National University of Civil Engineering

While FGM sandwich plates are prevalent in aerospace and civil engineering for their tunable multi-directional properties, there is a dearth of research on 3D-FGM plates that account for geometric nonlinearity and moving mass effects while being partially supported by an elastic foundation. This paper presents a nonlinear finite element model based on Shi's higher-order plate theory and von Karman geometric nonlinearity to analyse the nonlinear dynamic response of sandwich plates partially supported on an elastic foundation. The sandwich plate consists of two outer layers made of three-dimensional functionally graded material (3D-FGM) and a core layer of two-dimensional functionally graded material (2D-FGM), both fabricated from ceramics and metals using power-law distributions. The equations of motion of the plate under the influence of a moving mass are derived via Hamilton's principle and solved using the Newmark-beta method in conjunction with the Newton-Raphson iterative scheme. Numerical results not only demonstrate the convergence and accuracy of the established model when compared with results published in the literature but are also used to evaluate and analyse the influence of volume fraction indices, geometric parameters, sandwich configuration, weight and velocity of the moving mass, and boundary conditions on the dynamic response of the sandwich plate. Several key findings are highlighted: (i) nonlinear models are essential for plates with low stiffness or few constraints (e.g., SFSF), where linear models overestimate deflection by up to 40%; (ii) volume fraction indices px,py,pz and layer thickness ratios are effective design parameters for controlling structural stiffness; (iii) the shear stiffness coefficient of a partially elastic foundation has a stronger influence on deflection reduction than the Winkler stiffness coefficient; and (iv) the dynamic amplification coefficient peaks within a critical velocity range before decreasing.

Purpose There are limited studies that have explored a programmatic approach (systematic approach, agency-wide approach) to delivering and managing alternative project delivery methods (APDMs) in highway. This study aims to identify and document the benefits and risks of programmatic approaches to APDM for highway projects. Design/methodology/approach Data were collected from 50 targeted participants from state highway agencies. A survey of 50 highway agency experts in the USA and principal component analysis to analyze risks associated with APDMs were conducted. The purposive sampling based on participants' APDM experience was used for the survey. Statistical software (e.g. SPSS and R) was used for analyzing survey data. Findings The top five benefits of implementing APDM programmatic approaches include better risk management, schedule flexibility, innovation flexibility, earlier cost certainty, and effective change management. The top five risks of APDM programmatic approaches include utility issues, environmental permits and approvals, schedule and phasing issues, coordination with government agencies or other authorities having jurisdiction, and scope changes. Further, market conditions and staff experience risks showed statistically significant risk perception differences between experienced and less experienced agencies. Originality/value This study seems to be one of the first academic efforts in the USA to examine the benefits and risks of APDM programmatic approaches for highway construction, offering practical insights that enable agencies to identify key advantages and strategically allocate resources to manage risks associated with each approach.

Purpose The piston effect of a high-speed train passing through a tunnel produces pressure transients that drive tunnel cross-section design and impose loads on rolling stock and equipment. This paper verifies an open-source one-dimensional solver for these transients and defines the limits of its predictive capability. Design/methodology/approach The train is represented as a moving cross-sectional-area blockage in the quasi-one-dimensional compressible Euler equations, discretised with a second-order MacCormack scheme. The solver is verified against the analytical entry-wave solution, validated against a published full-scale measurement of the piston-wind field, benchmarked against published three-dimensional computational fluid dynamics (CFD), subjected to a five-level grid-refinement study with dissipation and nose-ramp sensitivity tests and applied to a single-train design case. Findings The compression-wave amplitude agrees closely with both the analytical solution and the published three-dimensional CFD results. The principal result concerns the localised suction peak beneath the train nose, commonly assumed to lie beyond the reach of area-averaged one-dimensional models: once the cell size resolves the nose ramp, it is grid-convergent, with a Richardson value within a few per cent of the three-dimensional CFD result. What had appeared to be non-convergence was due to under-resolution. Coupling to a cabin-sealing model shows that a narrower tunnel is viable only if the rolling stock carries a more demanding sealing specification. Originality/value The solver is, to the author's knowledge, the first permissively licensed one-dimensional tool for high-speed compression-wave transients released with a reproducible verification-and-validation suite, providing a common baseline for benchmarking new closures. The grid study also corrects a limitation commonly attributed to this class of model.

This paper focuses on the investigation of the free vibration and buckling behaviour of honeycomb auxetic bidirectional functionally graded sandwich (2D-FGASW) plates. The 2D-FGASW plates under consideration consist of two face sheets made of bi-directional functionally graded materials (2D-FGM) whose mechanical properties vary along thickness and longitudinal directions according to the power law and a core made of a re-entrant auxetic honeycomb material with a negative Poisson's ratio. The face sheets incorporate a combination of two ceramics and one metallic material, providing a diverse range of mechanical characteristics. The core is fabricated from the same metallic material used in the face sheets, ensuring compatibility and continuity throughout the structure. A finite element model is developed using a four-node rectangular element, with eight degrees of freedom per node. This model is based on the four-variable shear deformation refined plate theory and Hamilton's principle. To ensure the reliability and accuracy of the proposed model, several comparative examples are presented, demonstrating its convergence and capability in capturing the behaviour of the plates. Finally, some new investigations evaluating the influence of material and geometrical parameters on the vibration and buckling responses of the 2D-FGASW plates are presented in detail, shedding light on the design considerations necessary for optimizing their performance.

Landslides in mountainous regions, such as Son La province in northern Vietnam, pose significant risks to human life, property, and infrastructure. Rapid urbanization and deforestation in Vietnam exacerbate landslide risks, making effective landslide risk assessment crucial for disaster mitigation and management. This study introduces a new integrated framework combining machine learning models and multi-criteria decision analysis to estimate landslide risk. We utilized 1,771 landslide locations from various sources and fifteen landslide influencing factors as model input to create landslide susceptibility maps using advanced hybrid machine learning models. The Analytic Hierarchy Process is used to weight indicators of social-economic and infrastructure impacts, resulting in a comprehensive landslide risk assessment map. The final risk map showed the landslide susceptibility and consequences in a matrix, highlighting that 3.25