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Volume 25, Number 5, May 2020

A new type of pure torsional yielding damper made from steel pipe is proposed and introduced. The damper uses a special mechanism to apply force and therefore applies pure torsion in the damper. Uniform distribution of the shear stress caused by pure torsion resulting in widespread yielding along pipe and consequently dissipating a large amount of energy. The behavior of the damper is investigated analytically and the governing relations are derived. To examine the performance of the proposed damper, four types of the damper are experimentally tested. The results of the tests show the behavior of the system as stable and satisfactory. The behavior characteristics include initial stiffness, yielding load, yielding deformation, and dissipated energy in a cycle of hysteretic behavior. The tests results were compared with the numerical analysis and the derived analytical relations outputs. The comparison shows an acceptable and precise approximation by the analytical outputs for estimation of the proposed damper behavior. Therefore, the relations may be applied to design the braced frame system equipped by the pure torsional yielding damper. An analytical model based on analytical relationships was developed and verified. This model can be used to simulate cyclic behavior of the proposed damper in the dynamic analysis of the structures equipped with the proposed damper. A numerical study was conducted on the performance of an assumed frame with/without proposed damper. Dynamic analysis of the assumed frames for seven earthquake records demonstrate that, equipping moment-resisting frames with the proposed dampers decreases the maximum story drift of these frames with an average reduction of about 50%.

Key Words
yielding damper; pure torsion; finite element method; pipe; dissipated energy

Department of Civil Engineering, Faculty of Civil Engineering & Transportation, University of Isfahan, Iran.

This paper demonstrates the possibility of evaluating the safety of a building right after an earthquake using consumergrade surveillance cameras installed in the building. Two cameras are used in each story to extract the time history of interstory drift during the earthquake based on camera calibration, stereo triangulation, and image template matching techniques. The interstory drift of several markers on the rigid floor are used to estimate the motion of the geometric center using the least square approach, then the horizontal interstory drift of any location on the floor can be estimated. A shaking table collapse test of a steel building was conducted to verify the proposed approach. The results indicate that the accuracy of the interstory drift measured by the cameras is high enough to estimate the damage state of the building based on the fragility curve of the interstory drift ratio. On the other hand, the interstory drift measured by an accelerometer tends to underestimate the damage state when residual interstory drift occurs because the low frequency content of the displacement signal is eliminated when high-pass filtering is employed for baseline correction.

Key Words
consumer-grade surveillance cameras; post-earthquake building safety evaluation; interstory drift

(1) Ting Y. Hsu:
Department of Civil and Construction Engineering, National Taiwan University of Science and Technology, Taipei 10607, Taiwan;
(2) Ting Y. Hsu, Quang V. Pham:
Taiwan Building Technology Center, National Taiwan University of Science and Technology, Taipei 10607, Taiwan;
(3) Wei C. Chao, Yuan S. Yang:
Taiwan Department of Civil Engineering, National Taipei University of Technology, Taipei 10608, Taiwan.

This paper presents a series of experimental and numerical investigations on a vertical isolation system with quasi-zero stiffness (QZS) property. The isolation system comprises a linear helical spring and disk spring. The disk spring is designed to provide variable stiffness to the system. Orthogonal static tests with different design parameters are conducted to verify the mathematical and mechanical models of the isolation system. The deviations between theoretical and test results influenced by the design parameters are summarized. Then, the dynamic tests for the systems with different under-load degrees are performed, including the fast sweeping tests, harmonic excitation tests, and half-sine impact tests. The displacement transmissibility, vibration reduction rate, and free vibration response are calculated. Based on the test results, the variation of the transmission rule is evaluated and the damping magnitudes and types are identified. In addition, the relevant numerical time history responses are calculated considering the nonlinear behavior of the system. The results indicate that the QZS isolation system has a satisfactory isolation effect, while a higher damping level can potentially promote the isolation performance in the low-frequency range. It is also proved that the numerical calculation method accurately predicts the transmission character of the isolation system.

Key Words
quasi-zero stiffness; static test; dynamic test; transfer function

State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, 200092 Yangpu District, Shanghai, China.

Vibration at the tip of various flexible manipulators may affect their operation accuracy and work efficiency. To suppress such vibrations, the feasibility of using MFC actuators and sensors is investigated in this paper. Considering the convergence of the famous filtered-x least mean square (FXLMS) algorithm could not be guaranteed while it is employed for vibration suppression of plants with varying secondary path, this paper proposes a new multiple model switching adaptive control algorithm to implement the real time active vibration suppression tests with a new multiple switching strategy. The new switching strategy is based on a cost function with reconstructed error signal and disturbance signal instead of the error signal from the error sensor. And from a robustness perspective, a new variable step-size sign algorithm (VSSA) based FXLMS algorithm is proposed to improve the convergence rate. A cantilever beam with varying tip mass is employed as flexible manipulator model. MFC layers are attached on both sides of it as sensors and actuators. A co-simulation platform was built using ADAMS and MATLAB to test the feasibility of the proposed algorithms. And an experimental platform was constructed to verify the effectiveness of MFC actuators and sensors and the real-time vibration control performance. Simulation and experiment results show that the proposed FXLMS algorithm based multiple model adaptive control approach has good convergence performance under varying load conditions for the flexible cantilever beam, and the proposed FX-VSSA-LMS algorithm based multiple model adaptive control algorithm has the best vibration suppression performance.

Key Words
active vibration control; MFC actuators and sensors; adaptive control; multiple model switching

School of Mechatronic Engineering and Automation, Shanghai University, No. 333 Nanchen Road, Shanghai, P.R. China.

The identification of delays and delay compensation are critical problems in real-time hybrid simulations (RTHS). Conventional delay compensation methods are mostly based on the assumption of a constant delay. However, the system delay may vary during tests owing to the nonlinearity of the loading system and/or the behavioral variations of the specimen. To address this issue, this study presents an adaptive delay compensation method based on a discrete model of the loading system. In particular, the parameters of this discrete model are identified and updated online with the least-squares method to represent a servo hydraulic loading system. Furthermore, based on this model, the system delays are compensated for by generating system commands using the desired displacements, achieved displacements, and previous displacement commands. This method is more general than the existing compensation methods because it can predict commands based on multiple displacement categories. Moreover, this method is straightforward and suitable for implementation on digital signal processing boards because it relies solely on the displacements rather than on velocity and/or acceleration data. The virtual and real RTHS results show that the studied method exhibits satisfactory estimation smoothness and compensation accuracy. Furthermore, considering the measurement noise, the low-order parameter models of this method are more favorable than that the high-order parameter models.

Key Words
real-time hybrid simulation; delay compensation; adaptive compensation; discrete model

(1) Zhen Wang, Bin Wu:
School of Civil Engineering and Architecture, Wuhan University of Technology, Wuhan 430070, China;
(2) Zhen Wang, Guoshan Xu, Qiang Li:
Key Lab of Structures Dynamic Behavior and Control of the Ministry of Education, Harbin Institute of Technology, Harbin 150090, China;
(3) Zhen Wang, Guoshan Xu, Qiang Li:
Key Lab of Smart Prevention and Mitigation of Civil Engineering Disasters of the Ministry of Industry and Information Technology, Harbin Institute of Technology, Harbin 150090, China;
(4) Zhen Wang, Guoshan Xu, Qiang Li:
School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China.

Magneto-rheological fluids and magneto-strictive materials are of the well-known smart materials which are used to control and reduce the vibrations of the structures. Vibration analysis of a smart annular three-layered plate is provided in this work. MR fluids are used as the core

Key Words
smart materials; magneto-rheological fluids; magneto-strictive materials; vibration analysis; annular plate; visco-pasternak foundation

(1) Saeed Amir, Ehsan Arshid:
Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, Kashan, Iran;
(2) Zahra Khoddami Maraghi:
Faculty of Engineering, Mahallat Institute of Higher Education, Mahallat, Iran.

Temperature may have more significant influences on structural responses than operational loads or structural damage. Therefore, a comprehensive understanding of temperature distributions has great significance for proper design and maintenance of bridges. In this study, the temperature distribution of the steel box girder is systematically investigated based on the structural health monitoring system (SHMS) of the Sutong Cable-stayed Bridge. Specifically, the characteristics of the temperature and temperature difference between different measurement points are studied based on field temperature measurements. Accordingly, the probability density distributions of the temperature and temperature difference are calculated statistically, which are further described by the general formulas. The results indicate that: (1) the temperature and temperature difference exhibit distinct seasonal characteristics and strong periodicity, and the temperature and temperature difference among different measurement points are strongly correlated, respectively; (2) the probability density of the temperature difference distribution presents strong non-Gaussian characteristics; (3) the probability density function of temperature can be described by the weighted sum of four Normal distributions. Meanwhile, the temperature difference can be described by the weighted sum of Weibull distribution and Normal distribution.

Key Words
temperature distribution; steel-box girder; filed monitoring data; cable-stayed bridge; temperature difference; probability density

(1) Hao Wang, Qingxin Zhu, Zhongqin Zou, Tianyou Tao:
Key Laboratory of C&PC Structures of Ministry of Education, Southeast University, Nanjing, China;
(2) Chenxi Xing:
School of Law, Southeast University, Nanjing, China;
(3) Dongming Feng:
Weidlinger Transportation Practice, Thornton Tomasetti, New York, USA.

The existence of damages in structures causes changes in the physical properties by reducing the modal parameters. In this paper, we develop a two-stages approach based on normalized Modal Strain Energy Damage Indicator (nMSEDI) for quick applications to predict the location of damage. A two-dimensional IsoGeometric Analysis (2D-IGA), Machine Learning Algorithm (MLA) and optimization techniques are combined to create a new tool. In the first stage, we introduce a modified damage identification technique based on frequencies using nMSEDI to locate the potential of damaged elements. In the second stage, after eliminating the healthy elements, the damage index values from nMSEDI are considered as input in the damage quantification algorithm. The hybrid of Teaching-Learning-Based Optimization (TLBO) with Artificial Neural Network (ANN) and Particle Swarm Optimization (PSO) are used along with nMSEDI. The objective of TLBO is to estimate the parameters of PSO-ANN to find a good training based on actual damage and estimated damage. The IGA model is updated using experimental results based on stiffness and mass matrix using the difference between calculated and measured frequencies as objective function. The feasibility and efficiency of nMSEDI-PSO-ANN after finding the best parameters by TLBO are demonstrated through the comparison with nMSEDI-IGA for different scenarios. The result of the analyses indicates that the proposed approach can be used to determine correctly the severity of damage in beam structures.

Key Words
IsoGeometric Analysis; damage identification; TLBO; PSO-ANN; dynamic analysis

(1) S. Khatir, C. Le Thanh, H. Tran-Ngoc:
Soete Laboratory, Faculty of Engineering and Architecture, Ghent University, Technologiepark Zwijnaarde 903, B-9052, Zwijnaarde, Belgium;
(2) T. Khatir:
Institute of Science and Technology, Naama University , Algeria;
(3) D. Boutchicha:
University of Science and Technology Oran, Algeria;
(4) C. Le Thanh:
Faculty of Civil Engineering, Open University, Ho Chi Minh City, Vietnam;
(5) H. Tran-Ngoc:
Department of Bridge and Tunnel Engineering, Faculty of Civil Engineering, University of Transport and Communications, Hanoi, Vietnam;
(6) T.Q. Bui:
Institute for Research and Development, Duy Tan University, Da Nang City, Vietnam;
(7) T.Q. Bui:
Tokyo Institute of Technology, Department of Civil and Environmental Engineering, Japan;
(8) R. Capozucca:
Universitá Politecnica delle Marche, Ancona, Italy;
(9) M. Abdel-Wahab:
Division of Computational Mechanics, Ton Duc Thang University, Ho Chi Minh City, Vietnam;
(10) M. Abdel-Wahab:
Faculty of Civil Engineering, Ton Duc Thang University, Ho Chi Minh City, Vietnam.

This paper studies nonlinear free vibration characteristics of nonlocal magneto-electro-elastic (MEE) nanobeams resting on nonlinear elastic substrate having geometrical imperfection by considering piezoelectric reinforcement scheme. The piezoelectric reinforcement can cause an enhanced vibration behavior of smart nanobeams under magnetic field. All of previously reported studies on MEE nanobeams ignore the influences of geometric imperfections which are very substantial due to the reason that a nanobeam cannot be always perfect. Nonlinear governing equations of a smart nanobeam are derived based on classical beam theory and an analytical trend is provided to obtained nonlinear vibration frequency. This research shows that changing the volume fraction of piezoelectric constituent in the material has a great influence on vibration behavior of smart nanobeam under electric and magnetic fields. Also, it can be seen that nonlinear vibration behaviors of smart nanobeam are dependent on the magnitude of exerted electric voltage, magnetic potential, hardening elastic foundation and geometrical imperfection.

Key Words
piezo-magnetic nanobeam; geometrical imperfection; free vibration; piezoelectric reinforcement

Al-Mustansiriah University, Engineering Collage, P.O. Box 46049, Bab-Muadum, Baghdad 10001, Iraq.

To meet the urgent requirements of safety surveillance from civil engineering management authorities, this study proposes a refined and efficient approach to generate full-field high-resolution panorama of construction sites using cameraamounted UAV (Unmanned Aerial Vehicle). GPS (Global Position System) information extraction for pre-registration, feature points filtering for efficient registration and optimal seaming line seeking for fusion are performed in sequence to form the full-field panorama generation framework. Advantages of the proposed method are as follows. First, GPS information can sort images for pre-registration, avoiding inefficient repeated pairwise calculations and matching. Second, the feature points are filtered according to the characteristics of the construction site images to reduce the amount of calculation. The proposed framework is validated on a road construction site and results demonstrate that it can generate an accurate and high-quality full-site panorama for the safety supervision in a much efficient manner.

Key Words
full-field panorama; UAV; GPS information; image registration; image stitching

(1) Yapeng Guo, Haowei Niu, Zhonglong Li, Shunlong Li:
School of Transportation Science and Engineering, Harbin Institute of Technology, 73 Huanghe Road, Harbin 150090, China;
(2) Yang Xu:
School of Civil Engineering, Harbin Institute of Technology, 73 Huanghe Road, Harbin 150090, China;
(3) Yuhui E., Xinghua Jiao:
Liaoning Transportation Development Center, 128 Shashan Road, Shenyang 110000, China.

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