【作者】 方召欣；

【导师】 李惠强；

【作者基本信息】 华中科技大学 ， 结构工程， 2008， 博士

【摘要】 随着现代化进程加深,土木工程环境日趋复杂,结构持续安全面临严峻挑战,而新材料、新技术的运用更增添了结构安全中的不确定因素。另外,常规结构设计、分析假设结构是在理想或无损情况下抵抗外部作用,忽略了偶然局部损伤对结构体系安全的影响。在上述背景下,“非传统安全”问题凸显,一旦结构局部受损,发生不相称破坏的风险急剧增加。9.11事件令结构不相称破坏和鲁棒性问题受到空前关注。探究偶然局部损伤对结构安全的影响已是当务之急,有重要的理论和现实意义。本文重点是结构鲁棒性分析和不相称破坏风险控制,主要工作和结论如下:首先,从土木工程发展、典型工程安全问题、结构设计思路对比、耐久性以及风险控制和防灾减灾等角度深刻剖析了当前结构设计分析在应对“偶然局部损伤对结构体系安全的影响”问题上的滞后及不足。其次,通过归纳结构鲁棒性的定性要求并基于通用解释,将结构鲁棒性概括为结构体系在偶然局部损伤情况下保持整体稳定的性能。阐明了结构鲁棒性的内涵和外延:它强调结构在偶然损伤后维持体系安全、避免不相称破坏的能力,并不直接反映结构体系在其理想或无损状态下的承载力、延性、可靠度、赘余度或坚固程度;结构鲁棒性同时取决于结构自身性能及其外部环境。再者,提出了两种典型失效模式的能量解释,一是外界输入能量过程中,结构体系消能能力不足,二是结构构造缺陷阻碍了外界释放能量向结构消能的转化。结合损伤发展的现象学概率模型,提出鲁棒性的能量解释——在外界输入能量过程中,鲁棒结构应充分地转化或消纳能量,同时避免不相称破坏。基于消能观点并考虑结构安全的两个实现层次,提出以结构在满足实际设计能力基础上的消能量的无量纲形式衡量其鲁棒性水平。最后,基于消能观点,总结了改善结构体系鲁棒性需要考虑的两个方面,一是在结构响应过程中减少外界能量输入,降低结构消能压力,二是改善结构消能能力。基于此,提出了结构鲁棒性实现的五条策略,以期为结构不相称破坏风险控制提供理论依据。本文在结构鲁棒性内涵与外延、鲁棒性和结构失效的能量解释、量化评价以及不相称破坏风险控制方面取得了一些阶段性成果。为了应对复杂的内外环境,结构体系的系统效应、结构鲁棒性和消能能力的主要影响参数等问题还有待更进一步的研究。更多还原

【Abstract】 As the course of modernization progresses rapidly, civil engineering and its surroundings become so complex that continuing safety of structures is confronted with severe challenges. At the same time, the adoption of novel materials and techniques causes substantial uncertainties in structural safety. Moreover, routine structural design and analysis are performed based on the conception that structures resist external actions in pristine states, and the influence of accidental localized damage on structural system safety is neglected. Under these situations, unconventional safety problems manifest themselves, and the risk of disproportionate failure increases excessively in case that accidental damage occurs. The tragic events of 9/11 have led to unprecedented concerns on the issues of disproportionate failure and structural robustness, and so it becomes imperative to study accidental damage and its effect on structural safety.The thesis focuses on strutcural robustness analysis and mitigation of the risk of disproportionate failure, the main work and conclusions of which are listed as follows:First, the drawbacks of current mothods, regarding structural design and analysis, in dealing with the influence of accidental localized damage on structural system safety are analysed profoundly from five aspects, i.e. the development of civil engineering, typical problems associated with structural safety, the differences between routine design methods and those related to robustness, structural durability, risk control and disaster mitigation.Secondly, the thesis summarized existing qualitative requirements of structural robustness, and argued herein that structural robustness can be interpreted as the behavior of a structure to remain stable under accidental localized damage. The thesis clarifies the core idea and extension of structural robustness further: structural robustness stresses the ability of a structure to remain system safety and avoid disproportionate failure and, hence, it doesnot necessarily reflect the load-bearing capacity, ductility, reliability, redundancy or solidness of the structure in its pristine/pre-damaged state; in addition, structural robustness relies on the behavior of structural systems and the surroundings as well. Thirdly, two typical failure mechanisms of strucures are proposed from the viewpoint of energy: first, a structure fails when it cannot absorb the input of energy; second, a structure fails since the energy transform between the structure and its environment is arrested as a result of drawbacks of structural form. Structural robustness is explained in the light of phenomenological probabilistic models, i.e. a robust structure is capable of absorbing energy input arising from external actions, while keeping the resultant failure somewhat proportional to the original cause. Following these conceptions, a new method to robustness appraisal is developed, where a dimensionless form of the amount of energy the structure absorbs serves as a robustness index, on condition that the structure satisfies its design capacity requirement.Finally, based on the viewpoint of energy absorption, the thesis proposed two basic ways to improve the robustness of a structure, i.e. by mitigating the energy input during the course of structural response and thus reducing the energy absorption demand on the structure, or by improving the energy absorbing capability of the structure. Then five strategies for realizing structural robustness are proposed which aim to provide theoretical basis for mitigating the risk of disproportionate failure.The present thesis draws several conclusions in the subjects of the core idea and extension of structural robustness, the interpretation of robustness and structural failures based on energy principles, robustness apparaisal, and risk mitigation of disproportionate failure. In the face of the increasingly complex surroundings, considerably more work is needed to investigate system effect of structural systems, and to define key factors which influence robustness and energy-absorbing capability of structures.更多还原