考虑几何缺陷的钢管混凝土黏结滑移数值模拟

Numerical simulation of bond-slip of concrete filled steel tube considering geometric defects

摘要:

为研究钢管与混凝土界面黏结机理,参考规范引入钢管几何缺陷的方式,以低阶屈曲模态表征钢管整体几何缺陷,高阶屈曲模态表征钢管局部几何缺陷,在黏结界面插入面-面接触单元并设置100层接触对,通过库伦摩擦滑动准则定义界面黏结-滑移行为,利用ANSYS重启动分析功能实现化学胶结力逐步丧失过程,建立了含几何缺陷的钢管混凝土有限元模型。模拟结果表明:钢管低、高阶屈曲模态适用于模拟钢管整体、局部几何缺陷,叠加后的缺陷大小可模拟±0.5%钢管外径D的几何缺陷。有限元模型可对每级荷载步进行检测,较为准确地描述了推出过程中的时变状态,成功再现了钢-混黏结界面由试件两端向中部逐步发生剥离的过程。与两类黏结滑移曲线对应的钢管整体几何缺陷为:形成拐点后呈下降趋势的黏结滑移曲线与直线状母线的低阶屈曲模态对应,形成拐点后仍缓慢上升的黏结滑移曲线与曲线状母线的低阶屈曲模态对应。钢管局部几何缺陷可归纳为周期性波峰状缺陷,提出了局部几何缺陷波峰数目与钢管径厚比、黏结长度、混凝土强度之间的经验关系式。

Abstract:

To study the bond mechanism of steel tube and concrete interface, referring to the method of setting geometric defects in steel structure design code, low-order buckling modes were used to characterize the overall geometric defects and high-order buckling modes were used to characterize local geometric defects. The contact element was set with 100 layers of contact pairs, and the interface bond-slip behavior was defined by the Coulomb friction and sliding criterion. ANSYS restart analysis function was adopted to realize the gradual loss of chemical bonding force, and the finite element model of concrete filled steel tube with geometric defects was established. Simulation results show that the low-and high-order buckling modes of steel tubes were suitable for simulating the overall and local geometric defects of steel tubes, and the superimposed defect size could simulate the geometric defects of ±0.5%D (Dis the outer diameter of the steel tube). The finite element model (FEM) could monitor each load step, describe the time-varying state during the push-out process more accurately, and reproduce the process of the gradual peeling of the steel-concrete bond interface from both ends to the middle of the specimens. The overall geometric defects of the steel tubes corresponding to the two types of bond-slip curves included a downward trend curve after the formation of the inflection point, which corresponds to the low-order buckling mode of the linear meridian, and a slow rise curve after the formation of the inflection point, which corresponds to the low-order buckling mode of the curved meridian. The local geometric defects of steel tubes could be summarized as periodic wave crest-like defects. The empirical relationship between the number of local geometric defect crests and the diameter-thickness ratio of steel tube, bond length, as well as concrete strength was proposed.