摘要
随着科学技术的发展,大体积混凝土在现代工程建设中的应用越来越广泛,例如,工业与民用建筑中的基础底板、水利水电工程中的大坝和桥梁工程中的支墩等。对其温度裂缝的控制也越来越引起人们的重视。大体积混凝土结构在浇筑和固化早期,水化热剧烈变化而形成的温度应力很容易导致该类结构非载荷性开裂,从而对其整体性和耐久性造成不可忽视的威胁。
现阶段对施工期大体积混凝土结构温度裂缝的控制措施,以控制其浇注温度和内外温差为主,如施工时放置一期和二期水平冷却水管、分层浇筑施工和留设伸缩缝等措施都以基于测温技术的内外温差作为控制依据,而很少采取“温差-温度应力”的双控制措施。本文从“温差-温度应力”双控制出发,探索了一种新的对大体积混凝土结构进行温度裂缝控制的方法,即将分层浇筑施工与预埋垂直钢管有机结合的一种降温法,先从热传导基本理论出发分别分析了分层浇筑施工与预埋垂直钢管单方面对大体积混凝土底板的降温效果,为两者结合提供了依据;然后用ANSYS软件对分层浇筑施工过程中预埋垂直钢管的某一特定工程进行了仿真分析,对其可行性进行了验证;最后,找出了预埋垂直钢管在某一特定浇筑层厚度下的具体降温效果。本文的具体工作如下:
1.通过阅读国内外大量资料,简述了大体积混凝土结构温度裂缝的相关理论,并对常用的温度裂缝控制措施进行了阐述。
2.介绍了一般大体积混凝土温度场及温度应力的基本理论,其中重点介绍了大体积混凝土底板施工过程中温度场和温度应力的分布规律。
3.介绍了有限元热分析的步骤与方法,先从理论上分析了分层浇筑施工和预埋垂直钢管单方面对大体积混凝土底板温度场和温度应力的影响,然后分别讲述了分层浇筑施工和预埋垂直钢管在ANSYS有限元分析中的实现方法,为两者结合提供了理论依据。
4.用ANSYS软件对某大体积混凝土基础底板在预埋垂直钢管时的分层浇筑过程进行了仿真分析,并从“温差-温度应力”双控制出发对分层浇筑过程中预埋垂直钢管的可行性进行了验证。
5.用ANSYS软件对相同尺寸大体积混凝土基础底板在不预埋垂直钢管时的分层浇筑过程进行了仿真分析,通过与预埋垂直钢管的温度场和温度应力场进行比较,找出了预埋垂直钢管在某一特定浇筑层厚度下的具体降温效果,为进一步将分层浇筑施工与预埋垂直钢管相结合提供了依据。
With the development of the science and technology, the massive concrete is more and more popular used during engineering construction period in modern times. For example, the container foundation in industrial and civil buildings , the dam in water conservancy and hydropower engineering and the rest pier in bridge engineering and so on. It pays more and more attention to control the temperature cracks in engineering field. At early age of construction and hardening of massive concrete structure, the unloading cracks in massive concrete structures are mainly caused by the thermal stress which due to hydration heat of cement, so this will threaten the integrity and the durability.
At the present time, the measures to control the temperature cracks in massive concrete structure during construction period are mainly control the temperature of mixture placing to mold and the temperature difference of center and surface. For example, the measures such as placing phase I and II horizontal tubes with water during construction period, layered construction and installing deformation seam are based on the temperature difference of center and surface, and rarely take temperature and thermal stress double-control measures. Based on the double-control measures, this paper explores a new method to control the temperature cracks of massive concrete structure, this method combines the layered construction with placing vertical steel tubes. At first, it respectively analyses the effect of reducing temperature only by layered construction or placing vertical steel tubes by the basic theory of heat conduction, and provides the basis for the combination of both; and then studies the temperature field and stress field of massive concrete structure with vertical steel tubes during layered construction period by ANSYS finite element software, obtains that this method is useful; at last, obtains the steel tubes’specific effect of reducing temperature. Specific work of this paper is as follows:
1. By reading a lot of data at home and abroad, describes the related theory of temperature cracks in massive concrete structure, and explains the common measures to control the temperature cracks in massive concrete structure.
2. Introduces the basic theory of the temperature field and thermal stress in massive concrete structure, general mass concrete, in which highlights the distribution of the temperature field and thermal stress during construction period.
3. Introduces the procedure and method of thermal analysis by the finite element, at first analyses the effect of reducing temperature only by layered construction or placing vertical steel tubes by related theory, and then respectively describes the way how to realize the simulation by ANSYS finite element software, and provides a theoretical basis for combination of layered construction and placing vertical steel tubes.
4. Studies the temperature field and stress field of massive concrete structure with vertical steel tubes during layered construction period by ANSYS finite element software, obtains that this method is useful from temperature and temperature stress.
5. Studies the temperature field and stress field of the same size of massive concrete structure without vertical steel tubes during layered construction period by ANSYS finite element software, by comparing with the temperature field and stress field with vertical steel tubes, obtains the steel tubes’specific effect of reducing temperature, and provides a further theoretical basis for combination of layered construction and placing vertical steel tubes.
引文
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