*BUCKLING ENVELOPE

Data line to define the buckling strut envelope

First (and only) data line

1. $\xi$, coefficient defining $P_y=\xi {\sigma }^{0}A$ (default value 0.95).

2. $\gamma$, coefficient defining the isotropic hardening slope $\gamma EA$ (default value 0.02).

3. ${\alpha }_0$, coefficient defining $\alpha ={\alpha }_0+{\alpha }_1\frac{L}{D}$ (default value 0.03).

4. ${\alpha }_1$, coefficient defining $\alpha ={\alpha }_0+{\alpha }_1\frac{L}{D}$ (default value 0.004).

5. $\kappa$, coefficient defining compressive force for discontinuity in buckling envelope (default value 0.28).

6. $\beta$, buckling envelope slope coefficient (default value 0.02).

7. $\zeta$, coefficient defining the force axis intercept point (default value $\text{min}\left(1.0,\frac{5.8}{\xi }{\left(\frac{t}{D}\right)}^{0.7}\right)$).

In the above data line A is the cross-section area, ${\sigma }^0$ is a yield stress value, E is Young's modulus, L is the element length, D is the outer pipe diameter, and t is the pipe wall thickness.