Effectiveness Of Base Isolation Research Articles

Influence of biocementation treatment extent on dynamic system performance: A centrifuge liquefaction study

Previous centrifuge experiments have shown Microbially Induced Calcite Precipitation (MICP) is a viable ground improvement technique to mitigate liquefaction. However, in these past experiments the entire sample in the model container was MICP treated. This study is an investigation of the effect of treatment extent on the system seismic performance by varying the depth of improvement, while maintaining the same cross-sectional area. Specifically, MICP treated zones (10 cm × 10 cm in model scale in plan view) were varied in depth to 100%, 75%, and 37% of the liquefiable sand layer depth. As a comparison, two additional models were constructed, an untreated and fully treated model. The treated models were initially prepared to a relative density of less than 40% and MICP treatment applied until a change of shear wave velocity (Vs) of 300 m/s was measured. All models were instrumented with accelerometers and pore pressure transducers to capture the dynamic responses during the same sequence of eight shaking events. Cone penetration resistance was measured to verify the uniformity of the untreated zones in the models and track the evolution of penetration resistances at three different times during the shaking sequence. Vs was measured after each shaking event to assess the cementation integrity of the MICP treated zones. Linear potentiometer and pre- and post-surface measurements were obtained to track seismic-induced settlements. Pore pressure generation and settlements were reduced in the MICP treated zones compared to untreated zones, showing the increased liquefaction resistance and system performance of MICP. Amplification of the strong ground motions in the models with treatment through the full liquefiable layer lead to significant degradation of the MICP. While a base isolation effect was observed in the models not treated to the full depth of the liquefiable layer, reducing seismic demands to the MICP treated zoned, and leading to minimal changes in cementation integrity. These findings suggest that there may be a benefit to not improving the entire liquefiable depth for maintaining cementation integrity of MICPtreated soils.

Predicting crosswind response of tall buildings: Base isolation and nonlinear aeroelastic effects

This study introduces an analysis framework to evaluate the crosswind response of tall buildings under the influence of base isolation and nonlinear aeroelastic effect near the vortex lock-in wind speed. The motion-induced and buffeting forces are determined based on those in a building with a fixed base. The primary focus is on modeling the motion-induced force in tall buildings with base isolation, where no pre-existing model exists. The fundamental modal displacement is used to describe the building motion relative to the base. The Bouc-Wen model is employed to capture the hysteresis in the relation of shear force and displacement of the isolation system. Through response history analysis, the response statistics of a 65-story building with a square cross-section are determined and compared with those of a fixed-base building. An investigation is conducted to examine the impact of different isolation layer parameters on building response. Additionally, this study explores how the motion-induced force model influences the building response. The findings indicate that base isolation effectively mitigates nonlinear aeroelastic effects, leading to a significant reduction in crosswind response.

Advancements in base isolation for seismic mitigation: Perspectives on elastomeric and lead rubber bearings

Base isolation represents an environmentally sustainable and highly effective technique for mitigating structural responses to strong seismic forces generated by plate boundary tectonic activities. Its primary benefits include preventing structural collapse, minimizing property damage, and safeguarding human lives during severe earthquakes. This passive, energy-efficient approach is often complemented by supplementary dampers to further reduce seismic impact. This study provides a comprehensive overview of elastomeric and lead rubber isolators, covering their theoretical, experimental, and numerical aspects. The paper examines the seismic response of structures equipped with elastomeric and lead rubber bearings, including a discussion of their pros and cons. This paper presents the comparison of fixed base and rubber isolated base in SAP 2000 to assess the effectiveness of base isolation. Additionally, it presents findings from shaking table tests, relevant building codes, and practical applications, considering the impact of events beyond initial design parameters. The review delves into the historical evolution of elastomeric and lead rubber-bearing systems, offering valuable insights into their contemporary understanding. Furthermore, the paper introduces three-dimensional isolators designed to attenuate ground motion responses in both horizontal and vertical directions. It investigates the effects of soil-structure interaction and evaluates isolator responses under blast and impact aircraft loading conditions. Notably, specific types of bearings exhibit exceptional energy dissipation capabilities during catastrophic seismic events, leading to reduced floor acceleration and inter-storey sway at critical levels. In conclusion, the study offers future recommendations and identifies potential constraints in this field

Seismic behavior of base-isolated building structures with lead rubber bearings (LRBs)

This study is designed to evaluate the efficacy of multi-storey buildings in mitigating seismic responses, particularly through the implementation of a base isolation system. Our focus centers on two reinforced concrete structures, one eight stories high and the other ten stories high, both outfitted with a base isolation system featuring lead rubber isolators to proactively minimize seismic risks. The primary objective of introducing a base isolation system is to curtail the potentially destructive impact of earthquakes on a building by attenuating the transmission of seismic forces from the superstructure to the foundations. This seismic protection technique involves strategically installing isolators between the building's superstructure and its foundations. The integration of lead rubber bearing (LRB) isolators into the building's base constitutes a pivotal approach to significantly augmenting the seismic performance of a structure. This method boasts several advantages, chief among them being a notable reduction in floor drift, a critical factor for ensuring the safety and stability of a structure amidst seismic activity. The outcomes of our study underscore the remarkable effectiveness of base isolation in substantially decreasing the overall seismic responses of buildings in the studied region. The observed reductions range from 50% to 70%, affirming the robustness and resilience that this innovative approach imparts to buildings in earthquake-prone areas.

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.

Hybrid Vibration Control of Hospital Buildings against Earthquake Excitations Using Unbonded Fiber-Reinforced Elastomeric Isolator and Tuned Mass Damper

Lifeline structures such as hospital buildings need to be specifically designed such that they experience reduced vibrations when subjected to earthquake excitations because it will be difficult to vacate hospital buildings under the event of any earthquake. Therefore, to ensure operational condition under earthquake excitations in an existing hospital building, the present study utilizes flexible unbonded fiber-reinforced elastomeric isolators (UFREIs) for its seismic isolation. The UFREI-based isolation system is designed to restrict the structural acceleration within the tolerable limits for the building inhabitants even during earthquake hazards. However, the use of such flexible isolators results in excessively large bearing displacements, which either may not be practical and/or pose several serviceability issues. Therefore, tuned mass damper (TMD) is attached to the base floor of the UFREI-isolated hospital building to reduce the large isolator displacements. Properties of the hybrid vibration control system are designed according to the site-specific scenario in New Delhi, India. Further, nonlinear time-history analyses of the UFREI-isolated hospital building with the TMD are carried out, and responses are compared with its uncontrolled response. Results show that the peak bearing displacement response of the UFREI-isolated hospital building is reduced by 9% to 27%, due to the addition of the TMD. Importantly, the required design displacement of the UFREI-based isolation system is decreased by 27%, without compromising the effectiveness of base isolation. In fact, the performance of the hybrid vibration control system is superior to the base isolation system alone.

High-performance isolation systems with rate-independent linear damping for seismic protection of high-rise buildings

There is currently growing concern within the earthquake engineering community regarding the potential for base-isolated structures to experience significant responses during extreme earthquakes. This concern is primarily driven by the observation that induced ground motions can contain influential long-period components, which may exacerbate the structural response. Supplementing damping using conventional damping devices contributed to a significant reduction in the responses whereas perhaps compromises the effects of base isolation itself when subjected to more frequently occurring short-period ground motions, particularly for base-isolated high-rise building structure. The present study employs rate-independent linear damping (RILD) to control the seismic response of high-rise building structures subjected to both short- and long-period ground motions. RILD is a damping mechanism that exerts a control force that is independent of the vibration frequency under harmonic deformation. This method is implemented in conjunction with isolators to achieve the desired control objectives. For passive realization of RILD, both the Maxwell-negative-stiffness (MNS) and modified tuned Maxwell–Wiechert (MTMW) models were considered. A regression technique is presented in this study to optimally design the properties of the MTMW model, and a recursive formulation is developed to conduct structural response history analyses efficiently. The proposed method for seismic protection of high-rise structures was demonstrated using a 20-story benchmark building structure as the analytical model. This approach serves to illustrate the advantages of the proposed method in a practical context. Both short- and long-period ground motions are used for examining the performance of rate-independent damping models incorporated into base-isolated high-rise structures. The findings suggest that the combined isolation systems, in conjunction with rate-independent linear damping (RILD), offer significantly enhanced protection against conventional short-period ground motions, without sacrificing performance during long-period ground motions. Compared to commonly utilized isolation systems, this approach demonstrates superior performance in safeguarding high-rise structures.

Effect of Base Isolation under Different Soil Conditions

Severe seismic activity is a cause of grave concern for all kinds of structures. In order to safeguard buildings from earthquakes we use novel techniques based on performance-based seismic design. The base isolation method is one such technique utilized to reduce the effect of large-scale vibration produced during a seismic vibration. In this paper, we analyze two models: the first G+6 building and the second G+18 building using Lead Rubber Bearing (LRB). The analysis is done using ETABS software and here we use the non-linear time history method. Using the soil intrinsic effects like flexibility and stiffness, this research considers variation in displacement, drift, and repositioning of the soil in accordance with IS code 1893:2016. A greater spectral displacement was detected in medium soil in a fixed base structure. The time period for Lead Rubber Bearing building is greater than the conventional building. Base shear is minimized in (LRB) Lead rubber bearings as compared to a conventional building.

Soil-structure interaction in a base and mid-story seismically isolated building

The main goal of this study is to analyze the performance of seismic isolation systems by implementing isolation to the base and inter-story of the buildings together, in order to reduce the earthquake impact in multi-story buildings. In addition the soil-structure interaction for these cases are taken into consideration. An example building model was composed to observe the effect of base isolation and mid-story isolation numerically. Analyses were performed by using SAP2000 software. A five story building was used as an example structure. Investigations were carried out for six different combinations that are: fixed base buildings, buildings with soil-structure interaction, buildings incorporating single base isolation system with and without consideration of soil-structure interaction, buildings with base and mid story isolation system with and without consideration of soil-structure interaction. Two different earthquake motions were selected for time-history analysis. The results obtained from time-history analysis were discussed comparatively, for all the base-isolation cases including and excluding soil-structure interaction. It has been concluded that the seismic isolation application of the base and mid-story improves the seismic performance of the building. In addition, it has been observed that the soil-structure interaction affects the building seismic performances according to the reference ground type.

Performance of RC Building with Different base Isolators

Abstract: The paper evaluates the application of base isolation methods based on the location of site. Building various sorts of structures while assuring their safety, serviceability, and durability is the focus of civil engineering. Seismic activity has severe impact on the structures' serviceability and safety. The type of building, the type of soil, the technology utilized for seismic resistant, and the location of the building, all the effects how much damage an earthquake may cause to structures. Because an earthquake alters the motion of the ground, which causes foundation failure, the effects of an earthquake are primarily dependent on the type of soil used for building foundations. Therefore, it is crucial to study how different types of soil behave during occurrence of earthquakes. A base isolation technique is one of the methods utilized in construction that can resist earthquakes. It enhances a building's structural performance when it is subjected to lateral stresses. This paper studies the effect of an earthquake response of isolated buildings and provides analysis of the base isolation on the structure's nature as well as a discussion of various isolator types. It compares the performance of two types of isolators: Lead Rubber Bearing (LRB) and Friction Pendulum Bearing (FPB). G+12 R.C structure is taken in this study & Time History analysis is performed with ETABS software. Time Period and Story Stiffness are compared for the building with the base isolator against the building with the fixed base. In comparison with a fixed base building, parameters are changed in each direction due to the presence of an isolator. The analysis examines the characteristics and the effects of base isolation on structures with the Bhuj earthquake.

Seismic Performance of Multi Story Building with Different Base Isolators

Abstract: Earthquakes are one of nature's most dangerous hazards; throughout history, they have resulted in substantial loss of life and serious property damage, particularly to man-made structures. Seismic activity of large magnitude is a major source of risk for all types of constructions. We apply unique methodologies based on performance-based seismic design to protect structures from earthquakes. One way for reducing the influence of large-scale vibration created during an earthquake is the base isolation method. Seismic isolation can be used to give an efficient solution for a variety of seismic design difficulties according to well-established practices that have been examined by several researchers. It compares the performance of two types of isolators: Lead Rubber Bearing (LRB) and Friction Pendulum Bearing (FPB). G+12 R.C structure is taken in this study & Time History analysis is performed with ETABS software. Story drift and Story force are compared for the building with the base isolator against the building with the fixed base. In comparison with a fixed base building, parameters are changed in each direction due to the presence of an isolator. The analysis examines the characteristics and the effects of base isolation on structures with the Uttarkashi earthquake.

Effect of Base Isolation using LRB on Stepped Building

Abstract: The base isolation design strategy uncouples the superstructure from the foundation, reducing the effects of earthquake ground motion. The structure is isolated from the ground motion by a flexible base. Installing base isolators in columns. The structural response accelerations are usually less than the ground motion acceleration. In general, base isolation reduces storey shear and acceleration while simultaneously increasing time period, and storey drift, allowing rigid buildings to be more flexible by dispersing energy to the foundation. The basic seismic isolation design provides a shielding technique, allowing the structure to function without harm even after significant earthquakes. The current study explores the seismic effects of a G+6 stepped building with an LRB isolator. An isolator with a lead rubber bearing was used. E-tabs is used to conduct the base isolation study and seismic analysis. The reaction of the structure, lateral shear force, time period, and base shear, was observed. This paper presents time-history analysis and performance assessment analyses on a base isolated stepped building using Bhuj Earthquake ground motion data.

Mitigation of the Seismic Impact on Storage Gas Tanks by Using Isolation System

The paper presents the studies carried out on a big storage gas tank for the seismic vulnerability assessment and the retrofit through isolation system. This Gasometer, constructed in the early eighties, consists in a steel cylinder of 70 m height and 44 m diameter. The tank bearing structure is composed by a classical steel frame closed with curved steel plates. Inside the tank, a piston-fender and rubber sealing system allow the variation of the container volume and control the gas pressure. The latter represents half of the seismic mass and its position can vary along the tank height. The seismic vulnerability of the steel structure of the Gasometer on its as-it-is state is assessed through the execution of Incremental Dynamic Analyses, placing particular attention on the definition of possible limit states. Subsequently, the seismic retrofit through base isolation system, adopting Double Curved Surface Sliders, is proposed and numerically assessed. The results and comparison between the as-it-is state and the retrofitted state supplies important information about the effectiveness of base isolation for the risk mitigation of gas tanks.

Effects of Base Isolation and Infill Panels on the Nonlinear Time History Analysis of Reinforced Concrete Building

This paper presents the predicted results of nonlinear time history analysis of 11 storey (G+10) Reinforced Concrete (RC) residential building under the effects of a strong earthquake. The paper includes studying the effects of using Lead Rubber Bearings (LRB) as base isolators to improve the performance of RC building to sustain the impact of an earthquake. It also includes the effects of the infill panels on the overall dynamic response of both fixed base and base-isolated buildings subjected to a strong earthquake. The main results that are presented in this study include the variation of roof acceleration, roof displacement, base shear with time. The effects of using LRB and including the infill panels on the storey drift are also presented. Maximum reduction in the story drift was obtained when infill panels are included in the analysis of the base isolated building. The inclusion of the infill panels has only marginal effects on the variation of roof displacement with time when the building is isolated by LRB. The main important improvements that emerged from using LRB as well as the infill panels in the analysis are the reduction of inelastic energy and upgrading the elastic one that is summed up along the period of the earthquake.

Effect of Base Isolation in Multistoried RC Regular and Irregular Building by Using Response Spectrum Analysis

Effect of Base Isolation in Multistoried RC Regular and Irregular Building by Using Response Spectrum Analysis

Comparative Seismic Fragility Analysis of Conventional and Base Isolated Hospital Buildings Having Different Structural Systems

ABSTRACT After the 2010 Maule earthquake, Chilean authorities now require the implementation of base isolation systems in new public hospital build-ings. However, in Chile the typical seismic force-resisting system of non-isolated hospitals is made up of reinforced concrete shear walls, whereas that of isolated buildings is made up of reinforced concrete frames. Since the former is much stiffer than the latter, there is then a question on the actual effectiveness of base isolation in reducing the seismic demands on new hospitals with respect to that on conventional hospitals, particularly the interstory drift demand under relatively low levels of ground shaking. Motivated by this context, this study evaluates the main results of a comparative analysis of the seismic performance of isolated and non-isolated hospitals considering the typical structural system in each case. Representative structural layouts were defined for both types of hospital buildings based on the Chilean state of the practice. Further, possible influence of the number of stories was considered. Member sizes and isolation system properties were determined in accordance to the current Chilean seismic design codes. The structural models were subjected to nonlinear time history analyses under two simultaneous horizontal components of ground motions selected from the Chilean database of earthquake records. The seismic response was evaluated through fragility curves, which were developed from results given by incremental dynamic analysis. Several limit states associated with the isolation systems, structural elements and nonstructural components of hospitals were considered. Results are compared with empirical observations on the effects of earthquakes on the Chilean building inventory, and the suitability of limit state thresholds defined in the literature is discussed.

Seismic response of highway viaducts equipped with lead-rubber bearings under low temperature

Based on a FEM based nonlinear dynamic numerical method, this study investigates the detrimental effects of low temperature on the seismic responses of a highway viaduct equipped with Lead-Rubber Bearings (LRBs). In this method, a dynamic bearing property definition is introduced to account for the temperature variation caused by the absorbed earthquake energy and the corresponding property variation of LRBs. Under low temperature conditions, the base isolation effect of LRBs which are well-designed for room temperature is significantly weakened, manifested by shorter fundamental structural natural periods and more damages and forces imposed to structure members, such as a 5–13% increment of shear force transferred by the LRBs, an increasing area of the hysteresis loop of the bending moment at the bottom of piers, and an increasing residual displacement at the top of piers. In addition, through jointed investigating the seismic responses under both long and short durations of earthquake motions, it is demonstrated that the heat production in LRBs over an earthquake can alleviate the detrimental effect of low temperature, and the extent of this alleviation is positively correlated to the earthquake duration. Therefore, the low temperature effect and the property variation of LRBs over an earthquake should be comprehensively considered for the designation of LRBs installed in bridge viaducts located in cold regions and the realization of an accurate seismic analysis of the bridge viaducts.

The effect of base isolation and tuned mass dampers on the seismic response of RC high-rise buildings considering soil-structure interaction

The most effective passive vibration control and seismic resistance options in a reinforced concrete (RC) high-rise building (HRB) are the base isolation and the tuned mass damper (TMD) system. Many options, which may be suitable or not for different soil types, with different types of bearing systems, like rubber isolator, friction pendulum isolator and tension/compression isolator, are investigated to resist the base straining actions under five different earthquakes. TMD resists the seismic response, as a control system, by reducing top displacement or the total movement of the structure. Base isolation and TMDs work under seismic load in a different way, so the combination between base isolation and TMDs will reduce the harmful effect of the earthquakes in an effective and systematic way. In this paper, a comprehensive study of the combination of TMDs with three different base-isolator types for three different soil types and under five different earthquakes is conducted. The seismic response results under five different earthquakes of the studied nine RC HRB models (depicted by the top displacement, base shear force and base bending moment) are compared to show the most suitable hybrid passive vibration control system for three different soil types.

A coupled BE–FE–BE study for investigating the effect of earthquake frequency content and predominant period on seismic behavior of base-isolated concrete rectangular liquid tanks

Main purpose of this study is to numerically simulate a three-dimensional soil–structure–liquid interaction problem in order to scrutinize the dynamic behavior of base-isolated concrete rectangular tanks under horizontal seismic excitations. It has been deduced that in many earthquakes, the isolation systems reduce the earthquake effects on structures by lengthening their fundamental natural periods against excessive drifts of the superstructure. However, in exceptional cases of the soil stiffness and shaking frequency, the base-isolation systems could have noxious effects. Therefore, the numerical seismic response of rectangular liquid tank system isolated by bilinear bearings is investigated under three real earthquakes with different frequency characteristics in this paper. To this end, finite shell elements for tank wall and boundary elements for liquid and soil are used. Subsequently, fluid–structure–soil equations of motion are coupled with isolator governing equation in the time domain, to gain the whole system response. For different concrete tanks from slender to broad ones, the variations of base forces, sloshing responses, shell radial displacements, and hydrodynamic pressures are illustrated under various system parameters such as the flexibility of the isolation system and the soil properties, to censoriously scrutinize the effects of various system parameters on the utility of the base-isolators. From the analyses, author has concluded that the base-isolation effect is intimately dependent on the earthquake characteristics and may amplify or control the structural responses.

Seismic vibration control of bridges with excessive isolator displacement

The effectiveness of base isolation (BI) systems for mitigation of seismic vibration of bridges have been extensively studied in the past. It is well established in those studies that the performance of BI system is largely dependent on the characteristics of isolator yield strength. For optimum design of such systems, normally a standard nonlinear optimization problem is formulated to minimize the maximum response of the structure, referred as Stochastic Structural Optimization (SSO). The SSO of BI system is usually performed with reference to a problem of unconstrained optimization without imposing any restriction on the maximum isolator displacement. In this regard it is important to note that the isolator displacement should not be arbitrarily large to fulfil the serviceability requirements and to avoid the possibility of pounding to the adjacent units. The present study is intended to incorporate the effect of excessive isolator displacement in optimizing BI system to control seismic vibration effect of bridges. In doing so, the necessary stochastic response of the isolated bridge needs to be optimized is obtained in the framework of statistical linearization of the related nonlinear random vibration problem. A simply supported bridge is taken up to elucidate the effect of constraint condition on optimum design and overall performance of the isolated bridge compared to that of obtained by the conventional unconstrained optimization approach.