考虑环境影响的混凝土梁式桥动力特性及抗震性能演化

Abstract: Concrete Girder Bridge is widely used in the highway and railway engineering of China. Its dynamic characteristics and seismic performance are constantly changing by the comprehensive effects of environmental factors and loading conditions. It is of great both theoretical and practical significance to accurately master the evolvement law of its dynamic characteristics for the bridge's safety running, condition assessment, reasonable maintenance and strengthening. By using a combination of theory and experiment methods, this project intends to analysis the time-varying material characteristics such as concrete elastic modulus and damping characteristics firstly. And then study the influence law caused by environmental temperature, humidity and the effects of long-term loading. Combined with the mechanical properties of the girder bridge, concrete column models and simply supported beam models are made. Conventional loading conditions and specific loading conditions (overload, earthquake action) are simulated. The impact of difference loading conditions on the structural natural frequencies and damping are further analyzed. A concrete rigid frame bridge is selected and the combined effects (material characteristics, stress distribution, boundary condition, soil-structure interaction, local-damage evolution) of environmental temperature and humidity, loading conditions on the particular structure are analyzed. And the evolution of its dynamic characteristics is calculated and analyzed. Energy dissipation performance of the bridge under different stress levels is considered. And based on the energy balance theory, further analysis of the seismic performance on the conditions of different seismic levels and different damage degrees are carried out.

混凝土梁式桥在我国公路和铁路工程中应用十分广泛，受环境因素和荷载条件的综合影响，其动力特性和抗震性能也在不断演化，准确把握其动力特性的演化规律对于桥梁安全运营、状态评估及合理养护、加固等都具有重要的理论研究意义和实际应用价值。本课题拟利用理论与试验相结合的方法，从研究混凝土材料弹性模量、阻尼特性的依时变化规律入手，开展环境温湿度和长期荷载作用的影响；结合梁式桥的受力特点，制作混凝土柱、简支梁模型，模拟常规和特定荷载条件（超载、地震等）的影响，进一步分析不同荷载条件对结构自振频率和阻尼的影响；选择混凝土刚构桥梁，分析环境温湿度、荷载条件等对结构的综合影响（如材料特性、应力分布、边界条件、土结相互作用、局部损伤演化等），计算分析其动力特性的演化规律；考虑不同应力水平下结构能量耗散特性，采用基于能量平衡的理论，进一步分析不同地震水平、不同损伤程度条件下的桥梁结构抗震性能。

桥梁的健康监测和性能评估是保证交通运输正常进行和国民经济快速发展的重要环节。由于受环境因素和荷载作用的影响，梁式桥的静力和动力特性在不断演化。只有认清这些外在因素对梁式桥静动力特性的影响，才能准确地评估桥梁的健康状况。本课题采用理论和试验相结合的方法，从材料层次入手，研究了混凝土材料弹性模量的依时变化规律；环境温度和湿度对混凝土材料弹性模量的影响。接下来在构件层次，制作混凝土柱、简支梁模型，分析了环境温湿度对其动力特性的影响以及长期附加荷载作用对混凝土柱动力特性的影响。最后进行了一座混凝土简支梁和一座混凝土连续梁桥的32小时动力测试，进一步分析环境温湿度和边界条件等对结构的综合影响。结果表明：随着龄期的不断增长，混凝土的弹性模也逐渐变大，增长速度先快后慢；温度和湿度对混凝土材料弹性模量的影响规律相反。随着温度的升高，混凝土材料的弹性模量降低；而随着湿度的增大，混凝土材料的弹性模量升高。且在自然环境条件下，温度对混凝土弹性模量的影响较大。温湿度对混凝土模型梁和模型柱自振频率的影响规律也相反，并与温湿度对弹性模量的影响类似。随着温度的升高，混凝土结构的自振频率降低；随着湿度的增大，混凝土结构的自振频率升高。与温湿度对混凝土材料弹性模量的影响相比，其对混凝土结构自振频率的影响要小，这是因为结构的自振频率不仅与材料的弹性模量有关，还与边界条件等其它因素有关；长期荷载只在作用的初期会对结构产生影响，使结构的自振频率降低，在后期对结构几乎没有影响；环境温湿度和长期荷载对结构的阻尼比影响不明显。. 本课题的研究成果可以为桥梁结构的健康检测和性能评估提供参考，以剔除环境因素和荷载作用对桥梁动力特性的影响，准确判断桥梁的健康状况。