Base-isolated Structures Research Articles

Variability of Dynamic Properties of Rubber Compounds for Elastomeric Bearings

The λ-factors for stiffness and damping of rubber bearings should be experimentally assessed during the qualification process or deduced from tests performed on material specimens. Moreover, the λ-factors suggested in the informative annexes of EN 15129 and of EC8-part 2 can be also used as reference values. However, they are derived from outdated experimental campaigns and do not refer to all the sources of variability. In this paper, a statistical analysis on a significant set of rubber compounds, certified according to EN 15129 from different suppliers, is carried out to assess the current variability of the dynamic properties of such compounds. Different sources of variability may be identified by distinguishing between behavioural and environmental effects. For elastomeric bearings, especially high-damping rubber (HDR) ones, the main behavioural effects are strain amplitude, strain rate dependence, and cyclic degradation, whereas the environmental effects are due to temperature variation and ageing. All these sources of variability have been analysed in this paper. The results of the statistical analysis have been used to propose a new set of λ-factors for all the source of variability studied. Such new values have been compared with the ones suggested by the codes when available. The main inconsistencies found have been highlighted and commented in this paper. Finally, some considerations about the influence of such variability on the structural response of base-isolated structures have been drawn by focusing on both the isolation system and the superstructure.

The effect of an improved passive bumper on the seismic response of the base-isolated structure: Numerical simulations and optimization design

In this paper, a passive bumper, called Flexible Limit Protective Device (FLPD) which was proposed by the author before, was improved to better control the seismic response of the base-isolated structure when the isolation layer exceeds its limit deformation. To distinguish from the FLPD, the improved FLPD is called a Flexible Energy Dissipating Device (FEDD), and the FEDD has stronger dissipation capacity than the FLPD. Above all, the compression behavior of FEDDs is experimentally investigated and the experiment data of FEDDs are compared to that of FLPDs. Subsequently, the nonlinear model of FEDDs is obtained and verified using the experimental data. This obtained model was used to study the effect on the seismic response of the base-isolated structure (multi-degree-of-freedom system), namely isolator displacement and inter-story drift angle. An elite non-dominated sorting algorithm method (NSGA-II) is applied to optimize the design of FEDDs, the gap between isolators and FEDDs and stiffness of FEDDs. Finally, the seismic response of base-isolated buildings equipped with FEDD with optimal parameters is numerically simulated. The results show that FEDDs with optimal parameters can effectively reduce the isolator displacements, and keep the inter-story drift angle within the safe range when the isolation layer exceeds its limit deformation during earthquakes.

Assessment of structural robustness based on accident chain risk theory: Example of base-isolated buildings

Robustness is considered to be an important function of building structures, in addition to satisfying safety, applicability, and durability, and has received increasing attention by designers and scholars in recent years. However, the reason for the initial damage is often ignored in the current structural robustness analysis, and the chain process from structural damage to complete failure is often not described, which is unconducive to decision-making and optimization. In addition, the research on certain new or complex structural systems such as base-isolated structures has rarely been reported.Therefore, a framework for assessing the robustness of base-isolated buildings is proposed in the present work, which is grounded in analysis through accident chain risk theory. First, the damage accident chain of the base-isolated building is established, and the initial damage and the indirect consequences caused by the initial damage defined. Second, a chain risk assessment framework for the damage accident based on chain risk theory is proposed, which is employed to calculate the direct and indirect risks caused by disaster in terms of a building. Third, a quantitative evaluation index of the robustness is proposed by integrating the damage accident chain of the building structure, which is measured by the sensitivity of the indirect risk. Finally, numerical studies of one prototype base-isolated building are performed using this framework. The results of this study will broaden the notion of structurally robust optimization design for multi-hazard risks based on complex networks.

Influence of the soil liquefaction on dynamic characteristics of a base-isolated structure investigated by the experimental method

Influence of the soil liquefaction on dynamic characteristics of a base-isolated structure investigated by the experimental method

Design and analysis of LRB base-isolated building structure for multilevel performance targets

According to China's current code for the seismic design of buildings (GB50011-2010), in the course of designing base-isolated building structures, the isolation system and superstructure are designed separately. Hence, the horizontal seismic isolation coefficient in terms of the design-based earthquake (DBE) and horizontal deformation of the isolation system under the maximum considerable earthquake (MCE) cannot be considered simultaneously. Consequently, the optimum mechanical parameters for isolation bearing and the corresponding horizontal seismic isolation coefficient used in the seismic design of the superstructure cannot be obtained. To address these shortcomings, we propose an optimum seismic design procedure for LRB base-isolated building structures to meet multilevel performance fortification criteria, where explicit mathematical formulations for horizontal seismic isolation coefficients and the horizontal deformation of isolation systems in terms of the mechanical parameters of the LRB isolation system are established by combining equivalent linearization and modal decomposition response spectrum methods. Through a parametric study, we find the critical yield strength ratio, i.e., the ratio of the yielding shear of lead core to the total weight of the LRB base-isolated structure, which leads to the minimal value of the horizontal seismic isolation coefficient. Beyond this critical yield strength ratio, an optimum solution is unavailable, as the horizontal seismic isolation coefficient and horizontal displacement of the isolation system are of a conflicting nature. By converting the multi-criterion formulation into an auxiliary problem with a scalar objective, the optimum design method of an LRB base-isolated building structure oriented to multilevel performance fortification criteria is proposed, so as to obtain the optimum yield strength ratio and the optimum second shape coefficient for the seismic design of the superstructure. A numerical example demonstrates that the seismic horizontal seismic isolation coefficient and maximum horizontal displacement of the isolation system calculated from the optimum yield strength ratio and the optimum second shape coefficient agree well with the results from the time-history method. In a comparative study, LRB base-isolated building structures designed by the critical yield strength ratio, the optimum yield strength ratio and the optimum second shape coefficient, the optimum yield strength ratio and the corresponding fixed-base superstructure are subjected to MCE and mega earthquakes, where the LRB base-isolated structure shows good seismic performance in terms of the optimum yield strength ratio, even when subjected to mega earthquakes.

Analisa Perilaku Stuktur Gedung Bertingkat yang Menggunakan Base-Isolation Systems

Indonesia is an earthquake-prone region, which can lead to collapse of buildings and casualties. Thus, the building must be designed to withstand earthquakes. The use of building protection systems against earthquakes other than shear walls is base isolation, according to base isolation is a protection system that reduces the effects of earthquakes by separating structures from the ground that moves during an earthquake, so as to reduce structural shifts and floor acceleration. In this study, the author developed a study from (Nurseptiani, 2020), namely by replacing the shear wall into base isolation to get a better structural response. The method used is a design analysis that aims to determine the behavior of the structure and the effectiveness of base isolation in multi-storey buildings, as well as using three-dimensional structures in the ETABS program. With the results of the reaserch, the period of the structure produced using base isolation increased by 5.565 seconds compared to fixed base and shear walls is 4.813 and 2.953 seconds. This also occurs in simple structures from 0.22 seconds to 1.017 seconds with base isolation. The resulting variety shape has a difference between the base isolation, fixed base and shear wall structures, this also happens with simple structures. The value of the base shear force generated in the base isolation structure experienced the greatest decrease of about 58.09% compared to the shear wall by only 25.88%. The deviation value between floors produced using base isolation has decreased and the value is the smallest. Based on the sample results of normal, shear and moment force values, base isolation has the smallest value, so from some of these points, it can be stated that base isolation is more effective than shear walls.

Implementation and Verification of Real-Time Hybrid Simulation for the Dynamic Performance Assessment of Base-Isolated Structures

Real-time hybrid simulation (RTHS) is an economical and reliable method for the evaluation of structural dynamic performances, and the fixed analytical substructure model is often used in RTHS which may affect the accuracy of results. In this study, a real-time hybrid simulation platform (RTHSP) developed by configuring a generic National Instruments (NI) controller with hybrid programming strategy is presented in detail. The dynamic performances of a scaled base isolated structure, where the unscented Kalman filter (UKF) was used to update the analytical substructure Bouc–Wen model during the RTHSs was evaluated by presented RTHSP. RTHS of a base-isolated structure was performed where a lead rubber bearing (LRB) was tested physically as the experimental substructure of a part of the isolation layer and the superstructure with the rest of the isolation layer model updated by UKF was considered as the analytical substructure. Under the excitation of three natural earthquakes, the RTHSs with and without UKF updating were compared and analyzed the differences between the two. The results indicated that the displacements of experimental substructure generated by RTHS with UKF updating are the largest, while the relative displacements and acceleration of superstructure are the smallest overall, and the dynamic characteristics of the isolation layer of the analysis substructure updated by UKF are different from that without updated, which reflected the more authentic dynamic mechanical performance of the base-isolated structure under earthquake excitation. In addition, the RTHSP and the hybrid programming strategy are verified to be reliable in tests and experiments, and the components and implementation of a RTHSP for base-isolated structures is described in detail, providing a reference for research on RTHS method.

Seismic control of base-isolated structures using rate-independent damping devices

Rate-independent linear damping (RILD) is a viable option for addressing excessive displacement challenges in low-frequency structures, particularly those subjected to ground motions containing many low-frequency components. RILD can mitigate the floor response acceleration of base-isolated structures more effectively than linear viscous damping (LVD) because of the larger damping force generated in the low-frequency region. However, RILD is an ideal element that exhibits noncausal characteristics. Many researchers have attempted to find approaches to realizing RILD, including both theoretical and mathematical investigations. Thus far, the physical realization of RILD remains challenging. In this study, a tuned inertoviscous-negative-stiffness Maxwell−Weichert (IvNsMW) model and a tuned inerter-viscous damper-negative-stiffness Maxwell−Weichert (IVdNsMW) model are proposed to promote progress in the application of RILD. These models differ in terms of the connection between the inerter and viscous damper. A direct design method is presented to determine the coefficients of these two devices. The efficiency of the proposed RILD-based devices for seismic control of low-frequency structures was examined using a multistory base-isolated structure. The results demonstrate that the proposed RILD devices are promising tools for both displacement and acceleration control of low-frequency structures.

Seismic Fragility Analysis of Base-Isolated Structures Based on Response Surface Method

Seismic Fragility Analysis of Base-Isolated Structures Based on Response Surface Method

SEISMIC VULNERABILITY ASSESSMENT OF BASE-ISOLATED RC FRAME BUILDING USING DDBD METHOD

The direct displacement-based design (DDBD) method is widely used worldwide because it allows structures to be designed based on their expected performance criteria. The DDBD approach is utilized so that base-isolated building structures can meet the seismic performance parameters established by the displacement threshold. In the present study, an 8-story, 10-story and 12-storey base-isolated RC frame building is designed using the latest Indian seismic standards, with lead rubber bearing (LRB) as the base-isolation system. Force-based and DDBD methodology is implemented and compared for the selected base-isolated RC frame buildings. The nonlinear time-history analysis is conducted to evaluate the nonlinear lateral response of the RC frame buildings. The results indicated that the traditional force-based method shows almost 12% less top-storey displacement than the DDBD approach. The DDBD approach provides enhanced reliability, simplicity, and convenience in seismic design for base-isolated building frames with LRBs, making the observations more dependable and easier to employ.

EFFECT OF EPISTEMIC UNCERTAINTY ON SEISMIC FRAGILITY OF BASE-ISOLATED RC-BUILDING FRAME USING INCREMENTAL DYNAMIC ANALYSIS

The quantification and impact of epistemic uncertainty in the RC frame building can analyze due to recent advancements in processing power and the availability of reliable seismic vulnerability assessment techniques. In the present study, a base-isolated 10-story RC building frame is designed and analyzed per the latest Indian standards, with lead rubber bearing as the base isolation system. The selected base-isolated RC frame building was analyzed using probabilistic and deterministic approaches. As the fundamental epistemic uncertainty parameter, the mechanical strength of concrete and steel is considered. The Monte-Carlo method is determined the unpredictability of the RC frames' structures. The incremental dynamic analysis is conducted per the FEMA P695 guidelines to evaluate the wide range of 32 far-field ground motions on the base-isolated RC frame structure. Maximum roof drift ratio responses are utilized to generate the seismic fragility curve by adopting the several threshold values of damage index, such as, slight, moderate, severe, and complete. The traditional linear regression method is implemented to derive the seismic fragility curves of various damage thresholds. The study results reveal that the deterministic strategy is more likely to predict damage by 10 to 25 percent less than the probabilistic approach. The probabilistic analysis approach shows that epistemic uncertainty significantly affects the prediction of the seismic damage probability

Dynamic response and failure modes of base-isolated frame structures subjected to earthquakes under dynamic bearing removal scenarios

Dynamic response and failure modes of base-isolated frame structures subjected to earthquakes under dynamic bearing removal scenarios

The Effects of Near-fault Ground Motions on Optimized Triple Friction Pendulum in Asymmetric Superstructures

The effect of near-fault ground motions containing translational and rotational components is investigated by considering the analytic seismic response of a stiff single-story base-isolated asymmetric superstructure with triple friction pendulum bearing (TFPB). Firstly, six asymmetric base-isolated structures instrumented by optimum TFPBs were exposed to translational components of near-fault excitations with wide ranges of pulsive periods. Next, four single objective functions as target responses (including top floor absolute acceleration, maximum inter-story drift, base shear of structure, and isolator displacement), as well as a combined fitness function as a performance function, were determined to consider all the seismic responses simultaneously. Hence, the optimum design variables of TFPBs (including curvature radii, displacement capacity, and friction coefficient) were calculated using the Genetic Algorithm (GA) to minimize the fitness and performance functions separately for each defined eccentricity. Finally, the structural behavior in the presence of mass eccentricity on the optimum selected TFPB under transitional and transitional-rotational components was explored for a more careful comparison. Also, fifteen combinations of translational-rotational components were employed for a comprehensive investigation. The results demonstrate that roof acceleration could be increased by about 7.5% when mass eccentricity and rotational components are present at the same time.

Dynamic Compression Simulation of Magnetorheological Elastomer Using Bouc-Wen Hysteretic Model

This paper explores the versatility of Bouc-Wen hysteresis model in simulating the dynamic behaviour of magnetorheological elastomer (MRE) material. Bouc-Wen model have been used in many field of science including modelling the hysteresis phenomenon happen in magnetic material, elastomer, base isolation of structures and many more. Introduced by the Robert Bouc, this nonlinear hysteretic model has been modified by many researchers to suit different applications. Compression testing of MRE material under high strain amplitude produces nonlinear hysteresis curve based on stress-strain data. Bouc-Wen hysteretic model has been found to be able to simulate the hysteresis curve of MRE material using parameter identification method within MATLAB Simulink.

Implementation of a coupled FEM-SBFEM for soil-structure interaction analysis of large-scale 3D base-isolated nuclear structures

Accurately simulating the radiation damping of an infinite domain is a crucial issue for reasonably and effectively evaluating the isolation effect of three-dimensional (3D) base-isolated nuclear structures considering soil-structure interaction (SSI). The scaled boundary finite element method (SBFEM) has excellent advantages that enable it to precisely fulfil the radiation conditions. In this study, the finite element method (FEM) and SBFEM were combined to develop a coupled FEM-SBFEM technology. The structure and finite domain were discretized using FEM, and the infinite soil was realised using SBFEM. A complete and efficient calculation procedure for SSI analysis was developed based on the coupled FEM-SBFEM, improving the calculation efficiency through parallel programming. The accuracy of the developed procedure was verified using a numerical example. Furthermore, the dynamic response of a large-scale refined 3D base-isolated reactor building considering SSI was analysed using the proposed method. The results demonstrate that the 3D base isolation technology has excellent isolation performance. Additionally, we compared the response results of the proposed coupled FEM-SBFEM and direct method. The proposed procedure has broad engineering applicability and can be used for seismic SSI analysis of large-scale nuclear structures while maintaining high computational accuracy and stability.

Study on the seismic response of new staggered story isolated structure under different parameters

The new staggered story isolated structure is developed according to the base-isolated structure and the mid-story isolated structure. Quantitative calculation and evaluation of seismic damage are very important for structural safety. In this paper, the seismic damage evaluation of a new staggered story isolated structure is studied by numerical simulation and damage index calculation. A new staggered story isolated structure is established, and the effects of different layers and different chassis areas on the seismic response of the structure are studied. When the position of the bottom isolated layer stays the same, the upper isolated layer is set at different layers, which is set to the top of the 3rd, 6th and 9th layers. When the upper isolated layer keeps at the top of the 3rd layer, the chassis area is set at a different area, which is 26 m × 26 m, 36 m × 36 m and 46 m × 46 m. The results show that the new staggered story isolated structure has good isolated effects under the ground motion. For the structure set upper isolation layer is lower, the inter-layer shear force, inter-layer acceleration and inter-layer displacement are reduced. The energy dissipation effect of the structure improves. The core tube is less damaged and the plastic hinge is smaller. With the increase of chassis area, the isolated effect of the part above the upper isolated layer is good, while the shear force and acceleration of the part below the upper isolated layer of the structure increase, the damage at the core tube changed little and the appearance of the plastic hinge increased. Under earthquakes, with the change in position of the upper isolated layer and the area of the chassis of the new staggered story isolated structure, the displacement, tensile stress and compressive stress of the isolated bearing still meet the requirements of the standard.

A Review on the Modelling Techniques of Liquid Storage Tanks Considering Fluid–Structure–Soil Interaction Effects with a Focus on the Mitigation of Seismic Effects through Base Isolation Techniques

Globally, tanks play a major part in the provision of access to clean drinking water to the human population. Beyond aiding in the supply of fresh water, tanks are also essential for ensuring good sanitary conditions for people and for livestock. Many countries have realized that a robust water supply and a robust sanitation infrastructure are necessary for sustainable growth. Therefore, there is large demand for the construction of storage tanks. Further, liquid storage tanks are crucial structures which must continue to be operational even after a catastrophic natural event, such as an earthquake, to support rehabilitation efforts. From an engineering point of view, the various forces acting on the tanks and the behaviour of the tanks under various loads are important issues which need to be addressed for a safe design. Analyses of the tanks are challenging due to the interaction between the fluid and tank wall. Thus, researchers have conducted several investigations to understand the performance of storage tanks subjected to earthquakes by considering this interaction. This paper discusses the historical development of various modelling techniques of storage tanks. The interaction with the soil also influences the behaviour of the tanks, and hence, in this paper, various modelling approaches for soil structure interaction are also reviewed. Further, a brief history of various systems of base isolation and modelling approaches of base-isolated structures are also discussed in this article.

Real-complex hybrid modal response spectrum method for seismically base-isolated structures

In this study, a novel real-complex hybrid modal response spectrum method (RCHM-RSM) for seismically base-isolated (BI) structures is proposed, which only applies the modal analysis to a superstructure, avoiding the complex calculation. In contrast to the complex modal response spectrum method (CM-RSM), the RCHM-RSM is more reliable and easier to understand. Additionally, analytical expressions of the structural modal matrices are developed for seismically BI structures. A regular model and an irregular model of BI structures are developed to investigate the impact of the proposed method on the solution accuracy. The results show that the proposed method demonstrated its advantages of simple calculations and a high accuracy for two models. The maximum relative deviation of the superstructure story displacement and inter-story are 12.32% and 12.52% for the irregular BI structure, respectively, by comparing them with the response history analysis (RHA). Additionally, the forced decoupling response spectrum method (FD-RSM) significantly underestimates the superstructure response, the maximum relative deviation of the superstructure story displacement and inter-story displacement are 26.56% and 31.56%. The numerical results obtained also confirm that using the Bernoulli-Euler model to idealize the superstructure significantly underestimates the response of the superstructure, and the roof displacement is underestimated by 53%.

Optimal dynamic performance of partially Base-Isolated structure under seismic Excitations: Harmonic, Earthquake, and random

In the present paper, a structural system is introduced, in which instead of executing two commonly used methods of column installation, namely ground-fixing and ground-isolation, some of the columns of the structure are fixed to the ground, and the remaining ones are isolated from the ground by the seismic base isolator. The interaction of these two sections on each other is controlled by connection to a viscoelastic damper. The proposed system is called a partially base-isolated structure. The present work aims to find the optimal isolated mass ratio and the optimal parameters of connection under different excitations. Therefore, once the conformity of the performance of the partial isolation system with two commonly used structure control systems is validated, the fixed-points alignment method is defined in the optimization under harmonic excitation. By executing the optimization operation under near- and far-field earthquakes, the desired parameters and seismic responses are obtained. In the optimal design of this system, even the severely poor performance of the seismic base isolator in the near-field earthquake, which is big displacement and acceleration, is resolved. Finally, under white-noise random excitation, the root mean square of the responses of the structure's components is evaluated in terms of the isolated mass ratio. As indicated by the results, the desired performance of this novel structure can be obtained in the case of base isolation, merely for 10–30% of the total structure mass, selection of a non-dimensionalized frequency below 0.5, and damping coefficient less than 0.1 for the viscoelastic connection. Accordingly, the base isolation in>70% of the structure's total mass is avoided. Moreover, meeting the architectural considerations and eliminating the executive constraints such as a big separation gap would lead to reduced construction cost, yielding significant cost-effectiveness compared to the fully base-isolated structures.

Comparative Experiment and Analysis of a Base-Isolated Structure with Small Aspect Ratio on Multi-Layered Soft Soil Foundation and Rigid Foundation

Through conducting a comparative experimental study of small-aspect-ratio isolated structure models on multi-layered soft soil foundations and rigid foundations, this paper investigates the influence of soil–structure interaction (SSI) effects on the seismic response of small-aspect-ratio isolated structures on multi-layered soft soil foundations. An energy balance equation for isolated structure systems considering SSI effects is proposed, and the impact of SSI effects on the energy dissipation response of small-aspect-ratio isolated structures on multi-layered soft soil foundations is analyzed in depth. The analysis results reveal that SSI effects on multi-layered soft soil foundations reduce the first-order natural frequency of the isolated structure system and significantly increase the damping ratio of the system. Furthermore, the rotational effect of the isolated structure foundation is significant on multi-layered soft soil foundations, and the isolation layer has a certain amplification effect on the rotational effect of the foundation. The study shows that SSI effects on multi-layered soft soil foundations may either increase or decrease the seismic response of isolated structures. Moreover, due to the influence of SSI effects, the ratios of kinetic energy, damping energy dissipation, and hysteresis deformation energy dissipation of the isolated structure on multi-layered soft soil foundations are significantly different from those on rigid foundations. The research concludes that the influence of SSI effects is more significant during large earthquakes, where the ratios of kinetic energy and damping energy dissipation of the isolated structure increase, the hysteresis deformation energy dissipation ratio of the isolation layer decreases, and the magnitude of the decrease is related to the characteristics of the input seismic motion. This research has significant implications for improving the seismic design theory of small-aspect-ratio isolated structures on multi-layered soft soil foundations.