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CONTENTS
Volume 73, Number 4, February25 2020
 

Abstract
In recent railway projects where the railway connects between cities, newly planned tunnels are often located close to, or beneath an existing tunnel. Many claims and petitions have voiced public concern about the vibration and noise resulting from the situation. Vibrations and noises are engineering issues as well as environmental problems, and have become more important as people have become more concerned with their the quality of life. However, it is unlikely that the effects of vibration in situations where trains simultaneously pass a multileveled tunnel crossing have been appropriately considered in the phase of planning and design. This study investigates the superposition characteristic of ground-born vibrations from a multileveled tunnel crossing. The results from model tests and numerical analysis show that the ground-born vibration can be amplified by a maximum of about 30% compared to that resulting from the existing single tunnel. Numerical parametric study has also shown that the vibration amplification effect increases as the ground stiffness, the tunnel depth, and the distance between tunnels decrease.

Key Words
train-induced vibration; tunnel crossing; vibration superposition; model test; numerical analysis

Address
Hoon-Ki Moon: Dasan consultants, Songi-ro 30-gil, Songpa-gu, Seoul 05800, Republic of Korea
ang-Hyun Kim and Jong-Ho Shin: Department of Civil Engineering, Konkuk University, 120 Neungdong-ro, Gwangjin-gu, Seoul 05029, Republic of Korea
Ho-Jong Kim: Disaster Prevention Research Division, National Disaster Management Research Institute, Ulsan, Republic of Korea

Abstract
Study on the inelastic response of bare and masonry infilled Reinforced Concrete (RC) frames repaired using Carbon Fibre Reinforced Polymers (CFRP) and Glass Fiber Reinforced Polymers (GFRP) subjected to quasi- static loading is presented in the work. The hysteresis behaviour, stiffness retention, energy dissipation and damage index are the parameters employed to analyze the efficacy of FRP strengthening of bare and brick in-filled RC frames. It is observed that there is a significant improvement in load carrying capacity of brick infilled frame over bare RC frame. Also FRP strengthened brick infilled frame performs much better than FRP repaired bare frame under quasi static loading. Repair and retrofitting of brick infilled RC frame shows an improved load carrying and damage tolerance capacity than control frame.

Key Words
retrofitting; RC frame; brick infill; damage index; GFRP; CFRP; FRF

Address
Department of Civil Engineering, Thapar University, Patiala, Punjab, India-147004

Abstract
In this study size optimization of large-scale dome structures with dynamic constraints is presented. In the optimal design of these structure, the Jaya algorithm is used to find minimal size of design variables. The design variables are the cross-sectional areas of the steel truss bar elements. To take into account the constraints which are the first five natural frequencies of the structures, the finite element analysis is coded in Matlab programs using eigen values of the stiffness matrix of the dome structures. The Jaya algorithm and the finite elements codes are combined by the help of the Matlab - GUI (Graphical User Interface) programming to carry out the optimization process for the dome structures. To show the efficiency and the advances of the Jaya algorithm, 1180 bar dome structure and the 1410 bar dome structure were tested by taking into the frequency constraints. The optimal results obtained by the proposed algorithm are compared with those given in the literature to demonstrate the performance of the Jaya algorithm. At the end of the study, it is concluded that the proposed algorithm can be effectively used in the optimal design of large-scale dome structures.

Key Words
Jaya; optimization; finite element analysis; dynamic analysis; dome structure; large-scale structure

Address
Tayfun Dede: Karadeniz Technical University, Department of Civil Engineering, Trabzon, Turkey
Maksym Grzywiński and Jacek Selejdak: Czestochowa University of Technology, Faculty of Civil Engineering, 42200 Czestochowa, Poland

Abstract
In this present paper, a semi-analytical mesh-free method is employed for the three-dimensional free vibration analysis of a bi-directional functionally graded piezoelectric circular structure. The dependent variables have been expanded by Fourier series with respect to the circumferential direction and have been discretized through radial and axial directions based on the mesh-free shape function. The current approach has a distinct advantage. The nonlinear Green-Lagrange strain is employed as the relationship between strain and displacement fields to observe thermal impacts in stiffness matrices. Nevertheless, high order terms have been neglected at the final steps of equations driving. The material properties are assumed to vary continuously in both radial and axial directions simultaneously in accordance with a power law distribution. The convergence and validation studies are conducted by comparing our proposed solution with available published results to investigate the accuracy and efficiency of our approach. After the validation study, a parametric study is undertaken to investigate the temperature effects, different types of polarization, mechanical and electric boundary conditions and geometry parameters of structures on the natural frequencies of functionally graded piezoelectric circular structures.

Key Words
3D free vibration; functionally graded piezoelectric circular structures; nonlinear Green-Lagrange strain; mesh-free method; semi-analytical method

Address
Mahnaz Shamshirsaz, Shahin Sharafi, Javad Rahmatian, Sajad Rahmatian and Naserodin Sepehry: New Technologies Research Center, Amirkabir University of Technology, 424 Hafez Ave, 15875-4413, Tehran, Islamic Republic of Iran
Javad Rahmatian: Department of Mechanical Engineering, Razi University of Kermanshah, Tagh Bostan, 67144-15111, Kermanshah, Islamic Republic of Iran
Sajad Rahmatian: Department of Mechanical Engineering, University of Tehran, 16th Azar St., Enghelab Sq, 1417466191, Tehran, Islamic Republic of Iran
Naserodin Sepehry: Faculty of Mechanical and Mechatronics Engineering, Shahrood University of Technology, Shahrood, 3619995161, Islamic Republic of Iran

Abstract
The use of final IGS precise orbit and clock products for high-rate GNSS-PPP proved its effectiveness in capturing dynamic displacement of engineering structures caused by earthquakes. However, the main drawback of using the final products is that they are available after approximately two weeks of data collection, which is not suitable for timely measures after an event. In this study, the use of ultra-rapid products (observed part), which are available after a few hours of data collection, and rapid products, which are available in less than 24 hrs, are investigated and their results are compared to the more precise final products. The tests are designed such that harmonic oscillations with different frequencies and amplitudes and ground motion of a simulated real earthquake are generated using a single axis shake table and the PPP was used to capture these movements by monitoring timechange of the table positions. To evaluate the accuracy of PPP using ultra-rapid, rapid and final products, their results were compared with relative GNSS positioning and LVDT (Linear Variable Differential Transformer) data, treated as reference. The results show that the high-rate GNSS-PPP solutions based on the three products can capture frequencies of harmonic oscillations and dynamic displacement with good accuracy. There were slight differences between ultra-rapid, rapid and final products, where some of the tested events indicated that the latter two produced are more accurate and provide better results compared to the ultrarapid product for monitoring short-term dynamic displacements.

Key Words
PPP; high-rate GNSS; structural health monitoring; seismo-geodesy; shake table; precise satellite products

Address
Cemal O. Yigit, Ahmed El-Mowafy: School of Earth and Planetary Sciences, Curtin University, GPO Box U 1987, Perth, WA, Australia
Mert Bezcioglu: Department of Geomatics Engineering, Gebze Technical University, 41400, Gebze, Turkey
Ahmet A. Dindar: Department of Civil Engineering, Gebze Technical University, 41400, Gebze, Turkey

Abstract
The microstructure and mechanical properties of concrete will degrade significantly at high temperatures, thus affecting the bond strength between reinforcing steel and surrounding concrete in reinforced concrete members. In this study, the effect of individual and hybrid fiber on the local bond–slip behavior of lightweight aggregate concrete (LWAC) after exposure to elevated temperatures was experimentally investigated. Tests were conducted on local pullout specimens (150 mm cubes) with a reinforcing bar embedded in the center section. The embedment lengths of the pullout specimens were 4.2 times the bar diameter. The parameters investigated included concrete type (control group: ordinary LWAC; experimental group: fiber reinforced LWAC), concrete strength, fiber type, and targeted temperature. The test results showed that for medium-strength LWACs exposed to high temperatures, the use of only steel fibers did not significantly increase the residual bond strength. Moreover, the addition of individual and hybrid fiber had little effect on the residual bond strength of the high-strength LWAC after exposure to a temperature of 800°C.

Key Words
fiber reinforced lightweight aggregate concrete, residual bond strength, pullout test

Address
1Department of Civil Engineering & Geomatics, Cheng Shiu University, No. 840, Chengching Rd.,
Niaosong District, Kaohsiung City, Taiwan R.O.C.
2Center for Environmental Toxin and Emerging-Contaminant Research, Cheng Shiu University, No. 840,
Chengching Rd., Niaosong District, Kaohsiung 83347, Taiwan
3Super Micro Mass Research & Technology Center, Cheng Shiu University, No. 840, Chengching Rd.,
Niaosong District, Kaohsiung 83347, Taiwan

Abstract
Seismic isolation technology has a wide application to protect bridges from earthquake damage, a new designed bridge pier with seismic isolation are provided for railways in seismic regions of China. The pier with rocking isolation is a self-centering system under small and moderate earthquakes, and the unbonded prestressed tendons are used to prevent overturning under strong earthquakes. A numerical model based on pseudo-static testing results is presented to evaluate the seismic performance of isolation bridge piers, and is validated by the shaking table test. It is found that the rocking response and the loss of prestressing for the bridge pier increase with the increase of earthquake intensity. Besides, the intensity and spectral characteristics of input ground motion have great influence on displacement of the top and bottom of the bridge pier, while have less influence on the bending moment of the pier bottom. Experimental and numerical results show that the rocking-isolated piers presented in this study have good seismic performance, and it provides an alternative way for the railway bridge in the regions with high occurrence of earthquakes. Therefore, we provide the detailed procedures for seismic design of the rocking-isolated bridge pier, and a case study of the seismic isolation design with rocking piers is carried out to popularize the seismic isolation methods.

Key Words
railway bridges; seismic isolation with rocking pier; prestressed tendon; shaking table test; numerical simulation; seismic performance and design

Address
School of Civil Engineering, Lanzhou Jiaotong University, Lanzhou 730070, China

Abstract
The hybrid method using the extended finite element method (XFEM) and the forward Euler approach is widely employed to predict the fatigue life of plate structures. Due to the accuracy of the forward Euler approach is determined by a small step size, the performance of fatigue life prediction of the hybrid method is not agreeable. Instead the forward Euler approach, a prediction method using midpoint method and support vector regression (SVR) is presented to evaluate the stress intensity factors (SIFs) and the fatigue life. Firstly, the XFEM is employed to calculate the SIFs with given crack sizes. Then use the history of SIFs as a function of either number of fatigue life cycles or crack sizes within the current cycle to build a prediction model. Finally, according to the prediction model predict the SIFs at different crack sizes or different cycles. Three numerical cases composed by a homogeneous plate with edge crack, a composite plate with edge crack and center crack are introduced to verify the performance of the proposed method. The results show that the proposed method enables large step sizes without sacrificing accuracy. The method is expected to predict the fatigue life of complex structures.

Key Words
XFEM; support vector regression; stress intensity factor; crack growth rate; fatigue life prediction

Address
Zhansi Jiang: School of Mechanical and Electrical Engineering, Guilin University of Electronic Technology, Guilin, 541004, China
Jiawei Xiang: College of Mechanical & Electrical Engineering, Wenzhou University, Wenzhou, 325035, China

Abstract
This paper is aimed to address a simultaneous optimization of the size, shape, and topology of steel lattice towers through a combination of the radial basis function (RBF) neural networks and the artificial bee colony (ABC) metaheuristic algorithm to reduce the computational time because mere metaheuristic optimization algorithms require much time for calculations. To verify the results, use has been made of the CIGRÉ Tower and a 132 kV transmission towers as numerical examples both based on the design requirements of the ASCE10-97, and the size, shape, and topology have been optimized (in both cases) once by the RBF neural network and once by the MSTOWER analyzer. A comparison of the results shows that the neural network-based method has been able to yield acceptable results through much less computational time.

Key Words
optimization; power transmission towers; steel lattice towers; RBF neural network; artificial bee colony (ABC) algorithm

Address
Faezeh Taheri, Mohammad Reza Ghasemi: Department of Civil Engineering, University of Sistan and Baluchestan, Zahedan, Iran
Babak Dizangian: Department of Civil Engineering, Velayat University, Iranshahr, Iran


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