多轴加载状态下混凝土损伤特性研究

【作者】 王凤达；

【导师】 逯静洲；

【作者基本信息】 烟台大学 ， 结构工程， 2008， 硕士

【摘要】 混凝土结构的安全性、耐久性与维修加固已成为混凝土结构研究的重要研究方向,其中建立一种简便高效的损伤评估方法,对遭受损伤的新建和改建建筑物进行检测鉴定和评估是工程实践中迫切需要解决的问题。为了描述混凝土试件在经历各种荷载作用下,微裂纹萌生、扩展、汇集而造成材料的损伤过程,本文利用Najar损伤理论对混凝土在多轴加载条件下的损伤特性进行了比较深入的研究。首先,本文对混凝土开裂破坏的机理、损伤理论和各种类型的混凝土损伤模型进行了深入分析和综述,在此基础上,从能量损伤的角度出发,基于经典Najar损伤理论,利用高精度的Simpson积分方法建立了损伤模型及损伤演变方程。其次,本文重点是将单轴加载条件下的混凝土损伤模型推广应用到三轴受压状态,对单轴和多轴加载状态下混凝土损伤进行分析,为建立多轴加载条件下的混凝土损伤本构模型奠定理论基础。主要考虑的加载方式包括:单轴压缩、单轴拉伸、恒定单侧压比例加载,恒定不等双侧压比例加载,三轴比例加载及三向等压加载。结果表明,混凝土在多轴受压和单轴受压作用下的损伤有相似的发展趋势。各种类型加载历史下混凝土损伤都随着应变的增大而增大,且初始加载阶段损伤发展较快,加载末段损伤发展缓慢并趋于稳定值。但是,在相同应变历史条件下,三轴受压下的损伤值比单压下的损伤值明显偏小,而且随着侧压比例的增大损伤进一步减小,说明侧压有效限制了混凝土损伤的发展。另外,三向等比例加载状态下混凝土损伤近似沿直线增长,且损伤增长速率非常小,说明这种加载状态对于充分发挥混凝土受压特性是最有利的。最后,本文还以三轴比例加载为例,推演了峰值应力处损伤与峰值应变的关系,在一定加载比例范围内,可以利用混凝土峰值应变快速推演得到混凝土的损伤。更多还原

【Abstract】 The structural safety, durability and evaluation of damage in concrete under various loading patterns are of primary interest in every country. A simple and efficient method for the early and regular engineering measurement of damage, as well as for quality assurance during and after the construction of new structures and of reconstruction processes, is urgently required. Generally, it can be stated that the process of progressive cracking is the primary cause of the behavior of concrete observed under compression and subsequent failure. The density of fine cracking caused by the loading history is therefore a measure of material integrity, and is defined in the present work as damage.Firstly, the damage mechanism under various loading patterns, the theory of continuum damage mechanics and multiform damage constitutive models of concrete are investigated. Based on the damage theory by Najar, the damage model has been developed using the Simpson integral method.Secondly, the damage model of concrete under uniaxial compression has been applied to triaxial compressive state, to analysis damage evolvement of concrete under variety triaxial loading pattern, which is the most important part of the dissertation. In this paper, loading patterns include uniaxial compression, uniaxial tension, biaxial proportional compression, triaxial proportional compression and triaxial equi-compression. The damage evolution rule of concrete under triaxial and uniaxial compression shows the similar tendency. With the increase in the strain of the loading history, the incremental speed of damage becomes less and less, and finally the damage approaches a stable extreme value. Experienced the same axial strain loading history, the damage value of concrete is lower than that under uniaxial compression, and the damage of concrete in axial direction is reduced gradually with the increase in lateral pressures, which means that the lateral pressures can reduce the damage effectively. In addition, under triaxial equi-compression loading history, the damage of concrete is found to be in linear dependence relationship with the increase of axial strain, which means that kind of loading pattern could develop the compressive feature of concrete adequately.Finally, the relationship between the damage and the peak strain under the condition of triaxial proportional compression is investigated. It is concluded that the damage of concrete subjected triaxial proportional compression can be determined by the peak strain of the loading histories conveniently and accurately.更多还原