【作者】 吴俊；

【导师】 金伟良；

【作者基本信息】 浙江大学 ， 工程硕士（专业学位）， 2022， 硕士

【摘要】 钢筋混凝土结构的耐久性能、疲劳性能和徐变性能是结构全寿命周期内最为典型的三种时变性能。在长期环境、反复荷载和持续荷载作用下混凝土结构的力学性能和结构性能将会发生改变,这种改变往往使结构性能产生退化,且三种作用劣化效果彼此之间会相互影响、互相加速。在以往的众多研究中,这三部分内容大多是作为相互独立个体分别研究,而本文则以钢筋混凝土梁的耐久性能为主要研究对象,共同考虑循环荷载和持续荷载作用对钢筋混凝土梁耐久性能的影响,主要进行了如下的研究工作:(1)基于正交试验原则,设计了以耐久性为主考虑循环加载和持续荷载作用的试验方案:设计了三种不同的疲劳循环寿命比,分别为0.025、0.15和0.60;设计了两种不同的持荷时间,分别为持荷90 d和180 d;进行了疲劳损伤混凝土梁的通电加速锈蚀试验以及循环荷载和持续荷载作用后的通电加速锈蚀试验;获得了以锈胀裂缝宽度、混凝土氯离子含量、混凝土非稳态氯离子迁移系数和钢筋锈蚀率等损伤指标来表征钢筋混凝土梁耐久性能和承载性能退化的数据。(2)氯盐通电腐蚀环境下疲劳损伤混凝土梁的耐久性能试验研究表明,随着循环加载次数的增大,疲劳横向裂缝宽度逐渐增大,混凝土保护层锈胀开裂所需时间变短,锈胀裂缝宽度和钢筋锈蚀率会逐渐增大,抗弯承载能力逐渐降低;受压区混凝土氯离子含量先减小后增大,较低次数的循环荷载作用将使受压区混凝土变得密实,混凝土抵抗离子侵蚀的能力将得到增强,随着循环加载次数的增加,这种致密作用逐渐减小甚至消失。(3)氯盐通电腐蚀环境下经历循环加载和持续荷载共同作用的混凝土梁耐久性能试验研究表明,持荷时间对梁受压区混凝土抵抗氯离子侵蚀能力的影响因疲劳损伤程度的不同而不同,且与持荷时间t的长短有关:对低疲劳损伤混凝土梁,短期持荷对受压区混凝土抵抗氯离子侵蚀的能力几乎没有影响;对中高程度疲劳损伤混凝土梁,持荷90 d将显著提高受压区混凝土抗氯离子侵蚀能力,持荷180 d也提高混凝土抵抗氯离子侵蚀的能力,但提高效果有所降低。(4)氯盐通电腐蚀环境下经历循环加载和持续荷载共同作用的混凝土梁耐久性试验研究表明,梁纵筋锈蚀率、抗弯极限承载力、静载抗弯刚度与循环加载次数/持荷时间呈负相关关系;循环加载和持续荷载共同作用对梁受压区混凝土产生的损伤较受拉钢筋更大,导致梁在静载试验时破坏模式由完好梁的适筋破坏转变为损伤梁的受压区混凝土压碎破坏;最后,基于试验结果,建立了考虑循环加载次数、持荷时间和钢筋锈蚀率的钢筋混凝土梁抗弯刚度退化模型。(5)提出了考虑疲劳和徐变损伤钢筋混凝土梁的三种耐久性综合损伤指标;基于保护层锈胀开裂状态的耐久性可靠度实用设计方法,以随时间变化的腐蚀电流密度作为环境效应,将混凝土保护层锈胀开裂时刻的临界锈蚀深度作为结构抗力,得到了考虑疲劳和徐变损伤的钢筋混凝土梁抗力衰减系数和耐久性降低系数;通过对环境作用效应和结构抗力进行调整,建立了考虑疲劳和徐变损伤的耐久性极限状态方程,得到了考虑疲劳和徐变损伤的混凝土保护层锈胀开裂时间。更多还原

【Abstract】 The durability,fatigue,and creep properties of reinforced concrete structures are the three most typical time-varying properties in the whole life.The mechanical properties and structural performance of concrete structures under long-term environment,reciprocating load,and sustained load would be degraded,and the three degradation effects will interact and accelerate each other.In previous studies,the three deterioration factors are studied separately as independent individuals.Considering the performance degradation caused by reciprocating loading and sustained load,the durability performance of reinforced concrete beams is studied in this paper.The main research work is as follows:(1)Based on the principle of the orthogonal test,a test plan with reciprocating loading and sustained load as the main consideration was designed: three different fatigue life ratios with the value of 0.025,0.15,and 0.60,respectively,two different load-holding time with the ratio of 90 days and 180 days,respectively.The accelerated corrosion test of fatigue damaged concrete beam and the accelerated corrosion test after reciprocating loading and the sustained load was carried out,respectively.The damage indicators such as concrete chloride ion content,non-steady state chloride migration coefficient,and steel corrosion rate are obtained,which can be used to characterize the durability performance and bearing performance degradation of reinforced concrete beams.(2)The results of the durability of fatigue-damaged concrete beams in chloride attached corrosion environment show that with the increase of cycle loading times,the width of fatigue transverse crack gradually increases,the corrosion-induced cracking time of the concrete cover due to the rust expansion becomes shorter,and the width of corrosion-induced cracks and steel corrosion rate gradually increase,and the flexural bearing capacity gradually decreases.Meanwhile,the chloride ion content of the concrete in the compression zone decreases firstly and then increases with the increase of cycle loading times,because the concrete in the compression zone would become denser due to the lower number of cyclic loads,and the ability to resist ion erosion would be enhanced.(3)The results of the durability test of concrete beams subjected to cycle load and sustained load in the chloride attached environment show that the effect of load-holding time on the resistance of chloride attack in the compression zone of the concrete beam varies with the degree of fatigue damage,which is dependent on the load-holding time.For concrete beams under low fatigue damage,short-term load-holding time has almost no influence on the ability of concrete resisting chloride erosion in the compression zone.For concrete beams under medium and high fatigue damage,the resistance to chloride ion erosion of concrete in the compression zone is improved significantly under the load-holding time of 90 days,while the improvement effect decreases for the load-holding time of 180 days.(4)The results of the durability test of concrete beams subjected to combined cycle load and sustained load in the chloride attacked environment show that the corrosion rates of longitudinal bars,ultimate flexural bearing capacity,and static flexural stiffness are negatively correlated to cycle loading times or load-holding time.Meanwhile,the damage degree of concrete in the compression zone is larger than that of the tensile steel bars,resulting in the failure mode of the beam converting from the balanced failure to the failure of the concrete crushing in the compression zone.Moreover,a flexural stiffness degradation model of reinforced concrete beams considering the cycle loading times,load-holding time,and steel corrosion rate is established.(5)Three comprehensive damage indexes of the durability of reinforced concrete beams with the damage of fatigue and creep are proposed.Based on a practical design method for durability on the state of the corrosion-induced cracking time of concrete cover,with the corrosion depth of reinforcement being the environmental effect and the critical corrosion depth being the structural resistance,the structural resistance degeneration coefficient and durability reduction factor considering the damage of fatigue and creep are obtained.Furthermore,by adjusting the environmental effect and structural resistance,the durability limit state equation considering fatigue and creep damage is established,and corrosion-induced cracking time of concrete cover considering fatigue and creep damage is solved.更多还原