【作者】 刘玉萍；

【导师】 李术才；

【作者基本信息】 山东大学 ， 岩土工程， 2012， 博士

【摘要】 随着人类对海上空间的开发和利用,跨海大桥以其无与伦比的经济、社会效益和独特的造型、创新的技术如雨后春笋层出不穷。与陆地桥梁不同,跨海大桥下部支撑结构处于环境复杂的海洋内,特别是位于冰冻海域的桥梁结构,盐害、冻融、海冰、海浪、海流等多重腐蚀环境的综合作用严重影响其安全问题。大体积的流冰撞击结构引起的冰激振动,不仅能引起结构的疲劳破坏,而且还有可能引起上部结构或者设备的损坏和失效。此外,长期的冻融循环对混凝土结构的侵蚀破坏也会影响桥梁结构的耐久性和安全性。目前,海冰已成为跨海大桥及近海工程结构物设计的不可忽视的主要环境因子和控制荷载之一为保证冰冻海域跨海大桥的安全稳定,深入开展冰和结构的相互作用机理的相关研究,将会为跨海大桥的设计、施工、运营及改造提供重要的设计参数和理论根据。目前,此研究也越来越受到工程界的关注,并对海上工程提出了越来越多的更严格的限制和更可行的要求,这就对冰-结构相互作用机理的研究、结构安全性能评价等提出了更加迫切的需求和严格的要求。鉴于以上因素,本文综合考虑冻融破坏混凝土的性能衰退及冰激振动等因素,全面系统的研究冰厚、冰速、结构形状、柱顶集中荷载对结构的冰激振动的影响；采用多材料耦合的内聚力冰模型,在流固耦合作用下,分析了桩间距、尺寸比率及结构刚度等对结构的冰激振动的影响,并以青岛海湾大桥为工程背景研究了不同服役期内冻融损伤桥梁下部结构在冰激振动作用下的动力响应。本文的主要研究内容如下：1.建立了冻融损伤混凝土本构关系本文基于室内试验的基础上,研究分析了不同冻融循环次数的混凝土的力学性能衰退规律。在断裂力学理论的基础上,建立了不同冻融循环次数混凝土的本构关系。通过本构关系可以看出,随着冻融次数的增加,混凝土的应力-应变关系曲线逐渐趋于扁平,应力峰值明显降低,应力峰值所对应的应变值逐渐增加,曲线与坐标轴包围的面积减小,耗能能力逐渐降低。2.研究了结构的冰激振动及影响因素在理论分析的基础上,利用通用的ANSYS软件建立了冰与不同形状混凝土结构相互作用的有限元模型,选用显式非线性有限元软件LS-DYNA对其作用过程进行了数值计算。分析结果表明冰厚、冰速、结构形式以及有无柱顶集中质量等因素对冰破碎模式及结构的响应特征都有不同程度的影响,分别分析其物理过程及影响程度,探索了冰和结构动力作用的机理。3.建立了冰的内聚力模型及研究了结构的冰激响应根据冰的细观结构特征及冰与直立结构相互作用的楔形破坏理论,利用内聚力理论,建立冰的内聚力数学模型。借助于LS-DYNA庞大齐全的材料模型库,建立了多材料耦合的冰的内聚力有限元模型；利用该软件强大的动力计算功能,考虑海水的影响,采用流固耦合的算法分别对柱间距、结构刚度及尺寸比率对冰力及结构响应的影响进行分析,得出一些有益的结论,为工程施工和设计提供依据。4.将研究结果运用于工程实践,研究了冻融损伤混凝土桥梁下部结构在不同服役期内的冰激响应以青岛海湾大桥为工程背景,选取了两种最不利的结构类型,考虑了下部混凝土承台结构的冻融破坏的影响,采用多材料耦合的冰内聚力模型,分别建立了冰与结构相互作用的有限元模型。针对青岛海湾大桥的运营环境,选用了12种不利工况组合,考虑海水的作用,采用流固耦合算法,分别对不同服役期内不同工况下冰与结构相互作用进行数值模拟。结果表明：混凝土在冻融破坏作用下力学性能不断衰退,结构刚度下降,造成冰力峰值增加,位移最大偏移量增加,且在高设计水位工况下,最大位移偏移量增加的较快。结构位移加速度极值也随着服役期的延长逐渐变大。说明随着结构服役期的延长,在相同外力作用下会产生较大的偏移量,更容易产生冰激振动,冰激振动的位移加速度会变大。因此,为保证跨海大桥的安全性,随着服役期的延长,必须更加重视冰激振动可能带来的严重后果。更多还原

【Abstract】 Along with the development and utilization of marine space, Cross-sea bridge are springing up like bamboo shoots after a spring rain everywhere, based on its incomparable economic and social benefits, with distinctive architectural concept and endless innovative techniques. Alien from the other bridge structure, the lower support structure of Cross-sea Bridge is in the complex environment of the ocea. Its design, construction and operation will be many more competitive and difficulty. Especially for the bridge structure in the frozen waters, the multiple corrosion environment such as salt, freezing and thawing, sea ice, wave, current and so on seriously impact the safety and reliability of the units.The ice-induced vibration of structure, which impact by mass of ice sheet, can not only cause fatigue damage of structure, but also may lead the upper structure or equipment to damage and failure rupture.In addition, the long-term damage of freeze-thaw cycle to concrete structure will also affect the durability and security of bridge structure.At present, the sea ice has been one of the main environment factors and control loads that can not be ignored in the design prograss of bridge and offshore engineering structures.To ensure the security and stability of the sea-crossing bridge in frozen water, extensive efforts were made to improve the mechanism of interaction between ice and structure,which will provides scientific designing parameters and offer the important theoretical basis to the design, construction and operation of similar bridge works. At present, this research is also growing concern by the engineering community, who put forward more and more detail standards and feasible requirements on maritime engineering. So.the more pressing needs and strict requirements are put forward to the research on the mechanism of ice-structure interaction, safety evaluation and so on.In this paper, considering the decay of concrete freeze-thaw damage, the ice-induced vibration and other factors.A series of comprehensive and systematic studys were carried out on the characteristics of the structural dynamic responses influced by ice thickness, ice velocity, structural shapes, concentrated mass on the structur tops respectively by using nonlinear dynamic analysis software ANSYS/LS-DYNA.Based on the cohesive material coupling ice model was set up,the structural dynamical responses subjected to the pile spacing, aspect ratio and the stiffness of the structure respectively were numerically simulated. Based the engineering background of Qingdao Bay Bridge, the ice-induced respects of the bridge structure during different service period were analysed. This work are following:1. Development of the constitutive relationship for concrete suffered freeze-thaw damage.According to analyzing the results of indoor test, the mechanical properties of concrete suffered freeze-thaw damage with different cycles were studied. The constitutive relationship for concrete suffered freeze-thaw damage was suggested in the basis of the theory of fracture mechanics.It can be seen through the constitutive relations, with the increase of concrete freeze-thaw cycles, the stress-strain relationship curves tend to be flat, and peak stress was significantly reduced, the stress peak value corresponding to the strain value would increase gradually. The area under the curve was reduced; it was shown that energy dissipation capacity of material decreased gradually.2. Research on the structural dynamic responses induced by ice sheet and influencing factors.On the base of the theoty analysis, a series of finite element model of interaction between ice and structure was established on the basis of ANSYS. By calculating the models and showing the courses of the rock blasting process with nonlinear explicit dynamic finite-element program LS-DYNA, the characteristics of the structural dynamic responses influced by ice thickness, ice velocity, structural shapes and concentrated mass on the structur tops respectively were presented. The results showed that the above factors have different effect on the mode of ice sheet failure and the the characteristics of the structural dynamic responses.From the analysis of physical process and the influence degree of the different variables, the dynamic mechanism of interaction between ice and structure was explored.3. Establishment of the cohesive material coupling ice model and its application in numerical simulation.According to the mode of ice failure with a wedge-shaped edge during ice-vertical structure interaction and the material mesoscopic structure of ice, based on the cohesion theory of crack nucleation and extended, the cohesive material coupling ice model was established.By use of integrated and huge range of material modelbase systems of LS-DYNA, the finite element model of ice forming of several sorts of materials was achieved. By using nonlinear explicit dynamic finite-element program LS-DYNA, which can deal with fluid-solid coupling algorithm, the structural dynamical responses subjected to the pile spacing, aspect ratio and the structure stiffness respectively were numerically simulated. Some useful conclusions are obtained from the computational results. The results are useful to the construction and design of the similar bridge to a certain extent.4. Research on the ice-induced dynamic responses of substructure of bridge suffered freeze-thaw damage in different term of military service.Based the engineering background of Qingdao Bay Bridge, two kinds of the most unfavorable structure were selected. To take the adverse effect of freezing-thawing of concrete on bearing capacity into account, the finite element models of interaction between ice and structure were established by using of the cohesive material coupling ice model. With fluid-solid coupling algorithm of LS-DYNA, the physical process of interaction between ice and structure were simulated with the most unfavorable twelve combined operating conditions.It can be concluded from simulation results that with the dying out of the mechanics properties of concrete and the decline of structure rigidity, the relative ice force peak, max structure displacement and acceleration were increased. In addition.under the high-designed water level work condition, the max structure displacement increased more.That is to say the larger max structure displacement and acceleration would be occurred under the same external forces as service time prolonging, and the ice-induced vibration was more likely to suffer.so,to ensure the security of sea-crossing bridge in the whole process of design, construction and operation, more attentions should be paid to the serious effect caused by ice-induced vibrationthe with the years.更多还原