Update README.md

README.md

@@ -8,5 +8,13 @@ Reference: Gerolymos N. and Gazetas G. **Constitutive model for 1-D cyclic soil
 ```tcl
 uniaxialMaterial BoucWenGG $matTag $alpha $k0 $strainY $n $gamma $beta $s1 $s2 $mkur
 ```
+| parameter | description |
+| --- | --- |
 | `matTag` | integer tag identifying the material |
-| `alpha` | the |
+| `alpha` | ratio of the post-yielding stiffness to the initial elastic stiffness |
+| `k0` | initial elastic stiffness |
+| `strainY` | yielding strain $\varepsilon_y$ |
+| `n` | parameter that controls the transition between the initial and post-yielding branch. As $n$ increases the transition becomes sharper (when $n\to\infty$ the model is piece-wise linear). |
+| `gamma`, `beta` | parameters that control the shape of the hysteresis loop |
+| `s1`, `s2` | control the stiffness degradation upon reversal |
+| `mkur` | account for stress and tangent stiffness modification proposed by Drosos et al. (2012). `mkur`==1 modification is aplied, `mkur`==0 modification is not applied |