摘 要

与传统简支桥梁相比，整体式桥台桥梁（Integral abutment bridge，IAB）取消了支座和伸缩缝，在桥跨与桥台之间采用了刚性连接，避免了因支座和伸缩缝老化引起的桥梁损坏，具有良好的经济效益。但是季节性温度变化会引起混凝土桥跨发生伸缩变形，造成桥台后土压力的变化，而过大的土压力会对桥台造成损坏。通过在刚性桥台后设置膨胀聚苯乙烯（Expanded polystyrene，EPS）柔性垫层可以减小桥台后土压力。但是，EPS柔性垫层-整体式桥台桥梁（EPS-IAB）涉及复杂的土与结构相互作用，目前国内外相关研究较少。本文通过二维有限差分程序FLAC进行数值模拟，开展季节性温度变化作用下EPS-IAB的力学特性研究。主要研究内容和结论如下：

（1）建立EPS-IAB的FLAC数值模型，通过在桥台顶部施加位移边界条件，模拟季节性温度变化作用下桥跨长度变化对桥台的作用。研究不同幅值往复位移作用下，EPS-IAB的桥台水平位移和填土竖向位移、桥台后侧向土压力以及桥台弯矩的变化规律。结果表明：当桥梁受冷收缩，桥跨长度减小时，桥台后土体产生主动土压力，且不同加载位移条件下侧向土压力基本一致；当桥梁受热膨胀，桥跨长度增长时，桥台后土体产生被动土压力，随着加载位移增大，侧向土压力逐渐增大，尤其是桥台上部侧向土压力大幅增加。

（2）结合无EPS工况对比分析了EPS柔性垫层在IAB中的作用。结果表明：EPS柔性垫层可以显著减小桥台后侧向土压力，也可以在一定程度上减小桥台后填土顶面沉降。

（3）研究了EPS和填土的相关设计参数对EPS-IAB在温度变化作用下的变形特性和受力行为的影响规律，结果表明：随着EPS垫层弹性模量的减小和厚度的增大，桥台后侧向土压力有所减小；EPS柔性垫层的减载作用对于弹性模量较小的填土效果最为显著；增加填土强度（摩擦角和黏聚力）可以减小桥台后侧向土压力，但主要是由于土体自身强度的发挥，EPS垫层的影响较小。

关键词：整体式桥台桥梁；温度变化作用；膨胀聚苯乙烯；土压力；数值模拟

Abstract

The integral abutment bridge (IAB) has rigid connections between the bridge spans and the abutments and eliminates the use of bearings and expansion joints as compared with conventional simple-supported bridge. Hence, the IAB can avoid damage to the bridge as a result of aging of bearings and expansion joints, and has good economic benefits. However, the concrete bridge span can expand and contract due to seasonal changes of temperature, resulting in changes in earth pressure behind the abutment, and excessive earth pressures would cause damage to the abutment. The earth pressure behind the abutment can be reduced by placing expanded polystyrene (EPS) flexible cushion behind the rigid abutment. However, EPS flexible cushion-integral abutment bridge (EPS-IAB) will lead to complex soil-structure interaction, and related studies are limited. In this paper, numerical simulations were conducted to investigate the mechanical behavior of EPS-IAB under seasonal temperature changes using two-dimensional finite difference program FLAC. The main contents and conclusions are presented as follows:

(1) The FLAC numerical model of EPS-IAB was developed. This influence of the change of the bridge span length on the abutment under the effect of seasonal temperature changes was simulated by applying displacement boundary conditions on the top of the abutment. The mechanical properties of EPS-IAB under cyclic displacements with different amplitudes were investigated, with the focuses on horizontal displacements of abutment, vertical displacements of backfill soil, lateral earth pressures behind abutment and bending moment of abutment. Results indicate that when the bridge temperature decreases, the bridge span length decreases, and the active earth pressures develop behind the abutment. Meanwhile, the lateral earth pressures are almost the same under different displacements for active conditions. When the bridge thermally expands, the bridge span length increases, and the passive earth pressures develop behind the abutment. As the loading displacement increases, the lateral earth pressure on the abutment increases significantly, especially near the upper part of the abutment.

(2) The function of EPS flexible cushion layer in IAB was analyzed and compared with the case of conventional IAB without EPS. Results illustrate that the EPS flexible cushion layer can reduce lateral earth pressures behind the abutment, and can also reduce the backfill settlement behind the abutment to a certain extent.

(3) The influences of related design parameters of EPS cushion and backfill soil on the mechanical behavior of EPS-IAB under temperature changes were investigated. Results reveal that lateral earth pressures behind the abutment decrease to some extent with decreasing elastic modulus and increasing thickness for EPS cushion. The mitigation effect of EPS flexible cushions is more effective for the backfill soil with small elastic modulus. As the backfill soil strength increases, including friction angle and cohesion, the lateral earth pressure behind the abutment decreases. However, it is mainly due to the developed strength of the soil itself, and the EPS cushion has little influence.

Key Words：integral bridge abutment；temperature change effect；expanded polystyrene；earth pressure；numerical simulation

目 录

第1章 绪论 1

1.1 研究背景及意义 1

1.2 国内外研究现状 4

1.2.1 现场监测 4

1.2.2 室内模型试验 5

1.2.3 数值模拟 6

1.3 主要技术路线 7

第2章 数值模型 8

2.1 模型尺寸 8

2.2 网格划分与边界条件 8

2.3 材料模型及参数 9

2.4 数值模拟过程 10

第3章 EPS柔性垫层-整体式桥台桥梁力学特性 12

3.1 EPS柔性垫层-整体式桥台桥梁的变形特性与受力行为 12

3.2 EPS柔性垫层的作用 16

第4章 参数分析 18

4.1 EPS弹性模量 18

4.2 EPS厚度 20

4.3 填土弹性模量 22

4.4 填土摩擦角 23

4.5 填土黏聚力 24

第5章 结论与展望 27

5.1 主要成果与结论 27

5.2 主要创新点 27

5.3 研究展望 27

参考文献 29

致 谢 31

绪论

研究背景及意义

在传统的公路和铁路桥梁设计中，为了适应季节性温度变化引起的桥跨纵向伸缩，上部结构通常是通过支座简支在桥台和桥墩上，并在连接处设置伸缩缝（图1.1）。但是，桥梁伸缩装置长期暴露在外界环境中，受到温度变化作用、雨水侵蚀、车辆冲击和基础沉降等不利因素的影响，极易受损，进而引起桥梁结构的破坏，对行车安全也将产生不利影响。

图1.1 传统简支桥梁与整体式桥台桥梁

整体式桥台桥梁（Integral abutment bridge，IAB）取消了支座和伸缩缝，在桥跨与桥台之间采用了刚性连接，避免了因设置伸缩缝引起的各种缺陷。这类桥梁结构不仅提高了设计和建造效率，减少养护维修成本，还可以减少车辆冲击，有效提高桥头行车的平稳性，延长桥梁使用寿命。因为这些突出的优点，整体式桥梁在欧美国家得到了大规模的应用和推广^[1]。

如图1.2所示，在温度变化作用下，整体式桥梁的主梁与桥面板会沿桥梁纵向发生伸缩变形，与其刚性连接的桥台也随之发生往复水平位移^[2]。同时，桥台后填土顶面产生明显的隆起或沉降，导致了实际工程中的桥头跳车、搭板沉降等现象，严重影响了桥头行车平稳性。