Effect of Material Degradation on Fatigue Properties of Steel-Concrete Composite Bridge Welds
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摘要: 为研究材料劣化对钢-混凝土组合梁桥焊缝疲劳性能的影响,根据钢筋锈蚀规律、混凝土强度时变规律和钢材腐蚀规律,计算钢筋和钢板失重率、混凝土时变强度,利用ANSYS软件建立劣化梁桥有限元模型,以主梁跨中腹板与下翼缘交接处的焊缝节点为研究对象,首先在AASHTO标准疲劳车作用下,提取不同劣化工况下主梁焊缝节点的应力时程,探讨材料劣化对节点应力的影响;然后基于Miner线性累计损伤理论计算不同劣化年限下的疲劳损伤发展曲线,分析材料劣化对疲劳损伤曲线的影响,探讨车辆通行时桥梁最大应力幅与等效应力循环次数的变化规律;最后定义疲劳损伤比,研究材料劣化对组合梁桥焊接细节疲劳损伤的影响。
结果表明:焊缝节点区域的应力易受到材料劣化的影响,焊缝节点的应力值随劣化年限的增加而增大,且越接近加载位置应力值越大;桥梁焊接细节的疲劳损伤发展曲线呈现线性增长趋势,材料劣化会导致疲劳细节的疲劳损伤累积加速,在达到设计基准期时,疲劳损伤值的最大增幅达到7.5倍;最大应力幅对材料劣化更加敏感,疲劳细节产生的最大应力幅增长率呈递增趋势,在100 a劣化工况时,4个节点的应力幅增长率与未劣化时相比分别达到了10.4%,13.6%,8.5%及14.7%,但等效应力循环次数的增长率未呈现明显规律;疲劳损伤比随劣化时长非线性增长,在劣化时间为100 a时,梁桥中4个节点的疲劳损伤比较未劣化时分别为7.0,7.4,6.4以及7.52,且结构劣化程度越大,疲劳损伤比的非线性程度越高。Abstract: In order to study the influence of material degradation on the fatigue performance of steel-concrete composite beam bridge welds,the weight loss rate of reinforcement and steel plate and the time-varying strength of concrete are calculated according to the law of reinforcement corrosion,the law of concrete strength and the law of steel corrosion.The finite element model of degraded bridge was established by using ANSYS software.Taking the weld joint at the junction of main beam mid span web and lower flange as the research object,firstly,under the action of AASHTO standard fatigue vehicle,the stress time history of the welded joints of the main beam under different degradation conditions was extracted,and the influence of material degradation on the joint stress was discussed;then,based on Miner's linear cumulative damage theory,the fatigue damage development curves under different degradation years were calculated,the influence of material degradation on the fatigue damage curve was analyzed,and the variation laws of the maximum stress amplitude and the number of equivalent stress cycles of the bridge were discussed;finally,the fatigue damage ratio was defined to study the effect of material degradation on the fatigue damage of welding details of composite beam bridge.
The results show that the stress in the weld joint area is easily affected by material degradation.The stress value of the weld joint increases with the increase of degradation years,and the closer the loading position is,the greater the stress value is.The fatigue damage development curve of bridge welding details shows a linear growth trend,and material degradation will lead to the acceleration of fatigue damage accumulation of fatigue details.When reaching the design basis,the maximum increase of fatigue damage value reaches 7.5 times;the maximum stress amplitude is more sensitive to material degradation,and the growth rate of the maximum stress amplitude generated by fatigue details shows an increasing trend.The growth rates of the stress amplitude of the four nodes in the 100-year degradation condition reach 10.4%,13.6%,8.5% and 14.7% respectively.However,the growth rate of the number of equivalent stress cycles does not show an obvious law.The fatigue damage ratio increases nonlinearly with the degradation time.When the degradation time is 100 years,the fatigue damage ratio of beam bridges is 7.0,7.4,6.4 and 7.52 respectively.In addition,the greater the degree of structural degradation is,the higher the nonlinear degree of fatigue damage ratio is. -
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