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摘要: 毕业设计主要是关于大跨度预应力混凝土连续梁桥上部结构的设计。预应力混凝土连续梁桥以结构受力性能好、变形小、伸缩缝少、行车平顺舒适、养护工程量小、抗震能力强等而成为最富有竞争力的主要桥型之一。受时间和个人能力的限制，本次毕业设计没有具体涉及到下部结构、横向预应力及竖向预应力的设计。7205
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设计桥梁跨度为51+90+51m,横截面为单箱双室，桥面宽18.5m，分为双向4车道。主梁施工采用悬臂施工法，对称平衡浇筑混凝土。
设计过程如下：首先，确定主梁主要构造及细部尺寸，它必须与桥梁的规定和施工保持一致，考虑到抗弯刚度及抗扭刚度的影响，设计采用箱形梁。主梁的高度呈二次抛物线变化，因为二次抛物线近似于连续梁桥弯距的变化曲线。其次，利用Midas电算软件分析内力结构总的内力(包括恒载和活载的内力计算)。用于计算的内力组合结果也由Midas电算软件计算而得，从而估算出纵向预应力筋的数目，然后再布置预应力钢丝束。再次，计算预应力损失及次内力，次内力包括先期恒载徐变次内力、先期预应力徐变次内力、局部温度变化次内力。
然后进一步进行截面强度的验算，其中包括承载能力极限状态和正常使用极限状态。在正常使用极限状态验算中包括计算截面的混凝土法向应力验算、预应力钢筋中的拉应力验算、截面的主应力计算。另外，本设计对箱梁扭转计算，风载，地震，以及结构动力特性没有考虑。
关键词：预应力混凝土连续梁桥；次内力；悬臂施工
The design of pre-stressed concrete continuous beam bridge
ABSTRACT：The graduate design is mainly about the design of superstructure of short-span pre-stressed concrete continuous box Girder Bridge. Pre-stressed concrete continuous Girder Bridge become one of main bridge types of the most full of competion ability because of subjecting to the dint function with the structure good, having the small defomation, few of control joint,going smoothly comfort,protected the amout of engineering small and having the powerfully ability of earthquake proof and so on. For time and ability limited, the design of the substructure, transverse pre-stressing and vertical pre-stressing is not considered.
The spans of the bridge are 51+90+51m, has one box two rooms and four traffic ways, the width of the bridge surface is 18.5m.
The major girder applies Full scaffold construction , symmetric equilibrium construction .
The procedure of the design is listed below:
The first as to dimension the structural elements and details of which it is composed, it can’t and certainly should without being fully coordinated with the planning and working phrases of the project. Considering the distorting stiffness and the bending stiffness, box birder goes as second-parabolic curve, for second-parabolic curve is generally similar to the change of continuous bridge’s bending moments along.
The second is to use madis software to analyze internal gross force of the structures (including dead load and lived load), the internal force composition can be done by using the compute results. According to the internal force composited, the evaluated amount of longitudinal tendons can be worked out, then we can distribute the tendons to the bridge.
The third is to calculate the loss of pre-stressing and secondary force due to pre-stressing, first dead loads and temperature, bearing displacement, and so on.
The last is checking the main cross section. the work includes the load-caring capacity ultimate state and the normal service ability ultimate state as well as the main section’s being out of shape.
In addition, the torsion of box girder, wind load, seismic loads and the dynamic properties aren’t taken into account during the design.