3000 psi vs 4000 psi concrete
3000 psi vs 4000 psi concrete
(OP)
It is said that 3000 psi concrete are more ductile than 4000 psi.. by how many percentage? do you use 3000 psi or 4000 psi in your building (ordinary and special moment frames)? I know so many structural engineers who have never use 4000 psi.. they just use 3000 psi.. how about you?






RE: 3000 psi vs 4000 psi concrete
RE: 3000 psi vs 4000 psi concrete
http://www.eng-tips.com/viewthread.cfm?qid=255771
"Higher strength concrete is more brittle and less ductile. It is, however, higher strength... It behaves plastically a little better... but brittle none the less.
Dik"
You will notice that in stress-strain diagram.. lower strength concrete has greater strain.. see strain-stress diagram in Figure 1 of http://www.iitk.ac.in/nicee/wcee/article/0809.pdf
So do you guys prefer 3000 psi than 4000 psi because of greater strain per stress in the 3000 psi concrete in special moment frames?
RE: 3000 psi vs 4000 psi concrete
1. Less cost. 3000 psi uses less cement, therefore cheaper.
2. Less shrinkage. Less cement, less shrinkage.
And...let's be honest, 3000 psi concrete is probably closer to 4,500 psi in the real world after a few months.
RE: 3000 psi vs 4000 psi concrete
The coefficient of variation of concrete modulus is very high. The modulus of concrete can vary +/- 20%. Couple that variation with the likelihood that actual strengths will be 1200 psi or more than the specified, and you are left arguing within the margin of error.
Keep the design ductility predictable with steel.
"It is imperative Cunth doesn't get his hands on those codes."
RE: 3000 psi vs 4000 psi concrete
However, I would never use 3000psi these days for suspended structures more from a durability viewpoint. In Australia, 4500psi is about the minimum with 6000psi common especially for PT structures and RC structures in coastal areas.
RE: 3000 psi vs 4000 psi concrete
"It is imperative Cunth doesn't get his hands on those codes."
RE: 3000 psi vs 4000 psi concrete
RE: 3000 psi vs 4000 psi concrete
Most I met who designed residential 2 or 3 storey buildings never used 4000 psi. They stick to 3000 psi. Why is that.
RE: 3000 psi vs 4000 psi concrete
"High-strength" concrete cylinder under compression: https://www.youtube.com/watch?v=0gXHqKpg__A
Both have a similar modulus of elasticity and both fail in a brittle fashion. About the only major difference is the "normal" concrete at least gives some warning before failure while the high strength concrete fails almost instantly. Wouldn't consider either to be what I would call "ductile" though. Spec the concrete strengths you need or can achieve without much cost or hassle.
Edit: Fixed link.
Maine Professional and Structural Engineer
American Concrete Industries
www.americanconcrete.com
RE: 3000 psi vs 4000 psi concrete
I agree with rapt's summary. The difference in ductility is only significant for much higher strengths.
MightyEngineer - both of your links were to "normal" strength concrete (and it didn't say what strength that was).
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: 3000 psi vs 4000 psi concrete
As recently as 2005, I ran into a contractor who wanted to use 2000 psi in a residence. He steadfastly refused to consider anything stronger regardless of any arguments I offered. When I retired in 2008, most people were using a minimum of 25 MPa (3600) psi and many engineers were specifying 30 MPa (4350 psi) minimum in commercial structures to improve durability.
BA
RE: 3000 psi vs 4000 psi concrete
Well, if that doesn't raise a red flag. That is illegal concrete in the US!
"It is imperative Cunth doesn't get his hands on those codes."
RE: 3000 psi vs 4000 psi concrete
Maine Professional and Structural Engineer
American Concrete Industries
www.americanconcrete.com
RE: 3000 psi vs 4000 psi concrete
BA
RE: 3000 psi vs 4000 psi concrete
RE: 3000 psi vs 4000 psi concrete
Maine Professional and Structural Engineer
American Concrete Industries
www.americanconcrete.com
RE: 3000 psi vs 4000 psi concrete
I do residential & spec 20MPa (3000psi) for the vast majority of my RC work. Typically the only time I shoot up to 25MPa+ is when there are sulphates in the soil and you need a type 50 cement anyways. Few reasons:
-An increase in concrete strength rarely changes section sizes. 6" thick basement walls are allowed, but are exceptionally rare, and footing width is governed by the soil properties.
-Cheeper, in this scale builders would rather pour an extra yard or two of 20MPa rather than springing for a 30+.
-(biggest reason) It lets the concrete companies ship off-batches from commercial work to the residential customers. If they were supposed to pour a 35MPa for the new office building downtown but the mix was off they can shoot it down to joe shmo home builder at a discount as a 20MPa batch.
RE: 3000 psi vs 4000 psi concrete
State and commonwealth legislature's creates statutes (laws) to enforce local building code --> adopts model IBC with modification---> adopts ACI 318 with modification ---> structural concrete shall be 2500 psi ore greater. By definition, every adopted provision (not commentary or appendices) is absorbed into the statute. Now, obviously some are more glaring to those enforcing the intent of the statute. We all generally are aware of things that can be slipped by with no harm. Trying to pose 2000 psi concrete as "structural" concrete is asking for trouble (with the law), whether it works or not.
Regardless, I think the discussion is moving from the OP's original moment frames to residential foundation construction. This is apples to oranges. We all know 3 ksi concrete works all day long for single family residence basement walls.
"It is imperative Cunth doesn't get his hands on those codes."
RE: 3000 psi vs 4000 psi concrete
RE: 3000 psi vs 4000 psi concrete
RE: 3000 psi vs 4000 psi concrete
Not so sure about that, at 7 days, you reach 36% f'c @ 4 Degree / 62% f'c @ 13 Degree / 74% f'c @23 Degree
RE: 3000 psi vs 4000 psi concrete
RE: 3000 psi vs 4000 psi concrete
RE: 3000 psi vs 4000 psi concrete