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首页> 外文期刊>Journal of bridge engineering >Reliability-Based Dynamic Amplification Factor on Stress Ranges for Fatigue Design of Existing Bridges
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Reliability-Based Dynamic Amplification Factor on Stress Ranges for Fatigue Design of Existing Bridges

机译：既有桥梁疲劳设计中基于可靠度的应力范围动态放大因子

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摘要

A dynamic amplification factor (DAF) or a dynamic load allowance (IM) is typically used in bridge design specifications to include dynamic effects from vehicles on bridges. The calculated live-load stress ranges may not be correct because of varied dynamic amplification effects in different regions along the bridge, different road roughness conditions, and multiple stress-range cycles generated for one vehicle passage on the bridge. In this study, a reliability-based dynamic amplification factor on stress ranges (DAFS) for fatigue design is proposed to include the fatigue damage from multiple stress-range cycles resulting from each vehicle passage at varied speeds under various road conditions on the bridge's life cycle. A numerical simulation toward solving a coupled vehicle-bridge system, including a three-dimensional (3D) suspension-vehicle model and a 3D dynamic bridge model, is used to obtain the revised equivalent stress range. The revised equivalent stress range is defined on an equivalent fatigue-damage basis; namely, the fatigue damage from multiple stress ranges with varied amplitudes is equivalent to the fatigue damage from one stress cycle of the revised equivalent stress range. Dynamic amplification factor on stress ranges is then defined as the ratio of the nominal live-load stress range and the maximum static stress range. A parametric study on DAFS was carried out to analyze the effect from multiple variables on the bridge's life cycle, for instance, faulting days in each year, vehicle speed limit and its coefficient of variance, vehicle type distribution, and annual traffic increase. To appreciate the difference between the proposed DAFS and the traditional DAF, the calculated fatigue lives from the six approaches related to DAFS or DAF are compared with each other. Similar to DAF for dynamic response on displacements, DAFS is proposed to obtain dynamic stress ranges for fatigue design. As a result, once the DAFS values are available, the dynamic stress ranges for fatigue design can be easily obtained by multiplying the maximum static stress range and the DAFS, which helps to preserve both the accuracy and simplicity of bridge fatigue design.
机译：在桥梁设计规范中通常使用动态放大系数（DAF）或动态载荷余量（IM），以包括车辆在桥梁上的动态影响。由于沿桥梁的不同区域中不同的动态放大效果，不同的道路崎conditions状况以及桥梁上一条车辆通过时产生的多个应力范围循环，因此计算出的活载应力范围可能不正确。在这项研究中，提出了一种基于可靠性的应力范围动态放大因子（DAFS），以进行疲劳设计，其中包括在桥梁的生命周期中，在各种路况下，每辆车辆在不同的速度下通过不同速度产生的多个应力范围循环所造成的疲劳损伤。 。求解包含三维（3D）悬架车辆模型和3D动态桥模型的耦合车桥系统的数值模拟用于获得修正的等效应力范围。修正的等效应力范围是在等效疲劳损伤的基础上定义的；即，来自多个振幅变化的应力范围的疲劳损伤等同于来自修正等效应力范围的一个应力循环的疲劳损伤。然后将应力范围上的动态放大系数定义为额定活载应力范围和最大静态应力范围之比。进行了DAFS的参数研究，以分析多种变量对桥梁寿命周期的影响，例如，每年的故障天数，车速限制及其方差系数，车辆类型分布和年流量增加。为了了解拟议的DAFS与传统DAF之间的区别，将与DAFS或DAF相关的六种方法计算出的疲劳寿命进行了比较。与DAF相似，它对位移具有动态响应，提出了DAFS来获得用于疲劳设计的动态应力范围。结果，一旦DAFS值可用，就可以通过将最大静态应力范围与DAFS相乘轻松获得疲劳设计的动态应力范围，这有助于保持桥梁疲劳设计的准确性和简便性。

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