Numerical failure analysis of a continuous reinforced concrete bridge under strong earthquakes using multi-scale models

Previous failure analyses of bridges typically focus on substructure failure or superstructure failure separately. However, in an actual bridge, the seismic induced substructure failure and superstructure failure may influence each other. Moreover, previous studies typically use simplified models to analyze the bridge failure; however, there are inherent defects in the calculation accuracy compared with using a detailed three-dimensional （3D） finite element （FE） model. Conversely, a detailed 3D FE model requires more computational costs, and a proper erosion criterion of the 3D elements is necessary. In this paper, a multi-scale FE model, including a corresponding erosion criterion, is proposed and validated that can significantly reduce computational costs with high precision by modelling a pseudo-dynamic test of an reinforced concrete （RC） pier. Numerical simulations of the seismic failures of a continuous RC bridge based on the multi-scale FE modeling method using LS-DYNA are performed. The nonlinear properties of the bridge, various connection strengths and bidirectional excitations are considered. The numerical results demonstrate that the failure of the connections will induce large pounding responses of the girders. The nonlinear deformation of the piers will aggravate the pounding damages. Furthermore, bidirectional earthquakes will induce eccentric poundingsto the girders and different failure modes to the adjacent piers.

Controllable Delamination of CNT-Reinforced Carbon Fiber Films by Harnessing Mechanical and Topological Characteristics of the Composites

Carbon nanotubes(CNTs)offer a remarkable reinforcement effect for the interlaminar toughness of laminated films,and optimizing the delamination of films through their toughening mechanism is of particular interest.Herein,we propose a theoretical model that combines the spatial evolution of aligned CNTs to describe the mode I fracture between opposing carbon fiber films.Our theoretical predictions quantitatively agree well with previous tests,and the influence of interfacial energy and modulus of films on toughness enhancement is considered.Our findings have demonstrated that aligned CNTs play a crucial role in enhancing delamination resistance,with the performance being highly sensitive to their volume fraction,mechanical properties,and geometric characteristics.We optimized interlaminar toughness by selecting appropriate strength and aspect ratio of CNTs based on two competitive failure modes.This work presents new concept for the topological design of composite laminates,bridging the properties of microfibers and macrostructures and ultimately achieving greater strength and toughness.