Smearing rebar material properties

[rh142]

Is there an equation to smear the modulus of elasticity of rebar on a solid element.

I have a 3D model of a concrete structure and only the concrete is modeled as an isotropic material. The natural frequency is coming out to be too low. I wanted to smear the stiffness of rebar without changing the element type to a concrete element. Is there a easy way of doing this.

Thanks,

 

[EdR]

rh142:

E(composite)=E(concrete) AREA(concrete) + E(steel) AREA(steel)

and

AREA(concrete)=1.0-AREA(steel)

AREA(steel) = % steel expressed as a decimal i.e. 1%=.01

Ed.R.

 

[GBor]

Unless the rebar is closely spaced enough and in an even mesh pattern (including vertically), you may have to switch to an orthotropic brick so that you can differentiate material properties along the element axes. For instance, if the rebar is running along the x- and y-axes, but not the z-axis, you will need to increase the x- and y-moduli, but not the z-modulus.

Garland E. Borowski, PE
Borowski Engineering & Analytical Services, Inc.
Lower Alabama SolidWorks Users Group
Magnitude The Finite Element Analysis Magazine for the Engineering Community

 

[JAE]

EdR,

Don't you mean the following:

E(composite)=

E(concrete) AREA(concrete) + E(steel) AREA(steel)
TOTAL AREA

??

 

[GregLocock]

the neutral axis moves as well.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[rh142]

thanks for all your responses, for the orthotropic material will the shear modulus change the same way? What about poisson's ratio?

GregLocock,
I don't understand the neutral axis if its being modeled with solid elements

Thanks,

 

[EdR]

JAE:

Nope...By defining the Area's as I did the total area becomes 1.0 and you don't have to consider the total area of each element.....

rh142:

It's probably a decent first approximation to use the same idea for the shear modulus...Once you have E and G Poisson's ratio's are defined.....You may have to look up the orthotropic (anisotropic?) relationships between E, G, and Nu....

Greg:

True if bending is present...Typically when using this technique the element size is controlled so that the smeared properties are representative of each region (and as Garland said also in each direction) ...Thus if bending was present one would have multiple elements, each with a different % of steel, to represent the various regions....The technique can be extended to bending elements by extending the "transformed section method" of composite materials but it becomes complicated.....


Ed.R.

 

[JAE]

EdR - thanks...I missed that % that you were using.

 

[GregLocock]

Ah OK, I was thinking beam elements, not bricks.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.