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

(l)裂纹扩展程序的开发尝试用裂纹单元开发裂纹扩展程序。在最大主拉应力发生的点处和与之垂直的方向上插入裂纹单元。（2）离散裂缝单元的建立用等参二次线性单元表示，用混凝土单元间的接触单元模拟。用拉伸软化曲线（σ_n-δ_n）、剪应力-位移关系（σ-δ）和断裂能（G_f）来区分所提出的裂纹单元。(3)离散粘结单元的建立用等参二次线性单元表示，用混凝土与钢筋的接触单元模拟。通过试验分析，将分析结果与试验结果进行拟合，得到了各试验中最合适的粘结（σ-δ）和传力（σ_n-δ_n）特性。(4)F. E. M.采用裂缝单元和粘结单元对无剪力钢筋混凝土梁的抗剪性能进行了研究，提出了一种适用于无剪力钢筋混凝土梁受弯受剪的离散裂缝单元和粘结单元分析方法，并对受弯裂缝和斜裂缝的产生、发展及受剪承载力进行了分析研究。利用该分析方法，可以揭示无抗剪钢筋混凝土梁的抗剪承载机理。

(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.