钢桥面板纵肋对接焊缝疲劳开裂主动加固方法研究

为实现钢桥面板纵肋对接焊缝疲劳开裂的主动加固,提出基于铁基形状记忆合金(Fe-SMA)的主动加固方法,即通过栓接Fe-SMA并采用热电阻激励使其自动产生预应力实现主动加固。为验证其有效性,采用ANSYS软件建立港珠澳大桥的单纵肋节段试验模型的实体有限元模型,利用线弹性断裂力学对纵肋对接焊缝处疲劳裂纹前缘的应力强度因子进行了分析,研究了基于Fe-SMA的主动加固方法的加固效果及预应力水平对主动加固效果的影响。结果表明:纵肋对接焊缝的疲劳裂纹扩展以Ⅰ型开裂为主导,疲劳裂纹出现后,扩展速率加快,严重影响结构安全性;基于Fe-SMA的主动加固方法对未穿透型疲劳裂纹有良好的加固效果,当裂纹深度较大时,应适当提高加固件的预应力水平以增强加固效果;为保证纵肋对接焊缝细节处各种尺寸的未穿透型疲劳裂纹均达到理想止裂状态,预应力水平至少为300 MPa。

Research on a Positive Reinforcement Method for Fatigue Cracking in Longitudinal Rib Butt Welds of Orthotropic Steel Bridge Deck

In order to realize positive reinforcement of fatigue cracking in longitudinal rib butt welds of the steel bridge deck,a positive reinforcement method taking advantage of iron-based shape memory alloy(Fe-SMA)is proposed,by which Fe-SMA is bolted and prestressed automatically by thermal resistance excitation to achieve the goal of positive reinforcement.A solid finite element model of a section with single longitudinal rib based on Hong Kong-Zhuhai-Macao Bridge was established by ANSYS to verify its effectiveness.The stress intensity factors at the front edge of fatigue cracks at the longitudinal rib butt welds were analyzed using linear elastic fracture mechanics.The reinforcement effect of the positive reinforcement method based on Fe-SMA as well as the influence of prestress level on the positive reinforcement effect was studied.The results indicate that the fatigue crack propagation in the longitudinal rib butt welds is dominated by type-I cracking,and the propagation rate is accelerated after the appearance of fatigue crack,which drastically threatens the structural safety.The positive reinforcement method based on Fe-SMA is quite efficient for non-penetrating fatigue cracks.When the cracks propagate deeply,the prestress level of the reinforcement should be appropriately raised to enhance the reinforcement effect.In order to ensure all the non-penetrating fatigue cracks of various sizes in longitudinal rib butt welds to reach the predicted crack arrest state,the prestress level should be maintained above 300 MPa.