预应力作用引起的箱梁剪力滞效应研究

发布时间：2019-07-05 17:46

【摘要】：随着现代化交通需求、桥梁设计理念的推动和箱形截面梁与预应力技术的结合,箱形截面梁更加趋向于薄壁、长悬臂的结构形式,预应力箱梁已经成为桥梁建设的一种大趋势。本论文在国家自然科学基金《PC箱梁考虑预应力作用效应的剪力滞行为研究(51208242)》资助下,针对预应力混凝土箱梁,通过理论研究并结合数值模拟,系统研究了预应力效应下箱梁的剪力滞效应理论分析中的关键问题。主要研究内容及成果如下:(1)为了回答轴向力是否引起剪力滞效应,分别针对无悬臂板和有悬臂板的单室箱梁,采用板壳有限元分析了轴向力分散于箱梁不同部位时的纵向应力,引入轴向力剪力滞系数概念,研究了不同工况下的简支梁、悬臂梁和连续梁的轴向力剪力滞系数。结果表明,轴向力作用在箱梁时,梁体总体不会产生剪力滞效应,仅在靠近轴向力作用点部位存在局部应力集中区,其区域约为1倍梁宽的长度,其值与一般构件承受局部压力时的应力非均匀传递长度相等。(2)针对箱梁预应力束在梁端通常是偏心锚固,并非锚固在形心轴位置,等效预应力作用包括作用在形心轴的轴压力和梁端集中弯矩。本文将单箱双室箱梁预应力束偏心锚固时的预应力等效荷载中轴向力和集中弯矩分开计算,对集中弯矩作用下的箱梁剪力滞效应计算时,提出了在集中弯矩作用下能够反映箱梁各翼板间剪力滞翘曲位移差异的剪力滞翘曲位移模式,建立了集中弯矩作用下的箱梁剪力滞效应控制微分方程,得到解析解。系统的研究了集中弯矩作用部位不同时,箱梁的剪力滞分布规律。经本文解析解与ANSYS有限元数值解的对比分析,得到的结果基本规律和数值分析结果大小均基本相同,说明本文所取的翘曲位移函数是合理的,导出的控制微分方程和解析解计算公式是正确的,且计算精度较好。(3)对仅在集中弯矩作用下的简支单箱双室箱剪力滞效应分析,在集中弯矩作用部位的左右两侧各l/4范围内较大,剪力滞系数在集中弯矩作用部位取得最大值,当在l/4跨部位作用集中弯矩时,集中弯矩作用部位附近顶板与腹板交界处考虑剪力滞效应后的应力达到了初等梁理论值的2.24倍,而其余部位较小。并且剪力系数在各腹板之间存在差异,因此建议结构设计中有必要考虑到不同腹板间翼板应力差异。(4)针对预应力束偏心锚固时的钢束横向布置方式不同,研究了不同剪力滞荷载效应模式对箱梁截面的剪力滞效应影响,采用ANSYS有限元软件建立了简支梁、悬臂梁和连续梁分别在三腹板平均布束、两边腹板布束和仅中腹板布束时,典型截面和沿跨度方向的剪力滞效应。结果表明,不同偏心布束不同时,箱梁剪力滞效应分布不同,且差异较大,综合三种布束方式下典型截面顶、底板的剪力滞系数分析,仅在中腹板布置预应力束时,截面顶底板的剪力滞系数变化较大,顶板剪力滞系数从中腹板附近的1.22变化到了翼缘边缘附近的0.531,剪力滞效应明显;在三个腹板均匀布束的情况下,截面的剪力滞效应相对差异较小。同时,不同布束方式对不同边界条件下箱梁剪力滞效应影响不同,对连续梁影响最大,简支梁次之,悬臂梁影响较小。(5)针对超静定箱梁结构预应力次内力对箱梁剪力滞效应的影响进行了理论分析。理论上,在预应力锚固端部位因剪力滞效应引起的附加弯矩值和预应力初弯矩值同号,且大小只与箱梁截面的几何特性有关,在中支点处的附加弯矩同时与箱梁的截面几何参数、宽跨比有关。结合相关算例的有限元分析结果,得出理论与数值分析结果相符。(6)对于两跨连续梁在实际预应力束线形布置设计时,一般是非吻合索布束方式。这些布束方式都会在梁内产生次内力,结合预应力混凝土两跨连续箱梁中钢束不同线形布置方式,采用ANSYS有限元软件建立板壳模型,研究了直线布束、折线布束和抛物线布束时的箱梁剪力滞效应。得到,布束线形的改变对中支承截面的剪力滞效应有一定影响,直线布束与抛物线布束时,中支点截面上靠近边腹板的剪力滞系数大小相差达到了23.68%;左侧跨中截面靠近边腹板处更是达到了33.45%;腹板与顶板交界处的剪力滞效应沿跨度方向的分布趋势基本一致,但在中支点截面顶板靠近边腹板处的剪力滞系数差值达23.68%。从总体上看,截面剪力滞系数变化较大范围基本是在中支承位置附近L/4长度范围,在其他较远区域影响很小。
[Abstract]:With the development of modern traffic demand, the promotion of bridge design concept and the combination of box-section beam and pre-stressed technology, the box-section beam is more inclined to the structure of thin-wall and long cantilever, and the prestressed box girder has become a big trend of the construction of the bridge. In this paper, under the study of the shear lag behavior of the NSFC , the prestressed concrete box girder is studied by theory and combined with the numerical simulation. The key problems in the theoretical analysis of the shear lag effect of the box girder under the prestress effect are studied. The main research contents and results are as follows: (1) In order to answer whether the axial force causes the shear lag effect, the longitudinal stress in different parts of the box girder is analyzed by the finite element method of the plate shell for the single-chamber box girder without the cantilever plate and the cantilever plate, The axial force shear lag coefficient of simply-supported beam, cantilever beam and continuous beam under different working conditions is studied by introducing the concept of axial force shear lag coefficient. The results show that, when the axial force acts on the box girder, there is no shear lag effect in the beam body, and only the local stress concentration area exists near the point of action of the axial force, and the area is about 1 times the length of the beam width. The value is equal to the non-uniform transfer length of the general component under the local pressure. (2) The pre-stressed beam of box girder is usually eccentrically anchored at the beam end and is not anchored in the position of the mandrel, and the equivalent pre-stress includes the shaft pressure acting on the mandrel and the concentrated bending moment of the beam end. In this paper, the axial force and the concentrated bending moment of the pre-stressed equivalent load of a single-box double-chamber box-girder pre-stressed beam are calculated separately, and the shear lag effect of the box girder under the action of concentrated bending moment is calculated. In this paper, the shear lag-warping displacement model, which can reflect the difference of the shear lag and the difference of the shear lag between the flanges of the box girder under the action of concentrated bending moment, is put forward, and the differential equation of the shear lag effect of the box girder under the action of concentrated bending moment is established to obtain the analytical solution. The shear lag distribution of the box girder is not the same at the same time in the system. The result of the comparison between the analytical solution and the finite element numerical solution of ANSYS is that the basic law of the results and the size of the numerical analysis result are basically the same, and the warping displacement function as taken in this paper is reasonable, and the derived control differential equation and the analytical solution are correct. And the calculation accuracy is good. (3) The shear lag effect of a simply-supported single-box double-chamber box under the action of a concentrated bending moment is analyzed, The stress after the shear lag effect is considered to be 2.24 times the theoretical value of the primary beam, while the rest is smaller. And the shear coefficient is different between the web plates, and therefore, it is necessary to take into account the stress difference of the wing plates between the different web plates in the structural design. (4) The effect of different shear lag load effect mode on the shear lag effect of the section of the box girder is studied. The average distribution of the beam, the cantilever beam and the continuous beam on the three-web is established by using the finite element software of ANSYS. The shear lag effect in the typical cross-section and in the span direction is typical when both the web of the web and the web of the middle web are deployed. The results show that the shear lag effect of the box girder is different and the difference is large, and the shear lag coefficient of the top and bottom plate of the cross-section is larger when the prestressed beam is arranged in the middle web. The shear lag coefficient of the top plate is changed from 1.22 to 0.531 near the edge of the flange, and the shear lag effect is obvious; in the case of uniform distribution of three webs, the shear lag effect of the section is relatively small. At the same time, the effect of different beam patterns on the shear lag effect of box girder under different boundary conditions is different, the effect on the continuous beam is the largest, the simple-supported beam is the second, and the influence of the cantilever beam is small. (5) The influence of the internal force of the pre-stressed secondary internal force on the shear lag effect of the box girder is analyzed. In theory, the additional bending moment value and the pre-stress initial bending moment value which are caused by the shear lag effect at the position of the prestressed anchorage end are the same as the original bending moment value, and the size is only related to the geometric characteristics of the section of the box girder, and the additional bending moment at the middle supporting point is related to the cross-sectional geometric parameter and the width-span ratio of the box girder. The results of the finite element analysis of the relevant examples are given, and the results are in agreement with the numerical results. (6) For the design of the two-span continuous beam in the linear arrangement of the actual pre-stressed beam, the non-staple fiber bundle mode is generally used. In this paper, the internal force is generated in the beam, and the shear lag effect of the box girder is studied by using the ANSYS finite element software to establish the plate shell model in combination with the different linear arrangement of the steel beam in the two-span continuous box girder of the pre-stressed concrete. The results show that the change of the beam alignment has a certain effect on the shear lag effect of the middle bearing section, and the shear lag coefficient in the cross section of the middle supporting point near the side web is 23.68% when the straight-line cloth bundle and the parabolic distribution beam are arranged, and the cross-section of the left side is more than 33.45% near the edge web; The shear lag effect at the interface between the web and the top plate is generally consistent with the distribution trend in the span direction, but the difference of the shear lag coefficient at the top of the mid-pivot section near the edge web is 23.68%. In general, that large extent of the shear lag coefficient of the section is basically the L/4 length range near the middle support position, and the effect on the other remote areas is very small.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U441.5

【共引文献】