Steel reinforced concrete elastic modulus help

[taylaron]

I'm inputing data into a SolidWorks material profile, but I'm having difficulty determining the value of the elastic modulus (psi) of steel reinforced concrete

i'm looking at the following source for material properties:

http://www.fhwa.dot.gov/pavement/pccp/pubs/05081/chapt3.cfm [for elastic modulus of concrete and steel rebar]
Here it gives young's modulus of concrete and the value for the rebar.

"Young's modulus of concrete at 28 d, Ec,28 (GPa (x 106 lbf/in2)) 33.10 (4.80)1 and 34.48 (5.0)2

Young's modulus of steel rebar (GPa (x 106 lbf/in2)) 200.00 (29.00)"

I'm confused because steel reinforced concrete combines both steel and concrete, which value or at what proportions do I use? Of course the whole point of adding steel is to make the concrete less elastic, so obviously I can't use concrete, but I obviously can't use just steel either. See my dilemma?

Also I don't understand how to obtain psi from "(GPa (x 106 lbf/in2)) 33.10 (4.80)1 and 34.48 (5.0)2" either.

Thanks for your help,

-Tay

 

[taylaron]

Thoughts anybody?

 

[rafaelcidade]

One way to calculate mechanical properties, such as young modulus, of reinforced materials is to use the "Rule of Mixtures":

"Rule of Mixtures is a method of approach to approximate estimation of composite material properties, based on an assumption that a composite property is the volume weighed average of the phases (matrix and dispersed phase) properties."

http://www.substech.com/dokuwiki/doku.php?id=estimations_of_composite_materials_properties

For longitudinal direction:

$$E_{\mbox{composite}} = E_{\mbox{mat1}}*V_{\mbox{mat1}} + E_{\mbox{mat2}}*V_{\mbox{mat2}}$$

where $$V_{\mbox{mat1}}$$ and $$V_{\mbox{mat2}}$$ are the volume fractions of the materials on the composite.

however I am not sure if it can be used on reinforced concrete problems.

http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWM-4CS4S6P-4&_user=10&_coverDate=11/30/2004&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1260370583&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=849c74eae802eee3b22e8ff930c063be

 

[Studiot]

Edit just noticed the date of the original post.


If you are going to do it that way you need the 'equivalent section' concept.

You transform either the steel or the concrete to an equivalent section of the other, using the ratio of elastic moduli as 15:1 and the fact that you want both to reach maximum allowable stress simultaneously.

The actual calculation proceedure depends upon the structural nature of the problem, and the materials.

What sort of reinforcement do you mean, rods or fibres?

 

[alphy]

I would suggest using a weighted average approach to determine the elastic modulus of steel reinforced concrete. This means taking into account the proportions of steel and concrete in the mixture. The elastic modulus of steel is much higher than that of concrete, so the overall modulus will be closer to that of steel. However, the proportion of concrete still has an impact, so it cannot be ignored.

To obtain the value in psi, you can use the conversion factor of 1 GPa = 145038 lbf/in2. So, for example, the elastic modulus of concrete at 28 days in psi would be 33.10 x 145038 = 4800638 psi.

I would also suggest consulting with a structural engineer or using a concrete design software to obtain more accurate and specific values for your project. Good luck with your research!