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CONTENTS
Volume 18, Number 1, January 2020
 

Abstract
The vehicle-bridge interaction (VBI) analysis might be cumbersome and computationally expensive in bridge engineering due to the necessity of solving large number of coupled system of equations. However, VBI analysis can provide valuable insights into the dynamic behavior of highway bridges under specific loading conditions. Hence, this paper presents a numerical study on the dynamic behavior of a conventional highway bridge under strong near-field and far-field earthquake motions considering the VBI effects. A recursive substructuring method, which enables solving bridge and vehicle equations of motion separately and suitable to be adapted to general purpose finite element softwares, was used. A thorough analysis that provides valuable information about the effect of various traffic conditions, vehicle velocity, road roughness and effect of soil conditions under far-field and near-field strong earthquake motions has been presented. A real-life concrete highway bridge was chosen for numerical demonstrations. In addition, sprung mass models of vehicles consist of conventional truck and car models were created using physical and dynamic properties adopted from literature. Various scenarios, of which the results may help to highlight the different aspects of the dynamic response of concrete highway bridges under strong earthquakes, have been considered.

Key Words
vehicle-bridge interaction; recursive solution of coupled equation; far-field near-field earthquake motion; highway bridges; sprung-mass vehicle models

Address
Yildirim S. Erdogan: Yildiz Technical University, Civil Engineering Department, Istanbul, Turkey
Necati F. Catbas: Department of Civil, Environmental and Construction Engineering, University of Central Florida, Orlando, United States

Abstract
The seismic behaviour of reinforced concrete (RC) columns made from high-strength materials was investigated experimentally. Six high-strength concrete specimen columns (1:4 scale), which included three with high-strength stirrups (HSSs) and three with normal-strength stirrups (NSSs), were tested under a combination of high axial and reversed cyclic loads. The effects of stirrup strength and the ratio of transverse reinforcement on the cracking patterns, hysteretic response, strength, stiffness, ductility, energy dissipation and strain of transverse reinforcement were studied. The results indicate that good seismic behaviour of an RC column subjected to high axial compression can be obtained by using a well-shaped stirrup. Stirrup strength had little effect on the lateral bearing capacity. However, the ductility was significantly modified by improving the stirrup strength. When loaded with a large lateral displacement, the strength reduction of NSS specimens was more severe than that of those with HSSs, and increasing the stirrup strength had little effect on the stiffness reduction. The ductility and energy dissipation of specimens with HSSs were superior to those with NSSs. When the ultimate displacement was reached, the core concrete could be effectively restrained by HSSs.

Key Words
RC column; high-strength stirrups; seismic behaviour; high compression ratio; ductility

Address
Peng Wang,Qingxuan Shi. Qiuwei Wang: State Key Laboratory of Green Building in Western China, Xi\'an University of Architecture & Technology, Xi\'an 710055, China
Peng Wang, Qingxuan Shi, Feng Wang and Qiuwei Wang: College of Civil Engineering, Xi\'an University of Architecture & Technology, Xi\'an 710055, China
Peng Wang, Qingxuan Shi and Qiuwei Wang: Structure and Seismic Key Laboratory, Xi\'an University of Architecture & Technology, Xi\'an 710055, China

Abstract
This work presents a comparison of three performance-based seismic design methods (PBSD) as applied to plane steel frames having eccentric braces (EBFs) and buckling restrained braces (BRBFs). The first method uses equivalent modal damping ratios (�k)referring to an equivalent multi-degree-of-freedom (MDOF) linear system, which retains the mass, the elastic stiffness and responds in the same way as the original non-linear MDOF system. The second method employs modal strength reduction factors (�𝑘) resulting from the corresponding modal damping ratios. Contrary to the behavior factors of code based design methods, both �k and �k account for the first few modes of significance and incorporate target deformation metrics like inter-storey drift ratio (IDR) and local ductility as well as structural characteristics like structural natural period, and soil types. Explicit empirical expressions of �k and �k, recently presented by the present authors elsewhere, are also provided here for reasons of completeness and easy reference. The third method, developed here by the authors, is based on a hybrid force/displacement (HFD) seismic design scheme, since it combines the force-base design (FBD) method with the displacement-based design (DBD) method. According to this method, seismic design is accomplished by using a behavior factor (qh), empirically expressed in terms of the global ductility of the frame, which takes into account both non-structural and structural deformation metrics. These expressions for qh are obtained through extensive parametric studies involving non-linear dynamic analysis (NLDA) of 98 frames, subjected to 100 far-fault ground motions that correspond to four soil types of Eurocode 8. Furthermore, these factors can be used in conjunction with an elastic acceleration design spectrum for seismic design purposes. Finally, a comparison among the above three seismic design methods and the Eurocode 8 method is conducted with the aid of non-linear dynamic analyses via representative numerical examples, involving plane steel EBFs and BRBFs.

Key Words


Address
Nicos A. Kalapodis:Department of Engineering Science, University of Greenwich, Central Avenue, ME4 4TB Chatham, U.K.
George A. Papagiannopoulos:School of Science and Technology, Hellenic Open University, 26335 Patras, Greece
Dimitri E. Beskos:Department of Disaster Mitigation for Structures, College of Civil Engineering, Tongji University, Shanghai 200092, PR China
Dimitri E. Beskos:Department of Civil Engineering, University of Patras, 26054 Patras, Greece

Abstract
The application of critical excitation method with displacement-based objective function for multi degree of freedom (MDOF) systems is investigated. To this end, a new critical excitation method is developed to find the critical input motion of a MDOF system as a synthetic accelerogram. The upper bound of earthquake input energy per unit mass is considered as a new constraint for the problem, and its advantages are discussed. Considering this constraint, the critical excitation method is then used to generate synthetic accelerograms for MDOF models corresponding to three shear buildings of 10, 16, and 22 stories. In order to demonstrate the reliability of generated accelerograms to estimate dynamic response of the structures, three target ground motions with considerable level of energy contents are selected to represent \"real critical excitation\" of each model, and the method is used to re-generate these ground motions. Afterwards, linear dynamic analyses are conducted using these accelerograms along with the generated critical excitations, to investigate the key parameters of response including maximum displacement, maximum interstory drift, and maximum absolute acceleration of stories. The results show that the generated critical excitations can make an acceptable estimate of the structural behavior compared to the target ground motions. Therefore, the method can be reliably implemented to generate critical excitation of the structure when real one is not available.

Key Words
critical excitation; non-stationary random process; total input energy per unit mass; synthetic accelerograms; energy constraint

Address
Arsalan Bazrafshan: Faculty of Civil and Environmental Engineering, Tarbiat Modares University, P.O. Box 14115–397, Tehran, Iran
Naser Khaji: Department of Civil and Environmental Engineering, Graduate School of Engineering, Hiroshima University, 1-4-1, Kagamiyama,
Higashi-Hiroshima, Hiroshima 739-8527, Japan

Abstract
This paper presents the results of a monodirectional shaking table test on a full-scale unreinforced masonry cross vault characterized by asymmetric boundary conditions. The specimen represents a vault of the mosque of Dey in Algiers (Algeria), reproducing in detail the mechanical characteristics of masonry, and the constructive details including the presence of some peculiar wooden logs placed within the vault\'s configurations were studied by using an incremental dynamic analysis up to the collapse of the vault without the steel bars. The use of an innovative high-resolution 3D optical system allowed measure displacement data of the cross vault during the shake table tests. The experimental results were analysed in terms of evolution of damage mechanisms, and in-plane and out-of-plane deformations. Moreover, the dynamic properties of the structure were investigated by means of an experimental modal analysis.

Key Words
masonry cross vault; seismic response; shaking table; collapse mechanism; modal analysis

Address
Michela Rossi,Chiara Calderini,Sergio Lagomarsino:Department of Civil, Chemical and Environmental Engineering, University of Genoa, Via Montallegro 1, 16145 Genova
Ivan Roselli,Marialuisa Mongelli,Gerardo De Canio: 2ENEA – Italian National Agency for New Technologies, Energy and Sustainable Economic DevelopmentVia Anguillarese 301, 00123, Rome, Italy


Abstract
With the coal mining depth increasing, both stress and gas pressure rapidly enhance, causing coal and gas outburst risk to become more complex and severe. The conventional method for prediction of coal and gas outburst adopts one prediction index and corresponding critical value to forecast and cannot reflect all the factors impacting coal and gas outburst, thus it is characteristic of false and missing forecasts and poor accuracy. For the reason, based on analyses of both the prediction indicators and the factors impacting coal and gas outburst at the test site, this work carefully selected 6 prediction indicators such as the index of gas desorption from drill cuttings delta-h2, the amount of drill cuttings S, gas content W, the gas initial diffusion velocity index delta-P, the intensity of electromagnetic radiation E and its number of pulse N, constructed the Bayes discriminant analysis (BDA) index system, studied the BDA-based multi-index comprehensive model for forecast of coal and gas outburst risk, and used the established discriminant model to conduct coal and gas outburst prediction. Results showed that the BDA -based multi-index comprehensive model for prediction of coal and gas outburst has an 100% of prediction accuracy, without wrong and omitted predictions, can also accurately forecast the outburst risk even for the low indicators outburst. The prediction method set up by this study has a broad application prospect in the prediction of coal and gas outburst risk.

Key Words
coal and gas outburst; prediction; working face; Bayes discriminant analysis

Address
Liang Chen, Liang Yu, Jiangwei Fu: School of Energy & Environment Engineering, Zhongyuan University of Technology, 450007 Zhengzhou, Henan, China
Liang Chen: State Key Laboratory Cultivation Base for Gas Geology and Gas Control, Henan Polytechnic University, 454000 Jiaozuo, Henan, China
Jianchun Ou: State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, 221116 Xuzhou, Jiangsu, China
Yinbo Zhou: School of Safety Engineering, Henan University of Engineering, 451191 Zhengzhou Henan, China
Fei Wang:School of Mechanics and Safety Engineering, Zhengzhou University, 450001 Zhengzhou Henan, China

Abstract
The main structural elements of historical masonry arch bridges are arches, spandrel walls, piers and foundations. The most vulnerable structural elements of masonry arch bridges under transverse seismic loads, particularly in the case of out-of-plane actions, are spandrel wall. The vulnerability of spandrel walls under transverse loads increases with the increasing of their length and height. This paper computationally investigates the out-of-plane nonlinear seismic response of spandrel walls of long-span and high masonry stone arch bridges. The Malabadi Bridge with a main arch span of 40.86m and rise of 23.45m built in 1147 in DiyarbakIr,Turkey, is selected as an example. The Concrete Damage Plasticity (CDP) material model adjusted to masonry structures, and cohesive interface interaction between the infill and the spandrel walls and the arch are considered in the 3D finite element model of the selected bridge. Firstly, mode shapes with and without cohesive interfaces are evaluated, and then out-of-plane seismic failure responses of the spandrel walls with and without the cohesive interfaces are determined and compared with respect to the displacements, strains and stresses.

Key Words
long-span masonry arch bridge; out-of-plane response; seismic failure; masonry spandrel wall; transverse behavior

Address
Alemdar Bayraktar:Department of Civil Engineering, Karadeniz Technical University, Turkey
Emin Hökelekli:Department of Civil Engineering, BartIn University, BartIn, Turkey
Meral Halifeoğlu:Department of Civil Engineering, Dicle University, DiyarbakIr, Turkey
Zülfikar Halifeoğlu: Senior Civil Engineering, Zülfikar Halifeoglu Company, DiyarbakIr, Turkey
Ashraf Ashour: University of Bradford, Bradford, West Yorkshire, U.K.

Abstract
Cylindrical steel tanks are important components of industrial facilities. Their safety becomes a crucial issue since any failure may cause catastrophic consequences. The aim of the paper is to show the results of comprehensive FEM numerical investigation focused on the response of cylindrical steel tanks under mining tremors and moderate earthquakes. The effects of different levels of liquid filling, the influence of non-uniform seismic excitation as well as the aspects of diagnosis of structural damage have been investigated. The results of the modal analysis indicate that the level of liquid filling is really essential in the structural analysis leading to considerable changes in the shapes of vibration modes with a substantial reduction in the natural frequencies when the level of liquid increases. The results of seismic and paraseismic analysis indicate that the filling the tank with liquid leads to the substantial increase in the structural response underground motions. It has also been observed that the peak structural response values under mining tremors and moderate earthquakes can be comparable to each other. Moreover, the consideration of spatial effects related to seismic wave propagation leads to a considerable decrease in the structural response under non-uniform seismic excitation. Finally, the analysis of damage diagnosis in steel tanks shows that different types of damage may induce changes in the free vibration modes and values of natural frequencies.

Key Words
cylindrical steel tanks; numerical analysis; mining tremors; moderate earthquakes; non-uniform excitation; damage diagnosis

Address
Gdansk University of Technology, Faculty of Civil and Environmental Engineering, ul. Narutowicza 11/12, 80-233 Gdansk, Poland

Abstract
In this study, the behavior of external beam-column joints reinforced by plain and deformed bars with non-seismic reinforcement details is investigated and compared. The beam-column joints represented in this study include a benchmark specimen by seismic details in accordance with ACI 318M-11 requirements and four other deficient specimens. The main defects of the non-seismic beam–column joints included use of plain bar, absence of transverse steel hoops, and the anchorage condition of longitudinal reinforcements. The experimental results indicate that using of plain bars in non-seismic beam-column joints has significantly affected the failure modes. The main failure mode of the non-seismic beam-column joints reinforced by deformed bars was the accumulation of shear cracks in the joint region, while the failure mode of the non-seismic beam-column joints reinforced by plain bars was deep cracks at the joint face and intersection of beam and column and there was only miner diagonal shear cracking at the joint region. In the other way, use of plain bars for reinforcing concrete can cause the behavior of the substructure to be controlled by slip of the beam longitudinal bars. The experimental results show that the ductility of non-seismic beam-column joints reinforced by plain bars has not decreased compared to the beam-column joints reinforced by deformed bars due to lack of mechanical interlock between plain bars and concrete. Also it can be seen a little increase in ductility of substructure due to existence of hooks at the end of the development length of the bars.

Key Words
external RC beam-column joints; plain bars; deformed bars

Address
Mahdi Adibi, Fatemeh Aliakbari:School of Civil Engineering, College of Engineering, University of Bojnord, Iran
Jalil Shafaei:Faculty of Civil Engineering, Shahrood university of technology, Iran

Abstract
Seismic resilience is a key feature for buildings that play a strategic role within the community. In this framework, not only the structural and non-structural elements damage but also the protracted structural dysfunction can contribute significantly to overall seismic damage and post-seismic crisis situations. Reduction of the residual and peak displacements and energy dissipation by replaceable elements are some effective aspects to pursue in order to enhance the resilience. Control systems able to adapt their response based on the nature of events, such as active or semi-active, can achieve the best results, but also require higher costs and their complexity jeopardizes their reliability; on the other hand, a passive control system is not able to adapt but its functioning is more reliable and characterized by lower costs. In this study it is proposed a strategy for the optimization of the dissipative capacity of a seismic resistant system obtained placing in parallel two different groups dissipative Re-Centering Devices, specifically designed to enhance the energy dissipation, one for the low and the other for the high intensity earthquakes. In this way the efficiency of the system in dissipating the seismic energy is kept less sensitive to the seismic intensity compared to the case of only one group of dissipative devices.

Key Words
seismic retrofit; passive control systems; optimization; energy dissipation; re-centering devices

Address
Ivan Panzera, Francesco Morelli and Walter Salvatore: Department of Civil and Industrial Engineering, University of Pisa, Largo Lucio Lazzarino 1, 56122 Pisa, Italy


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