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CONTENTS
Volume 55, Number 5, September10 2015
 

Abstract
The goal of this study is to investigate computational convergence of optimal solutions, with respect to optimality criteria (OC) method and methods of moving asymptotes (MMA) as optimization model for non-linear programming of material topology optimization using an acceleration method that makes design variables rapidly move toward almost 0 and 1 values. 99 line topology optimization MATLAB code uses loop vectorization and memory pre-allocation as properly exploiting the strengths of MATLAB and moves portions of code out of the optimization loop so that they are only executed once as restructuring the program. Numerical examples of a simple beam under a lateral load and a given material density limitation provide merits and demerits of the present OC and MMA for 99 line topology optimization code of continuous material topology optimization design.

Key Words
acceleration method; OC; MMA; MATLAB; topology optimization; convergence

Address
Dongkyu Lee and Nguyen Hong Chan: Department of Architectural Engineering, Sejong University, Seoul, 143-747, Korea
Soomi Shin: Research Institute of Industrial Technology, Pusan National University, Busan, 609-735, Korea

Abstract
The ratcheting and strain cyclic behaviour of joined conical-cylindrical shells under uniaxial strain controlled, uniaxial and multiaxial stress controlled cyclic loading are investigated in the paper. The elasto-plastic deformation of the structure is simulated using Chaboche non-linear kinematic hardening model in finite element package ANSYS 13.0. The stress-strain response near the joint of conical and cylindrical shell portions is discussed in detail. The effects of strain amplitude, mean stress, stress amplitude and temperature on ratcheting are investigated. Under strain symmetric cycling, the stress amplitude increases with the increase in imposed strain amplitude. Under imposed uniaxial/multiaxial stress cycling, ratcheting strain increases with the increasing mean/amplitude values of stress and temperature. The abrupt change in geometry at the joint results in local plastic deformation inducing large strain variations in the vicinity of the joint. The forcing frequency corresponding to peak axial ratcheting strain amplitude is significantly smaller than the frequency of first linear elastic axial vibration mode. The strains predicted from quasi static analysis are significantly smaller as compared to the peak strains from dynamic analysis.

Key Words
ratcheting; cyclic loading; finite element analysis; conical-cylindrical shell; quasi-static; dynamic

Address
Jaskaran Singh and B.P. Patel: Department of Applied Mechanics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India

Abstract
To improve the durability and service life of reinforced concrete column such as bridge piers, an advanced composite column made of Ultra High Performance Cementitious Composites (UHPCC) permanent form is proposed. Based on elasticity plasticity theory, axial compression behavior of the composite column was studied theoretically. The first circumferential cracking load and ultimate limit loading capacity are derived for the composite column. Short composite column compression tests and numerical simulations using FEM method were carried out to justify the theoretical formula. The effects of UHPCC tube thickness on the axial compression behavior were studied. Using the established theoretical model and numerical simulation, the large dimension composite columns are calculated and analyzed with different UHPCC tube thickness. These studies may provide a reference for advanced composite column design and application.

Key Words
ultra high performance cementitious composites; composite column; cracking load; ultimate limit loading capacity; short column compression test

Address
Xiang-Guo Wu: Key Lab of Structures Dynamic Behavior and Control, Harbin Institute of Technology, Ministry of Education, Heilongjiang, Harbin, 150090, China; School of Civil Engineering, Harbin Institute of Technology, Heilongjiang, Harbin 150090, China
Ruofei Zou: Department of Civil and Environmental Engineering, University of Illinois, IL 61801-2352, USA
Xinyu Zhao and Qun Yu: School of Architecture Engineering, Harbin Engineering University, Harbin 150001, China

Abstract
A model has been proposed that can predict the ultimate torsional strength of single-box multicell reinforced concrete box girder under combined loading of bending, shear and torsion. Compared with the single-cell box girder, this model takes the influence of inner webs on the distribution of shear flow into account. According to the softening truss theory and thin walled tube theory, a failure criterion is presented and a ultimate torsional strength calculating procedure is established for single-box multi-cell reinforced concrete box girder under combined actions, which considers the effect of tensile stress among the concrete cracks, Mohr stress compatibility and the softened constitutive law of concrete. In this paper the computer program is also compiled to speed up the calculation. The model has been validated by comparing the predicted and experimental members loaded under torsion combined with different ratios of bending and shear. The theoretical torsional strength was in good agreement with the experimental results.

Key Words
reinforced concrete; multi-cell box girder; torsional strength; softening truss theory; failure criterion

Address
Qian Wang, Wenliang Qiu and Zhe Zhang: Faculty of Infrastructure Engineering, Bridge Science Research Institute, Dalian University of Technology, No.2 Linggong Road, Ganjingzi District, Dalian city, Liaoning Province, China

Abstract
Determination of dynamic parameters of a structure such as predominant frequency and damping ratio is one of the most important subjects in dynamics of structures. Different methods are used to determine predominant frequency. These methods are different in the cost, implement accessibility, accuracy, speed, applicability in different conditions, simplicity of calculations and required data accessibility. Calculation of damping ratio by using common experimental procedures is very difficult and costly, then it is assumed as a constant value in most calculations. Microtremor measurements and using spectral ratio method to determine the predominant frequency and damping ratio of structure is of interest in recent years. In this paper, as a case study, the effects of retrofitting on structural dynamic parameters of two four-story buildings by using microtremor measurements and also finite element analysis, is investigated. The results of this study show that microtremor measurements can be utilized to assess the improvement of dynamic behavior of the retrofitted structure and the effectiveness of the method of retrofitting.

Key Words
microtremor measurements; finite element analysis; spectral ratio method; predominant frequency; damping ratio; random decrement method

Address
Mohammad Ali Hadianfard, Ramin Rabiee and Azad Sarshad: Department of Civil and Environmental Engineering, Shiraz University of Technology, P.O. Box 71555-313, Modarres Blvd, Shiraz, Iran

Abstract
This paper proposes a novel reliability analysis method which computes reliability index, most probable point and probability of failure of uncertain systems more efficiently and accurately with compared to Monte Carlo, first-order reliability and response surface methods. It consists of Initial and Simulation steps. In Initial step, a number of space-filling designs are selected throughout the variables space, and then in Simulation step, performances of most of samples are estimated via interpolation using the space-filling designs, and only for a small number of the samples actual performance function is used for evaluation. In better words, doing so, we use a simple interpolation function called \"reduced\" function instead of the actual expensive-to-evaluate performance function of the system to evaluate most of samples. By using such a reduced function, total number of evaluations of actual performance is significantly reduced; hence, the method can be called Reduced Function Evaluations method. Reliabilities of six examples including series and parallel systems with multiple failure modes with truncated and/or non-truncated random variables are analyzed to demonstrate efficiency, accuracy and robustness of proposed method. In addition, a reliabilitybased design optimization algorithm is proposed and an example is solved to show its good performance.

Key Words
uncertainty; reliability; failure probability; Monte-Carlo simulation; reduced function evaluation

Address
Bahman Farahmand Azar, Ali Hadidi and Amin Rafiee: Department of Civil Engineering, University of Tabriz, Tabriz, Iran

Abstract
Bending analysis of functionally graded (FG) nano-plates is investigated in the present work based on a new sinusoidal shear deformation theory. The theory accounts for sinusoidal distribution of transverse shear stress, and satisfies the free transverse shear stress conditions on the top and bottom surfaces of the plate without using shear correction factor. The material properties of nano-plate are assumed to vary according to power law distribution of the volume fraction of the constituents. The size effects are considered based on Eringen\'s nonlocal theory. Governing equations are derived using energy method and Hamilton

Key Words
FG nano-plate; sinusoidal shear deformation theory; exact solution; bending

Address
Reza Kolahchi: Department of Mechanical Engineering, Shahinshahr Branch, Islamic Azad University, Shahinshahr, Iran
Ali Mohammad Moniri Bidgoli: Faculty of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran
Mohammad Mehdi Heydari: Young Researchers and Elite Club, Kashan Branch, Islamic Azad University, Kashan, Iran

Abstract
A three-dimensional (3D) numerical analysis for the train-bridge interaction (TBI) system is actively developed in this study in order to investigate the vibration characteristics of rigid-frame reinforced concrete (RC) viaducts in both vertical and lateral directions respectively induced by running high-speed trains. An analytical model of the TBI system is established, in which the high-speed train is described by multi-DOFs vibration system and the rigid-frame RC viaduct is modeled with 3D beam elements. The simulated track irregularities are taken as system excitations. The numerical analytical algorithm is established based on the coupled vibration equations of the TBI system and verified through the detailed comparative study between the computation and testing. The vibration responses of the viaducts such as accelerations, displacements, reaction forces of pier bottoms as well as their amplitudes with train speeds are calculated in detail for both vertical and lateral directions, respectively. The frequency characteristics are further clarified through Fourier spectral analysis and 1/3 octave band spectral analysis. This study is intended to provide not only a simulation approach and evaluation tool for the train-induced vibrations upon the rigid-frame RC viaducts, but also instructive information on the vibration mitigation of the high-speed railway.

Key Words
vibration response; rigid-frame RC viaduct; high-speed train; the train-bridge interaction; characteristic analysis

Address
Liangming Sun and Weiping Xie: School of Civil Engineering and Architecture, Wuhan University of Technology, Wuhan 430070, China
Liangming Sun, Xingwen He and Toshiro Hayashikawa: Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan

Abstract
This paper presents finite element (FE) based pushover analysis of a reinforced concrete structure with a two-leaf cavity wall (TLCW) to estimate the performance level of this structure. In addition to this, an unreinforced masonry (URM) model was selected for comparison. Simulations and analyses of these structures were performed using the DIANA FE program. The mentioned structures were selected as two storeys and two bays. The dimensions of the structures were scaled 1:1.5 according to the Cauchy Froude similitude law. A shake table experiment was implemented on the reinforced concrete structure with the two-leaf cavity wall (TLCW) at the National Civil Engineering Laboratory (LNEC) in Lisbon, Portugal. The model that simulates URM was not experimentally studied. This structure was modelled in the same manner as the TLCW. The purpose of this virtual model is to compare the respective performances. Two nonlinear analyses were performed and compared with the experimental test results. These analyses were carried out in two phases. The research addresses first the analysis of a structure with only reinforced concrete elements, and secondly the analysis of the same structure with reinforced concrete elements and infill walls. Both researches consider static loading and pushover analysis. The experimental pushover curve was plotted by the envelope of the experimental curve obtained on the basis of the shake table records. Crack patterns, failure modes and performance curves were plotted for both models. Finally, results were evaluated on the basis of the current regulation ASCE/SEI 41-06.

Key Words
reinforced concrete; shake table; finite element method; infill wall; pushover

Address
Onur Onat: Department of Civil Engineering, Tunceli University, Tunceli, Turkey
Paulo B. Lourenco: Department of Civil Engineering, Minho University, Guimaraes, Portugal
Ali Kocak: Department of Civil Engineering, Yildiz Technical University, İstanbul, Turkey

Abstract
The dynamic response of two-dimensional unbounded domain on the rigid bedrock in the time domain is numerically obtained. It is realized by the modified scaled boundary finite element method (SBFEM) in which the original scaling center is replaced by a scaling line. The formulation bases on expanding dynamic stiffness by using the continued fraction approach. The solution converges rapidly over the whole time range along with the order of the continued fraction increases. In addition, the method is suitable for large scale systems. The numerical method is employed which is a combination of the time domain SBFEM for far field and the finite element method used for near field. By using the continued fraction solution and introducing auxiliary variables, the equation of motion of unbounded domain is built. Applying the spectral shifting technique, the virtual modes of motion equation are eliminated. Standard procedure in structural dynamic is directly applicable for time domain problem. Since the coefficient matrixes of equation are banded and symmetric, the equation can be solved efficiently by using the direct time domain integration method. Numerical examples demonstrate the increased robustness, accuracy and superiority of the proposed method. The suitability of proposed method for time domain simulations of complex systems is also demonstrated.

Key Words
scaled boundary finite element method; multilayered unbounded domain; continued fraction approach; time domain analysis

Address
Shan Lu, Jun Liu, Gao Lin and Wenyuan Wang: School of Hydraulic Engineering, Faculty of Infrastructure Engineering, Dalian University of Technology, China
Jun Liu: State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116024, China; State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116024, China


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