超大跨度悬索桥CFRP主缆弯折效应和锚固性能研究

Sea-crossing engineering requires bridges with super long spans. Although a suspension bridge offers the best span capability, the mechanical performance of traditional steel cables can no longer meet the demand as the span increases. Carbon Fiber Reinforced Polymer, with its combination of high strength, light mass and good corrosion resistance performance, is considered to be the best substitute for high-strength steel to serve as the main cable for a super long-span suspension bridge. However, the effects of local bending of CFRP cable and the anchorage performance of cable strand become protuberant mechanical problem due to the poor transverse mechanical characteristics of CFRP. So, the research addresses this issue, and consists mainly of three parts: 1) establish a reduction mathematical model of cable tensile strength under complex stress states, taking into consideration the effects of shear, transverse extrusion and friction caused by the bending of a cable in the main cable saddle, the splay saddle and the cable clamp, using analytical method and numerical analysis; 2) study the distribution rule of section stress of CFRP strands in the anchorage zone using numerical analysis and model testing and propose a method for determining the proper diameter of CFRP cables; and 3) study the failure mode of the strand in the anchorage zone with varying value of pre-tightening force, friction coefficient, anchorage diameter etc., using nonlinear finite element methods, and establish a corresponding mathematical model and verify it by model testing. The research is of important theoretical value for the construction of super long span suspension bridges with CFRP cables

应跨海工程需求，桥梁工程向超大跨度发展，悬索桥虽是跨越能力最强的一种桥型，但传统的钢主缆形式却逐渐不能满足受力要求，CFRP材料具有轻质高强、耐腐蚀等优点，是目前代替钢材料应用于超大跨度悬索桥主缆的最佳选择。但其横向受力性能较差，由此引起的主缆局部弯折效应和索股锚固性能的力学问题突出。因此，本课题将基于这一问题展开，具体内容有：1）考虑主索鞍、散索鞍及索夹处因主缆弯折产生的剪切、横向挤压及摩擦等作用，运用解析法和数值分析法建立复杂应力状态下的主缆抗拉强度折减数学模型；2）运用数值分析和模型试验的方法研究CFRP索股锚固截面应力的不均匀分布规律，提出主缆锚固区合理分股直径的确定方法；3）运用非线性有限元分析方法研究预紧力、摩擦系数及锚固直径等因素对索股锚固破坏模式的影响，建立破坏模式数学模型，并通过试验验证。本课题的研究成果对超大跨度CFRP主缆悬索桥的建设具有重要的理论价值。

课题针对CFRP筋在弯拉状态下强度折减问题，进行了36组CFRP粘结型锚具试件的弯拉试验。明确了弯拉状态下筋材直径在5mm、8mm、10mm、14mm、弯拉半径在3m、8m、12m时锚具试件的锚固效率、破坏模式、相对滑移及极限承载力。同时结合数值分析方法揭示了筋材与台座表面摩擦系数与锚固效率的关系，给出了筋材直径和台座弯转半径的合理取值。其次，为了得到适合锚固大直径CFRP筋材的锚具，设计了一种新型多丝CFRP内锥+圆弧+直筒粘结型锚具。通过有限元方法对比分析了新型锚具与传统内锥+直筒型锚具的受力性能。研究结果表明新型锚具圆弧段设置能改善变截面处应力分布，适合多丝CFRP筋材锚固。此外，设计了以锚固长度、CFRP筋直径和传力介质厚度为变量的单根CFRP筋直筒式粘结型锚具、以CFRP筋数量为变量的CFRP筋平行索股新型粘结型锚具、以凹槽深度和间距为变量的有凹槽多根CFRP筋平行索股新型粘结型锚具。对以上锚固系统进行了静载锚固失效张拉试验，记录和分析了各试件的失效模式、失效位置、锚具效率系数、极限荷载和试验加载过程中的失效演化过程。最后，对新型锚具进行了疲劳试验，分析了新型锚固系统的疲劳破坏机理，验证了新型锚具具有良好的疲劳性能。此外，依据新型锚具的疲劳破坏形式，进一步对新型锚具进行了参数优化，明确了新型锚具内锥段倾角、过渡段圆弧半径、直筒段内径等参数对锚固系统疲劳寿命与累积疲劳损伤的影响。