截断后钢绞线锚下有效预应力检测技术及精度优化研究

Study on Techniques and Accuracy Optimization for Effective Anchorage-Zone Prestress in Steel Strands after Cutting

摘要: 针对在役预应力结构改造、病害修复及性能评估中，截断后钢绞线锚下有效预应力精准检测难的技术瓶颈，提出基于“反拉修正–应力释放耦合”的一体化检测方法体系。通过微观界面力学分析与宏观试验验证，揭示截断作业引发的夹片咬合力衰减(最大衰减率28%)、锚具变形滞后(72 h内应力持续下降3%~8%)等关键干扰机制；构建考虑了截断损伤的锚下应力场三维有限元模型(网格精度达5 mm，与试验偏差 < 4%)，明确检测参数与应力真值的非线性映射关系；开发集成夹片位移监测(精度0.001 mm)与力值动态修正的智能反拉系统，结合应力释放法形成双重验证机制。模型试验表明，该方法对截断后钢绞线锚下有效预应力的检测误差稳定控制在3.2%以内，较传统拐点判别法(误差12.7%)精度提升75%；依托某高速石某大桥加固工程(216根截断钢绞线)现场应用，检测偏差为−4.89%~4.38%，最大同束不均匀度4.32%，均满足《公路钢筋混凝土及预应力混凝土桥涵设计规范》(JTG D62-2004)要求。研究首次建立“截断长度–夹片磨损–时间滞后”多因子耦合修正模型，完善了截断预应力构件检测技术标准，为在役结构安全评估提供了可复制的工程范式。

Abstract: To address the technical bottleneck of accurately detecting the effective anchorage-zone prestress in prestressing strands after cutting during the retrofitting, damage repair, and performance assessment of in-service prestressed structures, an integrated testing methodology based on “back-pulling correction-stress-release coupling” is proposed. Through microscopic interface mechanics analysis and macroscopic experimental verification, the key disturbance mechanisms induced by cutting operations are revealed, including the attenuation of wedge gripping force (maximum reduction rate of 28%) and delayed deformation of the anchorage (continuous stress decrease of 3%~8% within 72 h). A three-dimensional finite element model of the anchorage-zone stress field considering cutting-induced damage is established, with a mesh size refined to 5 mm and a deviation of less than 4% from experimental results, thereby clarifying the nonlinear mapping relationship between the testing parameters and the true stress. An intelligent back-pulling system integrating wedge displacement monitoring (accuracy of 0.001 mm) and dynamic force correction is developed, and a dual-verification mechanism is formed in combination with the stress-release method. Model tests show that the proposed method can stably control the detection error of effective anchorage-zone prestress in cut prestressing strands within 3.2%, representing a 75% improvement in accuracy compared with the traditional inflection-point method (error of 12.7%). Based on field application in the strengthening project of a large expressway bridge involving 216 cut prestressing strands, the measured deviations range from −4.89% to 4.38%, and the maximum non-uniformity within the same strand bundle is 4.32%, all satisfying the requirements of the Specifications for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts (JTG D62-2004). This study, for the first time, establishes a multi-factor coupled correction model of “cutting length-wedge wear-time lag,” improves the technical standard for testing cut prestressed members, and provides a replicable engineering paradigm for safety assessment of in-service structures.