【作者】 詹猛；

【导师】 王社良；

【作者基本信息】 西安建筑科技大学 ， 防灾减灾工程及防护工程， 2009， 硕士

【摘要】 随着现代化建设的不断发展,越来越多的大体积混凝土结构被应用于工程实践中,但长期以来混凝土的裂缝问题一直困扰着工程技术人员。结构的破坏和倒塌都是从裂缝开始,裂缝的扩展是结构物破坏的初始阶段,其承载力也可能受到一定削弱。同时,结构物裂缝也可引起渗漏,使得其耐久性降低,如面层脱落,钢筋锈蚀,加剧冻融循环,混凝土碳化等。目前,大体积混凝土裂缝控制的主要措施是在保证质量的前提下,最大限度地降低温差,如在混凝土搅拌时加入冰块,通水冷却,喷雾隔热等,这些措施有效地减少了混凝土的开裂,但同时也增加了工程的造价。因此,在大体积混凝土裂缝控制中,需要统筹技术和经济两方面的要求,本文以试验为基础,主要进行了以下工作:(1)在已有研究成果的基础上,介绍了裂缝的成因和开裂机理,分析了温度场和温度应力的基本理论及温度场的计算方法,并根据变分原理建立了大体积混凝土非稳定温度场有限元公式,同时根据混凝土的弹塑性本构关系,建立了大体积混凝土温度应力弹塑性分析的有限元公式。(2)通过添加不同成分和数量的改性材料,采用模型试验方法,研究了改性混凝土材料物理力学性能的变化规律。研究表明:通过掺加适晕的粉煤灰和硅粉,可以降低其水化热,明显提高其密实度和强度等;通过加入适量的乳化沥青,可以比较明显地改善其和易性,同时起到减水作用;通过添加聚丙烯纤维,可以有效地提高混凝土材料的抗裂能力和极限拉伸变形。(3)运用SAP2000有限元分析软件,建立了大体积混凝土基础板的有限元分析模型,并以本次试验为基础,对添加改性材料和不添加改性材料的大体积混凝土板,进行了温度场和温度应力的比较分析,计算中主要对混凝土基础板模型的边界条件和尺寸等参数进行变化,以找出其与温度应力的变化关系和分布规律。(4)以控制混凝土温度和温度应力为目的,从原材料的选择、改性材料的掺入、配合比的优化、减小水化热等方面,研究延缓混凝土降温速率,控制施工质量,减少混凝土收缩,提高混凝土极限拉伸变形,改善约束程度,加强局部构造,进行温度实时监控的效果等,提出了相应的综合控制措施,可供同类结构设计施工时参考。更多还原

【Abstract】 With the continuous development of modernized construction,more and more mass concrete structures have been applied to the engineering practice.But cracks of concrete structure have obsessed the engineering workers for a long time.The damage and collapse of construction starts from occurring the crack in structures. Otherwise,the growth of cracks of structures is the initial stage of building’s damage as a result that the bearing capacity and durability of constructions are weakened, such as the leakage of roofs,the shedding of surfaces of concrete,the rebar corrosion in the concrete,the aggravation of freeze-thaw cycles,the concrete carbonation and soon.At present,in order to control the development of mass concrete cracks,many measuers and skills are took in the engineering projects,that reduces the temperture difference to the utmost level to make the concrete in the good condition.Such as adding the ice chippings in mixed concrete,cooling with moving recycling water, insulating heat by atomizing water,although those measures can greatly control the crack development,but greatly increase the project costs.Therefore,there is a need for balancing the method and cost as a whole in mass crack control projects.Based on the concrete test,the main work of this paper is follow as:1).Based on experience and measures of temperature control and crack prevention of mass concrete,this paper presents the formation cause and mechanism of cracking,and the basic theory and calculation method of temperature-field and thermal stress.Built upon variatbnal principles,the paper educes basic formulas of finite element methods in unsteady temperature-fie Id of concrete structures.Followed the concrete constitutive relationship of elastic-plastic body,the writer deduces the formula of finite element method of thermal stress in concrete. 2).Using the model test method,the paper discusses the improved materials effecting on physical and mechanical properties of concrete by adding into heterogeneous and diverse mixed quantities.In order to depress the hydration heat, the concrete is added into the fly-ash and silica fume.To reduce water consumption and to improve workability of concrete,the Emulsified asphalt is doped.The polypropylene fiber is added to strengthen the anti-crack performance and to enhance the capability of ultimate tensile of materials.3).The model of mass concrete slab is built by SAP2000 finite element analysis software.In this model,the temperature field and thermal stress of concrete slab are compared and analyzed between added-in and added-not materials.In addition,the different boundary conditions and dimensional parameters of the models are analyzed to find out its effects on thermal stress distribution in concrete baseplate.4).In order to control temperature and thermal stress in mass concrete slab,the paper mentions different measures,such as raw material selected,special materials added in concrete,mix proportion optimized and hydration heat reduced.Besides,this paper discusses the ways and means,for example,minished constraints degree, reinforced local structure and real-time monitored temperature of mass concrete structures,allround to keep cooling rate of concrete,enhance construction quality, decrease shrinkage of concrete.This work can offer a reference to the mass concrete design and construction.更多还原