Bond Splitting Strength in Reinforced Concrete Members

分别于1992年、1993年和1994年对8根全尺寸简支梁、4根荷载逆转下的半尺寸梁和4根柱进行了试验，以收集约束应力对纵杆粘结行为影响的实验数据。这些试件被设计成沿纵向杆的键裂破坏。试件的变量为试验杆的数量和直径、侧配筋间距、子箍的使用和轴向应力比。从试验结果来看，最大粘结应力随着侧向配筋量的增加而提高，并且观察到约束中间筋的子筋的有效性。观察到粘结应力受侧向钢筋提供的约束应力的支配。为了评估作用在劈裂面上的约束应力，1995年进行了分析研究。一个简单的解析模型由三部分组成：(1)梁代表覆盖混凝土；(2)钢柱与梁的连接采用销连接，销连接表示箍和子箍；(3)裂缝弹簧，表示混凝土在劈裂面上的拉伸力和裂缝张开度。从覆盖混凝土、环箍和副箍提供的约束应力分析来看，杆间混凝土对极限状态的约束没有贡献。分析预测的极限粘结应力与试验结果一致。

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.