预应力锚索锚固段荷载传递解析算法

Analytical solution for load transfer along anchored section of prestressed anchor cable

锚固是岩体工程增稳的主要措施,对充分发挥岩体的自承潜力,调节和提高岩体自身强度和自稳能力有着十分重要的作用。由于锚固工程本身的复杂性和多样性,导致目前锚固机制、设计理论以及计算方法都不够完善。现有的锚固段荷载传递解析解存在两大难题,一是没有反映锚固段应力变化过程,随着荷载不断加大,接触面是逐渐被破坏,剪应力的峰值将由端口逐渐向内转移;二是在端口处是一个应力奇异点,难以很好地解决。通过对当前多种锚固段荷载传递解析解的适用性及局限性进行分析归纳,指出应将锚固段应力分布划分为弹性、塑性和破坏3个阶段,在不同的阶段应力分布形式不一样,不能一概而论。在此基础上,基于传递系数,针对沿锚固段剪应力呈非均匀性分布形式,提出了一种能反映这3个阶段变化规律的荷载传递解析公式,获得了锚固段剪应力和轴力的分布规律和影响因素。对各解析解方法求出的临界锚固长度进行了算例对比,证实所提算法是合理和有效的。该算法适用于预应力锚索锚固段工程设计。

Prestressed anchor technics is a primary measure to reinforce rock masses in geotechnical engineering. It plays an important role in mobilizing the self-bearing capacity of the rock masses and improving the strength and self-stability of the rock masses. Because of the complexity and diversity of anchoring engineering, anchoring mechanism has not been well understood, and the design theory and related computational method are insufficient for engineering applications. Two important problems remain to be addressed, which are related to the existing analytical solutions of the stress transfer along the anchored section of the prestressed anchor cable. Firstly the stress variation along the anchored section of prestressed anchor cable has not been well characterized, and secondly the stress singularity at the endpoint has not been considered in the existing analytical solutions. Through the analysis of applicability and limitation of the previous analytical solutions, it is shown that the stress distribution along the anchored section can be divided into three stages： elastic stage, plastic stage and failure stage. The stress distributions are different in different stages. Within this context, an expression is developed for calculating the transferred load in the above three stages. The shear stress and axial force distributions along the anchored section are determined. For a practical case, the critical anchorage length is determined by the proposed equation, and the result is compared to those of other methods, showing the validity and capability of the proposed procedure