Abstract

Highway concrete bridges are subjected to fatigue, with stress cycles from the traffic defining the fatigue lives of reinforcement and concrete. Most existing studies on fatigue reliability of bridges address bending, ignoring the fatigue effect on stirrups. This paper evaluates the service life and reliability indexes, from the fatigue point of view, of longitudinal and transverse reinforcements of several concrete girders (prestressed and reinforced) for new bridge designs. Traffic loads are considered as measured by a high-speed weigh-in-motion system at an important highway in Brazil. It is found that reliability indexes for longitudinal reinforcements tend to decrease with the increase of “span length/girder height” ratio and reliability indexes for stirrups tend to increase with the introduction of intermediate crossbeams. Safety levels of stirrups are usually found to be lower than those of longitudinal rebars and tendons, especially for reinforced girders. It is found that deterministic fatigue live estimates lower than 50 years correspond to unsatisfactory reliability indexes (probabilistic analysis).

摘要

公路混凝土桥梁会受到疲劳的影响，交通中的应力循环决定了钢筋和混凝土的疲劳寿命。大多数现有的关于桥梁疲劳可靠性的研究都涉及弯曲，而忽略了对箍筋的疲劳影响。本文从疲劳的角度评估了用于新桥梁设计的几个混凝土梁（预应力和钢筋）的纵向和横向钢筋的使用寿命和可靠性指标。交通负荷被认为是由巴西一条重要高速公路上的高速动态称重系统测量的。研究发现，纵向钢筋的可靠性指标随着“跨长/梁高”比的增加而降低，箍筋的可靠性指标随着中间横梁的引入而增加。箍筋的安全水平通常低于纵向钢筋和钢筋束的安全水平，特别是对于加筋大梁。发现确定性疲劳寿命估计值低于 50 年对应于不令人满意的可靠性指标（概率分析）。