Journal of Materials and Engineering Structures
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316 research outputs found
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Stochastic finite element analysis of the free vibration of non-uniform beams with uncertain material
Full text linkThis paper deal with the stochastic finite element method for investigating the eigenvalues of free vibration of non-uniform beams due to a random field of elastic modulus. The formulation of stochastic analysis of the non-uniform beam is established using perturbation method in conjunction with finite element method. Monte Carlo simulation (MCS) used for validation with stochastic finite element approach. The spectral representation was used to generate a random field to employ the Monte Carlo simulation. The performance of results of the uncertain eigenvalue problem of non-uniform beams with random field of elastic modulus by comparing the first-order perturbation technique with the same moments evaluated from the Monte Carlo simulation. The numerical results show that the response of coefficient of variation of eigenvalue increases when the ratio of correlation distance of random field increases
Reliability evaluation of 2D semi-rigid steel frames accounting for corrosion effects
Full text linkNowadays, steel frames are widely used in civil and industrial engineering structures. The design process for steel frames with semi-rigid beam-column connections is an interesting topic for designers and researchers. However, the current design codes purely deal with the structural reliability at the pristine and the degradation of steel due to corrosion is not specified. This study proposes a procedure for evaluating the reliability of two-dimensional semi-rigid steel frames considering corrosion effects. A series of Monte Carlo simulations are performed to evaluate the reliability of the corroded steel structures. The random variables including corrosion phenomenon, semi-rigid connection, and applied load, are considered in the proposed method. The safety deterioration of the steel structures due to the corrosion phenomenon until 50 years is obtained. Additionally, the effects of input parameters, which are safety factors and coefficients of variation, on the reliability of structures are examined in the present study. Finally, a verification of this study and previous results is performed, highlighting the capability of the proposed method.
Random Dense Packing Parameters of Two-Dimensional Spherical Powders for Hot Isostatic Pressing Process Modeling
Full text linkIn this paper, we have used the hot isostatic pressing HIP models previously carried out for the study of the random dense packing densification (RDP) of spherical particles of the same size in order to adapt them to the RDP of two-dimensional spherical particles. A new microscopic approach is thus developed that allows the densification parameters of two-dimensional spherical powder aggregates to be evaluated as a function of the relative density, taking into account the morphological changes of the powder particles and the porosity. The equations obtained for each parameter (coordination number, mean contact area and effective pressure) made it possible to represent the results in the form of curves. These show that our new approach is well adapted to a realistic description of the densification of powder aggregates with particles of more or less similar sizes.
Modeling of Internally or externally prestressed concrete beams until fracture in nonlinear elasticity
Full text linkIn this paper, we present an analytical model to analyze reinforced and prestressed concrete beams loaded in combined bending, axial load and shear, in the frame of non linear elasticity. In this model, the equilibrium of the beam is expressed by solving a system of equations, governing beams equilibrium, based on the stiffness matrix of the beam, which connects the load vector to the node displacements vector of the beam. It is built from the stiffness matrix of the section which takes into account a variation of the shearing modulus (depending on the shear variation) instead of assuming a constant shearing modulus as in linear elasticity. For the internal tendons, the stiffness matrix is completed by the terms due to the prestress effect in flexural equilibrium and by the balancing of one part of the shear by the transverse component of the force in the inclined cables. A computing method is then developed and applied to the calculus of some internally or externally prestressed concrete beams. The comparison of the results predicted by the model with several experimental results show that, on the one hand, the model predictions give a good agreement with the experimental behavior in any field of the behavior (after cracking, post cracking, post steel yielding and fracture of the beam); and, on the second hand, that the model leads to the prediction of tendons slipping at deviators and to the tension increase in the tendons
Refinement of an inverse analysis procedure for estimating tensile constitutive law of UHPC
Full text linkAs regard to cementitious composite materials added a certain dosage of fiber, estimation of tensile constitutive law through inverse analysis methods is no longer extraordinary. However, development or improvement to achieve an effective method for estimating such a tensile behavior of fiber reinforced concrete (FRC) or Ultra high-performance concrete (UHPC) is still an interesting topic to researchers. In this respect, the paper presents a development of inverse analysis method developed by Lopez to obtain the stress-strain behavior of UHPC from the four-point bending test. By applying optimization algorithm into the iterative procedure of method, an improvement could be obtained for the inverse analysis with a high degree of automation in calculation. A post-process treatment for inverse analysis results is also proposed to bring a finer agreement between the tensile behavior curve obtained by the inverse analysis and result curve of uniaxial tensile test (UTT). The effectivity of process is shown through a comparison between the result obtained by the proposed method and the result in Lopez’s public paper
A Study on Derailment at Railway Turnout Using the Multi-body Dynamics Simulation
Full text linkIn this study, the locomotive and the turnout were simulated with three-dimensional models. The purpose of this study is prediction the derailment phenomenon of the locomotive running on the turnout in Vietnam. Multi-body simulations were implemented by SIMPACK software to determine the derailment coefficient, the wheel unloading factor, and the lateral force. The interaction between the locomotive and the track structure at turnout was considered unified. The derailment coefficient, the wheel unloading factor, and the lateral force were calculated for locomotive-D19E at turnout (tg0.15) for 1000 mm gauge according to QCVN 18:2011/BGTVT, EN 14363:2016, and TCVN 8784:2011. The derailment coefficient, the wheel unloading factor, and the lateral force for the locomotive at max speed V=27.8 km/h are 0.94, 0.61, and 67.46 kN, respectively. These results show that the locomotive will not derail when it passes the turnout at a speed V 27.8 km/h
Experimental Study of Prestressed Concrete Track Slab at Railroad Crossings
Full text linkCurrently, the prestressed concrete track slabs are testing installed at the field to replace the reinforced concrete track slabs at railroad crossings in Vietnam. Prestressed concrete track slabs used for 1000 mm gauge. The dimensions of each slab were designed with a length, width, and height of 2.5 m, 1.0 m, and 0.33m, respectively. This paper presents experimental measurements to analyze the behavior of the prestressed concrete track slab at railroad crossings under the action of train and truck dynamic load. Experiment measurements were implemented at the site. Eight strain gauges were mounted at three sections of the track slab to measure the deformation. HL-93 truck load and TY-7E train load were used in the test. The results show the eccentricity of the gravity center point of the prestressed wires to the centroidal axis of the transformed area. The deviation ratio between experimental and theoretical results is from 0.88% ÷ 1.25%. These results can be used to optimize the design process and limit cracks. In addition, tensile and compressive stresses in slabs are smaller than the allowable values. The results show that this track slab meets the requirements of durability and strength under the action of train and truck dynamic load
Multi-level damage detection using a combination of deep neural networks
Full text linkIn recent years, bridge damage identification using a convolutional neural network (CNN) has become a hot research topic and received much attention in the field of civil engineering. Although CNN is capable of categorizing damaged and undamaged states from the measured data, the level of accuracy for damage diagnosis is still insufficient due to the tendency of CNN to ignore the temporal dependency between data points. To address this problem, this paper introduces a novel hybrid damage detection method based on the combination of CNN and Long Short-Term Memory (LSTM) to classify and quantify different levels of damage in the bridge structure. In this method, the CNN model will be used to extract the spatial damage features, which will be combined with the temporal features obtained from Long Short-Term Memory (LSTM) model to create the enhanced damage features. The combination successfully strengthened the damage detection capability of the neural network. Moreover, deep learning is also improved in this paper to process the acceleration-time data, which has a different amplitude at short intervals and the same amplitude at long intervals. The empirical result on the Vang bridge shows that our hybrid CNN-LSTM can detect structural damage with a high level of accuracy
Performance improvement of recycled aggregate concrete using fly ash and Portland blast-furnace slag cement
Full text linkSeveral countermeasures are implemented in the manufacture of construction materials to avoid negative impacts on the environment. Using concrete debris in construction demolition waste as a recycled aggregate to make recycled aggregate concrete (RAC) is one of the countermeasures. Further, the use of recycled construction waste and industrial by-products, such as fly ash and ground granulated blast-furnace slag, in concrete not only promotes resource circulation and reduces CO2 emissions in the cement manufacturing process but also improves concrete performance. In this study, low-quality recycled aggregate was mixed with normal aggregate at various replacement ratios to produce RAC. Additionally, ground granulated blast-furnace slag in Portland blast-furnace slag cement and fly ash were introduced in concrete to improve concrete performance. Applying the relative quality index method for performance evaluation, it was possible to design a mix proportion of RAC that achieved the requisite performance through the application of Portland blast-furnace slag cement and fly ash as a cement substitute or as a fine aggregate substitute
Role of Excessive Iron on Hyper-Eutectic Al-Si Automotive Alloy: A Review
Full text linkAluminum alloys always content the element iron more or less as a common impurity. It is unavoidable and has undesirable effects to ductility and cast ability, mainly in cast Al-Si alloys. The quantity of Fe content as well has a significant effect on the mechanical properties of the Al-Si alloys. Heat treatment may also affect the different properties of these alloys. Hypereutectic alloys which contents more than 12% Si are attractive candidates for automotive applications. It is well known that the excellent properties of hyper eutectic aluminium alloy are based on the primary Si particles as distributed in the matrix. Experiments in this regards have been carried out on physical, mechanical, thermal etc. behavior of these alloys by a good number of researcher. This article presents a literature review on the early investigated role of excessive iron on the different properties of hyper-eutectic Al-Si automotive alloy. In addition, the main factors which affect its mechanism are scheduled