National University of Civil Engineering

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Hanoi, Vietnam
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Phung-Van P.,Ton Duc Thang University | Nguyen-Thoi T.,National University of Civil Engineering | Luong-Van H.,Ho Chi Minh City University of Technology | Lieu-Xuan Q.,Nguyen Tat Thanh University
Computer Methods in Applied Mechanics and Engineering | Year: 2014

A cell-based smoothed three-node Mindlin plate element (CS-MIN3) based on the first-order shear deformation theory (FSDT) was recently proposed for static and dynamics analyses of Mindlin plates. In this paper, the CS-MIN3 is extended to geometrically nonlinear analysis of functionally graded plates (FGPs) subjected to thermo-mechanical loadings. In the FGPs, the material properties are assumed to vary through the thickness by a simple power rule of the volume fractions of the constituents. The nonlinear formulation is based on the C0-type high-order shear deformation plate theory (C0-HSDT) and the von Kármán strains, which deal with small strains and moderate rotations. In the analysis process, both thermal and mechanical loadings are considered and a two-step procedure is performed including a step of analyzing the temperature field along the thickness of the plate and a step of analyzing the geometrically nonlinear behavior of the FGPs subjected to both thermal and mechanical loadings. The accuracy and reliability of the proposed method is verified by comparing its numerical solutions with those of available other numerical results. © 2013 Elsevier B.V.


Soutsos M.N.,Queen's University of Belfast | Le T.T.,National University of Civil Engineering | Lampropoulos A.P.,University of Liverpool
Construction and Building Materials | Year: 2012

The ductility of concrete made with commercially available steel and synthetic fibres has been investigated. Flexural stress-deflection relationships have been used to determine: flexural strength, flexural toughness, equivalent flexural strength, and equivalent flexural strength ratio. The flexural toughness of concrete was found to increase considerably when steel and synthetic fibres were used. However, equal dosages of different fibres did not result in specimens with the same flexural toughness. Flexural toughness differences of almost 35 J existed even at the same fibre dosage. This also resulted in considerable differences in the minimum required ground supported slab thickness. © 2012 Elsevier Ltd. All rights reserved.


Le T.-P.,French Institute for Advanced Mechanics | Le T.-P.,National University of Civil Engineering | Paultre P.,Université de Sherbrooke
Journal of Sound and Vibration | Year: 2012

This paper deals with the use of the continuous wavelet transform for modal identification from ambient vibration tests. The wavelet analysis of the free responses of a linear mechanical system has been used to estimate its natural frequencies, viscous damping ratios, and mode shapes, using either the modulus or the phase of the wavelet transform with ridge and skeleton notions. This technique is extended in this paper, to the response from ambient excitation tests based on the equivalent formulation between the free response and the correlation function of a linear mechanical system under stationary stochastic excitation. The main novelties involve the new formulation of continuous wavelet transform and the use of the singular value decomposition algorithm for ridges and skeleton detection under the noisy conditions of ambient vibration tests. A complete procedure for modal identification of ambient response, including these new formulations, is presented and then applied to numerical examples and experimental test to illustrate its validity. © 2012 Elsevier Ltd. All rights reserved.


Bui H.C.,National University of Civil Engineering
Thin-Walled Structures | Year: 2012

This paper presents a development of the finite strip method based on the shallow shell theory of Marguerre. Most of existing semi-analytical finite strips are based on the plate theories of Kirchhoff and of Mindlin. As it is showed in the paper, the plate theories can be considered as the particular cases of the shallow shell theory. Numerical results show the efficiency of the finite strip based on the shallow shell theory in the buckling analysis of prismatic structures which have curved corners. © 2011 Elsevier Ltd. All rights reserved.


Duc Luong N.,National University of Civil Engineering
Renewable and Sustainable Energy Reviews | Year: 2015

With a coastline of more than 3000 km and its location in the monsoonal climate zone, Vietnam is expected to have good potential for wind energy development. During the last years, several preliminary studies on assessment of wind energy potential in Vietnam have been carried out. Policies for supporting wind energy projects are still under development and improvement. The goal of this paper is to give an overview on wind energy potential and the current application as well as development of wind energy in Vietnam. This paper also presents the current policies for wind energy development and identifies the major barriers need to be addressed for the future development of wind energy in Vietnam. © 2014 Elsevier Ltd. All rights reserved.


Duc Luong N.,National University of Civil Engineering
Renewable and Sustainable Energy Reviews | Year: 2015

Due to the rapid population growth and economic development, energy demand is likely to triple over the next decade in Vietnam. Development and implementation of Energy Efficiency and Conservation (EE&C) policies and programs is of great importance for the Government of Vietnam that would help to improve the energy efficiency and contribute in meeting the increasing energy demand of the country in the future. In the recent years, the Government of Vietnam has made substantial progress in improving EE&C by initiating a number of EE&C policies and programs with the two most important ones are the Law on EE&C and the National Targeted Program on Energy Efficiency and Conservation (Phase I: 2006-2010 and Phase II: 2012-2015). However, implementation of these policies and programs has been challenged in reality. This paper mainly aims to provide an overview on the current and future energy context in Vietnam; review the evolution of the Government's EE&C policies and programs; and identify the challenges and provide the recommendations for implementing EE&C policies and programs more effectively in the future. This paper suggests that much more efforts relating to improvement on collection, analysis, and management of energy data; capacity building; close coordination among the relevant Ministries and the organizations and agencies during the implementation of EE&C policies and programs; etc. should be put forward in the coming years. In addition, a number of recommendations for promoting EE in three largest energy consumers in Vietnam - namely industrial, residential, and transport sectors has been made in this paper. © 2015 Elsevier Ltd. All rights reserved.


Thuat D.V.,National University of Civil Engineering
Structural Design of Tall and Special Buildings | Year: 2014

Damage levels of building structures under a design earthquake are closely related to the assigned values of strength reduction factors. This paper is to investigate the strength reduction factor demands of building structures that were designed considering various earthquake ground intensity levels, soil ground types, and strength reduction factors. In the investigation, a huge number of rigorous nonlinear inelastic dynamic response analyses of various analytical models of five-story and nine-story frame structures were conducted under various generated ground motions with variations in phrase angles but identical response spectral acceleration amplitudes. Various scaled earthquake records were also considered for evidence of the investigation. The obtained results showed that when the same values of the strength reduction factors were used for determination of the design lateral seismic forces, the damage and reliability level demands of the structures designed for moderate seismic areas were much less than those for severe seismic ones. As a result, it is proposed that the strength reduction factor demands given in design codes can additionally be expressed in a linear relation of the maximum ground acceleration. Copyright © 2012 John Wiley & Sons, Ltd.


Cheng M.-Y.,National Taiwan University of Science and Technology | Hoang N.-D.,National University of Civil Engineering
Journal of Computing in Civil Engineering | Year: 2014

In the construction industry, estimating groutability is a crucial task in the planning phase of a grouting project. Hence, establishing an effective groutability prediction model that is simple to implement and can deliver quick responses with high accuracy is a practical need of construction engineers. In this research, a novel instance-based learning approach - Evolutionary Fuzzy k-Nearest Neighbor Inference Model (EFKNIM) - is proposed to forecast the result of grouting activities that employ microfine cement grouts. In the proposed model, the fuzzy k-nearest neighbor algorithm is used to classify grouting activities into two classes: success and failure. Meanwhile, the differential evolution optimization approach is deployed to select the most appropriate tuning parameters of the fuzzy k-nearest neighbor algorithm, namely the neighboring size (k) and the fuzzy strength (m). This integrated framework allows the EFKNIM to operate autonomously without human prior knowledge or tedious processes for parameter setting. An experiment using 240 in situ data samples demonstrates that the newly established groutability prediction model can outperform other benchmark approaches including the k-nearest neighbor, fuzzy k-nearest neighbor, logistic regression and artificial neural network algorithms. © 2014 American Society of Civil Engineers.


Cheng M.-Y.,National Taiwan University of Science and Technology | Hoang N.-D.,National University of Civil Engineering
Journal of Civil Engineering and Management | Year: 2014

Completing a project within the planned budget is the bottom-line of construction companies. To achieve this goal, periodic cost estimation is vitally important not only in the planning phase, but also in the execution phase. Due to high uncertainty in operational environment, point estimation of project cost is oftentimes not sufficient to assist the decision-making process. This study utilizes Least Squares Support Vector Machine (LS-SVM), machine learning based interval estimation (MLIE), and Differential Evolution (DE) to establish a novel model for predicting construction project cost. LS-SVM is a supervised learning technique used for regression analysis. MLIE is employed for inference of prediction intervals. Moreover, our model deploys DE in the cross validation process to search for the optimal values of tuning parameters. The newly developed model, named as EAC-LSPIM, yields results consisting of a point estimate coupled with lower and upper prediction limits, at a certain level of confidence, to accentuate uncertainty. Simulation and performance comparison demonstrate that the new model is capable of delivering accurate and reliable forecasting results. © 2014 Vilnius Gediminas Technical University (VGTU) Press.


Minh N.Q.,National University of Civil Engineering
Procedia Engineering | Year: 2016

As twin sister concepts in urban planning, "car-free city" and "city of short walks" are usually combined and successfully implemented in Europe, for example in Vauban (Freiburg, Germany) and in Hammarby Sjöstad (Stockholm, Sweden). In these two pilot projects, clean environment, safe traffic flows and convenient services as three essential criteria for a good living quality as well as three key indices of sustainability have been secured. A number of conditions necessary for the establishment of the two new planning concepts in Hanoi should be analysed with an emphasis on mobility and logistics. Additionally, public participation needs to be discussed. © 2016 The Authors. Published by Elsevier Ltd.

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