

Its a jungle out here! Folks do half a job and get lost all the time!
Difficult to find a professional without paying exorbitant fees.

I am on a budget and every bit helps, so a design professional if I could find one would most likely be out of the question.

If I could pick your brain a little more, it would be appreciated?

Volume of steel is the key here, not the diameter.
2-10mm at a one meter length = volume 15707.96
1- 14mm at 1 meter = 15393 = volume of 15393.8

So if I was to tie 2 - 10mm to make a 14, would be acceptable or is there some other equation that comes into play?

Just to inform there are no 16 mm rebar available here, it would be a 2 month boat ride from Jakarta.
Just to give you an idea of things that come into play when you are doing things in a 3rd world country.
Beautiful place but you have to improvise to achieve here.

It would still be a huge saving over the term of the project.

Thanks,I appreciate your feedback.

Terry

 

[fracture_point]

Terrysteen - "Volume is key here" - this is only true when talking in terms of $, sure. But when we analyse structural members, it is the cross-sectional area of the reinforcement that is critical, not the volume! Therefore, as CANPRO pointed it, if a 16mm bar is specified for structural resistance, then it is not sufficient to use a 10mm + 6mm bar bundled.

 

[BridgeSmith]

There are different requirements for laps and development lengths for bundled bars. Flexural strength will be determined on where the centroid of bar area is, so you'll have to be sure if you replace bars that the centroid of the area of the bundled bars is in the same location as the single bar relative to the neutral axis.

 

[Lomarandil]

Come now FP-- for rebar, volume and cross-sectional area are analogous... no need to obfuscate the point.

Yes, Terry, two 10mm bars have the equivalent area of a 14mm bar (ever so slightly more). This can often be substituted, as long as the following are considered:
Lap requirements for bundled bars, if lapped.
Placement of end hooks, if present
Minimum bar spacings for concrete placement
(am I missing anything? development length is a wash)

It sounds like those concerns are not an issue in your case, so as much as you can rely on any sight-unseen advice, it seems that you're on the right track.

I just designed a structure bundling 16mm bars rather than using 28mm bar myself, for similar reasons. Plus the laborers are much happier handling the 16mm bars. Sounds like we're not that far away from each other, geographically or as far as construction practices go.

Hotrod -- if we're designing anything so tight that the difference between the centroid of a single bar and a bundled bar is the difference between working or not, we're fooling ourselves about the precision of our rodbusters.


----
just call me Lo.

 

[BridgeSmith]

Good point about the placement, Lo. Obviously, I've been sequestered in the office for too long.

Just for clarification, you're saying the development length for the 2 smaller bars bundled is similar to that of the one larger bar of equivalent area, not that the development length of the smaller bars bundled is the same as those bars individually, right?

 

[Celt83]

Lo
I agree mostly but there is still tolerances to be met on the steel centroid locations, the tolerances are generous but they still exist. Maybe more critical for a column take the example below I certainly would not be ok with the second bar layout as a substitution for certain loading conditions.

Open Source Structural Applications:

https://github.com/buddyd16/Structural-Engineering

 

[BAretired]

Volume of steel is the key here, not the diameter.https:
2-10mm at a one meter length = volume 15707.96
1- 14mm at 1 meter = 15393 = volume of 15393.8

So if I was to tie 2 - 10mm to make a 14, would be acceptable or is there some other equation that comes into play?

An easier comparison would be 2*10² = 200 > 1*14² = 196, so 2-10mm bars are 2% greater in area than 1-14mm bar.

I see nothing wrong with replacing the specified single bar with two smaller bars bundled if the area is the same or better. It is always advisable to get the approval of the designer before making the change as he may have different ideas.

BA

 

[Lomarandil]

HotRod -- exactly, development length (in ACI) gets taken for an equivalent single bar with the same area as the entire bundle, so as long as the bundled area is close to the original design area, development length will be about the same. Arguably, if the bundled bars provide more area (and have a longer basic development length), you could reduce the required length proportionally (for excess steel provided) in most cases.

And physically, my suspicion is that the bundled bars actually perform better than the single equivalent bar. More surface area, bond stresses, etc.

Celt -- Agreed. I wouldn't term the third case "substituting bundled bars" in the same sense we're describing, but this is internet engineering. Good to cover all the bases.

----
just call me Lo.

 

[Terrysteen]

Excellent!

I appreciate all your input.
Using the bundles will have no significant impact on the spacing of the rebar. Bundles to be place in the same drawing locations.

No lapping,straight runs.
To boot on top of the savings the workers will be happy not to have to use the big bars.

The saving will allow me to put together a gin pole hoist to move the mixed cement quicker and easier.
I am working on a tiered property and ease of local transport of material will have serious bonuses!!

Thanks for all your help folks, have a great day!

Terry