Bond Splitting Strength in Reinforced Concrete Members

为了收集约束应力对纵向钢筋粘结性能影响的试验数据，分别于1992、1993和1994年进行了8根足尺简支梁、4根半尺反荷载梁和4根柱的试验。试件被设计成沿纵向钢筋发生粘结断裂。试验变量包括试件的数量和直径、侧向配筋的间距、次锚杆的使用和轴向应力比。从试验结果可以看出，最大粘结应力随侧向配筋量的增加而提高，并观察到约束中间钢筋的次锚杆的有效性。粘结应力由侧向配筋提供的约束应力决定。为了评估作用在劈裂面上的约束应力，1995年进行了一项分析研究。一个简单的分析模型由三部分组成：(1)梁，代表保护层混凝土；(2)钢柱，与梁通过销钉连接，代表箍和子节点；(3)裂缝弹簧，代表混凝土在劈裂面上的拉力和裂缝张开。通过对保护层混凝土、箍筋和次混凝土所提供的约束应力的分析研究，得出钢筋间混凝土对极限状态下的约束没有贡献。分析预测的极限粘结应力与试验结果吻合较好。

Eight full-scale simply supported beams, four half-scale beams under load reversals, and four columns were tested in 1992,1993, and 1994, respectively, to gather experimental data about the effect of confinement stress on bond behavior in longitudinal bars. The specimens were designed to fail in bond splitting along the longitudinal bars. The variables of specimens were the number and the diameter of test bars, the spacing of lateral reinforcement, the use of sub ties, and axial stress ratio. From the test results, maximum bond stress was observed to improve as the amount of lateral reinforcement increases, and the effectiveness of sub-ties, which confine intermediate bars, was observed. Bond stress was observed to be governed by the confinement stress provided by lateral reinforcement. To evaluate the confinement stresses acting on the splitting plane, an analytical study was carried out in 1995. A simple analytical model consisted of three components : (1) beam which represents cover concrete ; (2) steel columns connected to the beam with pin connection, which represents hoops and sub-ties ; (3) crack spring which represent tensile force and crack opening of concrete in the splitting plane. From the analystical study of the confinement stresses provided by cover concrete, hoops and sub-ties, the concrete between bars does not contribute to the confinement at ultimate state. Analytically predicted ultimate bond stress agreed with the test results.