• Nuclear Engineering and Technology
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• 제50권1호
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• pp.170-181
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• 2018

Because of the design and construction requirements, the nuclear structures need to maintain the structural integrity under both design state and extreme earthquake shaking. The base-isolation technology can significantly reduce the damages of structures under extreme earthquake events, and effectively protect the safeties of structures and internal equipment. This study proposes a base-isolation design for the AP1000 nuclear shield building on considering the performance requirements of the seismic isolation systems and devices of shield building. The seismic responses of isolated and nonisolated shield buildings subjected to design basis earthquake (DBE) shaking and beyond-design basis earthquake (BDBE) shaking are analyzed, and three different strategies for controlling the displacements subjected to BDBE shaking are performed. By comparing with nonisolated shield buildings, the floor acceleration spectra of isolated shield buildings, relative displacement, and base shear force are significantly reduced in high-frequency region. The results demonstrate that the base-isolation technology is an effective approach to maintain the structural integrity which subjected to both DBE and BDBE shaking. A displacement control design for isolation layers subjected to BDBE shaking, which adopts fluid dampers for controlling the horizontal displacement of isolation layer is developed. The effectiveness of this simple method is verified through numerical analysis.

• Computers and Concrete
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• 제21권5호
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• pp.495-504
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• 2018

The possibility of earthquakes in vulnerable regions indicates that efficient technique is required for seismic protection of buildings. During the recent decades, the concept is moving towards the insertion of base isolation on seismic prone buildings. So, investigation of structural behavior is a burning topic for buildings to be isolated in base level by bearing device. This study deals with the incorporation of base isolation system and focuses the changes of structural responses for different types of Lead Rubber Bearing (LRB) isolators. A number of sixteen model buildings have been simulated selecting twelve types of bearing systems as well as conventional fixed-base (FB) scheme. The superstructures of the high-rise buildings are represented by finite element assemblage adopting multi-degree of freedoms. Static and dynamic analyses are carried out for FB and base isolated (BI) buildings. The dynamic analysis in finite element package has been performed by the nonlinear time history analysis (THA) based on the site-specific seismic excitation and compared employing eminent earthquakes. The influence of the model type and the alteration in superstructure behavior of the isolated buildings have been duly assessed. The results of the 3D multistory structures show that the lateral forces, displacement, inertia and story accelerations of the superstructure of the seismic prone buildings are significantly reduced due to bearing insertion. The nonlinear dynamic analysis shows 12 to 40% lessening in base shear when LRB is incorporated leading to substantial allowance of horizontal displacement. It is revealed that the LRB isolators might be potential options to diminish the respective floor accelerations, inertia, displacements and base shear whatever the condition coincides. The isolators with lower force intercept but higher isolation period is found to be better for decreasing base shear, floor acceleration and inertia force leading to reduction of structural and non-structural damage. However, LRB with lower isolator period seems to be more effective in dropping displacement at bearing interface aimed at reducing horizontal shift of building structure.

• Earthquakes and Structures
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• 제4권4호
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• pp.341-363
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• 2013

Earthquake response calculation, parametric analysis and seismic parameter optimization of base-isolated structures are some critical issues for seismic design of base-isolated structures. To calculate the earthquake responses for such non-symmetric and non-classical damping linear systems and to implement the earthquake resistant design codes, a modified complex mode superposition design response spectrum method is put forward. Furthermore, to do parameter optimization for base-isolation structures, a graphical approach is proposed by analyzing the relationship between the base shear ratio of a seismic base-isolation floor to non-seismic base-isolation one and frequency ratio-damping ratio, as well as the relationship between the seismic base-isolation floor displacement and frequency ratio-damping ratio. In addition, the influences of mode number and site classification on the seismic base-isolation structure and corresponding optimum parameters are investigated. It is demonstrated that the modified complex mode superposition design response spectrum method is more precise and more convenient to engineering applications for utilizing the damping reduction factors and the design response spectrum, and the proposed graphical approach for parameter optimization of seismic base-isolation structures is compendious and feasible.

• Earthquakes and Structures
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• 제7권6호
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• pp.1223-1240
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• 2014

Seismic isolation has been established as an effective earthquake-resistant design method and the lead rubber bearings (LRBs) are among the most commonly used seismic isolation systems. In the scientific literature, a sharp bilinear model is often used for capturing the hysteretic behaviour of the LRBs in the analysis of seismically isolated structures, although the actual behaviour of the LRBs can be more accurately represented utilizing smoothed plasticity, as captured by the Bouc-Wen model. Discrepancies between these two models are quantified in terms of the computed peak relative displacements at the isolation level, as well as the peak inter-storey deflections and the absolute top-floor accelerations, for the case of base-isolated buildings modelled as multi degree-of-freedom systems. Numerical simulations under pulse-like ground motions have been performed to assess the effect of non-linear parameters of the seismic isolation system and characteristics of both the superstructure and the earthquake excitation, on the accuracy of the computed peak structural responses. Through parametric analyses, this paper assesses potential inaccuracies of the computed peak seismic response when the sharp bilinear model is employed for modelling the LRBs instead of the more accurate and smoother Bouc-Wen model.

• Smart Structures and Systems
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• 제21권3호
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• pp.359-371
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• 2018

Strong seismic events commonly cause large drift and deformation, and functionality failures in the superstructures. One way to prevent functionality failures is to design structures which are ductile and flexible through yielding when subjected to strong ground excitations. By developing forces that assist motion as "negative stiffness forces", yielding can be achieved. In this paper, we adopt the weakening and damping method to achieve a new approach to reduce all of the structural responses by further adjusting damping phase. A semi-active control system is adopted to perform the experiments. In this adaptation, negative stiffness forces through certain devices are used in weakening phase to reduce structural strength. Magneto-rheological (MR) dampers are then added to preserve stability of the structure. To adjust the voltage in MR dampers, an inverse model is employed in the control system to command MR dampers and generate the desired control forces, where a velocity control algorithm produces initial required control force. An extensive numerical study is conducted to evaluate proposed methodology by using the smart base-isolated benchmark building. Totally, nine control systems are examined to study proposed strategy. Based on the numerical results of seven earthquakes, the use of proposed strategy not only reduces base displacements, base accelerations and base shear but also leads to reduction of accelerations and inter story drifts of the superstructure. Numerical results shows that the usage of inverse model produces the desired regulated damping, thus improving the stability of the structure.

• Earthquakes and Structures
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• 제18권3호
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• pp.275-284
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• 2020

The scope of this study is the comparison between experimental results of tests performed on a base isolated building using helical wire rope isolators (WRs), and results of Nonlinear Response History Analyses (NRHAs) performed using SAP 2000, a commercial software for structural analysis. In the first stage of this research, WRs have been tested under shear deformation beyond their linear range of deformation, and analytical models have been derived to describe the nonlinear response of the bearings under different directions of loading. On the following stage, shaking table tests have been carried out on a 1/3 scale steel model isolated at the base by means of curved surface sliders (CSS) and WRs. The response of the structure under ground motion excitation has been compared to that obtained using numerical analyses in SAP 2000. The feasibility of modelling the nonlinear behavior of the tested isolation layer using multilinear link elements embedded in SAP 2000 is discussed in this paper, together with the advantages of using WRs as supplemental devices for CSSs base isolated structures.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1997년도 가을 학술발표회 논문집
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• pp.231-238
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• 1997

Many methods have been proposed for achieving optimum performance of structures subjected to earthquake excitation. The conventional approach requires that structures passively resist earthquakes through a combination of strength, deformability, and energy absorption. Base isolation is a technique for mitigating the effects of earthquakes on structures through the introduction of flexibility and energy absorption capability. In this paper, a parametric study of effectiveness of isolation systems with various main structures' properties is carried out through the response spectrum analysis. It is shown that, most base isolators with its longer period and higher damping can significantly reduce the base shear force transmitted to the structures.

• Smart Structures and Systems
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• 제22권4호
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• pp.441-457
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• 2018

Characteristic parameter values of seismic isolators deviate from their nominal design values due to uncertainties and/or errors in their material properties and element dimensions, etc. Deviations may increase over service life due to environmental effects and service conditions. For accurate evaluation of the seismic safety level, all such effects, which would result in deviations in the structural response, need to be taken into account. In this study, the sensitivity of the probability of failure of the structures equipped with nonlinear base isolation systems to the uncertainties in various isolation system characteristic parameters is investigated in terms of various isolation system and superstructure response parameters in the context of a realistic three-dimensional base-isolated building model via Monte Carlo Simulations. The inherent record-to-record variability nature of the earthquake ground motions is also taken into account by carrying out analyses for a large number of ground motion records which are classified as those with and without forward-directivity effects. Two levels of nominal isolation periods each with three different levels of uncertainty are considered. Comparative plots of cumulative distribution functions and related statistical evaluation presented here portray the potential extent of the deviation of the structural response parameters resulting from the uncertainties and the uncertainty levels considered, which is expected to be useful for practicing engineers in evaluating isolator test results for their projects.

• Structural Engineering and Mechanics
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• 제22권6호
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• pp.761-783
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• 2006

The enlargement of interest in base isolators as an earthquake-proof design strategy has dramatically accelerated experimental studies of elastomeric bearings worldwide. In this paper, a new base isolator concept that is a hybrid system of rubber bearings is proposed. Uniaxial, biaxial, and triaxial shaking table tests are also performed to study the seismic behavior of a 0.4-scale three-story isolated steel structure in the National Center for Research on Earthquake Engineering in Taiwan. Experimental results demonstrate that structures with a hybrid system of rubber bearings composed of stirruped rubber bearings and laminated rubber bearings can actually decrease the seismic responses of the superstructure. It has been proved through the shaking table tests that the proposed hybrid system of rubber bearings is a very promising tool to enhance the seismic resistance of structures. Moreover, it is demonstrated that the proposed analytical model in this paper can predict the mechanical behavior of the hybrid system of rubber bearings and seismic responses of the base-isolated structures.

• Earthquakes and Structures
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• 제12권1호
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• pp.35-45
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• 2017

The current paper investigates the effect of the seismic pounding of neighboring buildings on the response of structures isolated by Triple Friction Pendulum Bearing (TFPB). To this end, a symmetric three-dimensional single story building is modeled for analysis with two specified levels of top deck and base deck, to capture the seismic response of the base isolators and building's roof. Linear elastic springs with different level of gaps are employed to calculate the impact between the buildings. Nonlinear Dynamic Time History Analyses (NDTHA) are conducted for seismic evaluation. Also, five different sizes with four different sets of friction coefficients are assumed for base isolators to cover a whole range of base isolation systems with various geometry configurations and fundamental period. The results are investigated in terms of base shear, buildings' drift and top deck acceleration of the superstructure. The results also indicate the profound effect of the stiffness of the adjacent buildings on the value of the impact they impose to the superstructure. Also, in situations of potential pounding, the increment of the fundamental period of the TFPB base isolator could intensify the impact force up to nearly five-fold.