OpenSees Concrete04 Material Test
Concrete04受压部分的包络线采用Popovics (1973) 提出的单调荷载下的应力—应变关系，并根据Karsan-Jirsa加卸载准则确定其加卸载刚度（线性）；受拉部分的包络线由线性上升段和指数下降段组成，其加卸载与再加载刚度取其与原点的割线刚度。(Concrete is a uniaxial Popovics concrete material object with degraded linear unloading/reloading stiffness according to the work of Karsan-Jirsa and tensile strength with exponential decay.)