Abstract: A tension force calculation method was put forward based on the face that ultrasonic guided wave transmission in steel strands will be influenced by tension force. Taking seven cores strands with diameter 15.2mm for example, the longitudinal guided wave frequency dispersion curve was derived from a single wire with different boundary conditions. Then the transmission of guided waves was simulated through finite element method in single wire and tension steel strands, and the reason for mode variation and the change laws of mode bifurcation angle under tensile force were analyzed. The results illustrate that, as the displacement restraint rigidity on wire surface became higher, the dispersion curves of the first order longitudinal guided wave offset to high frequency part integrally, and this phenomenon is more obvious in small wave number portion, which results in mode bifurcation angle around at 300 kHz; under different tensile conditions, the first order longitudinal guided wave mode bifurcation angle is mainly affected by the tangential friction force between the steel wires. A power function relation between mode bifurcation angle and tensile force is established by regression analysis, and the influence of screw pitch and friction coefficient on the function relation is considered.

Key words: bridge engineering, steel strands, tensile force, the first longitudinal guided wave, frequency dispersion curve, mode bifurcation angle

摘要： 基于超声导波在钢绞线中传播受钢绞线张拉力影响特性，提出了一种钢绞线张拉力计算方法。以直径15.2 mm七芯钢绞线为例，理论推导了单根钢丝受不同 边界约束条件下纵向导波频散曲线；用有限元方法模拟了导波在单根钢丝及有张力钢绞线中传播过程；分析了引起模态变化的原因及受张拉力影响下模态转角变 化规律。结果表明：随着钢丝表面位移约束刚度增大，一阶纵向导波频散曲线整体向高频位置偏移，且小波数部分向高频偏移更为明显，从而在频率300 kHz附近 形成模态转角；钢绞线在不同张拉力条件下，其一阶纵向导波模态转角主要受钢丝间的切向摩擦力影响；考虑钢绞线螺距及摩擦系数影响的钢绞线张拉力与导波 模态转角之间吻合幂函数关系。

关键词: 桥梁工程, 钢绞线, 张拉力, 一阶纵向导波, 频散曲线, 模态转角