疲劳损伤RC梁氯离子腐蚀后疲劳性能和氯离子扩散性试验研究

Experimental study on fatigue behavior and chloride diffusivity of fatigue damaged RC beams after chloride attack

对于沿海地区具有疲劳损伤的在役钢筋混凝土(RC)桥梁结构,其在氯腐蚀后的疲劳性能和氯离子扩散性对于结构耐久性设计和评估至关重要。为此,通过试验研究15根不同初始疲劳损伤程度RC梁在氯腐蚀后的疲劳性能和混凝土中氯离子含量,试验参数包括荷载水平(疲劳荷载上限与静载极限荷载之比,取0.2~0.5)、初始疲劳加载次数(1×10^(4)~120×10^(4))、氯腐蚀时间(90、180 d)和受拉纵筋配筋率(1.06%、1.59%和2.91%)。试验结果表明:疲劳损伤RC梁在氯腐蚀后进行疲劳加载时,梁挠度和混凝土应变等呈现典型的三阶段变化特征;荷载水平、初始疲劳加载次数、氯腐蚀时间和受拉纵筋配筋率均对其剩余疲劳寿命影响显著,荷载水平(不小于0.4)、初始疲劳加载次数(第一疲劳阶段)和氯腐蚀时间的增加均引起剩余疲劳寿命迅速降低,当配筋率增加到42%界限配筋率时,寿命有所增加;受拉混凝土氯离子扩散性的增加与RC梁剩余疲劳寿命的降低相关联,而受压混凝土的扩散性随荷载水平、初始疲劳加载次数和配筋率的增加而增加。

For in-service reinforced concrete(RC) bridges with fatigue damage in coastal regions, the fatigue behavior and chloride diffusivity after the chloride corrosion are essential to the durability design and assessment. In this paper, the fatigue behavior and chloride content in concrete of 15 RC beams with different pre-fatigue damage were experimentally studied after the chloride attack. The test parameters included load level(ratio of maximum fatigue load to ultimate static load, valued as 0.2-0.5), initial fatigue loading cycle(0.01×10^(4)-1.2×10^(4)), chloride exposure duration(90 and 180 days) and tensile reinforcement ratio(1.06%, 1.59% and 2.91%). The results indicate that the deflection and concrete strain follow the typical three-stage variation during the fatigue loading process. These four test parameters have significant effects on the residual fatigue life. The increases of load level(no less than 0.4), initial fatigue loading cycle(in the first fatigue stage) and chloride exposure duration markedly decrease the residual fatigue life, while increasing the reinforcement ratio to 42% of the balanced reinforcement ratio could increase the residual fatigue life. The increase of chloride diffusivity of tensile concrete is related to the decrease of residual fatigue life of RC beams, while the chloride diffusivity of compressive concrete could continuously increase with the increasing load level, initial fatigue loading cycles and reinforcement ratio.