Ghafoori Elyas, Motavalli Masoud
Empa, Swiss Federal Laboratories for Materials Science and Technology, Structural Engineering Research Laboratory, Überlandstrasse 129, Dübendorf 8600, Switzerland.
School of Civil Engineering, University of Tehran, Tehran 1417466191, Iran.
Polymers (Basel). 2016 Aug 18;8(8):308. doi: 10.3390/polym8080308.
Most research on fatigue strengthening of steel has focused on carbon fiber-reinforced polymer (CFRP) strengthening of steel members with existing cracks. However, in many practical cases, aging steel members do not yet have existing cracks but rather are nearing the end of their designed fatigue life. Therefore, there is a need to develop a "proactive" retrofit solution that can prevent fatigue crack initiation in aging bridge members. Such a proactive retrofit approach can be applied to bridge members that have been identified to be deficient, based on structural standards, to enhance their safety margins by extending the design service life. This paper explains a proactive retrofit design approach based on constant life diagram (CLD) methodology. The CLD approach is a method that can take into account the combined effect of alternating and mean stress magnitudes to predict the high-cycle fatigue life of a material. To validate the retrofit model, a series of new fatigue tests on steel I-beams retrofitted by the non-prestressed un-bonded CFRP plates have been conducted. Furthermore, this paper attempts to provide a better understanding of the behavior of un-bonded retrofit (UR) and bonded retrofit (BR) systems. Retrofitting the steel beams using the UR system took less than half of the time that was needed for strengthening with the BR system. The results show that the non-prestressed un-bonded ultra-high modulus (UHM) CFRP plates can be effective in preventing fatigue crack initiation in steel members.
大多数关于钢材疲劳加固的研究都集中在对已有裂缝的钢构件进行碳纤维增强聚合物（CFRP）加固。然而，在许多实际情况下，老化的钢构件尚未出现裂缝，而是接近其设计疲劳寿命的末期。因此，需要开发一种“主动”的改造解决方案，以防止老化桥梁构件中疲劳裂纹的萌生。这种主动改造方法可应用于根据结构标准已被确定为有缺陷的桥梁构件，通过延长设计使用寿命来提高其安全裕度。本文解释了一种基于等寿命曲线（CLD）方法的主动改造设计方法。CLD方法是一种能够考虑交变应力和平均应力幅值的综合影响来预测材料高周疲劳寿命的方法。为了验证改造模型，对采用非预应力无粘结CFRP板加固的工字钢进行了一系列新的疲劳试验。此外，本文试图更好地理解无粘结改造（UR）和粘结改造（BR）系统的性能。使用UR系统对钢梁进行改造所需的时间不到使用BR系统加固所需时间的一半。结果表明，非预应力无粘结超高模量（UHM）CFRP板可有效防止钢构件中疲劳裂纹的萌生。
