预制RPC柱降低大跨PC刚构桥跨中长期下挠效应分析

发布时间：2018-02-09 21:11

本文关键词： 长期下挠收缩徐变 RPC-NC复合截面内力重分布　出处：《湖南大学》2015年硕士论文　论文类型：学位论文

【摘要】：大跨PC刚构桥长期下挠的问题十分突出,同时它与开裂形成恶性循环,对结构的运营安全和耐久性构成很大威胁。受压混凝土收缩徐变是大跨刚构桥长期下挠的最主要原因,鉴于RPC(活性粉末混凝土)经热养护后强度高、收缩极小、徐变系数小的特点,提出在负弯矩区箱梁底板、跨中箱梁顶板中加入预制RPC柱形成局部RPC-NC(普通混凝土)复合截面的方案来控制刚构桥长期下挠。本文首先通过试验、理论、有限元分析探究了RPC-NC复合截面柱的应力重分布现象及其对复合截面柱后期变形的降低作用,同时分析了剪力键的受力性能,进而得到了复合截面RPC的合理面积比例。在此研究基础上设计了全桥加入RPC柱的布置方案,建立了全普通混凝土、加预制RPC柱刚构桥全桥有限元模型并进行对比分析。主要结论如下:(1)通过试验、理论、有限元分析知,由于RPC和C50混凝土在收缩徐变性质上的巨大差异复合截面将发生内力重分布的现象,C50应力随时间将逐渐减小,复合截面柱的后期变形、名义徐变系数也会随之减小;RPC的徐变系数可以取为CEB-FIP(1990)模式下同条件C50混凝土的15%进行分析计算;布置剪力键钢筋横截面积为复合柱横截面积的4%时,剪力键布置安全、有效;实桥应用中,布置RPC面积为复合截面总面积的40%比较合理、有效;(2)通过全桥有限元模型应力、变形、预应力损失的对比分析知,相对于全普通混凝土刚构桥,加入预制RPC柱的刚构桥十年收缩徐变所引起的竖向位移降低了54.5%,跨中长期下挠得到明显改善;中跨跨中梁底普通混凝土、0号块梁顶普通混凝土压应力略有增加,0号块梁底普通混凝土、中跨跨中梁顶普通混凝土压应力减小,中跨应力分布更加均匀;中跨底板后期束、负弯矩区顶板束由成桥后十年收缩徐变引起的预应力损失没有明显变化;(3)加入预制RPC柱后,刚构桥跨中长期持续下挠减小的主要原因是:刚构桥负弯矩区箱梁底板、跨中附近箱梁顶板形成了局部的RPC-NC复合截面,局部复合截面发生应力重分布导致普通混凝土压应力减小、后期名义徐变应变减小,进而减小了刚构桥负弯矩区的结构转角、跨中附近的竖向位移;(4)通过参数分析建议在负弯矩区0~8号块的箱梁底板,24~26号块、跨中合拢段的箱梁顶板布置预制RPC柱。综上可知加入适当比例的预制RPC柱,可使刚构桥成桥后的长期下挠降低50%左右,明显改善刚构桥的长期下挠问题,对于实际工程有一定的参考价值。
[Abstract]:The problem of long term deflection of long span PC rigid frame bridge is very prominent. At the same time, it forms a vicious circle with cracking, which poses a great threat to the operation safety and durability of the structure. The shrinkage and creep of compressed concrete is the main cause of long term deflection of long span rigid frame bridge. In view of the high strength, minimal shrinkage and low creep coefficient of RPC (reactive Powder concrete) after thermal curing, the bottom plate of box girder in negative bending moment region is put forward. The method of forming local RPC-NC (ordinary concrete) composite section by adding prefabricated RPC columns to the roof of span box girder is used to control the long-term deflection of rigid frame bridge. The stress redistribution phenomenon of RPC-NC composite section column and its effect on reducing the late deformation of composite section column are studied by finite element analysis, and the mechanical properties of the shear bond are analyzed at the same time. Then the reasonable area ratio of composite section RPC is obtained. On the basis of this research, the layout scheme of adding RPC column to the whole bridge is designed, and the whole ordinary concrete is established. The finite element model of the whole bridge with prefabricated RPC column rigid frame bridge is compared and analyzed. The main conclusions are as follows: (1) through experiment, theory and finite element analysis, Due to the great difference between the shrinkage and creep properties of RPC and C50 concrete, the internal force redistribution will occur in the composite section. The C50 stress will gradually decrease with time, and the post-deformation of the composite cross-section column will occur. The creep coefficient of RPCs can be taken as 15% of C50 concrete under the same condition under CEB-FIP1990) mode, and the shear bond arrangement is safe and effective when the cross section area of shear key steel bar is 4 of the cross section area of composite column. In the application of real bridge, it is reasonable to arrange RPC area to be 40% of the total area of composite section. (2) through the comparative analysis of the stress, deformation and prestress loss of the finite element model of the whole bridge, it is found that compared with the full ordinary concrete rigid frame bridge, The vertical displacement caused by 10 years shrinkage and creep of rigid frame bridge with prefabricated RPC column is reduced by 54.5 and the mid- and long-term deflection of span is improved obviously. The compressive stress of ordinary concrete at the top of No. 0 block beam increases slightly, the compressive stress of ordinary concrete at the top of middle span beam decreases and the stress distribution of middle span is more uniform. There is no obvious change of prestress loss caused by shrinkage and creep of roof beam in negative moment region after 10 years of bridge completion. (3) after adding prefabricated RPC column, the main reason of long-lasting deflection reduction of rigid frame bridge span is: the bottom plate of box girder in negative moment zone of rigid frame bridge, The local RPC-NC composite section is formed in the roof of the box girder near the middle span. The stress redistribution of the local composite section results in the reduction of compressive stress of ordinary concrete and the decrease of nominal creep strain in the later stage, thus reducing the structural rotation angle of the negative moment zone of the rigid frame bridge. Through parameter analysis, it is suggested that prefabricated RPC columns should be arranged on the bottom plate of box girder in block 0 ~ 8 of negative bending moment, and on the roof of box girder in the closing section of span. In summary, the appropriate proportion of prefabricated RPC columns should be added. The long-term deflection of rigid frame bridge can be reduced by 50% or so, and the long-term deflection problem of rigid frame bridge can be improved obviously, which has certain reference value for practical engineering.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：U441;U448.23

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