【作者】 刘小洁；

【导师】 余志武；

【作者基本信息】 中南大学 ， 结构工程， 2007， 博士

【摘要】 近年来,自密实混凝土以其优异的施工性能和良好的耐久性在我国土木工程中得到越来越广泛的应用,但是有关自密实混凝土梁在长期荷载作用下的性能研究,目前国内外都未见报道。为了进一步推广自密实混凝土在我国土木工程中的应用,本文对长期荷载作用下自密实混凝土梁的结构性能进行了系统的试验研究和理论分析。主要创新性研究成果如下:(1)根据混凝土材料组成与性能关系原理,探讨了自密实混凝土各组分相对用量对自密实混凝土工作性能及力学性能的影响,在此基础上对自密实混凝土配合比参数进行了优选。对自密实混凝土本构关系及收缩徐变性能进行了研究。建立了自密实混凝土应力—应变及粘结—滑移的本构关系模型。(2)在国内外首次对自密实混凝土梁进行了系统的的长期变形性能的试验研究。完成了两批共26根自密实和普通混凝土梁的长期试验,持续时间长达6年。探讨了不同因素对自密实混凝土梁长期变形性能的影响,为工程设计及理论分析积累了宝贵的试验资料,提供了重要的技术支撑。试验结果表明:自密实混凝土梁的挠度徐变系数与振捣成型混凝土梁基本相同,在工程中采用自密实混凝土时不需要对自密实混凝土的徐变加以特殊考虑。(3)对16根长期荷载作用下的自密实混凝土梁进行了卸载后的静力性能的试验研究和理论分析,探讨了混凝土成型工艺、早期养护条件、预加应力及自密实混凝土徐变对长期作用的自密实混凝土梁卸载后再次加载构件的刚度、裂缝分布、破坏形态、以及极限承载力的影响。(4)基于理论上比较完善而又实用的龄期调整有效模量法,以及在自密实混凝土的徐变度计算公式基础上建立的递推公式,考虑钢筋滑移的影响对自密实混凝土梁进行了长期荷载作用下的有限元分析。(5)运用截面分析建立了自密实混凝土梁长期变形的解析计算公式。提出了自密实钢筋混凝土梁长期变形的简化计算公式。(6)提出了采用灰色系统动态拓广模型利用短期试验数据对自密实混凝土梁的长期挠度变形进行预测的方法。更多还原

【Abstract】 In the past ten years, self-compacting concrete has gained wide use in civil engineering for its superior constructability and high durability. However, self-compacting concrete differs from normal concrete in terms of mechanical behavior due to the use of different material and different mix proportioning. Research into long-term properties of self-compacting concrete beams has not been actively pursued for the past 15 years. Few papers have been written on this subject. In view of this, this dissertation has systematically made experimental research and theoretical analysis on long-term behavior of self-compacting concrete beams. The main content is listed below.(1) The parameters for mix design of self-compacting concrete were optimized and the stress-strain relationship and bonding stress-slip relationship of self-compacting concrete were established.(2) Long-term tests of 26 prestressed and non-prestressed self-compacting concrete beams were done. The effect of different parameters on long-term deformation of self-compacting concrete beams including curing condition, mix-proportion, degree of prestress, mode of consolidation, magnitude of load and structural type was investigated. The reliable experimental data presented in this paper is useful to engineering design and theoretical analysis. The experimental results indicate that extra preventions concerning shrinkage and creep behavior of the structure are not needed in engineering practice.(3) Experimental research on self-compacting concrete beams under static loading after long-term actions was done. The effect of different factors including casting technique, curing condition, degree of prestress at age of loading and degree of indeterminacy on load-deflection relationship, load carrying capacity, mode of failure and distribution of crack along beam length was explored.(4) The element stiffness matrix concerning the contribution of concrete and reinforcement was constructed based on element displacement mode and virtual work principle, and the equivalent node load due to creep and shrinkage was established. Based on recurrence formula for any kind of expression of specific creep, nonlinear finite element analysis was done, which considered bond-slip behaviour and crack width. The analytical results show good agreement with the measured ones.(5) A formula for creep deflection of self-compacting concrete beams was constructed by section analysis using modified MC 90 creep and shrinkage model and age-adjusted effective modulus method. A design method for creep deflection was proposed, which will further perfect "Guidelines for design and construction of self-compacting concrete in China"(6) The extended grey dynamic model was used to predict the long-term deformation of self-compacting concrete beams on the basis of short-term experimental data. The predicted values are in good agreement with the measured ones, which shows that this method presented in this paper characterized by simplicity and high precision in prediction is practical and feasible.更多还原