Buckling and Rupture of Main Reinforcement Related to Ultimate Limit of Concrete Flexural Members

本文研究了单轴单调加载和循环加载条件下约束混凝土对纵筋屈曲应变的影响，在循环加载条件下，为了测量纵筋的应力，采用了一种新型的测力传感器（钢筋测力传感器），其是局部沿着钢筋定位的淬火硬化部分，由于时间的原因，无法对钢筋的断裂进行研究，主要结论如下.通过对试验结果的讨论，导出了约束混凝土中纵向受压钢筋屈曲应变的计算公式，并在单轴受压条件下，研究了横向钢筋间距与试件直径之比（S/D）、纵向钢筋间距与纵向钢筋间距之围压指数（ps siguma sy），横向钢筋的屈服强度（siguma sy）、侧向钢筋形状、素混凝土抗压强度（Fo）、纵向钢筋直径（phi）通过屈曲应变的试验结果与理论计算结果的比较，表明本文所推导的公式是成功的适用性约为 * 30%.钢筋测力传感器可以得到循环荷载作用下约束混凝土中钢筋屈服区的应力应变关系.循环加载试验表明，利用实测应力-应变曲线得到的骨架曲线和钢筋周围约束混凝土的应力-应变关系预测屈曲应变是可行的。

Investigations to make clear effects of confined concrete on buckling strains of longitudinal reinforcement under uniaxial monotonical loading and cyclic loading were carried out.On the case of cyclic loading, to measure stress of longitudinal reinforce-ment, a new type load cell (a rebar load cell), which was quench hardened portions located locally along the reinforcement, was used.Rupture of reinforcement could not be investigated owing to lack of time.Following main conclusions are obtained.1. Equations to estimate buckling strains of compressive longitudinal reinforcement arranged in confined concrete are derived, through discussions on results of our experimental studies.In the tests of confined concrete with longitudinal reinforcement under uniaxial compressive loading, effects of following factors on the buckling strains were investigated, such as ratios of lateral reinforcement pitches to specimen diameters (S/D), an index of confining stress (ps siguma sy), yield strength of the lateral reinforcement (siguma sy), shapes of lateral reinforcement, compressive strength of plain concrete (Fo), diameters of longitudinal reinforcement (phi) and locations of longitudinal reinforcement.Comparisons between test results of buckling strains and estimated ones show that the derived equation has successful applicability about * 30 %.2. Re-bar load cells could derive stress-strain relations over yielding region of reinforcement arranged in confined concrete under cyclic loading.3. Cyclic loading tests indicate that prediction of buckling strains may be feasible using skeleton curves obtained from the measured stress-strain curves, and stress-strain relations of confined concrete surrounding reinforcement.