Journal of Materials and Engineering Structures
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Stability of Cracked Plates with Nonlinearly Variable Thickness Resting on Elastic Foundations
Full text linkIn this paper, the stability of rectangular cracked plates with nonlinearly variable thickness resting on the elastic foundations is studied. The thickness of the plate varies exponentially along the x-axis. Meanwhile, the elastic foundation is modeled by a two-parameter Pasternak elastic foundation type. The crack is assumed at the center of the plate with variable length and angle of inclination. The establishment of the stability equations of the cracked plate is based on the Higher Order Shear Deformation Theory (HSDT) combined with the phase field theory. Next, using the finite element method to solve the equations to find the minimum force that causes plate instability. To test the reliability of the computational theory, the results are compared with several reputable published papers. Then, the article will investigate the influence of elastic foundation, crack location, crack length and crack inclination on the stability of plate. The results show that the elastic foundation has a great influence on the plate stability, while the crack inclination angle has less influence. Finally, there are some images of the destabilization patterns of cracked plates placed on an elastic foundation
Investigation on the effect of cross beams in single span bridges under dynamic aspect by using finite element method
Full text linkIn the 1980s and 1990s, most bridges in Vietnam employed simple beam for short-span river crossings that did not need navigation and mainly used the reinforced concrete T-beams or pre-stressed concrete. While the T-frame structure that has hang single span is widely applied for rivers that require navigation...The single girder is a basic span made of pre-stressed reinforced concrete T or I cross section, with spacing ranging from 2.2m to 2.6m, and the absence of diaphragms was a common feature of bridges built during this time period. All horizontal crashes almost have happened on the spans that did not have diaphragms. As a result, the impact force is concentrated mostly on the lateral girders, leading to total damage. Thus, researches to evaluate the effect of diaphragms in the distribution of horizontal impact forces as well as minimizing the damage in the span structures are crucial. This study focuses on simulating and studying the influence of the number and position of the diaphragms in terms of stress, deformation and damage when a collision occurs in order to propose additional and repair solutions to enhance the horizontal resistance of span
3-D Move Mechanistic Analysis and Cost Effectiveness of Asphalt Rubber and Polymer Modified Asphalt Pavement Under Various Axle Loading Conditions
Full text linkA variety of axle loading conditions can lead to different tensile strains in asphalt pavements. One way to increase resistance to these tensile strains is to add materials such as crumb rubber or polymers to the pavement mixture. Using three given asphalt pavement design mixtures, a 3D-Move mechanistic analysis was performed to determine the fatigue life of three given mixtures: unmodified reference, asphalt rubber, and polymer modified. These mixtures were tested under various axle loading conditions. This mechanistic analysis was then combined with a cost analysis which showed that despite the increase in cost, the asphalt rubber design mixture was the most cost-effective, with the polymer modified mixture finishing in second ahead of the unmodified reference mixture.
Structure de l’écoulement et de mélange dans un éjecteur supersonique gaz-gaz installé dans un système frigorifique d’une capacité de 10TR
Full text linkThe complexity of the flow in an ejector requires very careful visualization in order to describe the ejector behavior. This paper is based on a numerical simulation of the flow of R245fa through the gas-gas supersonic ejector installed in a real refrigeration system with a nominal capacity of 10 TR. The k-e RNG turbulence model is chosen for two modes of ejector operation, critical and sub-critical. Analysis shows that back pressure significantly affects both induced refrigerant flow and ejector operating regime. The use of the NIST-REFPROP database and a mesh adapted for each simulation allows to give results very close to the physical reality such that for the critical (on design) regime the relative errors do not exceed 4%, on the other hand, in under critical conditions (off design), they are of the order of 14%.La complexité de l’écoulement dans un éjecteur nécessite une visualisation très poussée afin de décrire le comportement de l’éjecteur. Cet article repose sur une simulation de l’écoulement de R245fa dans l’éjecteur supersonique gaz-gaz installé dans un système frigorifique réel d’une capacité nominale de 10 TR. Le modèle de turbulence k-e RNG est choisi pour deux modes de fonctionnement de l’éjecteur, critique et sous-critique. L’analyse montre que la contre-pression affect d’une façon significative, à la fois, le débit de réfrigérant induit et le régime de fonctionnement de l’éjecteur. L’utilisation de la base de données de NIST-REFPROP et un maillage adapté pour chacune de simulation permet de donner des résultats très proche à la réalité physique tel que pour le régime critique les erreurs relatives ne dépassent pas 4%, par contre, en régime sous critique, elles sont de l’ordre de 14%
Evaluation of circumferential properties of Jute/Epoxy tubes manufactured by filament winding based on the fiber orientation.
Full text linkThe introduction of bio-composites in the manufacture of tubes by the filament winding technique poses a real challenge for design engineers. This study aims to evaluate the mechanical properties in circumferential traction and in circumferential compression of Jute-Epoxy tubes whose winding angle is considered to be variable. The experimental study is carried out on 6 tube configurations of 92 mm in diameter. The tubes tested are made of 4 layers. The selected α fiber winding angles are (50 °, 55 °, 60 °, 65 °, 75 °, and 90 °). Circumferential tensile and stiffness tests are established according to the specifications of ASTM D2290 and ASTM D2412 respectively. The results obtained allowed us to analyze the influence of the winding angle on the properties of the tubes
Parent Concrete Quality of Recycled Concrete Aggregates on Some Engineering Properties of Concrete
Full text linkThis paper aims to investigate some properties of recycled aggregates concrete (RAC) containing various amount of recycled concrete aggregates (RCA) supplied from different parent concrete strength. Three concretes with different strengths were made. After hardening, they were crushed and the obtained RCA were used to substitute 20%, 40% and 60% of coarse ordinary aggregates (COA) in concrete mix. The properties of these RCA according to their parent concrete strength were analyzed and their effects on the workability, compressive strength and shrinkage were quantified. Concrete workability and final shrinkage seem to be related to the equivalent water absorption of coarse recycled aggregates. An equivalent granular expression can be used in classical model to predict compressive strength according to the RCA content and its parent concrete strength.
A study of 3D modelling the vibrations induced from grab shock at the Metro Line 3 project in Hanoi
Full text linkThe density of high-rise building is increasing over recent years in urban city. Construction activities, particularly piling processes, D-wall excavation, are paid attention due to ground borne vibrations. The impact of vibrations induced from construction activates on existing buildings is discussed in the past and so on. However, there is rarely study their vibrations in Vietname specially in construction activities such as grab shocking. Continuing the analytical and experimental studies of the grab shocking in the Metro Line 3 project in Hanoi, 3D modelling of vibrations induced from the grab shocking on the existing building is carried out by Plaxis software. The hardening soil model is used and the acceleration of the grabin the bentonite slurry is considered in the model. The comparison between the analytical solution and the 3D simulation is highlighted in the paper to show the accuracy and robustness of the 3D modeling. This study is applied to investigate the vibrations on existing building in the Metro Line 3 project and to control the grab drop length as well as the distance of existing building to the vibration source
Automatic detection of pavement crack feature on images taken from specialized road surface survey vehicle
Full text linkApproaching to PDCA (Plan - Do - Check - Take Action) in management of infrastructure asset requires digital transformation, sufficient data and strong database supporting management, analysis as well as creation of data-driven decision making tools. For pavements, data including condition indicators such as roughness and rutting depth are collected automatically during the survey vehicle travelling. However, pavement crack ratio and crack features of pattern and segmentation have not been detected by the system but manual in the case in Vietnam. The paper presents result of research on algorithm of statistic machine learning model in AI applying deep learning algorithm to automatically detect crack feature on pavement photos for enhancement of the performance and productivity of current survey technology. In the research, a deep architecture using convolutional neural network (CNN) for crack segmentation on gray scale images has been developed. The results show the CNN model for crack segmentation is better than other methods using traditional digital processing such as the Gabor filters or threshold and machine learning such as Adaboost
The investigation of Cut-and-cover, top-down construction method for a metro underground station; case study: 'Naghsh-e-Jahan Metro Station, Esfahan, Iran'
Full text linkNaghsh-e-Jahan subway station is located in Esfahan historical context with 186 meters' distance to the Sheikh Fazlolah mosque – one of the historical cosmopolitan attractions. The subway station is in a shallow depth, soft surrounding soils and with wide span and in a downtown location, have made the situation so critical that precise assessments, not only for the station support but also for compensating the ground settlement, are needed. One of the prerequisite procedures for large underground structures, the cut-and-cover approach, is constructed top-down using the Diaphragm Wall system. This method can be functional in conditions where minimum vertical displacements are essential since roof covering and improvement can be performed even when the excavation operation is not terminated. The embankment process can be done just right after the roof slab is complete and reaches reliable strength. This study uses the Finite Element method to simulate all the construction stages and analyze the ground behavior. It has been observed that the width and the length of diaphragm walls and middle barrettes on the ground settlements. Ground settlement for various stages of excavation at the cross-section and longitudinal section of the station is shown that settlements are spandrel and maximum settlements occur close to the diaphragm walls. As excavation continues, ground surface settlements become concave, and the maximum surface settlements occur at a bit of distance from the diaphragm walls for about 17mm. Furthermore, the diaphragm wall's thickness of 100 cm of diaphragm wall is recommended for optimum values
Dynamic response analysis of truss bridges under the effect of moving vehicles
Full text linkWith the characteristics of heavy and concentrated loads, the influence of moving loads on the dynamic response of the bridges is significant. Therefore, in this paper, the dynamic response of a large-scale truss bridge is studied to consider the effect of the various parameters of moving loads. The considered main parameters consist of moving mass, moving velocity, and type of moving loads. The nonlinear dynamics of the bridge based on time history analysis are obtained using the Wilson- method. Four time history – based dynamic analysis methods including modal superposition in frequency domain, modal superposition in time domain; direct time integration, and direct solution in the frequency domain are employed to analysis the obtained results. To compare the effectiveness of the aforementioned method. A large-scale railway truss bridge is employed for dynamic response analysis. The obtained results give more insight into the nature of the problem and help to determine the significant parameters of moving load affecting the bridge response