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Abstract
Modern seismic codes rely on performance-based seismic design methodology which requires that the structures withstand inelastic deformation. Many studies have focused on the inelastic deformation ratio evaluation (ratio between the inelastic and elastic maximum lateral displacement demands) for various inelastic spectra. This paper investigates the inelastic response spectra through the ductility demand µ, the yield strength reduction factor Ry, and the inelastic deformation ratio. They depend on the vibration period T, the post-to-preyield stiffness ratio α, the peak ground acceleration (PGA), and the normalized yield strength coefficient η (ratio of yield strength coefficient divided by the PGA). A new inelastic deformation ratio Cη is defined; it is related to the capacity curve (pushover curve) through the coefficient (η) and the ratio (α) that are used as control parameters. A set of 140 real ground motions is selected. The structures are bilinear inelastic single degree of freedom systems (SDOF). The sensitivity of the resulting inelastic deformation ratio mean values is discussed for different levels of normalized yield strength coefficient. The influence of vibration period T, post-to-preyield stiffness ratio α, normalized yield strength coefficient η, earthquake magnitude, ruptures distance (i.e., to fault rupture) and site conditions is also investigated. A regression analysis leads to simplified expressions of this inelastic deformation ratio. These simplified equations estimate the inelastic deformation ratio for structures, which is a key parameter for design or evaluation. The results show that, for a given level of normalized yield strength coefficient, these inelastic displacement ratios become non sensitive to none of the rupture distance, the earthquake magnitude or the site class. Furthermore, they show that the post-to-preyield stiffness has a negligible effect on the inelastic deformation ratio if the normalized yield strength coefficient is greater than unity.

Key Words
deformation ratio; yield strength reduction factor; ductility; inelastic spectra; earthquakes; seismic response

Address
Benazouz Chikh, Nacer Laouami, Youcef Mehani, Abderrahmane Kibboua: National Earthquake Engineering Research Center, CGS, Rue Kaddour Rahim, BP 252 Hussein-Dey, Algiers, Algeria Ahmed Mebarki: University Paris-Est, Laboratoire Modelisation et Simulation Multi Echelle (MSME), UMR 8208 CNRS, 5 Bd Descartes, 77454 Marne-La-Vallee, France Moussa Leblouba: Department of Civil & Environmental Engineering, College of Engineering, University of Sharjah, P.O. Box 27272 Sharjah, United Arab Emirates Mohamed Hadid: National School of Built and Ground Works Engineering (ENSTP), 01 Rue SidiGaridi, Vieux Kouba 16003, Algiers, Algeria Djillali Benouar: University of Science & Technology HouariBoumediene (USTHB), Faculty of Civil Engineering, BP 32, 16111 El-Alia / Bab Ezzouar, Algiers, Algeria

Abstract
Oil storage tanks are vital life-line structures, suffered significant damages during past earthquakes. In this study, a numerical model for an unanchored vertical vaulted-type tank was established by ANSYS software, including the tank-liquid coupling, nonlinear uplift and slip effect between the tank bottom and foundation. Four actual earthquakes recorded at different soil sites were selected as input to study the dynamic characteristics of the tank by nonlinear time-history dynamic analysis, including the elephant-foot buckling, the liquid sloshing, the uplift and slip at the bottom. The results demonstrate that, obvious elephant-foot deformation and buckling failure occurred near the bottom of the tank wall under the seismic input of Class-I and Class-IV sites. The local buckling failure appeared at the location close to the elephant-foot because the axial compressive stress exceeded the allowable critical stress. Under the seismic input of Class-IV site, significant nonlinear uplift and slip occurred at the tank bottom. Large amplitude vertical sloshing with a long period occurred on the free surface of the liquid under the seismic wave record at Class-III site. The seismic properties of the storage tank were affected by site class and should be considered in the seismic design of large tanks. Effective measures should be taken to reduce the seismic response of storage tanks, and ensure the safety of tanks.

Key Words
storage tank; seismic response; tank-liquid coupling; site class; uplift; liquid sloshing

Address
Rulin Zhang, Xudong Cheng, Youhai Guan: College of Pipeline and Civil Engineering, China University of Petroleum (East China), Qingdao Shandong 266580, People´s Republic of China Alexander A. Tarasenko: Industrial University of Tyumen, 38 Volodarskogo st., Tyumen, 625000, Russia

Abstract
Seismic analysis of local site conditions is fundamental for a reliable site seismic hazard assessment. It plays a major role in mitigation of seismic damage potential through the prediction of surface ground motion in terms of amplitude, frequency content and duration. Such analysis requires the determination of the transfer function, which is a simple tool for characterizing a soil profile by estimating its vibration frequencies and its amplification potential. In this study, numerical simulations are carried out and are then combined with a statistical study to allow the characterization of design sites classified by the Algerian Building Seismic Code (RPA99, ver 2003), by average transfer functions. The mean transfer functions are thereafter used to compute RPA99 average site factors. In this regard, coming up seismic fields are simulated based on Power Spectral Density Functions (PSDF) defined at the rock basement. Results are also used to compute average site factor where, actual and synthetic time histories are introduced. In absence of measurement data, it is found that the proposed approach can be used for a better soil characterization.

Key Words
transfer function; simulation; RPA99; site factor; Power Spectral Density; random vibrations

Address
Mohamed Beneldjouzi: Water, environment, Geomaterials and structures laboratory (LEEGO), Faculty of Civil Engineering, University of Science and Technology Houari Boumediene, Algiers, 16111, Algeria Nasser Laouami and Abdennasser Slimani: Earthquake Engineering Applied Research Center (CGS), Rue Kaddour Rahim, Algiers, 16040, Algeria

Abstract
The focus of this paper is the study on the seismic performance of RC buildings with two different connections at the base level under near-fault earthquakes. It is well-known that the impulsive nature of the near-fault ground motions causes severe damages to framed buildings especially at base connections. In the scope of this study, two types of 3-dimensional RC Moment Frames with Fixed Support (MFFS) and Hinged Support (MFHS) containing 5 and 10 stories are assessed under an ensemble of 11 strong ground motions by implementing nonlinear response history analysis. The most vulnerable locations of MFFS, are the connections of corner columns to foundation especially under strong earthquakes. On the other hand, using beams at the base level as well as hinged base connections in MFHS buildings, prevents damages of corner columns and achieves more ductile behavior. Results denote that the MFHS including Base Level Beams (BLB) significantly shows better behavior compared with MFFS, particularly under pulse-type records. Additionally, the first story beams and also interior components undergo more actions. Role of the BLBs are similar to fuses decreasing the flexural moments of the corner columns. The BLBs can be constructed as replaceable members which provide the reparability of structures.

Key Words
seismic performance; RC moment frame; hinged base; base level beam; near-fault ground motions

Address
Department of Civil Engineering, Faculty of Engineering, Kharazmi University, Tehran, 15719-14911, Iran

Abstract
In vertical seismic isolation (VSI), a building is partitioned intentionally by vertical layers into two dynamically different substructures for seismic response reduction. Initially, a 1-story frame was partitioned into two substructures, interconnected by viscous and visco-elastic links, and seismic responses of the original and the vertically isolated structures (VIS) were obtained, considering a large number of stiffness and mass ratios of substructures with respect to the original structure. Color contour graphs were defined for presentation and investigation of large amounts of output results. Dynamic characteristics of the isolated structures were studied by considering the non-classical damping of the system, and then the effects of viscous and visco-elastic link parameters on the modal damping ratios were discussed. On this basis, three states of mass isolation, interactional state, and control mass were differentiated. Response history analyses were performed by Runge-Kutta numerical method. In these analyses, interaction of isolation ratios and link parameters, on response control of VIS was studied and the appropriate ranges for link parameters as well as the optimal ranges for isolation ratios were suggested. Results show that by using the VSI technique, seismic response reduction up to 50% in flexible substructure and even more in stiff substructure is achievable.

Key Words
vertical seismic isolation; non-classical damping; viscous and visco-elastic dampers; Runge-Kutta method; response history analyses

Address
Reza Milanchian, Masoud Nekooei: Department of Structural Engineering, Science and Research branch, Islamic Azad University, Tehran, Iran Mahmood Hosseini: Structural Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran

Abstract
This paper presents a numerical investigation on the seismic behavior of isolated bridges with supplemental viscous damping. Usually very large displacements make seismic isolation an unfeasible solution due to boundary conditions, especially in case of existing bridges or high risk seismic regions. First, a suggested optimal design procedure is introduced, then seismic performance of three real bridges with different isolation systems and damping levels is investigated. Each bridge is studied in four different configurations: simply supported (SSB), isolated with 10% damping (IB), isolated with 30% damping (LRB) and isolated with optimal supplemental damping ratio (IDB). Two of the case studies are investigated under spectrum compatible far-field ground motions, while the third one is subjected to near-fault strong motions. With respect to different design strategies proposed by other authors, results of the analysis demonstrated that an isolated bridge equipped with HDLRBs and a total equivalent damping ratio of 70% represents a very effective design solution. Thanks to confirmed effective performance in terms of base shear mitigation and displacement reduction under both far field and near fault ground motions, as well as for both simply supported and continuous bridges, the suggested control system provides robustness and reliability in terms of seismic performance also resulting cost effective.

Key Words
seismic response; isolated bridges; optimal design; near-fault; elastomeric bearings; supplemental damping

Address
Daniele Losano and Giorgio Serino: Department of Structures for Engineering and Architecture, University Federico II, Via Claudio 21, 80125, Naples, Italy Houman A. Hadad: Department of Civil Architectural and Environmental Engineering, University of Miami, Florida, USA

Abstract
This paper concerns two new analytical approaches for solving high nonlinear vibration equations. Energy Balance method and Hamiltonian Approach are presented and successfully applied for nonlinear vibration equations. In these approaches, there is no need to use small parameters to solve and only with one iteration, high accurate results are reached. Numerical procedures are also presented to compare the results of analytical and numerical ones. It has been established that, the proposed approaches are in good agreement with numerical solutions.

Key Words
conservative systems; nonlinear vibration; Energy Balance method; Hamiltonian Approach

Address
M. Bayat: Young Researchers and Elite Club, Roudehen Branch, Islamic Azad University, Roudehen, Iran I. Pakar: Young Researchers and Elites Club, Mashhad Branch, Islamic Azad University, Mashhad, Iran M.S. Cao: Department of Engineering Mechanics, Hohai University, Nanjing, People

Abstract
This paper focuses on the post-earthquake serviceability of steel arch bridges installed with three types of seismic dampers suffered mainshock-aftershock sequences. Two post-earthquake serviceability verification methods for the steel arch bridges are compared. The energy-absorbing properties of three types of seismic dampers, including the buckling restrained brace, the shear panel damper and the shape memory alloy damper, are investigated under major earthquakes. Repeated earthquakes are applied to the steel arch bridges to examine the influence of the aftershocks to the structures with and without dampers. The relative displacement is proposed for the horizontal transverse components in such complicated structures. Results indicate that the strain-based verification method is more conservative than the displacement-base verification method in evaluating the post-earthquake serviceability of structures and the seismic performance of the retrofitted structure is significantly improved.

Key Words
post-earthquake serviceability; seismic damper; steel arch bridge; displacement-based verification method; strain-based verification method; seismic performance

Address
Ran Li: School of Civil Engineering, Southeast University, 2 Sipailou, Xuanwu District, Nanjing, 210096, China (Former Visiting Scholar, Meijo University, Nagoya, Japan) Hanbin Ge and Rikuya Maruyama: Department of Civil Engineering, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya, 464-8502, Japan

Abstract
This article aims to investigate the possible retrofitting of a deficient building with soft story failure mode by connecting it to an adjacent building which is designed based on current code with friction dampers at all floors. Low cost and high performance reliability along with significant energy dissipation pertaining to stable hysteretic loops may be considered in order to choose the proper damper for connecting adjacent buildings. After connecting two neighbouring floors by friction dampers, the sliding forces of dampers at various stories are set in two arrangements: uniform sliding force and then variable sliding force. In order to account for the stochastic nature of the seismic events, incremental dynamic analyses are employed prior and after the installation of the friction dampers at the various floors. Based on these results, fragility curves and mean annual rate of exceedance of serviceability and ultimate limit states are obtained. The results of this study show that the collapse mode of the deficient building can affect the optimum arrangement of sliding forces of friction dampers at Collapse Prevention (CP) performance level. In particular, the Immediate Occupancy (IO) performance level is not tangible to the sliding force arrangement and it depends solely on sliding force value. Generally it can be claimed that this rehabilitation scheme can turn the challenge of pounding two adjacent buildings into the opportunity of dissipating a large amount of the seismic input energy by the friction dampers, thus improving significantly the poor seismic performance of the deficient structure.

Key Words
coupled buildings; friction damper; incremental dynamic analysis; fragility curve; mean annual frequency

Address
Seyed Bahram Beheshti Aval, Amir Farrokhi and Ahmad Fallah: Department of Structural Engineering, Faculty of Civil Engineering, K.N. Toosi University of Technology, No. 1346, Vali Asr Street, Mirdamad Intersection, Tehran, Iran Apostolos Tsouvalas: Department of Structural Engineering, Faculty of Civil Engineering and Geosciences, Delft University of Technology, building 23, Delft, Netherlands

Abstract
Multi-Axial Testing System (MATS) is a 6-DOF loading system located at National Center for Research on Earthquake Engineering (NCREE) in Taiwan for advanced seismic testing of structural components or sub-assemblages. MATS was designed and constructed for a large variety of structural testing, especially for the specimens that require to be subjected to vertical and longitudinal loading simultaneously, such as reinforced concrete columns and lead rubber bearings. Functionally, MATS consists of a high strength self-reacting frame, a rigid platen, and a large number of servo-hydraulic actuators. The high strength self-reacting frame is composed of two post-tensioned A-shape reinforced concrete frames interconnected by a steel-and-concrete composite cross beam and a reinforced concrete reacting base. The specimen can be anchored between the top cross beam and the bottom rigid platen within a 5-meter high and 3.25-meter wide clear space. In addition to the longitudinal horizontal actuators that can be installed for various configurations, a total number of 13 servo-hydraulic actuators are connected to the rigid platen. Degree-of-freedom control of the rigid platen can be achieved by driving these actuators commanded by a digital controller. The specification and information of MATS in detail are described in this paper, providing the users with a technical point of view on the design, application, and limitation of MATS. Finally, future potential application employing advanced experimental technology is also presented in this paper.

Key Words
multi-axial testing system; degree-of-freedom control; advanced experimental technology; structural testing

Address
Te-Hung Lin and Ker-Chun Lin: National Center for Research on Earthquake Engineering, National Applied Research Laboratories, 200, Sec. 3, HsinHai Rd., Taipei 106, Taiwan Pei-Ching Chen: Department of Civil and Construction Engineering, National Taiwan University of Science and Technology, No.43, Keelung Rd., Sec.4, Taipei 106, Taiwan

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