Command manual

This material model can only be used for concrete reinforcement (see COMPONENT_REBAR, ELEMENT_REBAR). The plastic flow stress is defined as:

$\displaystyle{ \sigma_y = f(\varepsilon_{eff}^p) \cdot \left( 1 + \frac{\dot{\varepsilon}_{eff}^p}{\dot{\varepsilon}_0} \right)^c}$

where $f(\varepsilon_{eff}^p)$ is a user defined CURVE. Ductile failure is modeled with the Cockcroft-Latham failure criterion. A rebar element will be eroded once a damage parameter, $D$, has evolved from 0 to 1. The damage growth rate is defined as:

$\displaystyle{ \dot{D} = \frac{\mathrm{max}(0,\sigma) \cdot g(D)}{W_c} \cdot \dot{\varepsilon}_{eff}^p}$

$\displaystyle{ g(D) = \left\{ \begin{array}{ccc} 1 & : & D \leq D_{neck} \\ \frac{L_0}{D_0 r_{ref}} & : & D > D_{neck} \end{array} \right. }$

$\sigma$ is the tensile stress in the rebar. Note that damage only grows in tension (i.e. if $\sigma > 0$).

In uni-axial tension all deformations will be localized to a single element after onset of necking. This is a consequence of the one-dimensional stress formulation in ELEMENT_REBAR and it makes the global ductility element size dependent. $g(D)$ is a scale factor that is used to reduce this effect. Note that $g(D)$ is only used if $r_{ref} > 0$. The damage at onset of necking $D_{neck}$ is calculated automatically and it is based on $W_c$ and on the hardening curve. $L_0$ is the initial element length and $D_0$ is the initial rebar diameter.

$\tau_{max}$ is the maximum shear resistance between rebars and concrete. At shear stresses above $\tau_{max}$ the rebars begin to slide inside the concrete. In the current implementation, the shear resistance is maintained at $\tau_{max}$ even after initiation of sliding. An alternative to defining a maximum shear resistance is to define a slip-dependent shear resistance. This is done by setting parameter $\tau_{max}$ to crv(cid), where cid is the curve identification number of the CURVE containing data of shear resistance vs tangential slip.