Trang: 386-399 Vu Ba Thanh, Nguyen Xuan Lam, Do Anh TuTóm tắtIn recent times, the phase field method is a robust simulation tool that can predict crack formation and propagation in structures. In brittle and quasi-brittle materials, the strain tensor is decomposed into negative and positive parts corresponding to the compression and tension behaviors when the structure is loaded. In the previous studies related to the phase field method, the strain tensor decompositions do not satisfy the orthogonal condition of these two parts, even if the elastic stiffness tensor is isotropic. This problem leads to inaccuracies in the mechanical behavior of the materials. In this paper, the strain tensor orthogonal condition is applied to the bulk strain tensor parts representing the internal strain of the component phases. This orthogonal condition is implemented into the phase field method with interfacial damage to simulate crack propagation in a sample containing multi-phase heterogeneous materials. Furthermore, the shape and area fraction of these phases are recognized by a supplemental sub-function which was studied in our recent paper from image formats. Through several examples, the obtained results are compared with the relevant numerical ones to demonstrate the correctness and effectiveness of the proposed method.
Enhancing structural health monitoring of bridge beams through spectral moment analysis
Trang: 400-412 Thanh Quang Nguyen, Thuy Tien NguyenTóm tắtInvestigating the occurrence of defects in structures is currently a major issue of significant interest. In this paper, we present experimental research findings on the relationship between the moments of the power spectrum and the presence of damage in bridge beam structures. The study is based on analysing the random oscillation signal of the structure under the effect of random displacement loads. The results demonstrate that the value of the spectral moment is a sensitive feature to abnormal changes inside the structure. As a result, the output obtained from our study suggests using the spectral moment parameter as a new characteristic quantity for monitoring changes in bridge structures. Compared to traditional quantities like deflection, natural frequency, and mode shape, the value of the spectral moment can be more accurately determined. In the future, the spectral moment value can be extended to evaluate different types of structures under complex load conditions.
Trang: 413-427 Nguyen Ngoc Long, Nguyen Huu Quyet, Nguyen Ngoc Lan, Nguyen Tran HieuTóm tắtRecently, Structural Health Monitoring (SHM) has become a critical component of the maintenance and safety of lifeline infrastructures such as dams, skyscrapers, and bridges, thanks to its ability to detect structural failures at the early stages. In this paper, we evaluate the performance of the SHM damage identification tool using a novel metaheuristic algorithm called the Artificial Hummingbird Algorithm (AHA). The proposed approach is evaluated by two case studies of different bridge structures in Vietnam with different simulated damage scenarios. The potency of the AHA is compared against the other well-known metaheuristic algorithms such as Cuckoo Search (CS), Genetic Algorithm (GA), Particle Swarm Optimization (PSO), and Teaching-Learning Based Optimization (TLBO). The results show that the AHA performs much better than the other algorithms in terms of accuracy and computational cost. The application of AHA can help to reduce the cost and time required for structural maintenance significantly, as well as improve the lifecycle of the structure.
Trang: 428-444 Vu Ba ThanhTóm tắtRecently, the phase field modelling is widely used to model and simulate material damage. In present work, we present a framework of the topology optimization combined with the phase-field modelling with/ without interfacial damage for optimizing the damage resistance of the inclusion-matrix composites. The first phase field method with the interfacial damage described by the phase field variable d(x) and an interfacial phase field variable β(x), thus the crack occurs in the interaction between the bulk fracture and the interfacial one; the second phase field method without the interfacial damage describes the crack by using only a damage variable d(x), thus the crack initiates at the points where stress concentration occurs (damage only occurring in the phases). Extended bi-directional evolutionary structural optimization algorithm (BESO) is used to optimize the inclusion distribution in order to reduce its volume while keeping the fracture resistance value of the initial design unchanged. Moreover, the strain tensor orthogonal decompositions are implemented into the phase field methods to improve the inaccuracy in the mechanical behavior of the materials. We compare the inclusion optimal distribution, the crack propagation and the fracture resistance between the proposed models through several numerical examples.
Utilizing artificial neural networks to anticipate early-age thermal parameters in concrete piers
Trang: 445-455 Hoàng Việt Hải, Đỗ Anh Tú, Phạm Đức ThọTóm tắtRecently, researches have been used Artificial Neural Network (ANN) to predict the early-age thermal cracking of rectangle piers. But ANN has not resulted for different types of concrete piers. This article presents an evaluation of the early-age thermal characteristics of mass concrete piers with four distinct cross-sectional shapes. A finite element (FE) model was employed to estimate the maximum temperature, thermal stress, and cracking potential of the concrete pier at its early age. To investigate the impact of various pier geometries on the thermal cracking potential, different pier geometries were considered. In this study, an ANN model was utilized to predict the maximum temperature and decrease the risk of cracking in mass concrete piers at early age. The database of thermal mass concrete piers used in this study comprises 128 results obtained from the FE model. The results of the analysis indicate that the ANN model can predict early-age thermal parameters, and cracking risk in early-age concrete piers with good accuracy and help to the designer to choose the appropriate size in minimizing cracks on the pier concrete.
Analytical truss model for concrete beams reinforced with FRP bars
Trang: 456-468 Tran Cao Thanh NgocTóm tắtA truss model supplementing the concrete contribution is introduced in this paper to predict the shear strength of concrete beams reinforced with various types of FRP bars. The contributions from truss and direct strut mechanisms are considered in the analytical model. The truss model which has struts at various angles considering concrete contribution is derived in this paper. The concept of equivalent transverse FRP reinforcement is applied to integrate the concrete contribution into the proposed truss model. The shear strengths of concrete and FRP transverse reinforcements in the proposed model are calculated based on El-sayed et al. and CSA S806, respectively. The validity and applicability of the proposed model are evaluated by comparison with available experimental database, which consists of concrete beams reinforced with glass, carbon, aramid and basalt FRP bars. The comparison has shown a good correlation between the experimental data and analytical results. The proposed model is also compared with ACI 440.1R and CSA S806’s shear strength models and the better correlation is found. The results from this research shows that the properly-treated truss analogy can be used to assess the shear strength of concrete beams reinforced with various types of FRP bars.
A knowledge-based decision support system for incident traffic congestion management
Trang: 469-483 Trinh Dinh ToanTóm tắtA Knowledge-based Decision Support System (KB-DSS) based on a multi-stage Fuzzy Logic Controller (MS-FLC) is developed for traffic congestion management on expressways. The MS-FLC receives real-time traffic and incident data to analyse and anticipate the traffic conditions, to recommend alternative control measures in the form of natural languages for the human operator to select control decisions, and to calculate control settings to manage traffic congestion. In a case study, the KB-DSS is evaluated on a simulated network in comparison to ALINEA\Q, a popular ramp control method, across various traffic and incident situations. The results showed that: (i) the KB-DSS provides a systematic procedure in deriving control actions and a good capability to deliver linguistic expressions; (ii) the KB-DSS outperforms ALINEA\Q with respect to global objectives across many scenarios, attains significant improvements of mainline travel conditions and substantial reductions of ramp queues. These advantages make the KB-DSS a robust tool for traffic control for incident congestion management on expressways.
Trang: 484-496 Nguyen Trong HiepTóm tắtThe service quality and life of the runway, taxiway and apron pavement system heavily depends on the condition of its foundation, including base and/or subbase layers and subgrade. In the state of water-saturated condition, the strength of foundation would decline significantly, then inducing the downgrade of overall strength of the pavement. In the long term, the impacts from adverse environmental conditions and aircraft wheel loading will mix-up the materials of foundation layers, leading to the degradation of the original physical and mechanical properties of the original designed material. Furthermore, the accumulation of residual deformation and appearance of voids in the granular material can formulate the large holes beneath cement concrete slab. That, in turn, changes the load bearing model of the slab compared to the original design and causes the structural damage of the slab and threatens flight safety. Due to the complication of pavement foundation, the traditional treatment countermeasures usually need a long time for completion, while the airfield system often requires short and high-quality repair time. Therefore, there should be special solutions to satisfy the practical application. The article analyzes the cause, proposes the solutions for pavement foundation treatment and presents an initial application to Noi Bai International Airport. The findings of this study could be critical and significance basis for both academic and practical applications to maintain the service quality of airport construction infrastructure in Vietnam.
Trang: 497-506 Vinh Ha Ho, Ngoc Long Nguyen, Van Minh NgoTóm tắtThe composite girder, which combines a steel beam with an ultra-high-performance concrete (UHPC) slab, has gained significant attention in recent years as a new type of bridge structure. However, accurately estimating the bending capacity of such girders remains a challenge, as practical methods are limited. In this article, the authors propose a theoretical approach based on the Euler-Bernoulli beam theory to determine the bending capacity of composite girders. This approach considers the assumptions of plane sections remaining plane and infinitesimal strains during bending. By applying this theoretical approach, the authors derive a formula that allows engineers to calculate the bending capacity of the composite girder. The formula takes into account the dimensions and properties of both the steel beam and the UHPC slab. The derived formula serves as a valuable tool for evaluating the structural behavior and performance of composite girders. To validate its accuracy, the authors compare the results obtained from their calculations with numerical simulations of composite girder failures caused by bending. The close agreement between the theoretical calculations and the numerical simulation results confirms the reliability and applicability of the proposed formula. This research significantly contributes to the field of composite girder design by providing a practical and reliable method for estimating the bending capacity of steel beam-UHPC slab composite girders. The proposed theoretical approach, validated through numerical simulations, offers valuable insights for the design and optimization of these composite girders in various engineering applications.
Trang: 507-518 Pham Duc Tho, Luca SorelliTóm tắtRecent works have showed that the secondary creep of concrete under sustained high load level of load-to-strength ratio is likely due to a strong coupling between damage and drying shrinkage, which locally occurs in the fracture process zone. The scope of this work is to develop a simplified damage-poromechanical model for the secondary creep of concrete, which directly accounts for such coupling. It was simply assumed that microcracking affects the distribution of the moisture content by scaling the adsorption isotherm with damage. The proposed hydro-mechanical-damage model couplings has been implemented into a discrete lattice method based on dually coupled conduit elements and mechanical element. Notably, the drying shrinkage is accounted within the poromechanical framework of the partially saturated media. The hydro-mechanical-damage model can engender microcrack process zone which govers the secondary creep of concrete at high stress. The model has been validated on 2D experiments of secondary creep on FRC which considers the effect of water-to-cement ratio and aggregate inclusion Finally, the model is validated against experimental results on secondary creep fiber reinforced mortar (FRM) beam considering the effect of concrete heterogeneity.
Multi-task control of swarm robot with double integral model
Trang: 519-529 Le Thi Thuy Nga, Nguyen Thanh Hai, Nguyen Van Tung, Pham Xuan TichTóm tắtBiological individuals in the wild often have a definite size and mass, so simulation of the real biological swarm behavior should take these factors into account. The article focuses on building an algorithm to calculate the force acting on each individual robot in the swarm based on their mass through the “Double integral” model. When the robots are required to perform multi-tasks simultaneously, the priority order of tasks must be classified, and the task with lower priority will be projected into the Null space of the higher priority tasks. Each individual robot in the swarm has to fulfill following three tasks: avoid obstacles, move to the goal, maintain the swarm. In this study, the author chooses the priority level in the following order: avoiding obstacles, moving to the goal and finally maintaining the swarm. With an assumption that the obstacles are fixed and known in advance. Finally, the theoretical studies are simulated and verified by Matlab software.
Trang: 530-543 Thin Quynh Nguyen, Duc Le Hoai, Dunin A.YTóm tắtInternal combustion engines (ICEs), especially diesel engines, continue to play a huge role in the development of the global economy. The research trends to improve combustion is still the main research direction in recent years with the help of 3D simulation tools. In this study, a 3D-model of a four-stroke, single-cylinder diesel engine was built using AVL Fire software to evaluate the influence of injector geometry parameters on engine characteristics. The results have shown that, with the injection pressure reaching 3000 (bar), and the turbocharger pressure maintained at 0.15 (MPa), the engine achieves the maximum power and the minimum brake fuel consumption when the angle between the axis of the nozzle hole and the axis of the fuel injection nozzle is 150 degrees. However, at this angle value, the soot emission value is the lowest but the nitrogen oxides (NOx) value is close to reaching the maximum. Hydrocarbon (HC) and carbon monoxide (CO) emissions are the lowest value at 155 degrees of the angle between the axis of the spray hole and the axis of the fuel injection nozzle. Besides, the study also evaluated the engine's parameters when changing the injector hole diameter. With an injection hole diameter of 0.24 (mm), the maximum engine power increased by 5.3%, and the brake-specific fuel consumption decreased by 7.2% compared to other values of injection hole diameter. However, the engine emissions are not the best values in this case.
Stability of multi-cracked FG plate on elastic foundations
Trang: 544-556 Pham Minh Phuc, Le Vinh AnTóm tắtRecently, the stability calculation of the functionally graded (FG) plate has attracted many scientists, especially when considering the FG plate with many cracks. In this work, the plate is made from a new generation composite material consisting of two components, ceramic and metal, with the law of continuous exponential material distribution. The plate is placed on a Winkler - Pasternak elastic foundation with two background parameters. Then, we used the third-order shear deformation plate theory to establish the dynamical equations. After applying Phase-Field theory to simulate the crack state, we applied the finite element method to solve the equations to find the critical force causing instability of the plate. Next, we investigated the influence of material index, number of cracks, crack length, crack shape as well as elastic foundation parameters on the plate stability. The results show that the crack length and elastic foundation parameter have the great influence on the stability of the FG plate. Especially, the elastic foundation with large shear coefficient, creating high stability for the plate. That is very meaningful in exploiting and using plate structure when the cracks appear.
