Trang: 885-898 Nguyen Thi Tuyet Trinh, Pham Van KyTóm tắtUnder-slab resilient mats, referred to here as slab track mats (STMs), can reduce the dynamic force transmitted beneath a concrete track slab. This paper presents a preliminary analytical screening framework that distinguishes dynamic from static stiffness through α = kd/ks and equivalent participating mass from total statically supported mass through β = M/me. A harmonically forced single-degree-of-freedom model gives closed-form relationships among a prescribed force-isolation onset frequency, admissible dynamic stiffness and static compression. The illustrative input set is tied to an idealized concrete slab segment and a controlled stiffness-and-damping sensitivity sweep rather than to product-specific properties. For me = 5,000 kg, dynamic stiffnesses of 5–40 MN/m give natural frequencies of 5.03–14.24 Hz and force-isolation onset frequencies of 7.12–20.13 Hz. The results show that reducing mat stiffness does not necessarily improve performance because force isolation above the threshold may be accompanied by amplification near resonance. The calculated force transmissibility T is the transmitted-to-applied force ratio at the idealized mat–support interface; T < 1 identifies only the force-isolation region of this interface model and is neither insertion loss nor evidence of compliance at a receiving location. The framework provides an early consistency check for defining material-test targets and parameters for subsequent vehicle–track–structure analysis.
Trang: 899-913 Ngo Dang Quang, Bui Thi Thanh MaiTóm tắtThe convective heat transfer coefficient (hc) is a key parameter in heat transfer analysis and the thermal behavior of concrete structures. For the internal surfaces of enclosed structures, hc is typically determined under the assumption of zero air velocity. In the case of concrete box girders, empirical formulas have traditionally been used to estimate this coefficient. However, inside the box of a concrete box girder, temperature differences between the internal surfaces can drive air movement, which may affect hc. This paper presents the method and results of determining hc for the internal surfaces of concrete box girder bridges using computational fluid dynamics (CFD) simulation, coupling fluid flow with heat transfer. The numerical model was validated against benchmark experimental data and field-measured temperatures from six full-scale bridge cross-sections. The results show that the average hc ranges from approximately 3.71 to 4.90 W·m⁻²·K⁻¹ and varies with cross-sectional geometry, rather than remaining constant as assumed in conventional empirical approaches. Smaller and more square-like sections generally exhibit higher hc values. These findings provide more reliable reference values for thermal analysis of concrete box girder bridges.
Trang: 914-928 Nguyen Quang Si, Le Dang Dung, Nguyen Xuan Huy, Nguyen Hoang QuanTóm tắtReinforced concrete (RC) flat slabs are widely used in modern construction due to their architectural flexibility and construction efficiency. However, the presence of openings near columns can significantly reduce punching shear capacity and increase the risk of brittle failure. This study evaluates the predictive accuracy of existing methods by comparing seven international design codes (ACI 318-19, Eurocode 2, BS 8110-1997, TS500, ECP 203-2018, NBR 6118, and JSCE) with one analytical model, namely Model Code 2010 (MC2010) and three empirical models developed by Teng, El-Shafiey, and Köroğlu. The calculated results are validated against two independent experimental datasets reported by Anil et al. and El-Shafiey et al. The results reveal significant inconsistencies among the methods. For the Anil dataset, the Vexp/Vcal ratio ranges from 0.57 to 1.09 and is predominantly below 1.0, indicating a tendency toward unconservative predictions. In contrast, for the El-Shafiey dataset, the ratio varies between 0.93 and 1.26, reflecting a more conservative trend. Notably, the mean deviation reaches up to 88.33% for MC2010 (LoA-II), highlighting the limitations of current approaches. These findings indicate that the conventional critical perimeter reduction approach fails to fully capture the combined effects of opening location, size, and shape on stress distribution and load transfer mechanisms. Therefore, there is a clear need to develop new predictive models with a stronger mechanical basis that explicitly incorporate the geometric characteristics of openings.
Trang: 929-943 Nguyen Van HauTóm tắtSteel girders of ageing railway bridges deteriorate through corrosion, perforation, loose fasteners and local deformation; in Vietnam, 465 of 1,862 railway bridges are classified as vulnerable and their residual capacity must be re-evaluated. Inspection practice rates such defects by visual condition and area loss, whereas most act through local stress concentration, which governs fatigue life and is invisible to global measurements; this gap has not been quantified. This paper reviews the common damage types and quantifies their effect through two mechanisms, area loss and stress concentration, using classical elasticity solutions, the fatigue notch factor and the power-law S-N relation; examines TCVN 14478:2025, Eurocode 3, AASHTO LRFD and AISC 360; and re-analyses the inspection data of a 40-year-old steel truss railway bridge under local stress conditions. For perforations and loose fasteners the stress concentration factor reaches 2.5 to 3.5, two to three times the effect of area loss, and reduces fatigue life to a few percent of the intact value; none of the four standards quantifies it. On the bridge, the nominal stress at a member with a missing bolt is 57 % of the design strength and the frequency change lies within measurement error, yet the local stress at the hole edge exceeds the yield strength and the fatigue life there falls by one to two orders of magnitude. A look-up table of stress concentration factors, a screening factor, a fatigue check with the notch factor and recommended actions are proposed as a screening basis for inspection, pending validation.
Deep learning architecture to predict natural vibration frequencies of damaged structures
Trang: 944-954 Thanh Sang To, Hieu Nguyen VanTóm tắtStructural damage can arise from various unforeseen causes. Such damage exerts a substantial impact on the load-carrying capacity of the structure. In this study, we propose a Deep Neural Network (DNN) serving as a surrogate model to determine the severity of damage in beam structures Initially, a finite element model (FEM) was constructed in MATLAB to generate the training and testing datasets. Subsequently, a multi-layer deep learning architecture utilizing an artificial neural network is constructed. The Deep Neural Network is trained on this dataset, which encompasses numerous damage scenarios, to predict the output parameters (specifically, the first three natural frequencies of the structure). The reliability of the Deep Neural Network was subsequently verified on the test dataset, achieving an R^2value greater than 0.99. Consequently, this Deep Neural Network can serve as a substitute for the finite element method, thereby significantly accelerating the model updating process within the damage prediction framework
Trang: 955-964 Thanh Sang To, Tran Kien TuongTóm tắtAccurately predicting excavation-induced displacements remains a critical challenge in geotechnical engineering due to the inherent risks and complex soil-structure interactions during construction. To address this problem, this study proposes a hybrid predictive framework that integrates Finite Element Model (FEM) with Deep Neural Networks (DNN), called DNN-FEM. Initially, parametric simulations are conducted using commercial software in geotechnics, PLAXIS 2D, to simulate various deep excavation scenarios and generate a robust numerical dataset. This dataset is subsequently partitioned, allocating 80% of the data to train the DNN architecture and the remaining 20% to evaluate its predictive performance. The results demonstrate a high degree of agreement between the DNN-predicted displacements and the FEM-calculated values across both the training and independent test sets, as evidenced by R^2coefficients exceeding 0.99. Ultimately, this research demonstrates that the proposed DNN-FEM approach provides a highly accurate and computationally efficient tool for estimating Diaphragm Wall (DW) and soil displacements in deep excavation projects
Smart city development in asian countries: case studies and policy implications emerging economies
Trang: 965-982 Nguyen Thi Van Ha, Dao Duy Lam, Tran Thu HaTóm tắtAs emerging economies in Asia face rapidly accelerating urbanization, the "smart city" concept has been widely adopted as a strategic solution to address infrastructure gaps and environmental pollution. However, the transition from ambitious national strategies to effective local implementation remains a critical challenge for emerging economies like Vietnam. In our study, we try to explain the development stages of smart cities in Asia, moving beyond the traditional techno-driven view to analyze the institutional and socio-economic dimensions of urban governance. Employing a comparative multi-case study approach, the research synthesizes experiences from established models (Singapore, Seoul) and emerging hubs (Jakarta, Indonesia) to identify success factors and potential pitfalls. The research reveals that successful Asian smart cities are characterized not only by advanced ICT infrastructure but also by robust smart governance frameworks, high levels of data interoperability, and active citizen participation. Conversely, over-reliance on vendor-driven technology solutions without parallel institutional reform often leads to digital silos and unsustainable investments. Based on the results, we propose a tailored policy framework for emerging economies like Vietnam that advocates a shift towards a data-driven, integrated planning approach, the institutionalization of sustainable financing, and the prioritization of human capital over purely physical infrastructure
Trang: 983-1000 Tran Van Khoi, An Thi Hoai Thu AnhTóm tắtReal-time estimation of traction power demand plays an important role in the operation and energy management of urban railway systems. This paper proposes a hybrid digital twin framework that integrates physics-based modeling with machine learning techniques to reconstruct real-time traction power profiles at traction substations using SCADA measurements of power and energy recorded at intervals of 3–5 minutes. The proposed digital twin framework consists of three main components. First, a physics-based load-flow model of the DC traction network is employed to ensure physical consistency in representing the electrical energy system of the railway line. Second, a residual learning module to identify the SCADA measurement instants within the physical model cycle, thereby enabling the prediction of substation power evolution in real time until the next measurement interval. Third, a post-prediction power correction module is implemented using an adaptive correction coefficient in order to minimize discrepancies between the model output and the actual system behavior. The proposed approach is validated using real operational data collected over several representative days from the Cat Linh – Ha Dong urban railway line. The verification results show that the proposed digital twin framework is capable of reconstructing high-fidelity real-time substation power profiles that closely follow the dynamic patterns observed in SCADA measurements. The framework successfully enforces strict energy conservation, driving the cumulative daily energy deviation to near zero, while maintaining robust generalization capability in tracking highly non-linear peak power demands throughout the entire operational duration across individual substations.
Trang: 1001-1014 Yen Lien Nguyen ThiTóm tắtBlack carbon (BC) from diesel buses is a major contributor to urban PM2.5 and a significant short-lived climate forcer. This study quantifies how operation‑mode distributions (Bins) and vehicle‑specific power (VSP) characteristics across seven bus driving cycles influence the bus’s BC emissions. MOVES software was used to simulate bus BC emissions following selected driving cycles. A representative EURO II diesel bus (60–89 seats; 10 years in service) was used as the case study, while fuel and meteorology were held constant to isolate the effect of driving patterns. The driving kinematic attributes, VSP probability density, and Bin frequencies were analyzed across cycles. The New York City cycle recorded the highest PM2.5 and BC emissions (0.859 and 0.599 g/km, respectively), reflecting a driving pattern characterized by a large share of idling time, dominance of Bins 12–13, and the occurrence of high-VSP phases. The Transit Coach Operating Duty Cycle had the lowest PM2.5 and BC emissions (0.256 g/km and 0.196 g/km, respectively), indicating a shift toward Bin 22 and an almost complete absence of very high-VSP bins. The Hanoi bus driving cycle produced intermediate values (0.427 g PM2.5/km; 0.324 g BC/km), in line with Bins 12–14, which are typical of the city's stop-and-go traffic. Across cycles, BC contributed about 70–78% of PM2.5 emissions. The results suggest practical ways to reduce BC and PM2.5 in the short term, particularly when technological advancements are limited, such as reducing idling and aggressive acceleration, and improving steady-speed operation
Trang: 1015-1023 Pham Van Tien, Mai Van ThamTóm tắtIn high-speed railway traction drive systems, the deployment of Pulse Width Modulation (PWM) rectifiers represents an effective solution for mitigating harmonic pollution on the AC supply network, enhancing the power factor, and achieving energy efficiency due to the capability for seamless energy conversion between traction and regenerative braking modes. This paper investigates an instantaneous direct current control method combined with the Sinusoidal Pulse Width Modulation (SPWM) technique applied to single-phase two-level PWM rectifiers. This control method utilizes input AC current feedback to generate modulation signals, thereby offering the advantage of superior dynamic response. Furthermore, the control algorithm is simple to implement, and the DC output voltage is relatively smooth. Theoretical analysis and simulation results have validated the efficacy of utilizing active rectification, as well as the accuracy of the modulation technique and the applied control method. Based on the synthesis and systematization of relevant international literature, this paper constructs a general mathematical model of the control method and develops a simulation model to validate the theoretical foundation. Analytical and simulation results indicate that the PWM rectifier well satisfies the specified control requirements, concurrently confirming the effectiveness of the modulation technique and the applied control method. This research contributes an additional reference foundation for the research and application of high-speed rolling stock in Vietnam.
