RambergOsgoodSteel Material

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This command is used to construct a Ramberg–Osgood steel material object.

uniaxialMaterial RambergOsgoodSteel $matTag $fy $Es $a $n

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$matTag	integer tag identifying material
$fy	yield strength
$E0	initial elastic tangent
$a	“yield offset” and the Commonly used value for $a is 0.002
$n	Parameters to control the transition from elastic to plastic branches. And controls the hardening of the material by increasing the "n" hardening ratio will be decreased. Commonly used values for $n are ~5 or greater. ($n must be odd number).

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Introduction to the Ramberg–Osgood’s Material Model:

In earthquake engineering, Ramberg–Osgood functions are often used to model the behavior of structural steel materials and components. These functions are obtained when the power is normalized to an arbitrary strain, ε0, for which the plastic component of the strain, εplastic, is not zero. Generally the yield strain, εy, provides a good choice for normalization of strain, the Ramberg–Osgood function is expressed as:

<math>\epsilon = f^'_c \frac{n \left (\frac{\epsilon_c}{\epsilon_0}\right)}{n-1+\left ( \frac{\sigma_c}{\epsilon_0} \right )^{nk}}</math>