摘要
随着经济的发展以及人们环保意识的提高,具有环保、节能等特点的地源热泵系统逐渐受到人们的重视。地源热泵系统已经广泛应用于国内外建筑中,学者们也对这项技术展开了深入研究和探讨。目前制约地源热泵发展的一个重要障碍就是初投资高。传统的地热换热器采用钻孔竖直埋管的形式,但对于工程问题来说,钻孔的费用相当昂贵,占初投资的比例较大,致使初投资过高。考虑到传统换热器的成本、精度和复杂工艺,出现了“桩埋管换热器”。目前已有的桩埋管研究是把U型管换热器埋于建筑物混凝土桩基中,但这种方式传热面积小、易形成“热短路”,而螺旋盘管避免了这些缺点,因此提出桩埋螺旋盘管式换热器。同时,采用桩埋管地热换热器可承担一定量的空调负荷,不足的部分再由钻孔埋管来承担,这样可较大的降低初始投资的费用,减少地热换热器的占地面积。
在桩中埋管是一种新技术,其研究应用和工程实践较少,目前主要存在以下一些问题:对于设置埋管的桩的承载力特性研究还不成熟,很多问题还不深入;国内外对其全面的、系统的研究尚不多见,仅仅照搬无埋管桩的研究方法或者稍加修改,不能真实体现出埋管对桩的承载特性的影响。埋管对桩基承载特性的影响制约着桩埋管技术的发展,因此研究埋管对桩基承载特性的影响将有利于桩埋管技术继续完善和发展。
为了研究埋管对桩承载特性的影响,首先采用室内模型试验分别对无埋管和埋管的桩构件在压力、弯矩和拉力作用下的受力和变形情况进行分析,得到了埋管对桩构件承载特性的影响。然后采用有限元数值模拟软件ANSYS建立桩构件数值模型,分别分析其在压力、弯矩和拉力作用下的受力和变形情况,能较好符合物理试验。结合具体的工程实例,通过与有限元数值模拟分析结果的比较,得到合适的计算参数,并建立桩土数值模型,分析了埋管对桩基承载特性的影响。最后通过数值模拟分析了桩长、桩径、螺旋管径、螺旋管距等影响因素对桩基承载特性的影响。
With the development of economy and the increasing concern over the environmental problems, more and more attention is being paid to the Ground-source heat pump (GSHP) system, which is environment-friendly and energy-saving. Many scholars have done further research in the Ground-source heat pump system, which has been used in many domestic and foreign constructions. At present, the vast initial investment becomes a major obstacle to the development of the Ground-source heat pump system. The traditional ground heat exchanger takes the form of vertical U-tube in bore holes. However, the high cost of drilling bore holes, which accounts for a large percentage of the initial investment, leads to a vast initial investment. Taking into account the cost, accuracy and technical complexity of the traditional ground heat exchanger, people begin to use the "pile ground heat exchanger". In current studies, the U-tube heat exchangers are buried in the foundation of buildings, but their small transfer area may cause a "thermal short circuit", so the pile heat exchangers with spiral coils are proposed, which have no such drawbacks. Ground heat exchangers inside foundation piles can also bear a certain amount of air conditioning load and the remaining part can be borne by ground heat exchangers in vertical-bore holes. In this way, the initial investment can be reduced greatly and the area of heat exchangers can also be reduced.
It is a new technology to bury tubes in the pile,on which few studies, applications and engineering practices have been done. Currently the major problems are as follows:further research needs to be done on the loading capacity features of the pile with buried tubes and many problems of it are to be solved; a comprehensive and systematic research is rarely seen both home and abroad. It can't show the effects of the tubes on the loading capacity features to copy or slightly modify the research of the pile without buried tubes. Besides, the effects of the buried tubes on the loading capacity features of the pile have restricted the development of ground heat exchanger technology. As a result, the study of the effects of buried tubes on the loading capacity features of the pile will be beneficial for further development of the technology of buried tubes.
In order to study the effect of the loading capacity of the pile with buried tubes,firstly, based on the comparison tests on piles with buried tubes and piles without buried tubes, a study has been done on the load-carrying and deformation states of the pile over compression, bending and tension respectively, and the effects of buried tubes on the loading capacity features have been analyzed. The FEM software ANSYS has been employed to make numerical simulations of the compressed piles, the bending piles and the tensiled piles. The theoretical analysis corresponds to the test results. Secondly, combined with specific examples of pile engineering, through comparison between the results of static loading test and the results of ANSYS analysis, the effects of buried tubes on the loading capacity features of the pile have been decided on through ANSYS analysis, which has been conducted by selecting appropriate calculating parameter; Afterwards, a lot of numerical analysis has been done to decide on the effects of changes in the length of the pile, the diameter of the pile, the diameter of spiral coil and the distance of spiral coil on the loading capacity features of the pile.
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