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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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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The main idea of the study is the optimum design and the economic evaluation of reinforced (RC) conventional and isolated structures. For the purpose of the study two symmetrical RC structures were studied, designed both with and without seismic isolation, following a performance based concept. The seismic isolation was accomplished by the use of Lead-Rubber Bearings (LRB) and High Damping Rubber Bearings (HDNR).
In the first chapter, the seismic isolation technique is described, as well as the conditions and the applications of the method worldwide, along with the types of the isolation devices.
In the second chapter, the modeling, the preliminary design and the final design of the bearings is described.
In the third chapter, the analysis procedures are presented, and specifically the Linear Static Procedure (LSP), the Nonlinear Static Procedure (NSP) according to the recommendations of FEMA-356 and the Nonlinear Dynamic Procedure (NDP).
Thereafter, in the fourth chapter the structural optimization problem is described, along with the history of the technique and the formulation of the problem. The design variables, the objective function and the constraint functions are defined, as well as the three types of optimization. Finally, the Evolutionary Algorithms (EA) are presented, with emphasis to the Differential Evolution (DE).
In the fifth chapter the procedure of Life-Cycle Cost Analysis (LCCA) is presented, which can be used as an assessment tool of the response of the building during its expected lifetime. The calculation of the procedure is analyzed, as well as the steps to incorporate the nonlinear dynamic analysis in the calculation procedure.
Subsequently, in the sixth and seventh chapter the test cases of the study are presented analytically, along with the conclusions that are obtained from this process.
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Base isolation of an existing 10-storey building to enhance earthquake resistance
Author: W.D. Clark and J.E. Mason Sinclair Knight Merz, Wellington, New Zealand | Size: 334 KB | Format:PDF | Quality:Unspecified | Year: 2004 | pages: 8
The Rankine Brown Building at Victoria University of Wellington, New Zealand houses the University Library and is pivotal to the operation of the University. Built in the early 1960s, the building was of innovative form and construction for its time, with long span precast concrete waffle slabs over 10 floors supported on 16 main columns. Three years ago a review of the building structure suggested that increased protection of the building would be required to meet the University’s expectation for operational continuity after a moderate or major earthquake event in the Wellington area. This paper outlines: Probable areas of structural yielding in a major earthquake event. Structural analysis for base isolation using earthquake time history records. Details of base isolation bearings. Installation of the base isolation bearings.nOther structural details that allow movement of the superstructure to take place due to base isolation.
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SEISMIC PERFORMANCE ASSESSMENT OF NUCLEAR POWER PLANTS
Author: Yin-Nan Huang , Andrew S. Whittaker and Nicolas Luco | Size: 152 KB | Format:PDF | Quality:Unspecified | Publisher: The 14 th World Conference on Earthquake Engineering October 12-17, 2008, Beijing, China | Year: 2008 | pages: 8
Seismic assessments of a sample conventional and base-isolated nuclear power plant (NPP) are performed using a new procedure that builds on the methodology presented in the draft ATC-58 Guidelines and the widely used Zion method, which uses fragility curves defined in terms of ground-motion parameters. The new procedure improves the Zion method by using fragility curves that are defined in terms of structural response parameters since damage and failure of NPP components are more closely tied to structural response parameters than to ground motion parameters. The proposed performance assessment procedure is used to
evaluate the mean annual probability of unacceptable performance of the sample NPP reactor buildings. The
seismic performance assessment confirms the utility of seismic isolation at reducing seismic risk in NPPs.
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SEISMIC RISK AND DAMAGE COST EVALUATION OF BASE ISOLATED BUILDINGS
Author: Luis A. BEDRIÑANA1 and Taiki SAITO2 | Size: 372 KB | Format:PDF | Quality:Unspecified | Publisher: IISEE, Building Research Institute, Tsukuba, Japan. | pages: 8
A methodology to evaluate quantitatively the seismic risk and the cost-effectiveness of a base isolated building
during its lifetime is presented. The process starts with the hazard analysis and the earthquake ground motion
modeling for the studied area. Series of artificial earthquake ground motions are generated by a stochastic method.
To get the response distribution of the target building, several dynamic nonlinear analyses are carried out by using
the generated artificial motions as input waves. By assuming a structural response distribution, the seismic risk
analysis is performed in terms of three structural parameters such as: interstory drift ratio (IDR), floor acceleration
(FA) and the structural damage index (DI). Finally, the cost-effectiveness of using base isolation system is
examined, by comparing the exceedance probability of repair cost in the target building with and without base
isolation during a given time period.
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For structures that receive a large earthquake it is required to apply a good technique which suppresses a danger to the minimum irrespective of existing and establishment. A technique of seismic risk management dealt with the quantitative amount of information is to obtain the anticipative amount of the earthquake damages during access peri
od,and is the support tool to select the higher expense efficiency step to reduce an earthquake damage. In this study,the method of seismic risk management is searched for
using the earthquake proof reliability assessment technique. A seismic lose function is calculated from the earthquake damage factors that are modeled by using fragility curves and event trees. The seismic hazard curve is obtained by Nankai offshore scenario earthquake. The third floor or the eighth floor steel structures on a hard or soft ground in Kochi Prefecture are taken up as SRM(Seismic Risk Management Method) study cases. Using structures from as three kinds of seismic code,costs of both initial construction and life cycle are calculated. As the results,the seismic risk reduces to half by ground conditions. Though initial investment becomes high so that earthquake resi stant construction goes up,the life cycle costs and the seismic risk become small. The seismic risk of the base isolation structure is set to zero,and excels as the earthquake resistant construction. Then,the eighth floor steel structure with the base isolation system is applied to obtain time history responses in comparison of those by the different input wave motions. The base isolation building is able to reduce a strong motion because of the long time period shake,and is efective to the short period large earthquake motion
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The service-life performance of concrete bridge decks, including maintenance, repair, and rehabilitation needs, is directly related to the care exercised from the preconstruction through post-construction period. This guide provides recommendations for bridge deck construction based on considerations of durability, concrete materials, reinforcement, placing, finishing and curing, and overlays.
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