Development of a non-linear F. E. M. analytic program of reinforced concrete structures by the use of discrete element

(1)开发裂纹扩展程序，尝试利用裂纹单元开发裂纹扩展程序。在与最大主拉应力垂直的方向上，在发生最大主拉应力的点插入裂纹单元。(2)建立了离散裂纹单元，将其表示为等周二次线性单元，并采用混凝土单元之间的接触单元进行建模。通过拉伸软化曲线（σ_n-δ_n）、剪切应力-位移关系（σ-δ）和断裂能（G_f）来区分裂纹单元。(3)建立了离散键合单元entit，将其表示为等周二次线性单元，并采用混凝土与钢筋单元之间的接触单元进行建模。通过试验分析，将分析结果与实验结果拟合，得到了各试验中最合适的键（σ-δ）和销钉（σ_n-δ_n）特性。(4)无剪力配筋钢筋混凝土梁抗剪性能的有限元分析。将离散裂缝和粘结单元的分析方法推广到受弯剪作用的无剪力配筋钢筋混凝土梁，对梁的弯裂和斜裂的发生、发展及抗剪承载力进行了分析研究。利用这一分析方法，可以对无剪力配筋钢筋混凝土梁的受剪受力机理进行分析。

(l) Development of a crack propagation programIt tried the development of the crack propagation program by the use of crack element. A crack element was inserted at the point, where the maximum principal tensile stress occurred and to the direction perpendicular to it.(2)Development of a discrete crack elementIt was expressed as the isoperimetric quadratic linear element and it was modeled by the contact element between concrete elements. The proposed crack element was distinguished by tension softening curve (σ_n-δ_n), relationship between shear stress and displacement (σ-δ) and fracture energy (G_f).(3) Development of a discrete bond elementIt was expressed as the isoperimetric quadratic linear element and it was modeled by the contact element between concrete and re-bar elements. By trial analysis to fit the analytical results to the experimental results, the most suitable bond (σ-δ) and dowel (σ_n-δ_n) characteristics were obtained in each test.(4) F. E. M. study on the shear behaviors reinforced concrete beam without shear reinforcement by the use of crack and bond elementThe analysis using discrete crack and bond elements was developed to apply to the reinforced concrete beams without shear reinforcement subject to bending and shear, and the analytical study was carried out on the occurrence of flexural and diagonal crack, their development and shear bearing capacity of the beam. By using this analysis, it is possible to darify the shear bearing mechanism of reinforced concrete beam without shear reinforcement.