Author: L. Di Sarno | Size: 1.1 MB | Format:PDF | Quality:Unspecified | Publisher: INTERNATIONAL JOURNAL OF MECHANICS .Issue 3, Volume 7, 2013 | Year: 2013 | pages: 8
seismic vulnerability assessment of existing and
new lifelines, especially transportation systems, either highways or railways, is becoming of paramount importance in resilient social communities. The structural performance analysis of typical existing bridges for high speed railway is however not an easy task to accomplish. Additionally, the seismic assessment of such as-built bridges tend to emphasize the high vulnerability of the structural systems. In the present analytical work, the earthquake response analysis of typical existing bridges for high speed railway was carried out through linear and nonlinear dynamic analyses using refined finite element three-dimensional lumped-plasticity models and multiple component ground motions. The seismic vulnerability of such bridges was assessed through local and global response quantities. The retrofitting scheme adopted to augment the earthquake performance of the sample bridge structures is the base isolation system comprising either lead rubber bearings or steel dampers. The present study investigates and compares the response of such isolation devices. The outcomes of the numerical analyses proved that the use of base isolation systems lowered significantly the seismic demand, especially on the bridge piers and the foundation systems. Hysteretic metallic devices were found more suitable for the seismic isolation of railway bridges. Additionally, the need to comply with the serviceability requirements is found to be more stringent for the base isolation system in the design of retrofitting schemes for railway bridges than the fulfillment of the ultimate limit state. Further work is ongoing to account for the nonlinear modeling of the rail on the global response of base isolated railway bridges under multiple earthquake components.
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Author: Joaquín Martí, María Crespo and Francisco Martínez | Size: 2.4 MB | Format:PDF | Quality:Unspecified | Publisher: mathematical sciences publishers | Year: 2010 | pages: 19
In severe seismic environments, tanks for storage of liquefied natural gas may benefit from seismic isolation. As the design accelerations increase, the inner tank undergoes progressively greater demands and may suffer from corner uplift, elephant’s foot buckling, gross sliding, shell thickness requirements
beyond what can be reliably welded and, eventually, global uplift. Some of these problems cause extra costs while others make the construction impossible. The seismic environments at which the previous problems arise are quantified for modern 160,000m3 tanks, whether supported on shallow or pile foundations, for both a conventional design and one employing seismic isolation. Additionally, by introducing some cost assumptions, comparisons can be made as to the cost of dealing with the seismic threat for each seismic environment and tank design option. It then becomes possible to establish the seismic environments that require seismic isolation, as well as to offer guidance for decisions in intermediate cases.
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Three-Dimensional Analysis of Base-Isolated Structures
Author: David Alan Roke | Size: 607 KB | Format:PDF | Quality:Unspecified | Publisher: University of Pittsburgh | Year: 2005 | pages: 117
Base isolation has become a widely accepted method for earthquake resistant design of structures. However, the research in the field has been generally restricted to one-dimensional motion. Structural response is not limited to this one-dimensional motion, and the torsional effect of multidimensional motion contributes to the horizontal displacements. A threedimensional structure can not be modeled with multiple one-dimensional analyses; rather, a complete three-dimensional analysis must be undertaken, as shown in this study. Four separate analyses for the calculation of the dynamic response of a base-isolated structure will be presented in this study. The first two analysis procedures are for a single-story base-isolated structure. The last two procedures are for a multi-story base-isolated structure. The first procedure for each structure assumes a fully linear response, in which the bearings and the superstructure remain in the linear elastic range of response. The second procedure allows for a non-linear response from the bearings, in which each individual bearing may yield, changing the effective stiffness value. To expand upon the four analysis procedures, additional considerations presented in this paper include an appendix on the effect of bearing friction and an appendix on plasticity. These two concepts further enhance the applicability of the solution procedures.
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Recommendations for the Design and Construction of Base Isolated Structures
Author: R .W. G . Blakeiey , A. W. Charleson , H.C. Hitchcock, L . M . Megget , M.J.N. Priestley bf R.D. Sharpe R.I. Skinner | Size: 4.8 MB | Format:PDF | Quality:Unspecified | Publisher: BULLETIN OF THE NEW ZEALAND NATIONAL SOCIETY FOR EARTHQUAKE ENGINEERING, VOL. 12, NO. 2 JUNE 1979 | Year: 1979 | pages: 22
The philosophy of base isolation of structures, generally using
flexible mountings and mechanical energy dissipating devices, is reviewed. Applications of the approach to buildings, bridges, nuclear power plants, equipment and structures rocking on their foundations are described. Where possible, recommended code provisions and design rules are given. The characteristics of the mechanical energy dissipating devices developed to date are discussed and material specification provisions presented. The requirements for construction of base isolated structures and for maintenance of the devices are given. Finally, recommendations are made on matters for future research.
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Performance of Non-Linear Elastomeric Base-Isolated building structure
Author: Gomase O.P , Bakre S.V | Size: 506 KB | Format:PDF | Quality:Unspecified | Publisher: INTERNATIONAL JOURNAL OF CIVIL AND STRUCTURAL ENGINEERING Volume 2, No 1, 2011 | pages: 12 | ISBN: 0976 – 4399
The seismic response of multistory building supported on base isolation is investigated under real earthquake time history motion. The force deformation behavior of an isolator is modeled as Bi-linear hysteretic behavior which can be effectively used to model all isolation system in practice. Uniform Building Code (UBC-97) is widely used in design of base isolation systems which contains provision according for near fault effect. In order to investigate the performance of base isolation systems, design according to UBC-97 under near fault earthquake. Non-linear time history analysis of a four storey base isolated building, located at close to an active fault. The isolation system is composed of high damping rubber bearing. Design displacements are estimated using UBC-97 parameter. The building is subjected to 1979 El-Centro, 1995 Kobe and 1994 Northridge earthquakes. The analysis result shows that UBC-97 predicts isolator displacements successfully. Floor acceleration and inter-story drifts of the subject base isolated building are significantly reduced when compared to its fixed base counterpart.
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Author: KKVAZE | Size: 1.9 MB | Format:PDF | Quality:Unspecified | Publisher: Sa¯dhana¯ Vol. 38, Part 5, October 2013, pp. 971–997.c Indian Academy of Sciences | Year: October 2013 | pages: 27
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Seismic Analysis of a Low-Rise Base-Isolated Structural System
Author: Halit Kaplan and Ahmet H. Aydilek | Size: 462 KB | Format:PDF | Quality:Unspecified | Publisher: JOURNAL OF LOW FREQUENCY NOISE, VIBRATION AND ACTIVE CONTROL Pages 93 – 109 | Year: 2006 | pages: 18
A base-isolation system was developed for earthquake protection of low-rise structures. The system incorporates spherical supports for the base, a specially designed spring-cam system to keep the base supported under normal conditions, and moves for the duration of the earthquake under the constraint of a spring with optimized stiffness characteristics. The dynamic behaviour of a three-story concrete structure with and without the base isolation subjected to the Taft and El Centro earthquake loads was investigated. The results indicated that the absolute peak acceleration and displacement as well as shear forces decreased significantly with the application of a base isolation system, and it is possible to achieve 87 to 94% reduction in the maximum accelerations and transmitted forces. The movement of the base relative to the ground was less than 0.15 m in the optimized system, and the springs were not fully compressed at any time during application of the earthquake loads. The maximum induced vertical forces as a result of the spherical base support were found to be less than 1.5 % of the weight of the structure. Since the system performance is highly dependent on the rapid unlocking of the cams in the event of a seismic disturbance, careful consideration should be given to the optimal design of the spring-cam system.
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Posted by: aslam - 12-20-2013, 10:17 AM - Forum: Archive
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ETABS-2013-Video Tutorials/Training-DVD
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Seismic risk computation for the base-isolated reactor building of the IRIS NPP M.
Author: M. Domaneschi, F. Perotti | Size: 1.1 MB | Format:PDF | Quality:Unspecified | Year: 2011 | pages: 39
This report deals with the fragility assessment of the IRIS reactor building in its base-isolated version, following the previous configuration without any isolation system [1]. The aim of this step consists in the evaluation of the effectiveness of the base-isolation when applied to the IRIS NPP for the reduction of the seismic risk and in the comparison between the performance of the traditional and the isolated reactor building. Since the behavior of the isolators is markedly
hysteretic, the hypothesis of linearity of the building response, typical of the traditional building, has been removed herein, and a suitable force-displacement literature model is adopted to
represent the isolators inelastic response to horizontal loading.
The probabilistic assessment is based on the procedure described in [2], on a nonlinear analytical
model, by performing sequential seismic analyses in the MATLAB framework [3], with the application of an explicit direct integration method. Previous studies [4] on an extensive finite element model of the isolated IRIS reactor building allow to introduce the rigid body condition for the structural equation of motion. The most important requirement of the procedure remains to reduce as much as possible the
uncertainties related to the incomplete knowledge and accuracy in defining models and methods; this reduction is here sought by refining analysis procedures and using consolidated analytical and numerical tools. The characterization of the isolator devices has been preliminarily performed by testing scaled prototypes, in view of further full scale laboratory experimentations; the definition of the limit state domain for the reference device in terms of the total vertical and horizontal forces has been also evaluated.
The definition of the random variables and the generation of the seismic excitations are also key
aspects of the analysis. They represent significant requisites for setting up the probabilistic
assessment of the response of the structural system.
The exceedance probability of the control system limit state domain is here computed via Monte Carlo simulations; to reduce the computational effort, the response surface (RS) method is used to express the seismic response as a function of the variation of the adopted random parameters. The generation of the RSs is performed in terms of mean and standard deviation of the minimum distance from a specific limit domain. In such setting, the RS evaluation must be repeated for every value of peak ground acceleration; on the other hand, to evaluate the isolators’ behavior, the seismic behavior of the isolated building can be captured by means of a very simple mechanical model which can be based on the hypothesis of rigid-body motion of the building. Finally, the results of the fragility analysis are computed, also in view of a refinement of the response surfaces, within a complete risk assessment for a prototype site.
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Seismic performance assessment of a continuous highway bridge seismically isolated by lead rubber bearings
Author: A. R. Bhuiyan , R. Alam , N. Haque | Size: 481 KB | Format:PDF | Quality:Unspecified | Publisher: Asian Transaction on Engineering ( ATE ISSN: 2221 - 4267) Volume 02 Issue 03 | Year: JULY 2012 | pages: 10
This study is dedicated to wards conducting seismic performance assessmentof a three-spancontinuous
highwaybridgeisolated by lead rubber bearing (LRB)
subjected to near and far field earthquake ground motion records. A typical interior bridge pier modeled by a 2-DOF system comprising an isolation bearing (LRB) and a bridge pier is considered in the study. In the first step of the work, analytical models of the bridge pier and LRB are introduced. A visco -elasto-plastic rheology model for describing the mechanical behavior of LRB is employed , whereas a standard bilinear force-displacement relationship is employed for evaluating the nonlinearmechanical behavior of the bridge pier . In the second phase of the work, non linear dynamic analys is of the 2 - DOF system using a standard direct time integration approach is performed to compute the seismic response s such as pier displacement, bearing displacement, bearing force and input energy . The analytical results show that the seismic responses of the system are significantly affected by the characteristics of the earthquake ground motion records.
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