长期荷载作用下混凝土时变断裂过程试验研究

发布时间：2018-09-07 08:45

【摘要】：混凝土作为一种广泛应用于工程建设的多相复合材料,由于本身固有的缺陷以及外部因素的作用,混凝土裂缝广泛存在于建筑结构中,尤其是服役中的大体积混凝土结构。裂缝在长期荷载作用下的发展直接关系到工程结构的安全。因此,研究裂缝在长期荷载作用下的发展机理以及对结构本身的影响具有重大的现实意义和工程价值。目前,关于混凝土非时变断裂问题的研究已经取得了较为丰硕的成果,提出了多种混凝土断裂理论。然而,由于试验的复杂性,目前国内外对于混凝土时变断裂过程的相关研究极少。本文以尺寸为L×D×B=515mm× 1OOmm× 100mm标准三点弯曲梁试件为试验对象,采用实验与理论分析相结合的方法,对长期荷载作用下混凝土时变断裂过程进行了研究。论文的主要工作与结论如下:1.进行了常规的混凝土非时变断裂试验。持续加载至试件断裂,得到混凝土的最大荷载值Pmax及相关断裂参数。2.进行了混凝土时变断裂试验。对混凝土施加约为0.7Pmax、0.75Pmax、0.8Pmax、0.85Pmax、0.95Pmax的恒定荷载,得到了混凝土在不同荷载水平的长期荷载作用下的时变裂缝口张开位移CMOD(t)等试验数据。3.基于虚拟裂缝模型,对时变断裂试验数据进行计算分析,得到了混凝土在不同荷载水平的长期荷载作用下的时变裂缝尖端开口位移CTOD(t)、时变等效裂缝长度a(t)、时变应力强度因子K(t)的拟合公式,并总结了其发展规律。4.提出了混凝土时变断裂韧度KIcun(P)的概念及其计算方法。依据混凝土时变裂缝口张开速率CMOR(t)的变化规律,通过对CMOR(t)求解极值点,确定混凝土时变断裂由稳定扩展阶段转变为失稳扩展阶段的临界时刻tc,进而计算出混凝土时变断裂相关参数,并由此提出了混凝土时变双K断裂模型,判断准则如下:KIcini,裂缝不起裂;K=KIcini,裂缝开始稳定扩展;KIciniKKIcun(P),裂缝处于稳定扩展阶段;K=KIcun,裂缝开始失稳扩展;KKIcun(P),裂缝处于失稳扩展阶段。5.分析了荷载水平P/Pmax对混凝土时变断裂的影响,结果表明:随着荷载水平的增加,混凝土寿命、时变断裂参数均逐渐减小。并结合混凝土非时变断裂试验,建立了混凝土时变临界断裂参数与非时变临界断裂参数之间的关系。6.通过计算分析得到了混凝土的时变粘聚韧度Kc(t)、时变KR阻力曲线KR(t)的拟合公式,并提出了时变KR阻力曲线判断准则:K(t)KR(t),裂缝处于稳定扩展阶段;K(t)=KR(t),裂缝开始失稳扩展;K(t)KR(t),裂缝处于失稳扩展阶段。7.进行了混凝土时变裂缝扩展稳定性分析,结果表明:时变双K断裂模型和时变KR阻力曲线模型在原理上是相同的。
[Abstract]:As a kind of multiphase composite material, concrete is widely used in engineering construction. Because of its inherent defects and the effect of external factors, concrete cracks widely exist in building structures, especially in service mass concrete structures. The development of cracks under long-term load is directly related to the safety of engineering structures. Therefore, it is of great practical significance and engineering value to study the development mechanism of cracks under long term load and its influence on the structure itself. At present, the research on the time-invariant fracture of concrete has made a lot of achievements, and a variety of concrete fracture theory has been put forward. However, due to the complexity of the test, there are few researches on the time-varying fracture process of concrete at home and abroad. Taking L 脳 D 脳 B=515mm 脳 1OOmm 脳 100mm standard three-point bending beam specimen as experimental object, the time-varying fracture process of concrete under long-term load is studied by combining experimental and theoretical analysis. The main work and conclusions are as follows: 1. The normal time-invariant fracture test of concrete was carried out. The maximum load value Pmax and the fracture parameter of concrete are obtained by continuous loading to the fracture of the specimen. The time-varying fracture test of concrete was carried out. The concrete is subjected to a constant load of 0.7Pmax-0.75Pmax-0.8Pmax-0.85Pmax-0.95Pmax, and the experimental data of time-varying crack opening displacement (CMOD (t) of concrete under different load levels are obtained. Based on the virtual fracture model, the time-varying fracture test data are calculated and analyzed. The fitting formula of time-varying crack tip displacement CTOD (t), time-varying equivalent crack length a (t), time-varying stress intensity factor (K (t) for concrete under long term loads with different load levels is obtained and its development rule .4 is summarized. The concept and calculation method of time-varying fracture toughness (KIcun (P) of concrete are presented. According to the variation rule of the opening rate CMOR (t) of the time-varying crack opening of concrete, the extreme point is solved by the CMOR (t). The critical time of time-varying fracture of concrete is determined from stable stage to unstable stage tc, is used to calculate the parameters related to time-varying fracture of concrete and a time-varying double-K fracture model of concrete is proposed. The judgment criteria are as follows: KIcini, the crack does not start to crack, the crack begins to grow stably, the KIiniKIcun (P), fracture is in the stable growth stage, and the crack begins to unsteady propagation. The KIcun (P), fracture is in the unstable propagation stage. 5. The influence of load level P/Pmax on the time-varying fracture of concrete is analyzed. The results show that with the increase of load level, the life of concrete and the parameters of time-varying fracture decrease gradually. The relationship between the time-varying critical fracture parameters and the time-invariant critical fracture parameters of concrete is established. Through calculation and analysis, the fitting formula of time-varying KR resistance curve KR (t) for time-varying cohesion toughness Kc (t), of concrete is obtained. The criterion of judging the resistance curve of time-varying KR is put forward. The K (t) / KR (t), fracture begins to unsteady and the K (t) KR (t), fracture is at the stage of unstable propagation. The results show that the time-varying double-K fracture model and the time-varying KR resistance curve model are the same in principle.
【学位授予单位】：海南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU528

【相似文献】