【作者】 唐世斌；

【导师】 林皋； 唐春安；

【作者基本信息】 大连理工大学 ， 水工结构工程， 2009， 博士

【摘要】 混凝土的温度和湿度问题贯穿其整个服役期间。一方面,当混凝土处于变温环境时,结构除了承受外荷载的作用,还在很大程度上受到温度应力的影响作用;另一方面,当混凝土的湿度高于外界环境的湿度时,其中蕴含的水份则会向外界环境扩散,造成水份的损失,进而产生干缩效应。混凝土结构的应力状态受温度和湿度变化的影响显著,而且往往导致威胁结构完整性和稳定性的裂缝。因此,混凝土中温湿型裂缝发生发展过程的研究有助于了解裂纹扩展的内在机理,为工程施工提供必要的指导作用。到目前为止,混凝土温湿扩散特性研究的数值模型大多是基于材料在宏观层次均匀性假设基础上发展起来的,通过将实验室尺度的试验结果作为输入参数进而对更大尺度宏观结构温湿扩散特性进行分析。这种简化在研究混凝土结构稳定性的数值分析时是非常必要的,但难以研究混凝土材料在温湿变化条件下的裂纹萌生、扩展及贯通的整个断裂过程。目前,国际上有关混凝土材料性能的研究更倾向于从细观角度出发,建立能反映混凝土内部状态随外界环境而变化的数值模型。尽管如此,混凝土温湿扩散特性分析的细观数值模型还相对欠缺,尤其是温湿型裂缝萌生、扩展和贯通整个过程的研究更是少见。因此,本文从混凝土的细观结构入手,应用统计分布方法、传热传质理论以及损伤力学原理建立了混凝土温度-应力-损伤耦合以及湿度-应力-损伤耦合作用数值模型,并通过RFPA分析系统实现。本文主要的研究内容如下:(1)从混凝土的细观结构出发,假设混凝土是由砂浆基质、骨料颗粒以及两者之间的粘结带组成的三相复合材料,针对其中的每一相材料均采用Weibull统计分布方法进行其细观非均匀特性的表征。在此基础上,结合现有的温湿扩散相关理论,建立了混凝土的温度、湿度和应力之间相互作用的理论模型,并对模型中各参数之间的联系进行了探讨和标定,为后续的研究工作提供参考依据。(2)探讨了细观单元的损伤与温湿扩散过程之间的相互影响关系。在此基础上,运用有限元和有限差分方法建立了能研究混凝土类非均匀材料渐进破坏过程的温度、湿度和应力之间相互作用的数值模型。为了加快计算的速度和效率,二维数值模型采用基于多核PC机的并行计算技术,而三维数值模型则采用基于MPI的局域网并行计算技术。(3)运用数值模型进行了混凝土在细观层次上的温度传导特性分析,并通过宏观平均热学性能与细观热学特性的对比分析,探讨了损伤对混凝土热传导性能的影响;通过对热膨胀性能存在差异的试样内温度裂缝扩展过程的分析,揭示了混凝土的非均匀特性对其力学性能的影响;此外,文中还对温度裂缝与其它形式裂缝开裂过程的不同,以及水工结构工程中的温度探漏方法的原理进行了探讨。(4)运用数值模型分析了湿度、温度、骨料等参数对混凝土湿度扩散特性的影响作用;通过研究细观非均匀性对砂浆和混凝土湿度扩散性能造成的影响作用,建立了宏细观之间的联系;研究了裂缝和裂缝深度对湿度扩散的影响作用,进而探讨了湿度裂缝的萌生、扩展和贯通全过程的湿度扩散特性;最后,通过湿度的变化引起混凝土表面裂纹萌生和扩展过程的数值模拟分析,探讨了混凝土结构在湿度多变环境中的失效机制。(5)在三维数值模型的基础上探讨了温度变化引起的结构表面网状裂缝的萌生、扩展和贯通过程,再现了表面龟裂现象,揭示了裂缝的插入过程以及裂纹最终达到饱和状态现象的内在机理;同时,借助数值模型研究了不同的约束条件以及不同的材料均匀程度对网状裂缝形成过程的影响。更多还原

【Abstract】 The influences of temperature and humidity on the mechanical behavior of concrete structure exist throughout its period of service.On the one hand,the change of temperature results the structure not only subjected to external loads,but also bearing the effects of thermal stress;on the other hand,as the environmental humidity is lower than that of concrete, the concrete would loss its water and then have a drying effect.The deformations of concrete caused by change in temperature and humidity significantly affect its stress state,and often leading to cracks which would influence the integrity and stability of structures.Therefore, investigations on the initiation and propagation processes of thermo-hygro type of cracks are helpful to understand the failure mechanism of structure,as well as providing the necessary guidance for engineering.Up to now,the classic macroscopic heat and mass transfer models, which characterize the concrete as a continuum material at macroscopic level,use the tested data at laboratory scale as input parameters to analyze the thermo,hygro and mechanical response of structures with greater size.This kind of homogenization is very important to study the stability of concrete structures.However,it is difficult to use these models to study the complete initiation,propagation and coalescence of fracture processes in concrete structures as they subjected to external loading,temperature and humidity variation.At present,the international investigations on thermo-mechanical behavior of concrete structure are prefer to set up the numerical model on the bases of mesoscopic level,which are able to reflect the variation of internal states of material with the change of environment.However, there are a few numerical studies on heat and mass transfer characteristics of concrete at mesoscopic level,especially lack of investigations on the initiation,propagation and coalescence processes of thermo-hygro type of cracks.Accordingly,in this paper,a numerical model is proposed to investigate the thermo-mechannical-damage coupling processes during the initiation,propagation and coalescenece processes of thermo-hygro type of cracks.The work in the present paper can be summarized as follows:(1) In order to reflect the heterogeneity feature of concrete at mesoscopic level,the concrete is firstly assumed to be a three-phase composite composed of matrix,coarse aggregates and bonding interface between them,and additionally the thermo,hygro and mechanical parameters of each phase are assumed to be conform to the Weibull distribution law.And then the mathematical model of thermo,hygro,mechanical interaction in concrete is established on the basis of heat and mass transfer theory.Additionaly,the parameters among these equations are discussed and calibrated for the following studies.(2) The damage mechanics is used to establish the relationship between damage processes and thermo-hygro diffusion of meso-elements.And then the numerical model,which is able to reflect the heterogeneity feature and failure processes of material,is proposed on the bases of finite element method at spatial scale and finite difference method at time scale.In order to speed up the computing efficiency,the numerical model use the paralle computing method on multi-core PC for two-dimensional model,while the three-dimensional numerical model use the LAN- and MPI-based parallel computing technology.(3) The numerical model is used to analysis the feature of thermal transfer in concrete at the mesoscopic level.The discussion of different thermo-mechanical performances between macro and mesoscopic level of concrete indicate that the mesoscopic-based numerical model is more efficient than that of macroscopic-based model to analsy the thermal behavior of heterogeneous materials.The crack growth processes of sample with multi-phases but different in thermal expansion coefficient indicate that heterogeneity of material significantly influence the behavior of concrete.In addition,the different crack growth processes casued by thermal stress and other external loads,as well as the temperature indication method in seepage monitoring of hydraulic structures engineering are also discussed.(4) The numerical mode is used to analysis the influences of humidity,temperature and coarse aggregate on the humidity diffusion in concrete;Studies about the influence of heterogeneity degree of material on its effective diffusion coefficient is well to establish the relationship of mass diffusion between macro- and mesoscopic level;The effects of existing crack on mass diffusion has also been carried out,and then the analysis of crack depth,as well as cracks caused by change of humidity effect on humidity diffusion process are disscussed; Finally,the cracks initiation,propagation and coalsescence process in mortar overlays caused by hygro-stresses are numerically simulated to reveal the failure mechanism of concrete structure as it subjected to changes in humidity.(5) The initiation,propagation and coalescenes processes of surface cracks at three-dimention caused by variation of temperature are numerically simulated,which is helpful to understand the formation of honeycomb cracks of solids.The effect of restriction condition and heterogeneity feature of material on crack growth mechanism is also studied by the three-dimensional numerical model.更多还原