Influence of Long-term Climate on Fatigue Life of Bridge Pier Concrete and a Reinforcement Method

This paper quantitatively evaluated the fatigue life of concrete around the air-water boundary layer of bridge piers located in inland rivers, considering the long-term climate. The paper suggests a method to predict the low-cycle fatigue life by demonstrating a thermal-fluid-structural analysis of bridge pier concrete according to long-term climate such as temperature, velocity and pressure of air and water in the process of freezing and thawing in winter. In addition, it proposes a reinforcing method to increase the life of damaged piers and proves the feasibility of the proposed method with numerical comparison experiment

Application of Rothe's method to a parabolic inverse problem with nonlocal boundary condition

summary:We consider an inverse problem for the determination of a purely time-dependent source in a semilinear parabolic equation with a nonlocal boundary condition. An approximation scheme for the solution together with the well-posedness of the problem with the initial value $u_0\in H^1(\Omega )$ is presented by means of the Rothe time-discretization method. Further approximation scheme via Rothe's method is constructed for the problem when $u_0\in L^2(\Omega )$ and the integral kernel in the nonlocal boundary condition is symmetric

Structural and electrochemical trends in mixed manganese oxides Nax(M0.44Mn0.56)O2 (M = Mn, Fe, Co, Ni) for sodium-ion battery cathode

Developing cost-effective and high performance sodium-ion batteries (SIBs) relies mostly on advanced cathode materials with high electrode voltage, high capacity and fast sodium-ion diffusion. Here, we propose mixed sodium manganese oxides Nax(M0.44Mn0.56)O-2 (M = Mn, Fe, Co, Ni) as improved potential cathode materials for SIBs based on first-principles calculations. Our calculations reveal that these materials have relatively low volume expansion rates below 5%, and are thermodynamically stable. We find that the binding strength between the host and inserted Na atom gradually decreases as increasing the Na content x from 0.11 to 0.67 for each mixed compound, whereas it increases as going Mn -> Fe -> Co -> Ni at each value of Na content. Identifying the intermediate phases during Na insertion/extraction, we find a slight increase of electrode voltage with remarkably higher specific capacities by mixing due to extending the lower limit of Na content. We also investigate the sodium-ion diffusion by identifying plausible pathways , determining the activation barriers and diffusion coefficients , find fast migration within the S-shaped tunnel and moderate one within the small-sized tunnel. Through analysis of density of states, we find that these compounds exhibit half-metallic behaviour, demonstrating an enhancement of metallicity by mixing with higher valent transition metal atoms. Our calculation results show that these mixed compounds can be advanced cathode materials for high performance SIBs

A nonlinear local equivalent stress method in stress analysis of concrete gravity dam

When the stress state of the structure is analyzed by the finite element method (FEM), the stress at the stress concentration points such as the dam’s heel and toe gets infinitely larger as the element size decreases. In order to overcome this defect, many equivalent stress methods of normal stress have been proposed to convert the FEM stress into equivalent stresses on the boundary between the dam and the foundation. This paper proposes a nonlinear local equivalent stress method that reflects the mechanical equivalent conditions and material continuity in the areas near the dam’s heel and toe and proves that the stress state obtained by the nonlinear local equivalent stress method is close to the actual stress state through calculation experiment. Keywords: Stress analysis of dam, Finite element method, Stress concentration, Equivalent stress method, Nonlinear local equivalent stress method, ANSYS, MATLA