×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Concrete Elasticity and tensile strength

Concrete Elasticity and tensile strength

Concrete Elasticity and tensile strength

(OP)
Hi, I have the following expressions to asses Concrete Elasticity and tensile strength. My problem is that they are much different between them. Which criteria would recommend me? Thanks

1-
Ec: 15000*(f'c)^0,5 [kgf/cm2]
fr: 2*(f'c)^0,5 [kgf/cm2]
---------------------------------
2-
Ec: 47000*(f'c)^0,5 [kgf/cm2]
fr: 6.3*(f'c)^0,5 [kgf/cm2]
---------------------------------
3-
Ec: 8000*(f'c^2+8)^(1/3) [kgf/cm2]
fr: 0.3*(f'c^2)^(1/3) [kgf/cm2]

RE: Concrete Elasticity and tensile strength

(OP)
All of them are for normal concrete. Do you have other expressions?

RE: Concrete Elasticity and tensile strength

The ones in your concrete design code.

RE: Concrete Elasticity and tensile strength

(OP)
Sure, thanks. But this not only impact RC strength design, i need to estimate deflections in my structure and this parameters will change all i need to know.

RE: Concrete Elasticity and tensile strength

What is the source for these equations? Check the units used in the original source. The results given for E by all three are much too low with kgf/cm2 units.

All the widely used international codes have equations for these values, and they give similar results, but you have to use the specified units.

Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/

RE: Concrete Elasticity and tensile strength

(OP)
I think the first are from ACI318 but with SI units, i tooked them from a book which use ACI318 for design.
The second are what we use here, the are usually written in MPa
Ec=4700*(f'c)^0.5[MPa] is intended for secant young's modulus at 0,5*f'c
fct= 0.63*(f'c)^0,5 [MPa] refers for non direct stresses.
The third are ones i found between my university notes.

If I took the first and second pairs of expressions only. i'll still get a big differences with n=Es/Ec, critical rotation, critical bending, neutral axis position, yielding beginning.

I'm only trying to get an approximation of deflections under earthquake I've been checking for effective EcIg considerations for RC, cracks influence and that's ok, but my initial values and stress-and-strain curve rely on this parameters and i think that 47000/15000~=3,1 is a big difference to start the analysis.

RE: Concrete Elasticity and tensile strength

Quote (IDS)

The results given for E by all three are much too low with kgf/cm2 units.

That's not actually right. The first one appears to be about right with kgf/cm2 units.

The second one is the ACI metric equation, which should have a factor of 4700 with MPa units.

The units of the factors are (stress)^0.5, which explains why the results you are getting differ by a factor of about 3, since you have factored by 10, rather than 10^0.5.

If you want to compare the results, use the units they were written for, then convert the results to common units.

Both 1 and 2 give an E value of about 27 GPa.

I don't know what the intended units of the third one are.


Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/

RE: Concrete Elasticity and tensile strength

(OP)
yeah, what a relief :D

RE: Concrete Elasticity and tensile strength

(OP)
Reviewing this I like to say i was employing fc in MPa, that's why i got 47.000, my mistake was to simplify it sqrt(fc)/sqrt(fc) forgetting my units steps.

Thinking about the expression 4.700*sqrt(fc[MPa]) it's not just about making 4.700*sqrt(fc*10[kgf/cm2]),
this retrieves [MPa], so there should be a hidden sqrt(MPa) to achieve the result in proper units.
I mean 4.700*sqrt(fc[MPa])*sqrt([MPa]), so to change it i'll need:

4.700*sqrt(fc*10[kgf/cm2))*sqrt(10[kgf/cm2]), getting about 15.000*sqrt(fc), with fc expressed in Kgf/cm2 and also the result

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources