【作者】 罗许国；

【导师】 戴公连；

【作者基本信息】 中南大学 ， 桥梁与隧道， 2008， 博士

【摘要】 在桥梁结构向大跨、重载、轻质、高强、耐久方向发展的今天,高性能混凝土已日益成为混凝土桥梁的首选材料。高性能粉煤灰混凝土是可选方案之一。我国相关规范的规定,粉煤灰在预应力梁尤其是铁路预应力桥梁中的应用受到限制,阻碍了这一产品的应用。本文在高性能粉煤灰混凝土材料特性研究的基础上,对不同掺量高性能粉煤灰混凝土铁路桥梁的受力性能进行了试验和理论研究,以期对这一限制有所突破。论文的主要工作如下:(1)通过对不同掺量高性能粉煤灰混凝土模型梁进行200万次正常使用状态疲劳试验研究,探讨C50至C80预应力混凝土梁在疲劳荷载作用下的工作性质。试验结果表明,高性能粉煤灰混凝土预应力梁疲劳性能稳定,疲劳试验梁体未开裂,各梁在疲劳荷载作用下累积残余应变较小,各梁变形、应力与荷载呈良好线性关系,处于弹性阶段;试验证明以20%～40%的高性能粉煤灰等量取代水泥配制的高性能混凝土预应力梁疲劳性能满足规范要求。因此,在铁路建设中,高性能粉煤灰混凝土对铁路预应力混凝土梁的疲劳性能是有保证的。(2)通过对9组18根高性能粉煤灰混凝土模型梁累积残余应变的测量,给出了高性能粉煤灰混凝土梁在疲劳荷载作用下的累积残余应变回归曲线。在此基础上,基于分段线性的原理,对高性能粉煤灰预应力混凝土受弯构件进行了疲劳损伤的全过程非线性分析。理论分析与试验结果比较表明,该方法能够较好地描述出疲劳损伤的全过程,并能给出更符合实际情况的疲劳寿命。(3)通过对不同掺量高性能粉煤灰混凝土铁路桥梁模型为期一年的收缩徐变特性试验研究,由试验结果可知粉煤灰掺量20%~40%高性能混凝土梁在长期荷载作用下徐变早期发展较快,随着龄期的增长,混凝土的后期强度逐渐增长,徐变的增长趋于缓和。基于300多天的实测结果回归分析,其徐变系数终值为1.68~1.72之间,比不掺粉煤灰的高性能梁徐变系数终值2.17要低得多,说明粉煤灰掺量20%~40%的梁可以减小梁的徐变值。(4)以8根高性能粉煤灰混凝土预应力模型梁的收缩、徐变试验为基础,提出了从混凝土桥梁短期试验值推算相应混凝土桥梁在该桥梁工作环境下收缩应变及徐变系数的方法;结合桥梁规范JTG D62—2004收缩模型与徐变模型思想,得出计算混凝土桥梁收缩应变及徐变系数的桥梁规范JTG D62—2004修正公式。理论分析与试验结果比较表明,预测理论值给出了较好的精度。该预测方法,不需做材料的收缩、徐变试验,也避免从标准环境下试验值推算桥梁工作环境下收缩、徐变可能产生的误差。(5)通过对不同掺量高性能粉煤灰预应力模型梁的破坏试验研究,试验结果表明:掺高性能粉煤灰混凝土模型梁可以满足铁路桥梁极限承载力的要求;利用规范公式对模型梁的裂缝宽度进行了计算,并与试验值进行了比较,两者符合较好。说明可以利用现行规范计算高性能粉煤灰梁的裂缝宽度。(6)从高性能粉煤灰预应力模型梁的破坏试验中发现,随着荷载的增大,模型梁的基频呈下降趋势,最大裂缝宽度逐渐增大,但从模型梁初始加载到其接近破坏,基频的降低幅度为2%—6%之间,说明结构刚度变化不大;而其接近破坏时最大裂缝宽度值为其初始量测的最大裂缝宽度值的9.5——19倍左右,结构刚度显著降低,给人以明显的破坏预兆。这也说明仅利用量测基频来判断预应力混凝土桥梁的破坏程度是不可行的。(7)基于平面非线性梁单元理论建立了高性能粉煤灰预应力混凝土梁的有限元理论分析模型,该模型考虑了梁单元的材料和几何非线性,同时在模型中把无粘结预应力筋的效应转化为梁单元的等效节点荷载,并编制了相应程序,模型梁有限元计算结果和实测值比较表明:该程序是正确的和该模型可较好地预测预应力梁从开始加载直到失效的非线性全过程结构响应。(8)在高性能粉煤灰混凝土材料性能和模型梁试验的基础上,浇注了6片高性能粉煤灰掺量25%的C50混凝土实梁,架设于洛—湛铁路西阳河特大桥,通车运营至今梁体外观质量好,未发现梁体表面有裂纹,徐变上拱较普通混凝土梁小,工作性能稳定。更多还原

【Abstract】 With the development of bridge structure towards long-span, heavy load, light weight, high strength and durability, High Performance Concrete (HPC) has been the first choice of concrete bridge today. High performance fly ash concrete (HPFAC) is one of the alternative solutions. Because of specifications of relevant standards, the application of fly ash in prestressed bridge girder is limited, especially for railway prestressed bridge girder. Generally speaking, fly ash is not adopted in prestressed concrete girder, which obstructs its application. In this paper, based on the research of properties of high performance fly ash (HPFA), the experimental and theoretical studies of mechanical properties on the railway beams with different mixtures of HPFA are investigated, which is expected to make some breakthrough with regard to this limitation. The main works in this thesis are stated as follows:(1) The research of 2,000,000 fatigue test of model beams with different mixtures of HPFA investigates the performance data of C50-C80 under the fatigue load. Test results show that the fatigue properties of prestressed concrete beams with FIPFA are stable, and model beams of fatigue test do not crack, also, its remanent strain of accumulation is small under the fatigue load. The displacement and strain of beams remains linear with the increase of load, still in elastic stage. It is tested that the fatigue properties of HPC prestressed girders meet the requirements of railway code when 20～40% of cement is replaced equally by FIPFA. So in the railway construction, the fatigue performance of HPFAC has been guaranteed in the prestressed girders.(2) By measuring the remanent strain of accumulation of 18 model beams of 9 groups with HPFAC, a regression curve of the remanent strain of accumulation of concrete beams with FIPFA under the fatigue load is obtained. Preceding works basis, a full-range nonlinear analysis of fatigue damage with the principle of piecewise linearity on flexural member of prestressed concrete is studied. Calculated results indicate that the fatigue damage process of prestressed concrete beams can be presented with accepted accuracy; at the same time prediction for fatigue life can be much more reasonable.(3) Properties of the shrinkage and creep for one year on the railway model beams with different mixtures of HPFAC are studied in the experiment. The experimental results suggest that the creep of the concrete beams with 20%～40% HPFA develops faster at its early stage under long duration, but with the passage of time, later strength of concrete is increasing and the creep is becoming slower. Based on regression analysis of the experimental results over 300 days, its creep coefficient is between 1.68～1.72 and much smaller than its creep coefficient of 2.17 with HPC beams of the same strength but without fly ash, which indicates that the concrete beams with 20%～40% HPFA can diminish the creep of beams.(4) Based upon the experimental results of shrinkage and creep of eight prestressed concrete beams with different mixtures of HPFA ,a method of the shrinkage strain and creep coefficient deducing under the bridge working environment from short term test of concrete bridge is proposed. A modified formula of JTG D62-2004 is obtained for computing the shrinkage strain and creep coefficient of concrete bridge following the concept of JTG D62-2004 for the model of shrinkage and creep. The contrast between the theoretical analysis and the test results shows that the predicted value maintains a good accuracy. When the method is used, there is no need to implement material test for shrinkage and creep, thus it can avoid the errors that might be resulted from deducing the real shrinkage and creep of concrete under the bridge working environment through the test result obtained under the standard condition.(5) The damage experiment of prestressed model beams with different mixtures of HPFA concrete indicate that model beams with different mixtures of HPFA concrete can satisfy ultimate bearing capacity of railway bridges. And crack width of model beams is calculated with current specifications, which is in line with the experimental results. This illustrates that current specifications can be applied to calculate crack width of beams with different mixtures of HPFA concrete.(6) From the discoveries of the damage experiment of prestressed model beams with different mixtures of HPFA concrete, it is proved that with the increase of loading, the basic frequency of model beams decreases and the maximum width of crack increases. However, from initial loading to near destroying, the decreasing scope of the basic frequency around 2%-6% indicates that the change of stiffness is not obvious. But the maximum width of crack is around 9.5 times-19 times in comparison with the initial maximum width of crack, the decrease of structure rigidity is predominant, which is an obvious omen of destroyed girder. The experimental results also prove that the predication by only using the basic frequency to judge the destruction of prestressed concrete beams is unfeasible.(7) Finite element analysis model for concrete beams prestressed based on nonlinear beam element theory is established. This model involves material of beam element and geometrical nonlinearities. At the same time in the model, the effect of unbounded tendon transforms equivalent nodal loads of beam element, and the corresponding finite element program is designed. The results of model beams by the finite element program compared with the experimental results indicate that the program is verified and the analysis model can better predict a full-range nonlinear structure response of prestressed beams from loading to destroying.(8) Based on the experiments of HPFA properties and model beam fatigue and dead-load tests, 6 pieces of C50 HPC beam containing 25% HPFA were cast. And they were erected successfully on Xiyang River Bridge on Luo-Zhan railway. From its opening to transporting today, the appearance of girder is good, no crack has been found, its creep camber is smaller than ordinary concrete beam, and its serviceability of girder is stable.更多还原