大跨度桥梁非定常风致振动的非线性失稳机理及理论

Instabilities of wind-induced vibrations, including flutter and galloping, are the wind-induced phenomena most destructive to long-span bridges. Because real bridges have often non-streamline cross sections, their instabilities of wind-induced vibrations possess both the unsteady and nonlinear behaviors simultaneously, thus are without any critical onset point of sudden divergence. Therefore, how to determine the critical wind speeds of such nonlinear and unsteady instabilities of wind-induced vibrations has been one pendent subject of the research frontiers in the bridge wind engineering. A series of rectangular cross sections without any and with various corner modifications as well as four kinds of typical non-streamline bridge cross sections with medium ratios of width-to-depth are to be taken as research objects to explore the nonlinear mechanisms of unsteady aeroelastic self-excited forces and the energy evolution rules during the whole procedures of soft flutter and soft galloping. Wind tunnel tests of simultaneous measurements of force and vibration displacement of spring-suspended sectional model with inside-mounted force balances as well as wind tunnel tests of full-structure aeroelastic model are planed to be employed in the research in conjunction with theoretical investigation and analysis. Practical nonlinear mathematical models of unsteady self-excited forces with good applicability and reliability are expected to be presented. On this basis, a practical analysis theory and a more reasonable and feasible structural performance-based evaluation frame or criteria for critical wind speed are to be established for the non-linear instabilities of unsteady wind-induced vibrations, including the soft flutter and the soft galloping of long-span bridges with non-streamline cross sections. The research of this proposed project has hence important theoretical and practical significances.

风振失稳包括颤振和驰振等，是对大跨度桥梁危害最大且必须避免的风致振动现象，由于实际桥梁经常具有非流线形断面，其风振失稳都同时具有非定常和非线性特性，没有明显的突然发散临界点，因此，如何合理确其临界风速一直是桥梁风工程领域一个悬而未决的前沿课题。本项目以一系列典型矩形和修角矩形断面以及四种典型中等宽高比非流线形桥梁断面为对象，拟采用内置天平同步测力测振弹簧悬挂节段模型风洞试验、全结构气动弹性模型风洞试验和理论分析研究相结合的方法，探索软颤振和软驰振的非定常自激力非线性机理和全过程能量演化规律；提出适应性好、可靠性高的实用非定常自激力非线性数学模型；并以此为基础，建立大跨度桥非定常风振非线性失稳问题的实用分析理论，以及一种更加合理、切实可行的、基于结构性能的非流线形大跨度桥梁软颤振和软驰振这类非定常风致振动非线性失稳问题的评价体系或临界风速判断准则，具有重要的理论和实际意义。

颤振和驰振是大跨度桥梁抗风设计中需要面对的两种最危险自激失稳现象，但颤振理论至今未能突破基于微幅振动假设的线性理论范畴，不能满足具有现代柔性超大跨度桥梁抗风设计需求，而驰振理论至今也未能摆脱准定常假设，导致对其临界风速和响应幅值的预测严重偏离实际，埋下安全隐患。本项目针对上述问题开展系统研究，取得了如下原创性成果：.研发了小型高精度动态三分量测力天平以及准静态标定方法和系统，提出了能显著降低惯性力成分、提高了自激力测量精度的内置天平同步测力测振方法。建立了节段模型系统非线性瞬幅阻尼比和瞬幅频率（刚度）的时域识别方法，及非线性非风致附加气动阻尼和质量参数识别方法，进一步提高了自激力测量精度。.率先提出了多种宽高比矩形及凹角和切角矩形断面的横风向自激力非定常非线性精细化数学模型，建立了基于能量等效原理的模型参数识别三步最小二乘法，彻底摆脱了准定常假设的束缚。通过对自激力不同成分做功演化规律及其对驰振稳态幅值的影响，揭示了驰振“发生、发展和自限幅”的机理，提出了可精确预测细长钝体结构驰振稳态幅值的非定常自激力统一简化非线性数学模型。研究了凹角和切角措施的减振效果和机理。建立了考虑风速剖面的钝体结构非定常驰振三维非线性分析方法，得到了气弹模型试验验证。从功等效瞬幅阻尼系数随振幅演化规律出发阐明了驰振分岔和在较高风速区消失现象的机理。.通过自激力做功演化规律和稳态响应参数分析，揭示了双边肋梁和半封闭箱梁单自由度非线性扭转颤振的“发生、发展和自限幅”的机理，提出了自激扭矩精细化和简化非线性数学模型，建立了单自由度非线性扭转颤振全桥三维分析理论，得到了全桥气动弹性模型试验验证。.提出了全封闭箱梁弯扭耦合颤振自激升力和扭矩的非线性数学模型，建立了模型参数识别方法，并分析其耦合颤振“发生、发展和自限幅”的机理。建立了弯扭耦合非线性颤振分析的二维两自由度复模态时频混合理论和全桥多自由三维频混合分析理论。.项目研究解决了钝体驰振自激力数学模型的统一、驰振响应精确预测及颤振后非线性位移响应精确预测国际难题，具有前瞻性和创新性，为今后超大跨度桥梁非线性抗风稳定性设计理论奠定了扎实基础。