Effect of Transverse Deflection on Force State of Prestressed Concrete Trough Girders with Asymmetric Cross-Section
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摘要: 为了研究梁体横向偏位对截面不对称PC （prestressed concrete）开口薄壁梁顶推施工的影响，并提出合理纠偏阈值，以世界首例顶推施工的不对称截面槽形梁——天津第二大街跨津山铁路立交工程为背景，利用有限元软件ANSYS建立实桥模型，研究槽形梁在最不利状态下未发生横向偏位时受力状态，在此基础上以满足安全落梁的横向偏位距离为最大偏位距离，分析不同横向偏位方式对梁体受力的影响. 研究结果表明：槽形梁在未发生偏位时横截面受力不均衡，而平动向右偏位方式加剧受力的不均衡；梁体以最不利偏位方式偏移96 mm后，槽型梁整体内力变化值较小，且下一步顶推后可以安全落梁. 因此，认为顶推施工中，横向偏位纠偏阈值可适当放宽至96 mm.Abstract: This work aims to study the influence of transverse deflection of a beam body on pushing construction of an prestressed concrete (PC) open thin-walled beam with asymmetric cross-section and provide a reasonable deviation correction threshold for the incremental launching technique. Taking as a prototype the world’s first case of an asymmetrical cross-section trough girder—Tianjin Second Avenue Cross-Jinshan Railway Interchange Project, an actual bridge model was built using the finite element software ANSYS to study the stress state of the trough girder under the most unfavourable conditions. On this basis, using the maximum deviation distance that meets safety requirements for girder placement as the deviation limit, the influence of different transverse deflection modes on the force of the beam body was analysed. Results show that the cross-section force of the trough girder is not balanced when the deflection does not occur; however, the force imbalance is aggravated by translation to the right. When the most unfavourable transverse deflection occurs in the beam with a displacement of 96 mm, the internal force change of the trough girder is small. Therefore, it is suggested that the transverse deviation correction threshold could be relaxed to 96 mm in jacking construction.
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图 1 最大悬臂处桥型布置及4# 墩支点截面图（单位：cm）
Figure 1. Bridge arrangement at the maximum cantilever and the fulcrum section of the No.4 pie (unit：cm)
图 6 同侧梁体偏位方式（单位：cm）
Figure 6. Schematic diagram of deflection of beam body at the same side (unit：cm)
图 7 两侧梁体偏位方式（单位：cm）
Figure 7. Schematic diagram of deflection of beam body on both sides (unit：cm)
图 8 不同偏位方式引起梁体受力差值
Figure 8. Force difference between beams caused by different deflection modes
表 1 结构材料参数
Table 1. Parameters of structural materials
结构 单元类型 材料 弹性模量/Pa 泊松比 密度/（kg•m–3） 导梁 SHELL63 Q345 2.06 × 1011 0.3 7 850 横联 BEAM189 Q235 2.06 × 1011 0.3 7 850 主体 SOLID65 C50 3.25 × 1010 0.2 2 500 钢束 LINK8 1860钢绞线 1.95 × 1010 0.3 7 850 
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表 2 横向偏位工况
Table 2. Transverse deflection conditions
工况 工况描述 1 以L3# 墩中心为支点旋转右偏 2 平动向右偏位 3 以L3# 墩中心为支点旋转左偏 4 平动向左偏位
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表 3 行车道板左右侧应力对比
Table 3. Stress comparison between two sides of carriageway slab
工况 路径 1 路径 2 左侧应力/MPa 右侧应力/MPa 差值百分比/% 左侧应力/MPa 右侧应力/MPa 差值百分比/% 1 –2.64 –1.79 32.4 –6.71 –8.84 31.7 2 –2.64 –1.78 32.5 –6.71 –8.86 32.0 3 –2.35 –2.04 13.2 –7.04 –8.52 21.1 4 –2.34 –2.04 13.0 –7.04 –8.51 20.9
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表 4 导梁前端挠度值对比
Table 4. Comparison of vertical deflection values in front of guide beams
mm 工况 竖向挠度 横向挠度 累计横向偏位距离 左边梁 右边梁 差值 左边梁 右边梁 差值 1 –106.35 –111.67 –5.32 5.04 5.32 0.29 170.32 2 –106.34 –111.68 –5.34 5.01 5.30 0.29 101.30 3 –106.30 –111.50 –5.20 4.96 5.25 0.29 170.25 4 –106.30 –111.48 –5.18 5.00 5.28 0.29 101.28
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