Base Isolation Technique Research Articles

The assessment of the interaction between base isolation (BI) technique and soil structure interaction (SSI) effects with 3D numerical simulations

Base Isolation (BI) is a well-known technique that aims to reduce the seismic vulnerability of structures by increasing the structural deformability and the damping. However, these beneficial effects are significantly reduced when the system is founded on deformable soils and then Soil Structure Interaction (SSI) effects are considered. Even if both BI and SSI have been extensively studied in literature, the mutual effects of the two mechanisms are still object of discussion and this paper aims to fill this gap by performing 3D numerical simulations. Several structural systems of different soil conditions are herein modeled in order to account the period elongation and damping increase of the isolated systems. In particular, the paper proposes relationships to calculate these two effects to be used for preliminary estimations avoiding complex and time-consuming analyses. The models have been performed with Opensees to reproduce non-linear hysteretic materials and advanced soil models and consider the non-linear structural performance.

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.

Optimal design of Magnetorheological damper for seismic response reduction of Base-Isolated structures considering Soil-Structure interaction

The base isolation technique is a well-known strategy used for the seismic protection of structures. It introduces a highly deformable device between the structure and the foundation to isolate the main structure from the ground motions. Despite the continuous enhancement of base isolation techniques, the limitations of this strategy are well known to researchers and engineers. Base isolation systems undergo large displacement under strong earthquake motions, which usually results in structural damage and users’ discomfort. In this study, a magnetorheological (MR) damper is used to improve the performance of a benchmark base-isolated building by placing the MR damper between the base of the structure and the foundation. The soil-structure interaction (SSI) effect is included in the study by considering three types of soil, denoted dense, medium, and soft. The soil is introduced through two degrees of freedom, namely, sway and rocking, based on the cone simplified linear model. The MR damper parameters are optimized using a particle swarm optimization (PSO) algorithm under a set of benchmark earthquake records. The optimal local parameters related to each benchmark earthquake and soil type are averaged to obtain general optimum parameters. The acquired general optimum parameters are then used to study the dynamical response of the benchmark base-isolated building controlled by the MR damper, considering an array of 100 natural earthquake ground motions. The obtained results show an enhancement of the dynamic response under all soils conditions compared to non-optimized and base isolation only scenarios. Several engineering demand parameters (EDP) and response indicators were investigated in this study, including top floor and base displacements, inter-storey drift, storey drift, top floor acceleration, and base shear. The results obtained show the effectiveness of the optimization in improving the response of base-isolated structures. It also demonstrates the dependence of damper parameters on soil typologies.

Analysis of Scrap Tyre Rubber Pad Base Isolated Structure using MATLAB

The structure should be protected from adverse effects of earthquake forces or any seismic vibration. The base isolation technique is used to reduce most of the effects that are caused by these external forces. Isolation is achieved by using installing different types of flexible materials under the structure. Earthquakes cause lots of damage to the health and wealth of an economy. In the current study, a four-story structure with base isolation is analyzed. Scrap Tyre Rubber Pad is used as base isolation material for this study. The structural response is compared with a similar structure having fixed support without isolation. MATLAB software is utilized for determining the values of frequency and mode shapes for a structure. After comparing two structures base isolated structre was found to be more effective to higher frequencies.

Torsional Vibration Control of a Structure using Fluid Viscous Dampers

Damping plays a major role in design of structures resistant to earthquakes. The damping reduces the effective of the structure when they are assigned to lateral loads by energy dissipation. The number of dampers is available and in use today. Most of the dampers usually isolate the super structure from the substructure, dividing them in order to hamper the flow of vibrations into the superstructure. This classification is termed as base isolation techniques. While, the rest of the damping techniques, dissipates the oncoming vibrations on the superstructure itself and minimizes the damage to the superstructure. In this present study, Fluid Viscous Dampers (FVD) are used extensively over types of dampers. The structure endures two load types, the vertical loads and the sidewise loads, and conveys to the foundation. In order to have earthquake resistant structures, FVD have been used. In the present study, Dissymmetric Buildings are analyzed with and without Fluid Viscous Dampers. The software ETABS 2016 was used. Using Time history analysis in ETABS software, the RC building is considered and the structure is evaluated and connect with and without FVD.

Response Spectrum Analysis of Base Isolated Regular and Vertical Irregular Building in Different Types of Soil

Abstract: These days earthquake is a major problem for development of high rise building in seismic zone areas. Researchers have developed devices to overcome these earthquake problems. So we need to design a structure which can withstand against the seismic loads. There for it became necessity to provide passive control device “base isolation” to resists large horizontal and vertical loads which lead the structure to collapse. In present workthe effectiveness of the fixed base and Base isolation (LRB) with different type of vertical irregularities in different type of soil (Hard, Medium, Soft soil) in plan are concerned the vibration of the structure. The present work G+10 story Building of different vertical irregularities ( Regular building, vertical irregular Type-I, vertical irregular Type-II, vertical irregular Type-III ) Situated in zone IV are analyzed under the various Loading such as dead load, live load and earthquake load. Free vibration analysis, response spectrum analysis have been carried out for these model of building with a fixed base and base Isolation Devices. It is observed that story displacement in response spectrum is significantly increases at top stories with the base isolated building. And this work shows that the response of building reduced by using base isolation (LRB) devices in all different typeof vertical irregularities building, but the same isolation device is more effectively work in Vertical irregular Type-II Building Keywords: Base isolation Techniques, LRB, Base Shear and Etabs etc.

Application of Mode-Adaptive Bidirectional Pushover Analysis to an Irregular Reinforced Concrete Building Retrofitted via Base Isolation

In this article, the applicability of mode-adaptive bidirectional pushover analysis (MABPA) to base-isolated irregular buildings was evaluated. The point of the updated MABPA is that the peaks of the first and second modal responses are predicted considering the energy balance during a half cycle of the structural response. In the numerical examples, the main building of the former Uto City Hall, which was severely damaged in the 2016 Kumamoto earthquake, was investigated as a case study for the retrofitting of an irregular reinforced concrete building using the base-isolation technique. The comparisons between the predicted peak response by MABPA and nonlinear time-history analysis results showed that the peak relative displacement can be properly predicted by MABPA. The results also showed that the performance of the retrofitted building models was satisfactory for the ground motion considered in this study, including the recorded motions in the 2016 Kumamoto earthquake.

A Soil-Dependent Approach for the Design of Novel Negative Stiffness Seismic Protection Devices

Conventional base isolation (BI) techniques require a great reduction in the fundamental frequency of the system in order to mitigate the structural dynamic responses due to earthquake excitations. However, the resulting base displacements are large and can cause utility connection problems, rendering BI inadequate for retrofitting. This paper proposes a vibration control system (VCS) that can be used as a supplement to the conventional BI to increase the effective damping, and thus reduce the required base displacements. A novel passive negative stiffness (NS)-based vibration absorber, based on the KDamper, is implemented in parallel to a BI. The design of the VCS follows a constrained optimization approach that accounts for geometrical and manufacturing limitations. The NS is realized with a realistic displacement-dependent mechanism that generates controlled NS. The VCS is designed for various soil-types in order to determine its effectiveness and soil-structure-interaction (SSI) effects are accounted with respect to the soil-type. The earthquake excitation input is selected according to the EC8 by generating a database of artificial accelerograms for each ground type. Finally, the VCS is compared to a conventional BI, and based on the numerical results obtained, the VCS is an effective alternative to BI and a possible retrofitting option.

Role of Multiple Liquid Tuned Mass Dampers in Tall Buildings

High raised buildings with plan asymmetry arehighly vulnerable to seismic induced vibrations on account of 1)large amount of base shear, 2) large lateral displacement and 3)twist of each story. The asymmetry in the building plan can’t becompromised due to the architectural requirements and thebuildings utilities. Many techniques are attempted to minimizethe base shear, lateral displacement and the twist using methodssuch as base isolation techniques, tuned massed dampers and theliquid tuned mass dampers. However, though the attempts arefound to be fruitful, they are expensive, un acceptable andsometimes not feasible.In this study the liquid tuned mass dampers are found moresuitable and which are modeled making use of the overheadwater tanks in buildings. The effect of Multiple Liquid TunedMass Dampers on the unsymmetrical buildings is to be studiedin the present work. The study is carried-out on L-shapebuilding, T-shape building and U-shape and rectangularbuilding of 10, 15 stories height in different seismic zones usingE-Tabs. The structural analysis is to be carried using linear timehistory analysis. It was found that with the increase in numberof water head tanks and dampers, the base shear increased, butdisplacement decreased.

Investigation of a Base-Isolator System’s Effects on the Seismic Behavior of a Historical Structure

The earthquake performance of structures with seismic isolation is much better than that of fixed-base structures, and the application of seismic insulation ensures both structural integrity and the protection of the items present in the structures. The base-isolation system is used to extend the fundamental period of vibration of the structure and to obtain higher value from base-isolated structures relative to the fixed-base structure. Historical masonry mosques could be strengthened using a base-isolation technique. In this study, a historical masonry mosque was organized and modelled using SAP2000 software. Nonlinear Time History analyses were carried out for the historical masonry structure, firstly for the fixed-base mosque and secondly for the base-isolated mosque with lead rubber bearing (LRB). The use of a base-isolator system caused an increase in the historical mosque’s period, reducing the displacements, acceleration, and force applied on the mosque and the resulting structural deformation; the results of the analysis indicate a significant improvement in the seismic behavior. The modelling results show that such historical masonry buildings (especially those with high and delicate minarets) can be vulnerable to major earthquakes, and it may be useful to examine strengthening strategies for these buildings.

Comparison of Seismic Response of RCC Framed Structure With FPB & HDRB Isolators

Base isolation technique is introduced to improve the performance of the building. The base isolation technique is used to decouple the base from its superstructure during the ground motion caused by earthquakes. The installation of isolator in a building at a base level significantly increases the time period of the structure which means it reduces the possibility of resonance of the structure giving rise to better seismic performance of the building. The main aim of this paper is the use of Friction Pendulum Bearing (FPB) and High- Density Rubber Bearing (HDRB) as an isolation device and then to compare various parameters between fixed base condition and base-isolated condition. The modeling procedure for  both  building has been done using ETABS 2017 software for a regular (G+5) storied OMRF building. Linear analysis using Time History Analysis (THA) for the records of Elcentro earthquake (1940) and Response spectrum analysis (RSA) has been carried out

Analytical investigation of the seismic response of elastic oscillators placed on the top of rocking storey

In the present study the seismic response of elastic single degree of freedom oscillators placed on the top of a rocking storey is examined. A storey comprised of columns that may uplift under ground motion excitations can be regarded as an innovative and cost effective base isolation technique. Regarding the podium structural systems, apart from studying the rocking response in order to avoid the rocking overturn, it is important to examine the seismic demand on the superstructure so as to assess the rocking storey as base isolation system. From this point of view, structural as well as ground motion parameters that affect the seismic demands of the superstructure are examined. For this purpose, the superstructure’s response spectra, of various structural configurations, under free rocking response, analytical pulses and natural ground motions are presented and discussed. Finally, the effect of different assumptions regarding energy dissipation during impact on the response of the superstructure is investigated. The study of the podium structures results in useful remarks concerning the performance of the rocking storey as a base isolation system.

Performance of elevated water tank staging with base isolation under blast loading

In this present study aims to evaluate the performance of base isolation device under different intensity blast induced ground excitations for an elevated water tank staging. In this study mainly focused to improve the performance of the base isolator and minimize the damage of the structure. To know the performance of base isolator two models are considered one is fixed base model and another one is supported with base isolator model for both non-linear time history analysis is carried out with the help of SAP 2000 software subjected to four different underground blast intensities. From the analysis, it is observed that by using base isolator supported model structural responsive parameters such as base shear, top storey accelerations are efficiently reduced when compared to the fixed base structure. Hence it is proved that adopting base isolation technique we considerably reduce the damage of the structure subjected to underground blast vibrations.

Performance Evaluation of the Base Isolation Technique on the Blast Mitigation of Spatial Structures

Unpredictable threat and danger may occur in a structural system due to blast loading. Long-span spatial structures are very practical and common in airport terminals, exhibition centers, stadiums, and other public buildings. For high-rise and multi-story structures, horizontal pressure plays a major role in the level of damage to a structure, whereas long-span structures may be influenced by both horizontal and vertical pressure. In the current study, the applicability of lead rubber bearing (LRB) has been evaluated on a low-rise, long-span structure. The analysis is carried out by using the MATLAB Simulink platform. The simulation results indicate that the base isolation system which is usually adopted for seismic control of structures can adequately reduce the structural responses under blast loadings.

Advanced Techniques for Pilotis RC Frames Seismic Retrofit: Performance Comparison for a Strategic Building Case Study

Pilotis buildings have widely spread out in developed countries since World War II onwards. From the structural point of view, Pilotis RC frames exhibit substantial lack in ductility capacity and shear resistance localized at the first floor, since they have been mainly realized before the seismic codes’ era. The present study shows the performance comparison of four advanced retrofit techniques when applied to typical Pilotis RC frame designed for gravity loads only according to Italian building code of ‘60s. A preliminary investigation has been performed to select non-linear numerical models suitable to describe the considered RC frame behavior, involving flexural inelastic hinges of RC beams and columns and in-plane axial inelastic hinges of masonry infill panels. Two seismic retrofit projects have been designed at a local level, by strengthening the masonry infilled panels with Fiber Reinforced Cementitious Matrix (FRCM) technique and alternatively by replacing infilled panels with prefabricated panels disconnected from the structure, so that no infill/frame interaction occurs. Two more retrofit projects have been designed at a global level, in order to improve the overall structural performance making use of energy dissipation and, alternatively, base isolation techniques. Nonlinear time history analysis and structural assessment have been carried out for the as-built case as well as for the four retrofit solutions according to Eurocode 8 and Italian Building Code, in order to highlight the structural deficiencies and relative improvements, respectively. Performances offered by the proposed retrofit techniques have been finally compared in terms of structural behavior, expected damage, and economic impact.

Protection from overturning of rigid block‐like objects with linear quadratic regulator active control

In recent years, several studies proposed new techniques aimed at improving the performances of rigid block-like objects under base excitation. The majority of these studies considered passive control methods, such as base isolation or other techniques based on the tuned mass damper principle. Only few studies considered active and semi-active control methods applied to the dynamics of rigid blocks. This paper proposes an active control method for symmetric rigid blocks that is based on the LQR approach. The optimal control law is obtained starting from the linearized equation of motion. The effectiveness of the proposed control method is investigated comparing the behaviour of rigid blocks with and without active control under harmonic and seismic excitation. The results are summarized in overturning spectra, in the case of harmonic excitation, and rocking maps, in the case of seismic excitation. Although the proposed active control method is expected to work well for slender blocks, specific analyses show that the method also improves the dynamics of no-slender blocks and is effective for blocks with different geometrical characteristics. Moreover, the results show that the control law has a good robustness with respect to the sampling time and the time delay.

Seismic Base Isolation System using Scrap Old Tyres

Enfeebling the effects of vibration caused by the movement of tectonic plates has been the major topic of research in the field of Structural Engineering. Base isolation is a technique used to counteract the effects of seismic vibration and ensuring the safety of the superstructure. Even though, the strategy of base isolation has been used in interminable number of structures, there is a need for economized, effective base isolation technique. India has been recycling and reusing waste tyres for four decades, it is estimated that 60% are disposed of through illegal dumping. India, being the second largest manufacturer of rubber after China, there is a menace of rubber disposal in the country. Despite the numerous efforts of technologists of recycling and utilizing the scrap rubber tyres, 17% of the scrap rubber tyres are diverted to landfill creating disposal problem. Therefore, there is a need for utilizing the used scrap rubber tyres in an innovative way instead of dumping it. Scrap Rubber tyres, being elastic in nature serve to be a potential shock absorber of seismic vibrations. In the present study, an attempt is made to utilize the recycled scrap rubber tyre in seismic isolation of structure. This technique proves to be a low- cost earthquake mitigation technique which can potentially reduce the damage caused by seismic shock propagation into the structure and hence ensure overall safety of the structure. An experimental analysis is done to evaluate the properties of assembly of rubber tyres and utilization of the same for isolating base of structures to check for the effectiveness in enfeebling the shocks produced by seismic vibrations. Furthermore, using the properties of scrap rubber tyres obtained from the experimental results, performance of the scrap tyres as a base isolation system for a multistoried building and stability of the structure was studied using Finite element analysis tool.

Seismic Response Of Retrofitted Low Rise Structure Under Strong Earthquakes Using Nonlinear Time History Analysis

This paper summarizes the response quantities of existing and retrofitting for three story reinforced concrete (RC) structure under selected seismic excitation. The retrofitting technique addressed in this study include carbon fiber reinforced polymer (CFRP) bar strengthening on beam, steel cage column jacketing, high strength concrete column jacketing, CFRP strengthening of column, and applying the base isolation technique. To evaluate the effect of seismic excitation on the structural responses, three ground motion records, i.e., Newhall, Northridge and Sylmar are selected and scaled to match response spectra design of Indonesian code. Material non-linearity was taken into account and modelled as plastic hinges at the both end of columns and beams element. Nonlinear time history analyses were performed using Newmark’s integration method for existing and all retrofitting models. Finally, the comparisons of the response quantities in term of base shear, roof acceleration, story drift index are presented and discussed.

A comparative study of floor accelerations of different structural systems with lead-rubber-bearing (LRB) isolators

Seismic base isolation technique has been successfully used to protect structural as well as nonstructural components from the damaging effects of earthquakes by reducing floor accelerations and inter-story drifts for many decades. The level of floor acceleration is a key issue in the protection of acceleration-sensitive nonstructural components. The intensity of floor acceleration varies depending on the vibration characteristics of the structural system. Furthermore, the viscous damping devices sometimes are used to improve the performance of the superstructure as well as the base isolation system. The characteristics of the ground motions are also influential in the performance of the viscous damping devices. In this paper, the floor acceleration performance of seismically isolated buildings with different lateral load resisting systems such as moment resisting frame, dual system, moment resisting frame plus viscous wall dampers, and dual system plus viscous wall dampers is investigated under near-fault and far-fault earthquake ground motions. Moreover, the effectiveness of supplemental viscous damping devices equipped in parallel with lead-rubber-bearing isolators is studied. It is inferred from the study that the most effective way of reducing floor accelerations is to provide more rigidity to the superstructure. Utilizing supplemental viscous dampers along with lead-rubber-bearing isolators having about 20% of effective damping ratio is meaningless or harmful in relation to floor acceleration and base shear.

Performance improvement of base isolation systems by incorporating eddy current damping and magnetic spring under earthquakes

An innovative subsystem with the incorporation of eddy current (EC) damping and magnetic negative stiffness spring (MNSS) is proposed to develop feasible strategies for performance improvement of existing base isolation techniques. The concept of integrating the eddy current damping mechanism and the nonlinear negative stiffness spring is firstly introduced for better energy transition behavior under earthquake excitations. The analytical expressions of the force characteristics of the EC and the MNSS components are presented accordingly, and a parametric study is conducted to evaluate the inherent properties of the integrated magnetic subsystem. To demonstrate the advantages of the EC–MNSS subsystem, an illustrative example of a two-DOF model simulating both the superstructure and the isolation layer is numerically investigated by adopting two representative isolators and the proposed subsystem. The EC–MNSS subsystem is illustrated to significantly and simultaneously improve the isolation performances in terms of base drift and structural acceleration. The energy exchange and dissipation behavior are further revealed by employing time history analysis and energy-displacement-velocity plots. Furthermore, the proposed EC–MNSS subsystem is implemented in a benchmark isolation problem adopting an eight-story frame structure subjected to bidirectional earthquake excitations. The simulation results indicate the superior and the comparable performances of the integrated isolation system as compared to those of the passive and the control-augmented isolations, respectively.