For the doubly r/f beams, why we use yield tensile strength than compressive strength of steel? 5

[Pretty Girl7]

I noticed that, for the doubly reinforced beams, the formula use characteristic yield tensile strength (fyk) than compressive strength of steel, for the top reinforcement.

Why are we not using the compressive strength of steel, if we're trying to provide compressive strength support through the top reinforcement?

What am I missing?

 

[JStephen]

I've never seen a mill test report that showed compressive strength of steel- normally, it would be assumed conservatively to be the same as the tensile strength.

 

[Celt83]

Steel typically is assumed to be a linearly elastic isotropic material.

Tie detailing rules preclude bar buckling allowing the bars to reach yield in compression.

 

[HTURKAK]

The tension and compression strength is taken to be the same.

Refer to clause 3.2.7 Design assumptions.. Copy and paste of the clause and idealized design stress-strain diagrams for reinforcing steel (for tension and compression)..

If you put garbage in a computer nothing comes out but garbage. But this garbage, having passed through a very expensive machine, is somehow ennobled and none dare criticize it. ( ANONYMOUS )

 

[rb1957]

what is the ultimate compression strength of steel ? We use ftu as a substitute for "fcu" as an expedience. Is it "truth" ? no, but we cant' afford the truth ...

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[Pretty Girl7]

The tension and compression strength is taken to be the same.

Refer to clause 3.2.7 Design assumptions.. Copy and paste of the clause and idealized design stress-strain diagrams for reinforcing steel (for tension and compression)..

Thank you

 

[Pretty Girl7]

what is the ultimate compression strength of steel ? We use ftu as a substitute for "fcu" as an expedience. Is it "truth" ? no, but we cant' afford the truth ...

Yeah now I get it, it's nearly impossible to measure it as it is, as it's very ductile, so we're using tensile strength instead. But it's very interesting though. I wonder if anyone have tried to measure the compressive strength with any other methods though. We can obviously see it provides better compressive strength when it's deep in the concrete. So somebody must have done similar research how steel behaves when it's in the concrete, than just blindly use tensile strength than compressive strength.

 

[HTURKAK]

COMPRESSION TEST OF STEEL ;

https://www.tec-science.com/material-science/material-testing/compression-test/

If you put garbage in a computer nothing comes out but garbage. But this garbage, having passed through a very expensive machine, is somehow ennobled and none dare criticize it. ( ANONYMOUS )

 

[Pretty Girl7]

COMPRESSION TEST OF STEEL ;

https://www.tec-science.com/material-science/mater...

Thanks for the link. But, I can only see an artistic 'sterss/strain' drawing but unfortunately it does not have proper/true scientific data in it. I don't see the page actually even mentioned the compressive strength results with N/mm2 or MPa for a cylinder specimen. I will try to find if there are any "real" research done on this

 

[IDS]

A couple of other points:

1. The stress limit in the steel is the yield stress, not the tensile strength and the yield stress of steel is typically the same in tension and compression.

2. The strain in compression is governed by the maximum strain in the concrete so the compression reinforcement at the Ultimate Limit State will usually be in the elastic range anyway, especially with high strength concrete which has a smaller strain limit.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[Pretty Girl7]

A couple of other points:

1. The stress limit in the steel is the yield stress, not the tensile strength and the yield stress of steel is typically the same in tension and compression.

2. The strain in compression is governed by the maximum strain in the concrete so the compression reinforcement at the Ultimate Limit State will usually be in the elastic range anyway, especially with high strength concrete which has a smaller strain limit.

Thank you for the information. It's useful.