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CONTENTS
Volume 16, Number 1, July 2015
 

Abstract
Minimizing construction cost and reducing seismic damage are two conflicting objectives in the design of any new structure. In the present work, we try to develop a framework in order to solve the optimum performance-based design problem considering the construction cost and the seismic damage of steel moment-frame structures. The Park-Ang damage index is selected as the seismic damage measure because it is one of the most realistic measures of structural damage. The non-dominated sorting genetic algorithm (NSGA-II) is employed as the optimization algorithm to search the Pareto optimal solutions. To improve the time efficiency of the proposed framework, three simplifying strategies are adopted: first, simplified nonlinear modeling investigating minimum level of structural modeling sophistication; second, fitness approximation decreasing the number of fitness function evaluations; third, wavelet decomposition of earthquake record decreasing the number of acceleration points involved in time-history loading. The constraints of the optimization problem are considered in accordance with Federal Emergency Management Agency\'s (FEMA) recommended seismic design specifications. The results from numerical application of the proposed framework demonstrate the efficiency of the framework in solving the present multi-objective optimization problem.

Key Words
performance-based design; steel moment-frame structures; Park-Ang damage index; non-dominated sorting genetic algorithm; simplified nonlinear modeling; fitness approximation; wavelet analysis

Address
A. Kaveh, M. Fahimi-Farzam and M. Kalateh-Ahani: Centre of Excellence for Fundamental Studies in Structural Engineering, Iran University of Science and
Technology, Narmak, Tehran 16844, Iran

Abstract
Active surface adjustment of cable net structures is becoming significant when large-size cable net structures are widely applied in various fields, especially in satellite antennas. A general-duty adjustment method based on active cables is proposed to achieve active surface adjustment or surface profile reconfiguration of cable net structures. Piezoelectric actuators and voice coil actuators are selected for constructing active cable structures and their simplified mechanical models are proposed. A bilevel optimization model of active surface adjustment is proposed based on the nonlinear static model established by the direct stiffness method. A pattern search algorithm combined with the trust region method is developed to solve this optimization problem. Numerical examples of a parabolic cable net reflector are analyzed and different distribution types of active cables are compared.

Key Words
active surface adjustment; cable net structure; smart actuator; direct stiffness method; pattern search algorithm

Address
Zuowei Wang and Tuanjie Li: School of Electromechanical Engineering, Xidian University,2 South Taibai Road,
Xi\'an, Shaanxi 710071, China

Abstract
A novel finite element (FE) model updating method based on multi-resolution analysis (MRA) is proposed. The true stiffness of the FE model is considered as the superposition of two pieces of stiffness information of different resolutions: the pre-defined stiffness information and updating stiffness information. While the resolution of former is solely decided by the meshing density of the FE model, the resolution of latter is decided by the limited information obtained from the experiment. The latter resolution is considerably lower than the former. Second generation wavelet is adopted to describe the updating stiffness information in the framework of MRA. This updating stiffness in MRA is realized at low level of resolution, therefore, needs less number of updating parameters. The efficiency of the optimization process is thus enhanced. The proposed method is suitable for the identification of multiple irregular cracks and performs well in capturing the global features of the structural damage. After the global features are identified, a refinement process proposed in the paper can be carried out to improve the performance of the MRA of the updating information. The effectiveness of the method is verified by numerical simulations of a box girder and the experiment of a three-span continues pre-stressed concrete bridge. It is shown that the proposed method corresponds well to the global features of the structural damage and is stable against the perturbation of modal parameters and small variations of the damage.

Key Words
model updating; multi-resolution analysis; damage identification and second generation wavelet

Address
Xin Zhang, Danying Gao, Yang Liu: Zhengzhou University, Zhengzhou, P.R. China
Xiuli Du: Beijing University of Technology, Beijing, P.R. China

Abstract
Acoustic emission analysis is an effective technique for monitoring the evolution of damage in a structure. An experimental analysis on a set of reinforced concrete beams under flexural loading was carried out. A mixed AE analysis method which used both parameter-based and signal-based techniques was presented to characterize and identify different failure mechanisms of damage, where the signal-based analysis was performed by using the Hilbert-Huang transform. The maximum instantaneous energy of typical damage events and the corresponding frequency characteristics were established, which provided a quantitative assessment of reinforced concrete beam using AE technique. In the bending tests, a \"pitch-catch\" system was mounted on a steel bar to assess bonding state of the steel bar in concrete. To better understand the AE behavior of bond-slip damage between steel bar and concrete, a special bond-slip test called pullout test was also performed. The results provided the basis of quantitative AE to identify both failure mechanisms and level of damages of civil engineering structures.

Key Words
acoustic emission; reinforced concrete beam; four-point bending; Hilbert-Huang transform; bond-slip damage

Address
Aijun Gu: Key Laboratory for Mechanical Structure Damage Detection Technology, P.O. Box 84, Jiangsu University, Zhenjiang, China;
Faculty of Civil Engineering and Mechanics, Jiangsu University, Zhenjiang, China;
School of Hydraulic, Energy and Power Engineering, Yangzhou University, Yangzhou, China
Ying Luo: Key Laboratory for Mechanical Structure Damage Detection Technology, P.O. Box 84, Jiangsu University, Zhenjiang, China;
Faculty of Civil Engineering and Mechanics, Jiangsu University, Zhenjiang, China;
Baiqiang Xu: Faculty of Science, Jiangsu University, Zhenjiang, China

Abstract
This paper presents nonlinear analysis of an arbitrary functionally graded circular plate integrated with two functionally graded piezoelectric layers resting on the Winkler-Pasternak foundation. Geometric nonlinearity is considered in the strain-displacement relation based on the Von-Karman assumption. All the mechanical and electrical properties except Poisson\'s ratio can vary continuously along the thickness of the plate based on a power function. Electric potential is assumed as a quadratic function along the thickness direction. After derivation of general nonlinear equations, as an instance, numerical results of a functionally graded material integrated with functionally graded piezoelectric material obeying two different functionalities is investigated. The effect of different parameters such as parameters of foundation, non homogenous index and boundary conditions can be investigated on the mechanical and electrical results of the system. A comprehensive comparison between linear and nonlinear responses of the system presents necessity of this study. Furthermore, the obtained results can be validated by using previous linear and nonlinear analyses after removing the effect of foundation.

Key Words
Winkler-Pasternak foundation; nonlinear responses; functionally graded material; piezoelectric; circular plate

Address
Mohammad Arefi: 1Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan,
Kashan 87317-51167, Iran
M.N.M. Allam: Mathematics Department, Faculty of Science, Mansoura University, Mansoura 35516, Egypt

Abstract
In this paper, it is aimed to investigate the restoration effect on the structural behavior of masonry arch bridges. Dandalaz masonry arch bridge located on the 4km east of Karacasu town of Aydin, Turkey is selected as a numerical example. The construction year of the bridge is not fully known, but the bridge is dated back to 15th century. Considering the current situation, it can be easily seen that the structural elements such as arch, side walls and timber blocks are heavily damaged and the bridge is unserviceable. Firstly finite element model of the bridge is constituted to reflect the current situation (before restoration) using building survey drawings. After, restoration project is explained and finite element model is reconstituted (after restoration). The structural responses of the bridge are obtained before and after restoration under dead load, live load and dynamic earthquake loads. For both conditions, maximum displacements, maximum-minimum principal stresses and maximum-minimum elastic strains are given with detail using contours diagrams and compared with each other to determine the restoration effect. From the study, it can be seen that the maximum internal forces are consisted under dynamic loads before and after restoration. Also, the restoration projects and studies have important and positive effects on the structural response of the bridge to transfer these structures to future.

Key Words
dynamic earthquake loads; finite element model; masonry arch bridge; structural response; restoration effect

Address
A.C. Altunisik, A. Bayraktar and A.F. Genc: Department of Civil Engineering, Karadeniz Technical University, Trabzon, Turkey

Abstract
The magneto-rheological visco-elastomer (MRVE) is used as a smart core to control the stochastic micro-vibration of a sandwich plate with supported mass. The micro-vibration response of the sandwich plate with MRVE core and supported mass under stochastic support motion excitations is studied and compared to evaluate the vibration suppression capability. The effects of the supported mass and localized magnetic field on the stochastic micro-vibration response of the MRVE sandwich plate are taken into account. The dynamic characteristics of the MRVE core in micro-vibration are described by a non-homogeneous complex modulus dependent on vibration frequency and controllable by applied magnetic fields. The partial differential equations for the coupled transverse and longitudinal motions of the MRVE sandwich plate with supported mass are derived from the dynamic equilibrium, constitutive and geometric relations. The simplified ordinary differential equations are obtained for the transverse vibration of the MRVE sandwich plate under localized magnetic fields. A frequency-domain solution method for the stochastic micro-vibration response of sandwich plates with supported mass is developed based on the Galerkin method and random vibration theory. The expressions of frequency-response functions, response power spectral densities and root-mean-square velocity responses of the plate in terms of the one-third octave frequency band are obtained for micro-vibration evaluation. Finally, numerical results are given to illustrate the large response reduction capacity of the MRVE sandwich plate with supported mass under stochastic support motion excitations, and the influences of MRVE parameters, supported mass and localized magnetic field placement on the micro-vibration response.

Key Words
micro-vibration; stochastic excitation; sandwich plate; magneto-rheological visco-elastomer; root-mean-square velocity response

Address
Z.G. Ying: Department of Mechanics, School of Aeronautics and Astronautics, Zhejiang University, Hangzhou 310027, P.R. China
Y.Q. Ni: Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
Y.F. Duan: Department of Civil Engineering, College of Civil Engineering and Architecture, Zhejiang University,
Hangzhou 310058, P.R. China


Abstract
This research investigates the structural health monitoring of nonlinear structures after a major seismic event. It considers the identification of flag-shaped or pinched hysteresis behavior in response to structures as a more general case of a normal hysteresis curve without pinching. The method is based on the overall least squares methods and the log likelihood ratio test. In particular, the structural response is divided into different loading and unloading sub-half cycles. The overall least squares analysis is first implemented to obtain the minimum residual mean square estimates of structural parameters for each sub-half cycle with the number of segments assumed. The log likelihood ratio test is used to assess the likelihood of these nonlinear segments being true representations in the presence of noise and model error. The resulting regression coefficients for identified segmented regression models are finally used to obtain stiffness, yielding deformation and energy dissipation parameters. The performance of the method is illustrated using a single degree of freedom system and a suite of 20 earthquake records. RMS noise of 5%, 10%, 15% and 20% is added to the response data to assess the robustness of the identification routine. The proposed method is computationally efficient and accurate in identifying the damage parameters within 10% average of the known values even with 20% added noise. The method requires no user input and could thus be automated and performed in real-time for each sub-half cycle, with results available effectively immediately after an event as well as during an event, if required.

Key Words
structural health monitoring; flag-shaped hysteresis system; structural parameter identification; least squares; log likelihood ratio; seismic response; system identification; SHM

Address
Cong Zhou, J. Geoffrey Chase, Geoffrey W. Rodgers and Hamish Tomlinson: Department of Mechanical Engineering, University of Canterbury, Christchurch, New Zealand
Chao Xu : School of Astronautics, Northwestern Polytechnical University, Xian, China



Abstract
Shape memory alloy (SMA) helical springs have found a large number of different applications in industries including biomedical devices and actuators. According to the application of SMA springs in different actuators, they are usually under tension and torsion loadings. The ability of SMAs in recovering inelastic strains is due to martensitic phase transformation between austenite and martensite phases. Stress or temperature induced martensite transformation induced of SMAs is a remarkable property which makes SMA springs more superior in comparison with traditional springs. The present paper deals with the simulation of SMA helical spring at room temperature. Three-dimensional phenomenological constitutive model is used to describe superelastic behavior of helical spring. This constitutive model is implemented as a user subroutine through ABAQUS STANDARD (UMAT), and the process of the implementation is presented. Numerical results show that the developed constitutive model provides an appropriate approach to captures the general behavior of SMA helical springs.

Key Words
shape memory alloy; helical spring; martensite transformation; constitutive model; finite element method

Address
Reza Mehrabi: Department of Mechanical Engineering, Vali-e-Asr University of Rafsanjan, Rafsanjan, 77139-36417, Iran
Mohammad Reza Karamooz Ravari: Department of Mechanical Engineering, Graduate University of Advanced Technology,
Kerman, 76311-33131, Iran


Abstract
This paper presents nonlinear analysis of a functionally graded square plate integrated with two functionally graded piezoelectric layers resting on the Winkler-Pasternak foundation. Geometric nonlinearity was considered in the strain-displacement relation based on the Von-Karman assumption. All the mechanical and electrical properties except Poisson\'s ratio can vary continuously along the thickness of the plate based on a power function. Electric potential was assumed as a quadratic function along the thickness direction and trigonometric function along the planar coordinate. The effect of non homogeneous index was investigated on the responses of the system. Furthermore, a comprehensive investigation has been performed for studying the effect of two parameters of assumed foundation on the mechanical and electrical components. A comparison between linear and nonlinear responses of the system presents necessity of this study.

Key Words
plate; Winkler-Pasternak foundation; nonlinear responses; functionally graded material; piezoelectric

Address
Mohammad Arefi: Department of Solid Mechanic, Faculty of Mechanical Engineering, University of Kashan,Kashan 87317-51167, Iran


Abstract
Early detection and precise location of leakage is of great importance for life-cycle maintenance and management of municipal pipeline system. In the past few years, acoustic emission (AE) techniques have demonstrated to be an excellent tool for on-line leakage detection. Regarding the multi-mode and frequency dispersion characteristics of AE signals propagating along a pipeline, the direct cross-correlation technique that assumes the constant AE propagation velocity does not perform well in practice for acoustic leak location. This paper presents an improved cross-correlation method based on wavelet transform, with due consideration of the frequency dispersion characteristics of AE wave and the contribution of different mode. Laboratory experiments conducted to simulate pipeline gas leakage and investigate the frequency spectrum signatures of AE leak signals. By comparing with the other methods for leak location identification, the feasibility and superiority of the proposed method are verified.

Key Words
acoustic emission; pipeline leak detection; cross-correlation analysis; wavelet transform; energy feature

Address
Suzhen Li: Department of Structural Engineering, Tongji University, Siping 1239, Shanghai 200092, China;
State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Siping 1239,
Shanghai 200092, China
Xinxin Wang and Ming Zhao: Department of Structural Engineering, Tongji University, Siping 1239, Shanghai 200092, China

Abstract
Wireless sensor networks (WSNs) have emerged as a novel solution to many of the challenges of structural health monitoring (SHM) in civil engineering structures. While research projects using WSNs are ongoing worldwide, implementations of WSNs on full-scale structures are limited. In this study, a WSN is deployed on a full-scale 17.3m-long, 11-bay highway sign support structure to investigate the ability to use vibration response data to detect damage induced in the structure. A multi-level damage detection strategy is employed for this structure: the Angle-between-String-and-Horizon (ASH) flexibility-based algorithm as the Level I and the Axial Strain (AS) flexibility-based algorithm as the Level II. For the proposed multi-level damage detection strategy, a coarse resolution Level I damage detection will be conducted first to detect the damaged region(s). Subsequently, a fine resolution Level II damage detection will be conducted in the damaged region(s) to locate the damaged element(s). Several damage cases are created on the full-scale highway sign support structure to validate the multi-level detection strategy. The multi-level damage detection strategy is shown to be successful in detecting damage in the structure in these cases.

Key Words
multi-level damage detection; full scale structure; wireless sensor network

Address
Zhuoxiong Sun and Sriram Krishnan: School of Mechanical Engineering, Purdue University, USA
Greg Hackmann and Chenyang Lu: Department of Computer Science and Engineering, Washington University in St. Louis, USA
Guirong Yan: Department of Civil Engineering, University of Texas at El Paso, USA
Shirley J. Dyke: School of Mechanical Engineering, Purdue University, USA;
School of Civil Engineering, Purdue University, USA
Ayhan Irfanoglu: School of Civil Engineering, Purdue University, USA

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