【作者】 朱红兵；

【导师】 余志武；

【作者基本信息】 中南大学 ， 桥梁与隧道工程， 2011， 博士

【摘要】 钢筋混凝土梁桥在公路工程中应用非常普遍。随着服役时间的增长,在车辆荷载作用和环境侵袭下,钢筋混凝土梁桥的承载力会逐步衰减,而交通对承载力的需求却逐步上升,使得很多桥梁在还没到设计基准期时就会失效破坏。为了确保桥梁的运营安全,为桥梁加固、限载或拆除重建提供技术依据,对桥梁进行剩余寿命评估非常重要。本文通过多年交通调查及实验室疲劳试验,对钢筋混凝土梁桥剩余寿命进行了理论和试验研究,具体内容如下：(1)基于贵新公路交通、车重调查资料,等效换算出各简化车型的等效轴重、轴距、车辆总重及各类车占车辆总数百分比,拟合出各种车型的总重概率密度函数,建立了公路钢筋混凝土梁桥疲劳荷载车辆模型。运用蒙特卡罗法对车辆荷载抽样得到作用于梁桥跨中截面的弯矩幅历程,采用雨流计数法得到应力幅计数及不同弯矩幅的分布频数,拟合出弯矩幅双指数分布函数,得到疲劳分析及试验用弯矩幅。建立了交通量增长灰色马尔科夫随机过程预测模型,用于预测未来年份交通量发展；拟合出所有车辆总重分布的双指数概率密度函数；建立了计算任意年份通过桥梁的某一车辆荷载总重范围内车辆数的车辆荷载随机过程模型,采用该模型对贵新公路交通量及车重进行了预测。(2)对5根空心板梁和5根T梁进行等幅疲劳试验,得到等幅疲劳的裂缝、挠度、应变发展规律及疲劳寿命、破坏形态与特征、S-N曲线。完成了4根高-低应力幅、低-高应力幅疲劳试验。根据公路桥梁疲劳荷载谱编制了实验室疲劳试验用的随机疲劳加载弯矩幅,完成2根梁的随机加载疲劳试验。分析了应力幅值、加载上限、截面型式、加载方式等对疲劳试验的影响。基于Miner准则和Corten-Dolan准则,推导出多级变幅荷载或随机荷载的等效等幅疲劳应力幅值计算公式及用于疲劳验算或疲劳寿命评估的方法,采用该公式预测了茅草冲大桥引桥的疲劳寿命。(3)基于刚度和承载力的退化是疲劳损伤的外在表现且存在唯一对应关联的假设,建立了桥梁承载力退化-刚度退化关联模型。以桥梁受荷时的挠度曲线方程反算刚度,揭示了钢筋混凝土梁在疲劳试验进程中刚度退化的三阶段线性规律,并建立了钢筋混凝土梁的刚度退化计算公式。利用该关联模型预测了某预制钢筋混凝土T梁桥的承载力。(4)基于热力学基本原理证实了可采用应变能来衡量梁在疲劳损伤过程中的能量耗散情况,将耗散能密度定义为每一循环中消耗的不可逆塑性功。测试了5根T梁的耗散能密度,发现疲劳试验中耗散能密度具有很明显的三阶段规律。对各试验梁的耗散能密度发展进行分段直线拟合,建立了耗散能密度和荷载幅与线刚度比之间的非线性方程及疲劳寿命与疲劳稳定阶段耗散能密度的非线性方程,通过对随机疲劳试验梁寿命的预测,验证了基于耗散能密度的疲劳寿命预测方法可行。利用该方法对贵新公路茅草冲大桥引桥进行了疲劳剩余寿命预测。(5)建立了受环境影响的车辆荷载作用下既有钢筋混凝土梁桥的承载力时变模型和时变可靠度预测模型,利用JC法求解出桥梁在任意时段的可靠指标。对茅草冲大桥引桥进行剩余寿命预测,得到了设计基准期内时变可靠指标,预测出在目标可靠指标和临界可靠指标时的寿命。更多还原

【Abstract】 Reinforced concrete bridges were very rife in highway engineering. Along with the servicing time increasing, bridges’bearing capacity will be attenuated gradually under the action of vehicle load and environment attack, and this induced much bridges’be destroyed before design reference period. To insure bridges safety and to provide technology gist for bridges’ reinforce, load limited or rebuilt, it is very important to evaluate existing bridges’residual service life. Based on the several years traffic investigation and laboratory fatigue experiment, this paper researched the reinforced concrete bridges’residual service life by experiment and theory manner, which were listed as following:(1) Based on the traffic and vehicle weight investigation information, predigest vehicle type’s equivalent axis weight and wheelbase, vehicle’s gross weight and percentage of every kind vehicle were calculated out. Gross weight’s probability density function of every kind vehicle was imitated. Then fatigue load vehicle model was established. The bending moment breadth in middle span of Maocaochong Bridge was achieved by Monte Carlo method. Then the the stress and distributing frequency of different moment bending breadth were acquired. Double-exponent distributing frequency formula of bending moment were imitated, the bending moment breadth which can be used in fatigue test and fatigue analysis was achieved out. A grey-Markov stochastic process traffic forecasting model which considering the disciplinarian and randomicity of traffic development was set up using GM(1,1) model and Markov chains model, and it can forecast the traffic development of future years. The probability density function of gross weight of traffic was acquired, the vehicle load stochastic process model which can calculate the vehicle numbers in a certain gross weight range overpassing the bridge in No. N years were established. The traffic and vehicle load of Guixin highway was forecasted using the model.(2) The unvaried amplitude fatigue experiment of deferent stress breadth were carried using 5 hollow slab beams and 5 T beams, and the unvaried amplitude fatigue test properties of crack development, deflection development, reinforcing steel bar and concrete’s strain development, as well as fatigue life, destroy form and destroy property when the beam fatigue destroyed. The S-N curves were fitted out. The low-high amplitude and high-low amplitude (two grade varied amplitude) fatigue experiment were carried using 2 hollow slab beams and 2 T beams. According to the highway bridge’s fatigue load spectrum, a random fatigue load bending moment breadth which can be used at laboratory fatigue experiment were weaved, then the random load fatigue experiment using a hollow slab beams and a T beams were done, the beam’s random load fatigue life and the fatigue destroy properties were obtained. Based on Miner ruler and Corten-Dolan ruler, a equivalent unvaried amplitude fatigue stress breadth calculation formula of multilevel or random load was deduced, Fatigue life of Maocaochong Bridge was triumphantly doped out by the formula.(3) Bridge’s relationship model of bearing capacity degeneration-stiffness degeneration was established. The stiffness of the bridge was calculated by deflection curve equation under load action, and it showed three phases linearity disciplinarian of bridge stiffness degeneration in fatigue experiment, a stiffness degeneration formula was established at last. A beam bridge’s bearing capacity was forecasted by using the model.(4) It was approved that the strain energy can showing the energy dissipating in fatigue processand the irreversible plastic power dissipated in every circular were defined as dissipated energy density. Five T beams’ dissipated energy density were tested, and researches detected that the dissipated energy density in fatigue test had quite obviously three phase law. The non-linear equation between dissipated energy density and the ratio of load breadth to stiffness as well as the non-linear equation between fatigue life and dissipated energy density in fatigue stabilization phase were established. The fatigue life forecasting method based on dissipated energy density were validated to be feasible through random fatigue experiment, and Maocaochong Bridge’s service life were triumphantly doped out with this method.(5) Using the bearing capacity degradation time-dependent model under environment infection and the fatigue bearing capacity degradation time-dependent model under vehicle load repeated action, existing reinforcing steel concrete bridge’s bearing capacity degradation time-dependent model under the action of environment and repeated vehicle load was established. Using existing bridge’s permanent load and load effect probability model, reinforcing steel concrete bridge’s time-dependent reliability forecasting model was erected, and the reliability index of bridge in every period of time were calculated out by using JC method. Maocaochong Bridge’s residual life forecast, reliability index in design reference period was acquired, and the Maocaochong Bridge’s service life at target reliability index and critical reliability index were doped out.更多还原