your average RC beam span 3

[pattontom]

What's the usual length of beam span you work with? In my place I know many engineers who only work with 4 meter or less beam span. In such short span, the moments (Mu) at supports is only roughly 40kN.m and they have confidence only working with this. When beam span reaches 6 meter. The moments at supports reach 200 kN.m because the slabs get thicker than 100mm. How about in your place. What is the average beam space you work with often? What moments at support you are getting?

 

[structSU10]

Are you refering to beam spacing? Your note about slab thickness is confusing otherwise. If not, the span is what it is, its more a span to depth ratio, and detailing based upon forces and stresses. deeper beam / slab results in less reinforcing due to decreased moment arm.

 

[pattontom]

I'm talking about beam span in between columns. When you use 4 meter beam span between columns. You don't need secondary beams. If you use secondary beams to support floor slabs. The beam can get heavy. So what beam span in between columns (meaning beam distance between columns) do you guys usually encounter in another country?

 

[JedClampett]

This all depends on layout and loads. Sometimes things work out that the span is 4 meters (although that's kind of short and hardly worth a beam) and sometimes it's 30 ft. (note the smooth segue to feet). Larger spans mean deeper beams and heavier reinforcing (stating the obvious) and more thought put into splices, partial length bars and stirrup spacing. Headroom might be an issue.
I also always try to work it out that my beams are continuous so I can take advantage of the moments in both directions (+ and -) and the support widths. It's not always possible, but it's nice to have it work out that way.
I guess if you're looking for an answer, I'd prefer not going over 30 ft for simple spans. I prefer a belt and suspenders, not just depending on the bottom reinforcing. I'd probably add 10 feet to that for 40 ft. total for continuous designs. But that's all a personal choice.

 

[TXStructural]

For a baseline, visit

http://concept.crsi.org/

(It's free)
The online tool will let you see what kind of concrete frame systems can carry your loads, and see the approximate material quantities required for carrying gravity loads. It's new, so we appreciate any feedback you might have. The underlying computation engine was developed by a well-respected, practicing structural engineer, with the idea of helping designers get better economy out of concrete buildings.

CRSI (

http://www.crsi.org)

publishes the CRSI Design Handbook, which includes design reference tables for slabs. From that publication, given certain design parameters for concrete compressive strength and reinforcement yield strength, for commercial loading, a 100 mm one-way slab CLEAR span would be limited to just under 4 meters. For typical residential loading, the spans might go to 5 meters, and are limited by deflection (l/360) rather than strength. Economy may not be achieved in this manner, since longer spans need more reinforcement, but once you reach deflection criteria, increasing the amount of reinforcement does not compensate for serviceability concerns.

 

[OldPaperMaker]

pattontom,
If you are using ACI 318 (in version 318-08) check out Chapter 9-Strength & Serviceability Requirements. That chapter has all sorts of guidelines for depth & spans for slabs & beams.

 

[JAE]

If you add up all the concrete beam spans in the world, and then divide that by the number of them, you will then know what the average beam span is.

 

[rowingengineer]

Normally Column layout for carparks or similar sets the spans.

Pattontom,
I assume from your posts thus far that you are designing a concrete building, about 6 stories. This is not a simple design exercise and I realize you are probably changing between your native language and English, But I do suggest you find a senior engineer that can mentor you on the basic design principles. I am very concerned that while this forum s providing you with useful information that this will not be handled in an appropriate manner such that a good design outcome is probable.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[BadgerPE]

"If you add up all the concrete beam spans in the world, and then divide that by the number of them, you will then know what the average beam span is."

Well played...gonna have to remember that one!

 

[pattontom]

I'm not asking about guidelines for span and depths and how to determine it. Of course I know about it. I'm just asking what is the typical beam spans in other countries? In my country. Most buildings that includes commercial and residential have only 3-4 meter beam length between columns. It is only the more modern ones that has longer spans.. maybe because of the bolder generations of engineers. But the moments at supports of say 6-9 meter span has Mu reaching 250 kN.m instead of just 40 kN.m in 4 meter length beam. In your design, what is the common Mu of beam at columns (or negative moments) you get? just wondering that is all.

 

[hokie66]

Most of our commercial buildings in Australia are designed for carparking on some of the levels. The spacing of columns to allow 3 or 4 cars between columns is therefore usually between 8 and 11 metres in one direction, which is usually the direction of the beam or band beam. The bending moment is whatever it is.

 

[JacksPanic]

There is no such thing as "average span i work with".
Its got nothing to with "being bold".
The span of a beam is a product of building use and physics.
Weird questions will get weird answers.