Defects between fiber reinforced polymer (FRP) and repaired concrete components may easily come out due to misoperation during manufacturing, environmental deterioration, or impact from external load during service life. The defects may cause a degraded structure performance and even the unexpected structural failure. Different non-destructive techniques (NDTs) and sensors have been developed to assess the defects in FRP bonded system. The information of linking up the detected defects by NDTs and repair schemes is needed by assessing the criticality of detected defects. In this study, FRP confined concrete columns with interfacial defects were experimentally tested to determine the interfacial defect criticality on structural performance. It is found that interfacial defect can reduce the FRP confinement effectiveness, and ultimate strength and its corresponding strain of column deteriorate significantly if the interfacial defect area is larger than 50% of total confinement area. Meanwhile, proposed analytical model considering the defect ratio is validated for the prediction of stress–strain behavior of FRP confined columns. The evaluation of defect criticality could be made by comparing predicted stress–strain behavior with the original design to determine corresponding maintenance strategies.

Chemical functionalization is an effective approach to address interfacial deterioration caused by environmental exposure in cellulose nanofiber (CNF)-epoxy nanocomposites. However, how functionalization affects interfacial deterioration and durability of nanocomposites in erosive environment is still lacked. In this work, the global mechanical properties and local interfacial intermolecular behavior of pristine and functionalized CNF-reinforced nanocomposites are investigated through molecular dynamics simulations. The results show that functionalization can enhance the interfacial energy barrier and debonding stress by 43% and 57%, respectively. Functionalized CNF inhibits the slippage of epoxy chains, ensuring better interfacial adhesion and efficient stress transfer between fiber and matrix. Functional groups promote the formation of interfacial bridging and topological structures and weaken the hydrogen bonding ability of water molecules, leading to stronger intermolecular adsorption effect and better interfacial integrity. The epoxy molecular configuration evolution and intermolecular interactions, caused by the functionalization of CNF in the interfacial region, enhance the interfacial erosion resistance, contributing to the durability of the nanocomposites. This study reveals the in-depth interfacial deterioration mechanism of functionalized nanocomposites under erosive environment, inspiring a novel strategy for the design of durable CNF-reinforced nanocomposites.

A damped outrigger system (DO) has been proposed to enhance the seismic performance, in which links between outriggers and perimeter columns are artificially disconnected and implemented by dampers. Such an operation essentially destroys the structural integrity and becomes a potential threat for structural safety. Moreover, its performance is very sensitive to the stiffness of perimeter columns. In this study, a mega-sub controlled system is employed to propose a novel outrigger system, i.e., a damped substructure outrigger system (DSO). The novel system has good structural integrity due to its main structure consisting of the core tube, outrigger, and perimeter column. To present further investigation, the govern equations of DSO are derived by the simplified model which is regard as a cantilever beam system with a multirotation spring and energy dissipation substructure. Then, the energy distribution and seismic performance are parametric investigated. Finally, the damping effects of DSO are discussed. The results indicate that DSO possesses the superiority of damping performance. Compared with DO, DSO is less sensitive to perimeter column stiffness. Moreover, the proposed system can obtain the high efficiency in energy dissipation but with less damping cost than that of the viscous damper. Also, the larger stroke of the viscous damper can be found for DSO.