Abstract
Reliability-based design optimization (RBDO) is a powerful tool for design optimization when considering probabilistic characteristics of design variables. However, it is often computationally intensive because of the coupling of reliability analysis and cost minimization. In this study, the concept of reliability mapping function is defined based on the relationship between the reliability index obtained by using the mean value first order reliability method and the failure probability obtained by using an improved response surface method. Double-loop involved in the classical RBDO can be converted into single-loop by using the reliability mapping function. Since the computational effort of the mean value first order reliability method is minimal, RBDO by using reliability mapping functions should be highly efficient. Engineering examples are given to demonstrate the efficiency and accuracy of the proposed method. Numerical results indicated that the proposed method has the similar accuracy as Monte Carlo simulation, and it can obviously reduce the computational effort.
Address
Weitao Zhao, Xueyan Shi and Kai Tang: Key Laboratory of Liaoning Province for Composite Structural Analysis of Aerocraft and Simulation, Shenyang Aerospace University, Shenyang, 110-136, China
Abstract
For the conventional computational methods for structural reliability analysis, the common limitations are long computational time, large number of iteration and low accuracy. Thus, a new novel method for structural reliability analysis has been proposed in this paper based on response surface method incorporated with an improved genetic algorithm. The genetic algorithm is first improved from the conventional genetic algorithm. Then, it is used to produce the response surface and the structural reliability is finally computed using the proposed method. The proposed method can be used to compute structural reliability easily whether the limit state function is explicit or implicit. It has been verified by two practical engineering cases that the algorithm is simple, robust, high accuracy and fast computation.
Key Words
structural reliability; response surface method; improved genetic algorithm
Address
Yongfeng Fang: School of Mechanical Engineering, Guizhou University of Science Engineering, Bijie 551700, China
Kong Fah Tee: Department of Engineering Science, University of Greenwich, Kent ME4 4TB, United Kingdom
Abstract
In this work, various higher-order shear deformation beam theories for wave propagation in functionally graded beams are developed. The material properties of FG beam are assumed graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents, the governing equations of the wave propagation in the FG beam are derived by using the Hamilton\'s principle. The analytic dispersion relations of the FG beam are obtained by solving an eigenvalue problem. The effects of the volume fraction distributions on wave propagation of functionally graded beam are discussed in detail. The results carried out can be used in the ultrasonic inspection techniques and structural health monitoring.
Key Words
wave propagation; functionally graded beam; transverse shear deformation; higher-order beam theory
Address
Lazreg Hadji: Département de Génie Civil, Université Ibn Khaldoun, BP 78 Zaaroura, 14000 Tiaret, Algérie; Laboratoire des Matériaux and Hydrologie, Université de Sidi Bel Abbes, 22000, Sidi Bel Abbes, Algérie
Nafissa Zouatnia and Amar Kassoul: Laboratoire de Structures, Géotechnique et Risques, Université Hassiba Benbouali de Chlef, Algérie
Abstract
Two Chang-a dissipative family methods and two KR-a family methods were developed for time integration recently. Although the four family methods are in the category of the dissipative structure-dependent integration methods, their performances may be drastically different due to the detrimental property of weak instability or overshoot for the two KR-a family methods. This weak instability or overshoot will result in an adverse overshooting behavior or even numerical instability. In general, the four family methods can possess very similar numerical properties, such as unconditional stability, second-order accuracy, explicit formulation and controllable numerical damping. However, the two KR-a family methods are found to possess a weak instability property or overshoot in the high frequency responses to any nonzero initial conditions and thus this property will hinder them from practical applications. Whereas, the two Chang-a dissipative family methods have no such an adverse property. As a result, the performances of the two Chang-a dissipative family methods are much better than for the two KR-a family methods. Analytical assessments of all the four family methods are conducted in this work and numerical examples are used to confirm the analytical predictions.
Address
Shuenn-Yih Chang: Department of Civil Engineering, National Taipei University of Technology, 1, Section 3, Jungshiau East Road, Taipei 106-08, Republic of China
Abstract
This study presents a particle-wall filtration model for predicting the particle motion behavior in a typical rotational flow field-filtration in blower system of cooker hood. Based on computational fluid dynamics model, air flow and particles has been simulated by Lagrangian-particle/ Eulerian-gas approaches and get verified by experiment data from a manufacturer. Airflow volume, particle diameter and local structure, which are related to the particle filtration has been studied. Results indicates that: (1) there exists an optimal airflow volume of 1243 m3/h related to the most appropriate filtration rate; (2) Diameter of particle is the significant property related to the filtration rate. Big size particles can represent the filtration performance of blower; (3) More than 86% grease particles are caught by impeller blades firstly, and then splashed onto the corresponding location of worm box internal wall. These results would help to study the micro-particle motion behavior and evaluate the filtration rate and structure design of blower.
Address
Yan Yan, Yuanzai Lin, Jie Cheng and Zhonghua Ni: Department of Mechanical and Engineering, Southeast University, 79 Su Yuan Avenue, Nan Jing, 211189, China
Abstract
Nonlinear vibrations of an Euler-Bernoulli beam resting on a nonlinear elastic foundation are discussed. In search of approximate analytical solutions, the classical multiple scales (MS) and the multiple scales Lindstedt Poincare (MSLP) methods
are used. The case of primary resonance is investigated. Amplitude and phase modulation equations are obtained. Steady state solutions are considered. Frequency response curves obtained by both methods are contrasted with each other with respect to the effect of various physical parameters. For weakly nonlinear systems, MS and MSLP solutions are in good agreement. For strong hardening nonlinearities, MSLP solutions exhibit the usual jump phenomena whereas MS solutions are not reliable producing backward curves which are unphysical.
Key Words
beam on elastic foundation; direct perturbation method; Multiple Scales Lindstedt Poincare (MSLP) method; forced vibrations; strongly nonlinear systems
Address
M.M. Fatih Karahan and Mehmet Pakdemirli: Department of Mechanical Engineering, Manisa Celal Bayar University, Muradiye 45140, Manisa, Turkey
Abstract
The paper focuses on dynamic analyses of a series of simply-supported symmetric composite steel-concrete bridges loaded by an ICE-3 train moving at high speeds up to 300 km/h. The series includes five bridges with span lengths ranging from 15 m to 27 m, with repeatable geometry of the superstructures. The objects, designed according to Polish standards valid from 1980s to 2010, are modelled on the bridges serviced on the Central Main Line in Poland since 1980s. The advanced, twodimensional, physically nonlinear model of the bridge-track structure-high-speed train system takes into account unilateral nonlinear wheel-rail contact according to Hertz\'s theory and random vertical track irregularities equal for both rails. The analyses are focused on the influence of random track irregularities on dynamic response of composite steel-concrete bridges loaded by an ICE-3 train. It has been pointed out that certain restrictions on the train speed and on vertical track irregularities should be imposed.
Key Words
random vertical track irregularities; composite steel-concrete bridge; ICE-3 train; unilateral nonlinear wheelrail contact; dynamic analysis; Monte-Carlo method
Address
Monika Podworna: Faculty of Civil Engineering, Wroclaw University of Technology, 27 Wyspianskiego Street, Wroclaw, PL 50370, Poland
Abstract
Among various retrofitting strategies, use of semi-active control for retrofitting a building structure has gained momentum in recent years. One of the techniques for such retrofitting is to connect a weaker building to an adjacent stronger building by semi-active devices, so that performances of a weaker building are significantly improved for seismic forces. In this paper, a ten storey weaker building is connected to an adjacent stronger building using magneto-rheological (MR) dampers, for primarily improving the performance of the weaker building in terms of displacement, drift and base shear. For this, a fuzzy logic controller is specifically developed by fuzzyfying the responses of the coupled system. The performance of the control strategy is compared with the passive-on and passive-off controls. Pounding Mitigation between the two buildings is also investigated using all three control strategies. The results show that there exists a fundamental frequency ratio between the two buildings for which maximum control of the weaker building response takes place with no penalty on the stronger building. There exists also a fundamental frequency ratio where control of the weaker building response is achieved at the expense of the amplification of the stronger building. However, coupling strategy always improves the possibility of pounding mitigation.
Address
Mahdi Abdeddaim, Abdelhafid Ounis: LARGHYDE Laboratory, Department of Civil Engineering and Hydraulics, Faculty of Sciences and Technology, Mohamed Khider University, BP 145 RP, 07000 Biskra, Algeria
Mahendra K. Shrimali and Tushar K. Datta: Center of Disaster Mitigation and Management, Malaviya National Institute of Technology Jaipur, Rajasthan 302017, India
Abstract
Elevated water tanks are considered as important structures due to its post-earthquake requirements. Elevated water tank on reinforced concrete frame staging is widely used in India. Different response reduction factors depending on ductility of frame members are used in seismic design of frame staging. The study on appropriateness of response reduction factor for reinforced concrete tank staging is sparse in literature. In the present paper a systematic study on estimation of key components of response reduction factors is presented. By considering the various combinations of tank capacity, height of staging, seismic design level and design response reduction factors, forty-eight analytical models are developed and designed using relevant Indian codes. The minimum specified design cross section of column as per Indian code is found to be sufficient to accommodate the design steel. The strength factor and ductility factor are estimated using results of nonlinear static pushover analysis. It was observed that for seismic design category \'high\' the strength factor has lesser contribution than ductility factor, whereas, opposite trend is observed for seismic design category \'low\'. Further, the effects of staging height and tank capacity on strength and ductility factors for two different seismic design categories are studied. For both seismic design categories, the response reduction factors obtained from the nonlinear static analysis is higher than the code specified response reduction factors. The minimum dimension restriction of column is observed as key parameter in achieving the desired performance of the
elevated water tank on frame staging.
Key Words
frame staging; strength factor; ductility factor; pushover analysis; elevated water tank; response reduction
Address
Suraj O. Lakhade, Ratnesh Kumar and Omprakash R. Jaiswal: Department of Applied Mechanics, Visvesvaraya National Institute of Technology, Nagpur-440 010, India
Abstract
The purpose of this work is to predict ductile fracture of structural steel under extremely low cyclic loading experienced in earthquake. A cumulative damage model is proposed on the basis of an existing damage model originally aiming to predict fracture under monotonic loading. The cumulative damage model assumes that damage does not grow when stress triaxiality is below a threshold and fracture occurs when accumulated damage reach unit. The model was implemented in ABAQUS software. The cumulative damage model parameters for steel base metal, weld metal and heat affected zone were calibrated, respectively, through testing and finite element analyses of notched coupon specimens. The damage evolution law in the notched coupon specimens under different loads was compared. Finally, in order to examine the engineering applicability of the proposed model, the fracture performance of beam-column welded joints reported by previous researches was analyzed based on the cumulative damage model. The analysis results show that the cumulative damage model is able to successfully predict the cracking location, fracture process, the crack initiation life, and the total fatigue life of the joints.
Abstract
In the present paper a new Neuro-Wavelet control algorithm is proposed based on a cost function to actively control the vibrations of structures under earthquake loads. A wavelet neural network (WNN) was developed to train the control algorithm. This algorithm is designed to control multi-degree-of-freedom (MDOF) structures which consider the geometric and material non-linearity, structural irregularity, and the incident direction of an earthquake load. The training process of the algorithm was performed by using the El-Centro 1940 earthquake record. A numerical model of a three dimensional (3D) three story building was used to accredit the control algorithm under three different seismic loads. Displacement responses and hysteretic behavior of the structure before and after the application of the controller showed that the proposed strategy can be applied effectively to suppress the structural vibrations.
Key Words
wavelet neural network; 3D building model; structural response; non-linearity; hysteretic behavior
Address
Yasser Bigdeli and Dookie Kim: Department of Civil Engineering, Kunsan National University, Jeonbuk, 573-701, Republic of Korea
Abstract
Beam-like structures such as bridge, high building and tower, pipes, flexible connecting rods and some robotic manipulators are often excited by support motions. These structures are important in machines and structures. So, this study proposes an analytic method to accurately predict the dynamic behaviors of the structures during support motions or an earthquake. Using Timoshenko beam theory which is valid even for non-slender beams and for high-frequency responses, the analytic responses of fixed-fixed beams subjected to a real seismic motions at supports are illustrated to show the principled approach to the proposed method. The responses of a slender beam obtained by using Timoshenko beam theory are compared with the solutions based on Euler-Bernoulli beam theory to validate the correctness of the proposed method. The dynamic analysis for the fixed-fixed beam subjected to support motions gives useful information to develop an understanding of the structural behavior of the beam. The bending moment and the shear force of a slender beam are governed by dynamic components while those of a stocky beam are governed by static components. Especially, the maximal magnitudes of the bending moment and the shear force of the thick beam are proportional to the difference of support displacements and they are influenced by the seismic wave velocity.
Key Words
Timoshenko beam; support motions; eigenfunction expansion method; time-dependent boundary condition; quasi-static decomposition method; static component-dominated beam
Address
Yong-Woo Kim: Department of Mechanical Engineering, Sunchon National University, Jungangro 255, Sunchon, Jeonnam 57922, Republic of Korea
