Modulus of Elasticity

[flipperdpriest]

Hi,

Two Questions;

I am preparing to do a FEA model to determine the properties of a structure in vibration (natural freq, mode shapes etc).

Q.1 Should I specify the young's modulus of the material as that of the material under static conditions OR as that under dynamic conditions?? If you could point me in the direction of any literature I would greatly appreciate it.

Q.2 Say I am modelling an RC slab using 2-d elements. I am then applying material properties to these elements. As I have a composite material (concrete and embedded steel), how is this reflected in the Youngs Moduls which I specify for the planar element. Again if you could point me in the direction of any literature it would be a great help.


Best Regards,

Flipper.

 

[GregLocock]

1 dynamic

2 any decent structures texbook. basically work out the equivalent bending stiffness for a uniform material with the same average density. Do that by working out the neutral axis of the original section and plotting the strain through it.

3 I suggest you get the results checked very carefully. Dynamic analysis is easier in some ways than statics, but the questions you are asking seem rather fundamental.

Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

 

[structurallyyours]

Use E valuse as 5000sqrt(fck) MPa.
It is OK if you will ignore steel.

 

[GregLocock]

The previous poster structurallyyours will need to provide a great deal of justification for his comments.

Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

 

[bkal]

You can get some guidance in ACI 349. Similar value of Young's modulus for reinforced concrete is specified in ASCE 4-98 for use in seismic analysis. There are also some guidelines there on whether you need to consider cracked or uncracked sections which affect member's stiffnes.

 

[hacksaw]

In part your answer depends on the completeness finite element model being used.