Concrete Design Basis: Cube or Cylinder

[BigH]

G'day all: Am trying to wrap my head around the BS EN1992-1-1 and BS 8500-1:2006 to BS EN 206-1:2006 (British Complimentary).

It is my understanding that the concrete member design equations (beams, columns, etc) are done in BS EN 1992-1-1 using the characteristic strength that is based on cylinders. Hence, say the characteristic strength would be 30 MPa, then the concrete would be given Grade 30/37.

Under the British Complementary (BS 8500-1:2006 to BS EN 2006-1:2006) is the design member equations based on cube strength or cylinder strength? Then when specifying, if cube, and you have 37 MPa, then you would grade as Grade 30/37.

It seems that nothing I have been able to find easily really addresses the design equations.

Regards

 

[Agent666]

In Eurocode, all design equations use f_ck, and this is defined as the 'Characteristic compressive cylinder strength at 28 days'.

The reason I believe it has both in the designation for the strength class is simply to cover that in some regions where Eurocodes are applicable concrete may still be specified, manufactured and tested based on the cube strengths. I guess it gets get rid of the temptation/ambiguity to use the higher value in design if that's what your previous standards might have been based that allowed for the differences.

It also means everyone is talking the same language, or can translate between the two systems. If you just specified I want 30MPa concrete, you have no idea if its based on the cylinder or cube strength.

For testing it is graded on whatever test you did, cylinders or cubes, and the other missing value is simply matched as you note.

 

[BigH]

Thanks Agent666. I've worked with the testing of concrete in both cylinders and cubes - The British still, as far as I am aware - and in Malaysia they are using BS - are the actual design equations (BS8110?) written for cubes or written for cylinders. It is not the "strength" in testing but which is used in the actual design equations. My background is ASTM/ACI for design equations - it is just that I want to be sure when the designer is saying he needs X strength based on BS 8110, I "know" he means cubes or cylinders. Cheers - and again thanks.

 

[Agent666]

Well I think that's where if you are asking someone it pays to make 100% sure, so everyone's speaking the same language. If someone ask me a strength grade I automatically think the cylinder strength, but someone from the UK might think in cubes.

 

[Tommy385]

Agent666 is correct,
concrete is defined in EC as C(cylinder/cube), if you say for example: 30MPa concrete, it is ambiguous.
Designer should always use Cx/y designation. Than you are basically safe if you order concrete from other country (in theory, because there are a lot of national annexes...)

 

[rapt]

BigH

You have to decide which code you are talking about.

BS8110 - 1997 equations are in cube strength.

BS EN formulae are the Eurocode formulae are in cylinder strength.

I would be asking them to clarify which is used/defined, Cube or Cylinder.

 

[Tommy385]

isn't BS8110 - 1997 withdrawn?

 

[drbrainsol]

Beginner engineer here but as far as I know, everything we do in the UK (to BS EN 1992) is based on cylinder strength. Hence, BS 8500 would also be using cylinder strength. C30 concrete in BS 8500 should be specified as C30/37.

BS8110 is withdrawn - superseded by BS EN 1992.

 

[BigH]

Thanks all - that is what I thought - that all is to cylinder now. Then, depending on location (Malaysia) because they use cubes, we would ensure that the cube "equivalent" was used. I.e., if 25 MPa (cylinder), we would use 30 MPa for the cube value.

 

[rapt]

BigH,

Just make sure you qualify whether it is Cube or Cylinder on the drawings or specifications or whatever or do it the EN way with C24/30.

And note that the incompetent people who wrote Eurocode rounded the conversion to give nice looking numbers eg C25/30 should be C24/30.

 

[BigH]

Thanks Rapt - I've dealt with both before in the field - and you are correct. I just was unsure on which basis the design was done. Cylinders it is. So then here in Malaysia we would specify the second number (i.e., 30) since they use cubes here (wished it were cylinders).