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QUESTION: Hello.
My name is Bykov Antony, Im from Russia.
I graduated from the civil engineering faculty of Perm State Technical University in 2010. I am a certified engineer and now Im taking a postgraduate course.
The subject of my research is Externally Bonded FRP Systems for Strengthening Concrete Structures.
I have one question about concrete strength, about methods of its determination in USA and in Russia.
Can you help me with this?
In Russia the main characteristics of concrete are еру characteristic and design values of compressive strength of concrete and strength class for concrete. Strength class for concrete is determine by following equation B=Rm(1-tV), where Rm is the average value of compressive strength of concrete, determined in the test batch of standard cubes with dimensions of 150x150x150, V is the coefficient of variation, V=0,135, t is the fractile of the Student-t distribution with probability 0.95, t=1.64.
The relationship between the strength class for concrete and characteristic value of the cube strength Rbn is determine by following equation Rbn=B(0.77-0.00125B).
The design values of the cube strength Rb is determined by dividing of the characteristic value of the cube strength Rbn by the partial factor for concrete γc=1,3.

In ACI 318-05 the concrete strength is characterized by fc. What is this value. Is it average value of several consecutive tests? Or it is the value with accounting of dispersion?

If it is average value of several consecutive tests then I can write
fcube=Rm=1.25fc (EN 1992-1-1).

B=1.25fc (1-1.64*0.135)=0.973fc.

Rbn=0.973fc(0.77-0.00125*0.973fc)= 0.973fc(0.77-0.00122fc)

If it is the value with accounting of dispersion then I can write

fcube=Rm=1.25fc (EN 1992-1-1).

B=1.25fc

Rbn=1.25fc (0.77-0.00125*1.25fc)= 1.25fc(0.77-0.00156fc)

ANSWER: Dear Antony

It is a real challenging engineering question. I try to give you an answer after some time . Can you wait for?


Regards
BEH

---------- FOLLOW-UP ----------

QUESTION: Hello Babak Esmailzadeh Hakimi. It's me again.

Time goes by and I do not sit on the spot. That's what I understood on the subject.
In ACI 318-05 the concrete strength is characterized by fc. fc is the specified compressive strength of concrete with probability 0.91 (K.H. Reineck, D.A. Kuchma, K.S. Kim, S. Marx.  Shear Database for Reinforced Concrete Members without Shear Reinforcement. ACI Structural Journal, V. 100, No. 2, March-April 2003, рр. 240-249.)
In EN 2 the concrete strength is characterized by fck. fck is the characteristic compressive strength of concrete with probability 0.95.
There is the following relationship

fc=fck+1.6MPa (K.H. Reineck, D.A. Kuchma, K.S. Kim, S. Marx.  Shear Database for Reinforced Concrete Members without Shear Reinforcement. ACI Structural Journal, V. 100, No. 2, March-April 2003, рр. 240-249).

fck is the characteristic compressive cylinder strength of concrete with probability 0.95. fck,cube is the characteristic compressive cube strength of concrete with probability 0.95.

There is the following relationship
fck=0.8 fck,cube

In Russia the strength class for concrete B=Rm(1-tV), where Rm is the average value of compressive strength of concrete, determined in the test batch of standard cubes with dimensions of 150x150x150, V is the coefficient of variation, V=0,135, t is the fractile of the Student-t distribution with probability 0.95, t=1.64. So B is the characteristic compressive cube strength of concrete with probability 0.95.

Then B= fck,cube.
fck=0.8B
fc=0.8B+1.6MPa
B=(fc-1.6MPa)/0.8
Rbn=B(0.77-0.00125B)=( (fc-1.6MPa)/0.8 ) (0.77-0.00125((fc-1.6MPa)/0.8))

How do you think I am right?

Answer
Dear Antony

The formula you developed are correct regarding the interrelationship between parameters but I have doubt about to make such a relationship between parameters with different basis of research and statistics. I guess a tuning factor must be adjusted to make a better sense of the problem. I am excited to see such a strong basis of engineering knowledge and energy in you. I will do my best to find a response for your question as soon as possible.

Regards
BEH

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Babak Esmailzadeh Hakimi

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I can answer questions in Structural Engineering, Earthquake Engineering, Project Management and Project Control topics!

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I am experienced in the area of earthquake engineering in electrical power industry, i.e. Lifeline Earthquake Engineering. My focus has been on structural seismic design of power installations. Recently I have got involved in project management in the category of constructional engineering.

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Bs degree in Civil Engineering from Ferdowsi University ,1988, Mashhad Iran, Ms degree in Earthquake Engineering, Sharif University of Technology, 1993, Tehran, Iran

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