【作者】 张凯；

【导师】 元强；

【作者基本信息】 中南大学 ， 土木工程材料， 2025， 博士

【摘要】 超高海拔山区已成为我国铁路、公路、机场等交通基础设施建设的主战场之一。超高海拔山区严酷气候环境所致的混凝土裂损是影响交通基础设施长期服役的重大威胁,厘清超高海拔山区铁路钢筋混凝土(Reinforced Concrete,简称RC)实体桥墩等交通基础设施混凝土构件受力与变形演变特征,开发与超高海拔山区相匹配的高抗裂混凝土制备技术与理论,以满足超高海拔山区交通基础设施结构体系的安全性、可靠性和耐久性要求,对实现超高海拔山区铁路等交通基础设施长期安全高效服役意义重大。然而,当前有关超高海拔山区严酷服役环境下RC结构的受力特征、损伤形成与演变规律和裂损抑制技术仍缺乏系统研究。本文综合运用试验研究与数值模拟分析方法,探明了超高海拔山区(海拔为4360m与4480m)严酷环境下铁路RC实体桥墩全寿命周期受力特征,揭示了早期温度-湿度-约束等耦合作用下、后期日照辐射与环境昼夜温差循环作用下RC实体桥墩混凝土劣化机制,开发了超高海拔山区铁路RC实体桥墩抗裂性能提升技术。本文主要创新成果总结如下:(1)基于现场实测方法,探明了超高海拔山区典型气象参数变化规律,厘清了超高海拔山区低气压、低湿度环境下铁路RC实体桥墩混凝土早期温度变化规律,阐明了超高海拔山区强日照辐射、大温差、风速环境下RC实体桥墩混凝土温度与变形变化规律,总结了RC实体桥墩墩身混凝土开裂形态与裂缝分布特征。(2)考虑混凝土材料早期性能发展与随机损伤累积,建立了适用于RC实体桥墩早期受力与损伤特征分析的数值模拟分析方法。揭示了超高海拔山区严酷服役环境下铁路RC实体桥墩早期温度场、早期湿度场的时空分布特征,厘清了桥墩不同位置处混凝土早期力学性能发展规律,探明了桥墩混凝土早期变形分布与发展特征,探究了实体桥墩早期随机损伤的形成与演变规律。(3)考虑混凝土结构热力学行为与混凝土材料的随机损伤累积,建立了可高效模拟日照辐射与昼夜温差长期循环作用下RC实体桥墩损伤行为的有限元分析模型。探明了超高海拔山区长期日照辐射与昼夜温差循环作用下RC实体桥墩日照温度场的时空分布特征,明确了RC实体桥墩混凝土温度变形分布特征与演变机制,揭示了桥墩墩身混凝土随机损伤的累积规律,提出了RC实体桥墩混凝土抗拉性能设计阈值。(4)基于有机-无机复合技术,以降低水泥基材料早期收缩变形、提升力学性能为目标,开发了一种新型混凝土抗裂剂。探明了混凝土抗裂剂对水泥基材料力学性能与自收缩的影响规律,揭示了对水泥基材料自收缩的抑制机理与力学性能的提升原理。基于数值模拟分析方法,阐清了新型混凝土抗裂剂对超高海拔山区RC实体桥墩抗裂性能的提升效果,验证了其技术优越性。图92幅,表10个,参考文献207篇更多还原

【Abstract】 Ultra-high altitude mountain areas have become one of the important locations in China for the construction of transportation infrastructure,including railways,roads,and airports.The extreme climatic conditions in ultra-high altitude areas have resulted in concrete cracking and damage to transportation infrastructure,causing an important risk to the service capacity of these infrastructures.To ensure the long-term safety and efficiency of transportation infrastructure in ultra-high altitude mountain areas,it is essential to clarify the evolution of the mechanical and deformation properties of concrete elements under harsh environmental conditions,particularly focusing on reinforced concrete(RC)solid piers.Besides,it is important to develop the preparation technology and theory of high-crack-resistant concrete matching with ultra-high altitude mountain areas and ensure compliance with the safety,reliability,and durability requirements of the transport infrastructure structure system in ultra-high altitude mountain areas.However,systematic studies on the mechanical behavior,damage formation and evolution,as well as crack suppression techniques of RC structures under the harsh service environment of ultra-high altitude mountainous regions are still lacking.Based on the experimental studies and numerical simulation analysis,the development of the mechanical and deformation characteristics of RC solid piers(during construction and service life)under the harsh environment in ultra-high altitude mountain areas(altitude:4360 and 4480 m)was explored.The initiation and propagation mechanisms of damage to RC solid piers have been identified under the coupling effects of early-age temperature-humidity-constraint,long-term solar radiation,and diurnal temperature fluctuations cycles.Methodologies for improving the cracking resistance of railway RC solid piers in ultra-high altitude mountainous areas were proposed.The following innovative achievements have been established:(1)The on-site measurement approach was employed to identify the variation patterns of typical meteorological parameters in ultra-high altitude regions.The early-age temperature and deformation evolution characteristics of RC solid piers located in mountainous areas characterized by low atmospheric pressure and humidity were elucidated.Additionally,the spatial and temporal distribution of temperature and deformation in RC solid piers exposed to intense solar radiation,significant temperature fluctuations,and high wind speeds was thoroughly investigated.Moreover,the distribution patterns and characteristics of concrete cracks on the surfaces of RC solid piers were systematically analyzed.(2)A numerical simulation approach was developed to investigate the early-age stress distribution and stochastic damage behaviors of RC solid bridge piers,considering both the evolution of early-age material properties and the stochastic damage processes in concrete.The spatiotemporal distribution characteristics of early-age temperature and humidity fields within RC solid bridge piers subjected to severe environmental conditions in ultra-high-altitude areas were identified.Furthermore,the early-age mechanical properties of concrete at different locations within the piers were elucidated.The deformation patterns and evolution characteristics of RC solid piers during early-age stages were systematically examined.Additionally,the initiation and progression mechanisms of stochastic damage within the RC piers at early ages were thoroughly explored.(3)Considering the thermodynamic behavior of reinforced concrete(RC)structures and the stochastic damage evolution of concrete,a finite element model was developed to efficiently simulate the stochastic damage behavior of RC solid piers subjected to long-term cyclic solar radiation and diurnal temperature fluctuations.The spatiotemporal distribution characteristics of the temperature field in RC solid piers under long-term solar radiation and diurnal temperature variations at ultra-high-altitude mountainous regions were identified.The distribution patterns and evolution mechanisms of thermal effects within the RC piers were elucidated,and the cumulative characteristics of stochastic damage at the pier surface concrete were revealed.Furthermore,a design threshold for tensile strain in RC solid bridge pier concrete was proposed.(4)A novel concrete crack-resistant agent(CRA)was developed based on an organic-inorganic hybrid approach to effectively reduce early-age shrinkage deformation and enhance the mechanical performance of cement-based materials.The effects of the CRA on mechanical properties and self-shrinkage behavior of cement-based materials were systematically clarified.Furthermore,the underlying mechanisms for shrinkage inhibition,as well as the improvement in mechanical properties,were thoroughly elucidated.Through numerical simulation analyses,the effectiveness and superiority of the proposed CRA in enhancing the cracking resistance of RC solid bridge piers under harsh environmental conditions typical of ultra-high-altitude mountainous regions were comprehensively validated.更多还原