Seismic response analysis of an irregular base isolated building

Improved seismic performance objectives (Immediate Occupancy and Continued Operation) set by owners of high-tech manufacturing facilities have resulted in increased use of supplemental damping and base isolation designs. This article reviews the design and construction process of industrial base isolated buildings with focus on code requirements, design and analytical methodologies, and constructability challenges. Due to velocity/displacement dependent behavior of base isolation systems, the building code (IBC/ASCE-7) requires performing a Non-Linear Time History (NLTH) analysis to determine the seismic loading on the base isolated structure. However, due to the complexity of NLTH and because the superstructure must be essentially elastic, the code also permits performing a staged analysis. The staged analysis consists of: 1) performing a linear (modal) analysis of the superstructure to determine the lumped-mass dynamic characteristics of the building, 2) performing a NLTH analysis of the isolation system and superstructure to determine system forces, displacements, and base shears, 3) performing superstructure design using a linear (modal) analysis with scaled base shear forces, and 4) designing the base isolator footings and support framing to resist the system design displacements and resulting forces. The required series of time history analyses are performed for a suite of time history records, each scaled to the Design Earthquake (DE) and the Maximum Considered Earthquake (MCE), variations of upper bound and lower bound isolator properties, and position of center of mass at each floor. A case study of a multi-stage analysis, design, and construction of three concrete industrial buildings built on a single base isolation slab is presented to discuss details and challenges related to design and construction of isolator selection, mounting, and support, as well as the design criteria for utility displacement compatibility at the isolator moat, and reduced equipment and contents anchorage requirements.

Nonlinear dynamic analysis for multi-storey RC structures with hybrid base isolation systems in presence of bi-directional ground motions

The topic of this thesis is base isolation. The purpose of this thesis is to offer a relative understanding of the seismic performance enhancements that a typical 12-story steel office building can achieve through the implementation of base isolation technology. To reach this understanding, the structures of a fixed-base office building and a base-isolated office building of similar size and layout are designed, their seismic performance is compared, and a cost-benefit analysis is completed. The base isolation system that is utilized is composed of Triple Friction Pendulum (TFP) bearings. The work of this thesis is divided into four phases. First, in the building selection phase, the structural systems (SMF and SCBF), layout, location (San Diego, CA), and design parameters of the buildings are selected. Then, in the design phase, each structure is designed using modal response spectrum analysis in ETABS. In the analysis phase, nonlinear time history analyses at DBE and MCE levels are conducted in PERFORM-3D to obtain the related floor accelerations and interstory drifts. Finally, in the performance assessment phase, probable damage costs are computed using fragility curves and FEMA P-58 methodology in PACT. Damage costs are computed for each building and seismic demand level and the results are compared.

Recently, there are a lot of technological developments in the earthquake engineering field to reduce structural damage and one of them is a base isolation system. The base isolation system is one of the best technologies for the safety of human beings and properties under earthquake excitations. The aim of this paper is to review previous research works on simulation of base isolation systems for RC buildings and their efficiency in the safety of these buildings. Base isolation decouples superstructure from substructure to avoid transmission of seismic energy to the superstructure of RC buildings. The most effective way to assess the base isolation system for RC building under different earthquake excitations is by conducting experiment work that consumes more time and money. Many researchers had studied the behavior of base isolation system for structure through modeling the behavior of the base isolation in which base isolator is modeled through numerical models and validated through experimental works. Previous researches on the modeling of base isolation systems of structures had shown similar outcomes as the experimental work. These studies indicate that base isolation is an effective technology in immunization of structures against earthquakes.

This paper presents a numerical investigation of a smart base isolation system employing magneto-rheological (MR) elastomers or an MR elastomer-based base isolation system. MR elastomers are a new class of smart materials whose elastic modulus or stiffness can be adjusted depending on the magnitude of the applied magnetic field. Hence, they can be used as controllable stiffness elements in engineering systems. The primary goal of this study is to investigate the dynamic performance of the smart base-isolation in mitigating excessive vibrations of a building structure under earthquake loadings. To this end, a five-story shear building model coupled with a smart base-isolation is developed. Using this model, a series of numerical simulations is performed to evaluate the effectiveness of the MR elastomer-based base isolation system under several historic seismic excitations. The results show that the proposed base isolation system outperform the conventional passive-type base isolation system in reducing the responses of the building structure for all seismic excitations considered in this study.

A smart mechatronic base isolation system using earthquake early warning

During the past decade the need to perform nonlinear static and dynamic analyses on bridge structures has increased significantly. Nonlinear dynamic analysis has become the approach that is used when protective systems such as base isolators and isolation systems are present in the bridge structure. The commercial computer programs available that are used for these types of analyses and that can be understood and used by structural bridge engineers have been far from adequate. Recently, the research community has produced a number of useful computer programs. Among these are the IDARC-Bridge and 3D-BASIS family of programs from the State University of New York at Buffalo. Bridge engineers are not usually familiar with the available computer codes primarily used by researchers, and it is generally known that these programs are not user friendly. Prediction of the nonlinear dynamic responses of bridge structures has presented other challenges. These range from the volume of input and output to the computational effort needed to obtain solutions. The increase in computer speed and the use of faster-solution algorithms have drastically reduced the time needed to perform iterative nonlinear dynamic analysis. Use of the Microsoft Windows-based standardized graphical user interface with the ability for the seamless exchange of data between programs makes the volume of input and output manageable. The implementation of 3D-BASIS-ME—type nonlinear base isolators and isolation systems and the analysis methods used in the family of Microsoft Windows-based software LARSA, with which bridge engineers have become familiar over the years using a wide range of applications for bridges and buildings, are presented.

The ALSC base isolation system was investigated by testing a church model to the scale 1/3.5 on the two-component shaking table at the IZIIS’ Laboratory, Skopje, Macedonia. The investigation was performed within the frames of the European FP6 project PROHITECH, related to seismic protection of historical buildings by innovative and reversible mixed technology systems. This system was originally developed in 2001 and applied on a model of a steel reservoir. The church model was tested twice: with an active base-isolation system and fixed to the base. The effectiveness of the base-isolation system was investigated by the transfer function/floor response spectra technique. Special software for calculation of the transfer functions and floor response spectra based on experimental data, referred as “SPECTRA”, was developed by the authors of this paper. The main objective of the investigations presented in this paper was evaluation of the effectiveness of the ALSC floating sliding base-isolation system by using the Response Spectra approach. Comparison of the Floor Response Spectra was done for two cases a fixed base model and a base-isolated model. The base response spectrum was calculated from the input time history of the Montenegro earthquake compressed 3.5 times (geometry scale of the model). The Transfer Functions and the Floor response Spectra at a particular level were calculated from the Cross Power Spectra (CPS) and the Auto-Power Spectra. The obtained results showed that the effect of the base-isolation system was considerable, with a low transmissibility of energy from shake table to the model.

One of the main shortcomings in current base isolation design/practice is lack of adaptability. As a result, a base isolation system that is effective for one type earthquake may become ineffective or may have adverse effect for other earthquakes. The vulnerability of traditional base isolation systems can be exaggerated by two types of earthquakes, i.e. near-field earthquakes and far-field earthquakes. This paper addresses the challenge facing current base isolation design/practice by proposing a new type of seismic isolator for the base isolation system, namely an adaptive seismic isolator. The novel adaptive seismic isolator utilizes magnetorheological elastomer (MRE) for its field-sensitive material property. Traditional seismic isolator design with a unique laminated structure of steel and MRE layers has been adopted in the novel MRE seismic isolator. To evaluate and characterize the behavior of the MRE seismic isolator, experimental testing was conducted on a shake table facility under harmonic cycling loading. Experimental results show that the proposed adaptive seismic isolator can successfully alter the lateral stiffness and damping force in real time up to 37% and 45% respectively. Based on the successful development of the novel adaptive seismic isolator, a discussion is also extended to the impact and potential applications of such a device in structural control applications in civil engineering.

Magnetorheological elastomer (MRE)-based base isolation system has been proposed to compensate for the drawbacks of the existing passive-type base isolation system. MRE is one of smart material with magnetorheological (MR) effect that can change the stiffness and damping ratio in real time when the magnetic field is applied. The conventional MREbased base isolation system has inter-place between MRE and electromagnetic system. This is determined in consideration of the deformation of MRE, resulting in loss of magnetic flux density and excessive volume of MRE-based base isolation system. Since the strain of the MRE should be considered to be 100 % as base isolation system, the size of the base isolation system becomes large and the practical applicability is remarkably reduced. In addition, the loss of the magnetic flux density increases according to the size of the inter-space between MRE and electromagnetic system. Therefore, a new type of electromagnetic system is proposed to address these problems. In this study, an electromagnetic system which can move with MRE by separating it to the laminated type is proposed. MRE-based base isolation system with the laminated electromagnetic system occupies a small volume compared to the conventional MRE-based base isolation system and can form magnetic closed loop which can minimize the loss of the magnetic flux density. The numerical simulation was performed to compare the proposed electromagnetic system and the conventional MRE-based base isolation. From the numerical simulation, the lab-scale experiment was carried out and the proposed method can be utilized to improve the reality of MRE-based base isolation system.

The present study focuses on wake wash management in the Bay of Naples by time variant spectral analysis to establish more reliable operational strategies and mitigative measures. The time frequency analysis of several wake wash signals due to high-speed craft (HSC), both catamarans and monohulls, operating in the Gulf of Naples is carried out to derive the time-energy per unit area distribution and better characterize the wake wash event and relevant spectrum. A new spectral analysis procedure, which allows to filter the wind sea wave component, is proposed to evaluate the only wake wash component and to estimate both wake wash height and energy density. In this respect, in fact, the influence of wind sea waves may lead to more reliable coastal management guidelines and wake wash measures, even if the measurement campaign has been carried out under calm met-ocean conditions. A comparative study with wake wash values determined by time history analysis is finally carried out, showing that spectral analysis can be applied with good confidence for coastal management purposes, leading to more accurate and reliable operational strategies.

Seismic responses of secondary systems in base-isolated structures

The present work illustrates a dynamic nonlinear analysis of structures characterized by plan irregularity and base isolated by friction devices. Base isolation systems with friction pendulums are analysed to properly regularize the dynamic nonlinear behaviour of structures. Different isolation solutions with friction pendulums are investigated to optimize and regularize the dynamic nonlinear behaviour of structures with irregularities in plan. The nonlinear behaviour of the base-isolated structure is investigated when subject to representative dynamic events. Criteria for regularizing the dynamic behaviour of plan irregular structures are presented. The beneficial effects are illustrated for the adopted optimized isolation solution of friction pendulum system. The nonlinear behaviour of the isolation devices is determined as well as the nonlinear dynamic behaviour of the irregular in plan structure. A comparative dynamic nonlinear analysis is presented for the structure base isolated by the adopted solution of friction isolation system and the corresponding fixed base structure. In the comparative analysis, recorded accelerograms associated with dynamic events are considered and the nonlinear hysteretic cycles of isolation devices are presented, along with the time history of the base acceleration, the base shear, the base displacement and the inter-storey drifts of the structure.

This study investigates the seismic performance enhancement of a four-story reinforced concrete building retrofitted with a Rubber Bearing-High Damping Rubber Core (RB-HDRC) base isolation system. A three-dimensional numerical model was developed and subjected to nonlinear time-history analysis under two design earthquake levesl (BSE 1-E and BSE 2-E). The results indicate that the base isolation system significantly reduces seismic demands compared to the fixed-base condition. Peak base shear was reduced by approximately 48% at the BSE-1E level and by 52% at the BSE-2E level. Roof acceleration decreased by about 76% and 79% at the BSE 1-E and BSE 2-E levels, respectively. The maximum interstory drift ratio was also reduced, demonstrating improved deformation control in the isolated system. Furthermore, the number of plastic hinges decreased significantly, while the energy dissipation capacity increased due to the hysteretic behavior of the RB-HDRC isolator. These findings demonstrate that RB-HDRC base isolation effectively enhances structural resilience and represents a promising strategy for improving the seismic performance of reinforced concrete buildings.

This paper describes the behavior of a low-cost seismic isolator comprising a grout-filled tennis ball rolling on concrete plates. The isolator could be used for isolating lightweight structures. Initially, the axial response of the system was characterized. Subsequently, full-scale isolators were tested in combined compression and lateral cyclic loading. Parameters of investigation were the testing velocity (frequency), the bearing load, the degradation due to consecutive loading, the bearing temperature, the specimen-to-specimen variability, and the engagement of the displacement restrainer. Finally, a three-dimensional finite element model was developed to model in detail the response of the isolator and to explore the influence of the rubber thickness. This is the first study to characterize the above effects and to propose a finite element model of these isolators. Results showed that the lateral cyclic response of the isolators is bilinear and can be approximated by rigid-body equations, whereas the values of the rolling friction coefficient and the yield displacement are suitable for seismic isolation applications. The specimen-to-specimen variability was minimal. Unlike sliding isolation systems, an increased bearing compressive load leads to a higher rolling friction coefficient. Analytical equations are offered to describe this effect. The rolling friction coefficient does not depend on velocity (frequency) or temperature, and the isolators did not deteriorate under consecutive loading. The proposed displacement restrainer effectively limits the motion of the isolator. The developed finite element model accurately captures the experimental response. It was used to study the influence of the thickness of the rubber layer on the lateral response, to conclude that it is minimal, for rubber layers ranging from 3.4 to 7 mm.