Journal of Science and Technique
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COMPARATIVE INVESTIGATION OF THE COMPRESSIVE STRENGTH OF STEEL FIBER REINFORCED CONCRETE UNDER STATIC AND IMPACT LOADS
Full text linkThis study examines the effect of steel fiber content on compressive behavior of concrete under static and impact loading. The results indicate that increasing fiber dosage reduces workability: the mixture with 0.5% fibers reached the highest flowability (245 mm), while higher contents of (1.0-2.0)% progressively decreased it to 195 mm. This reduction is attributed to greater interparticle friction, the disruption of the granular framework, and fiber orientation resisting flow. Compressive strength under static loading exhibited only slight variation (176.97-179.87) MPa, suggesting limited influence of fibers on quasi-static strength. In contrast, impact loading significantly increased the compressive strength (189.54-194.06) MPa and the strain capacity, with corresponding DIF values of approximately 2.7. A fiber content of 1.5% (MT15) provided the best balance between strength and ductility, whereas 2.0% (MT20) produced the highest toughness but was affected by fiber clustering and stress concentration. Dynamic analysis further confirmed consistent improvements in compressive strength (7-8)% across all dosages, while toughness more than doubled under impact conditions, reaching 1.258 MJ/m³ for MT20. These improvements were governed by crack-bridging and fiber pull-out mechanisms, which delayed crack propagation and enhanced energy absorption. An optimal fiber dosage of 1.5% is recommended to balance workability, strength, and toughness in practical applications
EXPERIMENTAL STUDY ON STRENGTH DEVELOPMENT AND ADIABATIC TEMPERATURE OF HIGH-STRENGTH CONCRETE FOR BRIDGE PIERS
Full text linkThis article presents the design and experimental evaluation of a high-strength concrete mix for bridge pier applications, targeting a compressive strength of 50 MPa. The mix composition was designed according to ACI 211.1-91, incorporating cement, fly ash, blast furnace slag, superplasticizer, and a temperature rise inhibitor. The selected mix achieved a laboratory design strength of 60 MPa. Strength development tests were conducted on cubic and cylindrical specimens at 3, 7, 28, and 56 days. Results showed a compressive strength increase from 35.2 MPa at 3 days to 64.2 MPa at 56 days, while splitting tensile strength improved from 3.12 MPa to 5.19 MPa within the same period. The elastic modulus calculated according to CEB-FIP Model Code 2010, reached 40.47 GPa at 56 days. In addition, an adiabatic calorimeter was designed and improved to monitor the temperature rise of the concrete. Measurements revealed a maximum adiabatic temperature of 76.6°C, corresponding to a temperature rise of 52°C, with the most rapid increase occurring between 8 and 32 hours after casting. The study results provide the necessary data to evaluate the thermal behavior and minimize the risk of thermal cracking in large concrete structures such as bridge piers
NUMERICAL SIMULATION OF STRESS AND DISPLACEMENT BEHAVIOR OF TRC-STRENGTHENED FRP-REINFORCED CORAL CONCRETE PANELS UNDER BLAST LOADING
Full text linkThis article presents a numerical simulation of the stress and displacement responses of coral aggregate concrete (CAC) slabs reinforced with glass fibre-reinforced polymer (GFRP) bars and externally strengthened with textile-reinforced concrete (TRC) under blast loading conditions. The panel consists of a B22.5-grade coral concrete core (equivalent to C35/45), combined with a surface TRC layer composed of a Sigratex Grid 350 carbon textile embedded in high-strength fine-grained concrete (grade M600). The integration of GFRP, TRC, and CAC offers advantages in terms of corrosion resistance, utilisation of locally available marine aggregates, and enhanced dynamic load resistance, making it a promising solution for coastal and island infrastructure subjected to blast effects. The simulation results demonstrate that the inclusion of the TRC layer significantly reduces both stress concentration and peak displacement at the panel’s centre. Moreover, it contributes to the confinement of localised damage zones caused by the propagation of blast-induced shock waves. This study provides valuable insights into the potential application of TRC-strengthened CAC structures in marine, military, and defence-related constructions
EQUIVALENT ELASTIC MODULI FOR BRICK MASONRY: A COMPARATIVE STUDY OF PERIODIC HOMOGENIZATION APPROACHES
Full text linkThe mechanical characterisation of masonry remains a central challenge in structural analysis due to its heterogeneous composition of bricks and mortar joints. This study conducts a comprehensive comparative assessment of four approaches for determining the equivalent elastic properties of masonry: finite element modelling (FEM), the two-step homogenization method, the one-step Fourier-based scheme, and the interface-joint model. FEM simulations of a two-dimensional brick–mortar assemblage with varying mortar thicknesses serve as the benchmark. Analytical predictions are compared with FEM results for longitudinal and transverse Young's moduli, shear modulus, and Poisson’s ratio. The two-step method achieves excellent agreement with FEM, with errors typically below 3% across all parameters. In contrast, the one-step method consistently overestimates transverse and shear stiffnesses by up to 50-60%, while the interface approach underestimates them by 20-55%. These deviations grow with mortar thickness, reflecting the different modelling assumptions. Overall, the FEM results are bounded by the stiffer predictions of the one-step method and the more compliant interface model, while the two-step method aligns most closely with the reference values. The study concludes that the two-step scheme is most suitable for engineering design, while the interface model is valuable for nonlinear mortar analyses
AERODYNAMIC INTERFERENCE CHARACTERISTICS OF BUSEMANN BIPLANE AIRFOIL WITH SLAT AND FLAP IN LOW-SPEED FLOW
Full text linkIn this study, aerodynamic interference characteristics of a Busemann biplane incorporating both leading-edge slats and trailing-edge flaps are investigated, utilizing wind tunnel experiments and numerical simulations. The aerodynamic characteristics of the biplane configuration are assessed through a comparative analysis with the performances of its individual upper and lower wings when operating as single configurations. The deflections of the slat and flap are 15° and 30°, respectively. Stall occurred on both the upper and lower wings in the single configuration. The addition of the leading-edge slat enabled the single model to stall at a larger angle of attack, consequently leading to a higher maximum lift coefficient. In the biplane configuration with slat and flap, the lower wing did not experience stall, and its lift coefficient increased with the angle of attack, similar to the case with only trailing-edge flaps. The drag interference ratio was observed to exceed 1.0 at angles of attack below 5° for the biplane with only a trailing-edge flap and below 12° for the configuration including both a slat and a flap. This finding implies that, within these ranges, the biplane generated a higher total drag compared to the sum of the individual drag values of each element in a single-element configuration. The lift interference ratio exhibited a minimum value of 0.72 at 16° for the biplane with both slat and flap
ENHANCED SEPIC CONVERTER REDUCES CURRENT STRESS ON SWITCHING DEVICES AND DIODES WHILE MAINTAINING HIGH EFFICIENCY
Full text linkThis article presents an innovative DC buck-boost converter design that mitigates the excessive switching current stress inherent in SEPIC converters. The study highlights a significant reduction in current strain on switching devices and diodes during transitions. A thorough steady-state analysis has been conducted, encompassing voltage conversion ratios, power dissipation, and voltage stress on key switching components. Simulation and theoretical evaluations in buck and boost modes demonstrate that the proposed converter achieves exceptionally low source current overshoot across switches S1, S2, D1, and D2, even when the conversion ratio varies from 0.2 to 2. Compared to SEPIC and other analyzed topologies, this converter delivers superior efficiency with substantially lower power losses. Furthermore, experimental validation, considering the impact of parasitic resistances, confirms that this design outperforms existing solutions by maximizing efficiency, enhancing reliability, minimizing energy dissipation, and extending operational lifespan, making it an optimal choice for power electronics applications. Moreover, experiments with nonlinear load currents were conducted further to validate the superior performance of the proposed converter
CHALLENGES IN ENGINEERING GEOLOGICAL MAPPING AT LARGE SCALES 1:2000 FOR SUBMERGED CORAL ISLANDS
Full text linkThis article presents a methodology for creating large-scale engineering geological maps (1:2000) for submerged coral islands in Vietnam’s maritime zones, in accordance with the national standard TCVN 9156:2012. The primary objective is to provide a comprehensive representation of key geological and environmental factors, particularly coral sediments that influence land use planning, construction design, and implementation. As there are currently no specific national standards for engineering geological mapping in coral-based island areas, this study references various related standards and documents. It also highlights significant issues that need to be addressed when conducting large-scale engineering geological mapping in submerged coral environments.
The results demonstrate that large-scale engineering geological mapping is of considerable scientific and practical value for construction planning, resource management, and natural disaster mitigation. The article also recommends further research to enhance mapping accuracy and the development of appropriate technical standards. Future directions emphasize the integration of modern technologies, such as GIS-based digital mapping, 3D geological modeling, and virtual reality (VR) applications, to simulate geological conditions and assess geohazards in marine island environments. These advancements aim to address challenges posed by climate change and promote sustainable development
EFFECT OF VIBRATIONS ON THE DYNAMICS OF THE RING RESONATOR MICROMECHANICAL GYROSCOPE
Full text linkThis article examines the dynamics of a micromechanical gyroscope with a ring resonator, used in navigation and motion control systems. The gyroscope’s sensitive element consists of a thin elastic ring resonator supported by an elastic suspension, detecting small bending vibrations to measure angular motion. The study investigates the impact of external vibrations on the resonator’s mechanical design. A mathematical model is developed using the Hamilton-Ostrogradsky variational principle and the Bubnov-Galerkin projection method to analyze the system’s multimodal oscillations. Results show that vibrations mainly affect the first vibrational mode, with maximum deformation of the resonator is proportional to the magnitude of the peak impact acceleration and inversely proportional to the square of the lowest natural frequency in the first natural mode of oscillation. The second vibrational mode remains unaffected under normal conditions. Additionally, manufacturing errors can cause symmetry violations, impacting measurement accuracy. This study provides insights into improving ring resonator micromechanical gyroscope design for enhanced reliability under dynamic external vibrations
STRUCTURAL RESPONSE OF BAILEY BRIDGE SPANS UNDER MOVING VEHICLE LOADS
Full text linkBailey truss bridges are commonly used as temporary structures in emergency traffic situations, such as rescue operations and the repair of aging bridges. Studying the impact of load velocity on bridge structures is essential for determining appropriate operational conditions. This article examines the effect of vehicle speed on the internal forces of truss members and the deflection of the bridge span. The study employs the finite element method using SAP2000 software, the moving load model has an axial load diagram of the real truck. The results indicate that vehicle velocity has a minimal impact on the internal forces of the truss members and the deflection of the bridge spans. Based on these findings, suitable vehicle velocity regulations can be established to optimize traffic flow across the bridge when necessary
REVIEW OF KEY CRITERIA FOR SUSTAINABLE BUILDING MATERIALS
Full text linkOver the past decade, sustainable building materials (SBM) have increasingly been gained the interests from construction industries, leading to numerous studies that have been conducted to find out the criteria for evaluating the effectiveness and sustainability of such kinds of materials. Despite this growing interest, a systematic review of the key sustainability criteria used to select building materials, which is crucial for guiding future research and practical applications, is possibly still lacking. Thus, this article presents a literature review on sustainability criteria for building material selections for engineering designs and practices. This study employed a systematic literature review (SLR) method, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Data were extracted from the Scopus database, comprising 27 impactful peer-reviewed publications related to the selection of SBM criteria from 2015 to 2024. The review identified and synthesized four key criteria: environmental, economic, social, and technical. A model framework was also developed to understand these sustainability criteria better. The findings could enhance the understanding of critical sustainability considerations, assisting industry practitioners, policymakers, and sustainability-focused institutions in formulating more informed guidelines and strategies for sustainable material selection. Furthermore, the checklist and model framework presented in this article may offer valuable resources for researchers conducting further empirical studies in sustainable construction