【作者】 刘武军；

【导师】 陈尧隆；

【作者基本信息】 西安理工大学 ， 水工结构工程， 2010， 硕士

【摘要】 大体积混凝土结构在工程中的应用越来越广泛,由于温度变化而引起的裂缝是长期困扰人们的问题。在冬季负温季节或者突遇寒潮时,表层混凝土的温度梯度很陡,使混凝土表面的拉应力超限而产生很多表面裂缝,特别是当混凝土的龄期还很短,抗拉强度还很低,更容易产生裂缝。在混凝土表面铺设一定厚度的保温板可以有效的降低混凝土表面的拉应力,防止裂缝的产生。因此,研究大体积混凝土表面保温板的保温效果是很有意义的。本文依据大体积混凝土的温度场和温度应力场的有限单元法计算理论,以大型通用软件ANSYS为平台,采用APDL语言编制了碾压混凝土重力坝施工期和运行期的温度场、温度应力场的仿真计算程序。该程序在编制过程中考虑了碾压混凝土分层浇筑、施工间歇、弹性模量变化、绝热温升过程、环境温度的变化、混凝土徐变、不同蓄水高程等因素对坝体温度场及应力场的影响。用“生死”单元模拟混凝土的浇筑过程。在混凝土还没有浇筑的时候,单元是“死”的,没有温度值和应力值；当混凝土浇筑以后,激活单元,其温度场和应力场开始发展,这样就能形象的模拟和仿真混凝土的浇筑过程,计算出来的结果可以比较真实的反映大体积混凝土的真实工作性态。本文结合某高寒地区的碾压混凝土重力坝,采用表面散热系数法计算了无保温板覆盖和有不同厚度的保温板覆盖条件下的坝体温度场和温度应力场,并专门分析计算了寒潮对混凝土表面应力的影响。计算结果表明,在大坝上下游面铺设6cm厚的XPS保温板,进行长期永久保温,减弱了混凝土与外界的热交换,提高了混凝土表面的温度,使原来表层混凝土温度梯度变化最陡部位发生在保温材料内,而使表层混凝土温度变化速度减缓,梯度变平,从而减小冬季或突遇寒潮时表层混凝土的温度应力,有效的防止了表面裂缝的产生。同时,还分析了保温板的厚度、种类、保温时间、外界环境温度年变幅对混凝土表面保温效果的影响,对选择合适的保温板具有一定的参考价值。更多还原

【Abstract】 The mass concrete structures are applied more and more abroad in engineering project, the problem of the crack which is caused by temperature change is puzzled people always. In the winter negative temperature season or suddenly confronted cold wave, the concrete surface temperature gradient is precipitous, so concrete surface cracks occurs when the tension stress of concrete surface overrun, especially in the early-age of concrete the tensile strength is low and the crack easily occurs. Laying certain thickness heated board can reduce the concrete surface tension stress effectively to prevent crack. So researching the heat preservation effect of concrete surface heated board is significative.In this article according to finite element computational theory of mass concrete temperature field and temperature stress field, based on large general-purpose software ANSYS, using APDL language to design the simulation calculation program of roller compacted concrete gravity dam temperature field and temperature stress field in construction stage and during operation period. During preparation period of this program, we consider the effectiveness of stratified pouring,construction interval、the change of modulus of elasticity,the adiabatic rise of temperature,the change of ambient temperature,concrete creep,the breach flow of the roller compacted concrete gravity dam and so on. The‘life and death’unit is used to simulate the concrete casting process. Before placement of concrete, the unit is considered‘death’, there is no temperature and stress; When the concrete after pouring, the unit is activated, the temperature field and stress field begin to develop, so the image can be simulated and the simulation of concrete pouring process, the calculated results can more genuinely reflect mass concrete behavior.In this article, an alpine region of a roller compacted concrete gravity dam, equivalent surface coefficient of heat transfer method and compared is used to calculate the non-covered heated board and heated board covered with different thickness of the dam under the condition of the temperature field and temperature and stress field, and devoted to the analysis of the cold calculation of the impact of stress on the concrete surface. Results the surface of the dam upstream face laying 6cm thickness XPS heated board, long-term permanent heat preservation, weaken heat transmission between concrete and environment, raising the temperature of the concrete surface, so that the original surface concrete temperature gradient occurs in the steepest parts of heat preservation material inside, leaving the surface of concrete temperature change slowed down, the gradient flattens, thereby reducing the winter or cold temperature stress when the concrete surface, effective to prevent the generation of surface cracks. At the same time, also analyzed the surface of heated board thickness, type, holding time, annual percentage change in the external environment on the concrete surface temperature heat preservation effect, which is useful for selection of suitable heated board.更多还原