can we provide beam reinforcement like this? 3

[curiousinvite]

 

[hokie66]

You can, if you want to confuse the barsetters. Best just to stick with one size, especially with small bar sizes. M16 is my minimum size for beam reinforcement.

 

[curiousinvite]

Can we provide extra bar of higher diameter than main bars ?

 

[hokie66]

I thought my answer was sufficient. The bars don't know which ones are 'main' and which ones are 'extra'.

 

[Tomfh]

You can, but why not use the one bar size?

Eg 4 N16.

N16 isn’t an especially big bar. Like hokie66 it’s the smallest bar I’d consider in a structural beam.

 

[MIStructE_IRE]

I agree with hokie. In theory yes, but good luck getting this installed correctly.

 

[Enable]

Corner bars are typically what hold the stirrups in place until everything is tied as a cage. The minimum size with sufficient stiffness to accomplish that is typically 15M. Even if you drew the beam the way you have, and I caught the distinction, I'd still put 15M instead of what you've drawn because I'd need it that way just for constructability purposes.

BTW I am unfamiliar with the sizes you're specifying. What part of the world are you? In Canada, we order in metric but I've never heard of a 12M or a 16M bar. We have 10M and 15M and as far as I know generally go in increments of 5. Found this table and it looks like our European counterparts have oodles of sizes. Wowzer!

 

[RabitPete]

How large is the beam? I assume you are reinforcing the bottom only? As drawn, the only bars I see are on top and that's not how you reinforce the beam.

 

[Tomfh]

Enable,

Sizes 6,8,10,12,16,20,24,28,32… etc are the common denomination in many parts of the world.

In Australia a 15mm piece of reinforcing is something an apprentice would be sent to fetch as a joke.

 

[Settingsun]

We should remember that steel is still more expensive than labour in places so not try to enforce uneconomic solutions. Beams can be built with 12mm top bars in the compression zones.

Enable, I think only the Canadians were, um, clever enough to call a 16mm bar a 15M, along with the rest of the system. The 100mm2 increments are no benefit to computers and it takes approximately one day of concrete design to memorise the mm2 of normal bar sizes (80, 110, 200, 310, 450, 615, 800).

 

[Tomfh]

Oh a 15M is 16mm anyway is it? Lol

 

[Enable]

Hey! Don't tar me because I'm not worldly!

But I sure am curious now since our practice seems to be the odd one! What's the benefit of so many different sizes? Seems of questionable help in design (just round up) and more of a PIA for suppliers / installers to maintain stock and keep track of? I dont buy it's more economical but maybe that's just my market. Labour + site time would kill us with 2mm increments.

 

[canwesteng]

Is Canadian practice the odd one? It's basically the same as the US, where they use nice round numbers for bar diameter increments as well, only in imperial. The European system is strange, but surely they only stock certain bars and you just get used to it in practice.

 

[Settingsun]

 dont buy it's more economical but maybe that's just my market. Labour + site time would kill us with 2mm increments.

Probably a function of going metric earlier when the materials/labour cost ratio was different. The smaller sizes are nearest even mm to old imperial sizes . Some places then went 4mm increments, others went closer to imperial with 20-25-32.

Is Canadian practice the odd one? It's basically the same as the US

 

[Enable]

LMAO steveh49...I'm teaching a class right now via zoom and my students instantly cocked their heads when they saw me react to your picture. Absolute gold. Much appreciated

 

[curiousinvite]

this is the output I got from etabs ,
so , 2 12mm dia bar throughout which is 226mm2 which is more than 155mm2
Since we need more rebar at support (near column up to 0.3L/0.25L)
I provided 2 16mm extra bar near support so total reinforcement of 628mm2 near support which is more than 550.

 

[hardbutmild]

Seems of questionable help in design

When looking at confined masonry requirements in europe you need stirrups at 15 cm spacing or less. It's usually D6/15cm. If I had to use the smallest canadian bar at the same spacing that would be 3.5 times more steel. 6mm bars are also significantly easier to bend at site.
I don't really get those huge diameters, unless they're for bridges. But you don't have all of the diameters at one project, it's just that for different things different sizes are used.
I assume that many sizes used in europe are because different diameters are preferred in different countries and until recently most had their own codes and standards.
EDIT: OP, you could use 2D14 at midspan and 4D14 at edges or 2D12 and 5D12 if the beam is wide enough... or 2D16 and 3D16.

 

[Lomarandil]

Ha, I'm in a market opposite of Hokie and Tomfh (although only a few thousand km away). M16 is the largest bar size we use in beams. Anything bigger is too difficult to bend by hand.

I do try to keep a 4mm difference between bars on any given project, but in my market, we use everything between 6mm and 16mm (rarely 20mm). And the cost difference across a 2mm bar size change is quickly a few laborers wages for the month.

Haven't seen anything to validate it, but my suspicion is that when the beam stirrups are 6 and 8mm, developing them around a 10mm or 12mm corner bar works just fine.

----
just call me Lo.

 

[hokie66]

Lo,

Where Tomfh and I are, we don't bend any bars by hand. It is all done in a bar bending shop, with the exception of 250 MPa yield M12 bars for freeform swimming pool construction.

 

[Lomarandil]

I'll bet you all have proper UBs and TimTams too...;-)

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just call me Lo.