How to define a composite section

[minjie]

dear all:

i have 2 questions:

1. if a section is of a concrete rectangle slab and steel wide flange section girder, like this
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how to simulate this section in opensees. Can I just define two elements between two nodes?

2. in the command [b]uniaxialMaterial[/b] , $E means F=Eu or sigma=E*epsilon, how the right equation is decided? $eta depends on u' or epsilon'?

Thank you!

[silvia]

1. use a fiber section.
2. i don't understand the question

[hugo.esquivel]

2.

For a linear material, E means the Young's Modulus. Yes, sigma=E*epsilon.
For a nonlinear material, E means the initial Young's Modulus.

In some cases, you can use E as the force constant, k, to define a section Aggregator or a zeroLength element. F=kx.

Please, define eta.