RC和PC箱梁短期及长期剪力滞效应研究

发布时间：2018-12-25 07:39

【摘要】：近几十年来,世界上大量经过多年运营使用的混凝土箱梁桥出现跨中下挠过大和梁体开裂现象,严重影响了结构的安全性和适用性。本文依托国家自然科学基金项目“在役混凝土箱梁桥时变承载力的分析理论及试验研究(51178416)”,以混凝土箱梁结构为研究对象,探索了其短期和长期剪力滞效应的分析方法,主要研究内容及成果如下:(1)在箱梁位移场中引入箱梁腹板的纵向位移函数,以消除传统剪力滞分析方法假定箱梁截面中性轴与形心轴重合引起的计算误差,据此提出了考虑中性轴变化及剪切变形的剪力滞效应分析方法。通过算例分析,将所提方法计算值与文献试验值、有限元值及传统分析方法计算值对比,表明所提方法能较为准确地计算箱梁的剪力滞效应。(2)运用所提出的方法,探讨了宽跨比、悬臂板宽与顶板半宽比、底板与顶板宽度比、高宽比及板厚比四个几何参数对箱梁翼板应力差值比的影响,结果表明,宽跨比、悬臂板宽与顶板半宽比、底板与顶板宽度比对箱梁集中荷载作用截面和中支点截面上翼板与腹板交界处的应力差值比影响较大,而高宽比与板厚比则仅对连续箱梁集中荷载作用截面和中支点截面上翼板与腹板交界处的应力差值比影响显著。(3)基于虚功原理及龄期调整有效模量法,提出了考虑剪力滞效应和混凝土收缩徐变的RC箱梁长期性能分析方法,通过与典型简支RC箱梁的有限元模型和初等梁理论计算结果对比,验证了所提方法的有效性和精度。此外,详细分析了收缩和徐变对RC箱梁长期性能的影响,指出混凝土徐变及收缩是影响RC箱梁长期挠度和混凝土应力的主要因素,其同样也影响RC连续箱梁的支反力和内力分布。(4)基于预应力等效荷载法与Timoshenko梁理论,提出了考虑剪切变形的预应力作用下箱梁剪力滞分析方法,该法能考虑轴向力引起的剪力滞效应。通过算例分析,将该法计算值与文献试验值、有限元值比较,验证了提出方法的精度。通过对典型预应力布束方式的简支梁和两跨连续箱梁的分析,表明剪切变形对预应力作用下箱梁挠度计算影响很大;预应力等效轴向力会在钢束锚固端引起显著的剪力滞效应。(5)引入混凝土材料的时变性,采用不同的有限单元(梁、实体单元)数值模拟方法,分别建立了考虑悬臂施工阶段的典型悬臂施工PC连续箱梁桥的分析模型,比较研究了在非均匀及均匀收缩徐变作用下,考虑剪力滞效应的PC连续箱梁桥的时变变形、混凝土应力和钢束应力。结果表明,忽略剪力滞效应会严重低估大跨PC箱梁桥的跨中下挠;非均匀收缩徐变对跨中长期挠度影响较小,而对钢束应力和混凝土应力影响较大。
[Abstract]:In recent decades a large number of concrete box girder bridges which have been used for many years in the world have appeared the phenomenon of excessive span deflection and beam body cracking which seriously affected the safety and applicability of the structure. In this paper, based on the National Natural Science Foundation project "Analysis theory and experimental study of time-varying bearing capacity of in-service concrete box girder bridge (51178416)", this paper takes concrete box girder structure as the research object, and probes into the analysis method of its short-term and long-term shear lag effect. The main research contents and results are as follows: (1) the longitudinal displacement function of the box girder web is introduced in the displacement field of the box girder to eliminate the calculation error caused by the assumption that the neutral axis of the box girder section coincides with the centroid axis of the box girder by the traditional shear lag analysis method. Based on this, a method for analyzing the shear lag effect considering the variation of neutral axis and shear deformation is proposed. Through the example analysis, the calculated value of the proposed method is compared with the experimental value, the finite element value and the calculated value of the traditional analysis method. It shows that the proposed method can calculate the shear lag effect of the box girder more accurately. (2) the proposed method is applied to the calculation of the shear lag effect of the box girder. The effects of four geometric parameters, the ratio of width to span, the ratio of cantilever width to roof width, the ratio of bottom to roof width, the ratio of height to width and the ratio of plate to thickness, on the stress difference ratio of box girder wing plate are discussed. The results show that the ratio of width to span, the ratio of cantilever plate width to roof width, The ratio of the width of the bottom plate to the top plate has a great influence on the stress difference ratio between the flange and the web at the interface of the central fulcrum section and the concentrated load section of the box girder. However, the ratio of height to width to the thickness of the plate has a significant effect on the stress difference ratio between the flange and web at the junction of the flange and the web on the central support section and the concentrated load section of the continuous box girder. (3) based on the virtual work principle and the age adjustment effective modulus method, A long-term performance analysis method for RC box girder considering shear lag effect and concrete shrinkage and creep is proposed. The effectiveness and accuracy of the proposed method are verified by comparing with the finite element model of typical simply supported RC box girder and the theoretical calculation results of elementary beam. In addition, the effects of shrinkage and creep on the long-term performance of RC box girder are analyzed in detail. It is pointed out that concrete creep and shrinkage are the main factors affecting the long-term deflection and concrete stress of RC box girder. It also affects the distribution of the supporting reaction force and internal force of RC continuous box girder. (4) based on the prestressing equivalent load method and Timoshenko beam theory, the shear lag analysis method of box girder considering shear deformation is proposed. The shear lag effect caused by axial force can be considered by this method. The accuracy of the proposed method is verified by comparing the calculated value with the experimental value and the finite element value. Through the analysis of simple supported beam and two-span continuous box girder in typical prestressing beam distribution mode, it is shown that shear deformation has great influence on the deflection calculation of box girder under prestressing force. The equivalent axial force of prestressing force will cause significant shear lag effect at the end of steel bundle anchoring. (5) introducing the time variation of concrete material, different finite element (beam, solid element) numerical simulation methods are used. The analytical models of typical cantilever construction PC continuous box girder bridge are established, and the time-varying deformation of PC continuous box girder bridge considering shear lag effect under the action of non-uniform and uniform shrinkage and creep is compared. Concrete stress and steel bundle stress. The results show that ignoring the shear lag effect will seriously underestimate the mid-span deflection of long-span PC box girder bridge, and the effect of non-uniform shrinkage and creep on the mid-long span deflection is small, but on the steel beam stress and concrete stress is greater.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：U441

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