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

为弄清约束混凝土对纵向钢筋在单调荷载和循环荷载作用下屈曲应变的影响，进行了试验研究。在循环荷载作用下，采用了一种新型的测力计(钢筋测力计)来测量纵向钢筋的应力，该测力计是由沿钢筋局部淬火的部分组成的。由于时间不够，无法对钢筋的开裂进行研究。主要结论如下：1.通过对试验结果的讨论，推导出了纵向配筋约束混凝土的屈曲应变估算公式。在纵向配筋约束混凝土单轴压缩试验中，研究了侧向配筋节距与试件直径之比(S/D)、围压应力指标(PS Siguma Sy)、侧向配筋屈服强度(Siguma Sy)、侧向配筋形状、素混凝土抗压强度(Fo)等因素对屈曲应变的影响。纵向配筋直径(Phi)和纵向配筋位置。屈曲应变试验结果与估算结果的比较表明，导出的公式具有约30%的成功适用性。在循环荷载作用下，钢筋荷载单元可以推导出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-应变关系来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.