Seismic Isolation Of Bridges Research Articles

Longitudinal seismic displacement analysis of Quasi Seismic Isolation Bridge based on Energy-based Multimodal Pushover Method with and without collision

This paper aims to evaluate the longitudinal seismic displacement of the Quasi Seismic Isolation Bridge (QSIB) based on the Energy-based Multimodal Pushover Method (EMPM), including the pier-beam relative displacement and the collision effect. As a simplified seismic analysis method, the EMPM invokes the concept of energy balance into the modal pushover analysis to assess the nonlinear seismic behavior of Laminated Rubber Bearing (LRB) on bridges. In this method, the energy-based capability curve is obtained by the modal pushover analysis, while the energy-based demand curve is estimated under the ground motion record. The target performance criterion can be derived by intersecting the capability curve with the demand curve. The effect of several key factors in EMPM, such as the mode classification and selection, collision effect, energy coefficient and ductility factor, are studied by a case study of a prototype QSIB under ChiChi and El Centro earthquakes. The results of EMPM are compared with those from Nonlinear Time History Analysis (NTHA), to illustrate the effectiveness and accuracy of this method for evaluating the maximum seismic displacement, and the pier-beam relative displacement with and without collision. Results show that the EMPM is found to be able to estimate the longitudinal seismic displacement of the QSIB with and without collision, and can be used as an effective alternative for rapid assess the seismic performance of bridges. The results also indicate that LRB stiffness for modal analysis should be taken as the stiffness pre- or post-sliding when without or with the gap element. Collision effect enlarges the peak displacement and the maximum bias of EMPM.

Seismic isolated bridge performance evaluation and design proposal using artificial neural network

AbstractSeismic isolators such as rubber bearings and other dampers are critical components of seismic design. The hysteresis behavior of such bearings is complicated, and engineers are using a bilinear model or equivalent linearization method in design practice. The response evaluation and initial design parameter assumptions are highly dependent on engineers' expertise and need repeated analysis. Therefore, this study proposed a machine learning‐based approach to conduct bridge seismic isolation performance evaluation and design parameters proposal without repeating the nonlinear simulations. The training data were generated by conducting a nonlinear time history analysis of the bridge structure model with input design earthquakes. Four trained three‐layer neural network models could perform bridge seismic response evaluation, predict the structure's seismic response, and suggest design proposal using some input parameters.

Earthquake Damage Index and Fragility Analysis of Steel Damper for Seismic Isolation Bridge

As an important component in seismic isolation bridges, steel dampers should have excellent low-cycle fatigue performance. This paper performs destructive tests of two types of steel dampers to accurately evaluate the fatigue damage of steel dampers under earthquake action. The damage index of steel dampers under the combined effect of cumulative energy dissipation and maximum deformation is established based on the damage states’ development during the testing process, which can characterize the degree and state of damage of steel dampers under earthquake action. The seismic performance of a seismic isolation continuous girder bridge is evaluated using the frequency statistical method of incremental dynamic analysis beyond the designated functional state, and the fragility analysis of steel dampers was carried out. The results show that the faster the loading rate, the more susceptible steel dampers are to fatigue failure. Under the design earthquake, the basic state of most dampers enters the energy dissipation state, realizing the seismic design goal of protecting bridge piers. The results indicate that the dampers’ overall performance state is slightly damaged, and the fatigue failure of steel dampers is not prominent in most earthquake cases.

Probabilistic Damage Analysis of Isolated Steel Tub Girder Bridge Excited by Near and Far Fault Ground Motions

Friction Pendulum Bearing (FPB) has emerged as a popular solution for damage protection of bridges under seismic events. The study presents the probabilistic damage analysis for the isolated tub girder continuous bridge under the near and the far fault earthquakes using fragility analysis. The steel tub girder continuous bridge is considered with friction pendulum isolator as the seismic isolation mechanism. In order to represent the hysteretic behavior of friction pendulum isolators, a bilinear force-deformation model was used. Fragility curves are developed for various damage measures namely rotational ductility of pier and girder displacement with the peak ground acceleration (PGA) as an intensity measure (IM). Incremental dynamic analyses (IDA) were performed to develop the fragility curves and probabilistic damage model considering the four threshold damage states. The results suggest that in the case of low PGA level, the near fault earthquake leads to the high probability of exceedance in the case of isolated tub girder bridge. Damage model for piers and girder were developed to correlate component responses levels to overall bridge deterioration states. Finally, recommendations for the bridge developers in the stage of the early bridge seismic isolation design utilizing friction pendulum isolators are discussed.

Data-driven reliability assessment of dynamic structures based on power spectrum classification

The power spectral density function is a widely used tool to determine the frequency components and amplitudes of environmental processes, such as earthquakes or wind loads. It is an important technique especially in the engineering field of vibration analysis and in determining the response of structures. When using a large amount of data, a load model can be generated, which describes the characteristics of the underlying stochastic process. This load model enables artificially generated excitations to be created within the framework of Monte Carlo simulations. If multiple data records are utilised, a problem that can occur is that the individual records have a high variance in the frequency domain and are therefore too dissimilar from each other, even though they appear to be similar in the time domain. A load model derived from this data does not represent the entire data set, because not the whole spectral range is covered. Therefore, every attempt must be made to group the records according to their characteristics and thus combine similar data to derive two or more load models accordingly. In this work, an approach is proposed to classify real earthquake ground motion records using the k-means algorithm based on similarities within the data ensemble as determined by the Bhattacharyya distance. The silhouette method enables the identification of the optimal number of groups for the classification. The classified data thus form a subset of the entire data set from which load models can be generated and can be applied separately to the structure under investigation, leading to more accurate simulation results. The advantages of this classification approach are illustrated by means of an academic example and a seismic-isolated bridge pier model as a non-linear dynamic system.

Stochastic Optimization of Multiple Tuned Inerter Dampers for Mitigating Seismic Responses of Bridges with Friction Pendulum Systems

Friction pendulum systems (FPSs) are increasingly being used for bridge seismic isolation, and the isolated response is generally achieved at the expense of inducing large bearing displacements. Setting up a tuned inerter damper (TID) is an approach for improving seismic performance. Nevertheless, the optimization and performance enhancement of multiple TIDs to mitigate the seismic responses of bridges isolated with the FPSs are limited. In this study, the stochastic optimization of multiple TIDs for controlling stochastically excited bridges with FPS bearings was pursued. By describing the hysteretic characteristics of the FPS using the Bouc–Wen model, augmented systems of the bridge model, FPS bearings, and TIDs were formulated and combined with the modeling of stochastic excitation as filtered Gaussian white noise. A stochastic optimization procedure of multiple TIDs for controlling the bridge response considering the nonlinearity of the FPS bearings is proposed and illustrated using examples of continuous bridges. The effects of FPS friction on the optimization and robustness of the TID parameters were identified. A parametric study was performed to determine the mechanism of TID performance enhancement depending on the number of TIDs, multiple modes of tuning, and inertance distribution. Numerical results indicate that the TIDs designed via stationary-stochastic-global (SSG) optimization significantly reduced the responses of the isolated bridge, and the performance was improved by increasing the TID number. Considering the multi-mode contributions to the transversal responses, the performance of spatially distributed TIDs can be substantially enhanced by adding the TID inertance as a design parameter.

Sliding-LRB incorporating superelastic SMA for seismic protection of bridges under near-fault earthquakes: A comparative study

To enhance the resilient performance of the sliding-lead rubber bearing (sliding-LRB), the sliding-LRB combining superelastic shape memory alloy (SMA), termed as superelastic sliding-LRB, is developed for bridge seismic isolation. A comparative study is conducted to demonstrate the advantages of the superelastic sliding-LRB by comparing with the SMA-based friction pendulum bearing (SMA-based FP) considered in the current study. A parameter-seeking procedure is proposed to optimize the parameters of the two superelastic isolation systems, which are conducted considering the equivalent characteristic strength and post-yield stiffness. A three-span seismically isolated bridge is employed to demonstrate the seismic mitigation capability and cost efficiency of the two superelatic isolation systems with various isolation periods. Results show that the parameter-seeking procedure is effective in achieving the parameters of the two superelastic isolation systems. The superelastic sliding-LRB can effectively balance the displacement and base force for isolated bridges and using a relatively smaller amount of SMA, demonstrating higher cost efficiency than that of the SMA-based FP system with relatively long isolation period. The case studies revealed the effectiveness of superelastic sliding-LRB for enhancing the response mitigation and recentering performance with higher cost efficiency for bridges by using NiTi (50.8% Ni) wire. • The superelastic sliding-LRB system is suggested to improve the seismic resilience of bridges. • A parameter-seeking procedure is suggested to achieve the optimum parameters of two superelastic isolation systems. • A comparative study is conducted to demonstrate the effectiveness of superelastic sliding-LRB compared with SMA-based FP. • Case study demonstrated seismic mitigation performance and cost efficiency of the superelastic sliding-LRB system. • Superelastic sliding-LRB can achieve an optimum improvement in balancing the displacement and base force using less amount of SMA.

Effect of lead rubber bearing on seismic performance of steel box girder bridge

Rubber isolation bearings have been proven to be helpful in reducing bridge seismic damage. The response of bridges with rubber bearings are complex under seismic action due to the varying characteristics of isolation bearings. The effect of using rubber isolation bearings on seismic performance of continuous steel box girder bridges exposed to near-field and far-field ground vibrations is the focus of this paper. For this study a four-span continuous steel box girder bridge isolated with lead rubber bearings in Delhi, India is considered for numerical study. Nonlinear Response history analyses are carried out on the selected bridge to evaluate the sensitivity impact of hysteric energy of rubber bearing, bearing displacement limit, deck acceleration, and base shear. The influence of seismic ground motion and lead rubber bearing parameters on the behavior of seismically isolated bridge is investigated using a parametric study. The goal is to look at the impact of ground motion on the lead rubber bearing as well as the bridge. Due to bearing hysteric energy, the bridge with seismic isolation, such as lead rubber bearings (LRB), has roughly 20%-30% lower seismic reaction than non-isolated bridge. This indicates that the isolation bearings improve the seismic performance of the bridge. The results also reveal that when the frequency content of ground motion increases, it results in a substantial risk of damage of the bearing as well as bridge. The near-field earthquakes significantly alter the energy ratio dissipated to total input energy by the lead-rubber bearings in comparison to far-field earthquakes. Finally, recommendations are presented that will be valuable for bridge designers during the early bridge seismic isolation design with lead rubber isolators for varying features of ground motions.

An extended probabilistic demand model with optimal intensity measures for seismic performance characterization of isolated bridges under coupled horizontal and vertical motions

Intensity Measures (IMs) provide the relationship between Engineering Demand Parameters (EDPs) and seismic hazard characteristics for different structures and hence, their role in performance-based bridge design is significant. A few studies have investigated the optimal IMs for bridges under horizontal ground motions, however, detailed studies to explore the optimal IMs for isolated-bridges under the coupled vertical and horizontal records are very rare. This paper presents a procedure for the selection of optimal IMs for seismic-isolated bridges under the combined strong Horizontal Component (HC) and Vertical Component (VC) seismic excitations. Soil-Structure-Interaction (SSI) effects, the high level of uncertainties for soil properties, uncertainties for structural and geotechnical issues and advanced plasticity model for non-liquefied soil are included to explore the optimal vector-valued IMs. Four individual situations are considered to investigate the geometry effects on the selected optimal IMs. Optimal IMs criteria including efficiency, practicality, proficiency and sufficiency are investigated and developed to achieve a set of optimal vector-valued IMs for critical EDPs: drift ratio, pile-cap displacement and bearing displacement, which are affected by both HC and VC in isolated Soil-Pile-Bridge (SPB) systems. The results show that velocity-related IMs: peak ground velocity (PGVH), Housner spectrum intensity (HIH) and root mean square of velocity (VRMSH) are optimal IMs as representative of HCs. In addition, structure-dependent spectral IMs: vertical spectral acceleration at T = 0.2 s ( $${\text{S}}_{\text{a}0.2}^{\text{V}}$$ ) and square-root-of-the-sum-of-square of vertical spectral acceleration at the first and second vertical periods ( $${\text{S}}_{\text{a}}^{\text{V}}\left({\text{T}}_{\text{s}}\right)$$ ) are the appropriate optimal IMs as representative of VCs. However, the displacement-related IM, peak ground displacement of HCs (PGDH), may be treated as optimal IMs for SPB system supported by inclined pile foundations to investigate pile-cap displacement. In addition, the sufficiency term is investigated extensively with respect to seismological parameters.

Determination of the own forms of vibration of the span of beam bridges on elastic supporting parts

The authors consider the determination of the eigenforms of a beam on elastic support parts. Elastic support parts made of rubber and laminated metal plates find a wide use for seismic isolation of bridges in earthquake-resistant construction. Determination of eigenforms of structures is the main stage when designing the buildings and structures for resisting the seismic impacts. The span structure of girder bridges is considered as a system of uniformly distributed load, the free vibrations of which are described by a homogeneous fourth-order partial differential equation. By solving the differential equation, formulas for determining the eigenforms of a beam on elastic support parts were obtained. The reliability of the obtained formulas is confirmed with the substitution of other boundary conditions of the beam. The formulas obtained are considered as a general case, and from them the special cases for different ways of fixing of beams can be obtained.

Seismic evaluation of isolated skewed bridges using fragility function methodology

A methodology, based on fragility functions, is proposed to evaluate the seismic performance of seismic isolated 45o skewed concrete bridge: 1) twelve types of seismic isolation devices are considered based on two different design parameters 2) fragility functions of a three-span bridge with and without seismic isolation devices are analytically evaluated based on 3D nonlinear incremental dynamic analyses which seismic input consists of 20 selected ground motions. The optimum combinations of isolation device design parameters are identified comparing, for different limit states, the performance of 1) the Seismic Isolated Bridges (SIB) and 2) Not Seismic Isolated Bridge (NSIB) designed according to the AASHTO standards.

Comparing Rubber Bearings and Eradi-Quake System for Seismic Isolation of Bridges.

Seismic isolation systems have been used worldwide in bridge structures to reduce vibration and avoid collapse. The seismic isolator, damper, and Shock Transmission Unit (SUT) are generally adopted in the seismic design of bridges to improve their seismic safety with economic efficiency. There are several seismic isolation systems, such as Natural Rubber Bearing (NRB), Lead Rubber Bearing (LRB), and the Eradi-Quake System (EQS). EQS as a new technology is expected to effectively reduce both seismic force and displacement, but there is still some need to verify whether it might provide an economical and practical strategy for a bridge isolation system. Moreover, it is important to guarantee consistent performance of the isolators by quality control. A comparative evaluation of the basic properties of the available seismic isolators is thus necessary to achieve a balance between cost-effectiveness and the desired performance of the bridge subjected to extreme loading. Accordingly, in this study, the seismic response characteristics of the seismic isolation systems for bridges were investigated by conducting compressive test and compressive-shear test on NRB, LRB, and EQS.

Inelastic Displacement Spectra and Its Utilization of DDB Design for Seismic Isolated Bridges Subjected to Near-Fault Pulse-Like Ground Motions

A variety of research has focused on the inelastic displacement demand of a single degree of freedom (SDOF) system when subjected to near-fault pulse-like ground motions, in which the concerned ductility, μ, is typically lower than ten for normal structures. However, for seismic isolated structures that are more prone to large displacement, the corresponding research is limited. The purpose of this paper is to investigate the inelastic displacement spectra of an SDOF system with μ ranging from 5 to 70 and further proposes a direct displacement-based (DDB) design method for seismic isolated bridges. More concretely, a pool of near-fault pulse-like records is assembled, the mean Cμas a function of T/ Tpis developed, and the influences of the ductility, μ, and the post-to-pre-yield ratio, α, on Cμare carefully investigated. Then the corresponding inelastic displacement spectra, Sd, are obtained, and a comprehensive piecewise expression is proposed to fit Sd. After that, the utilization of the spectra for the DDB design of a three-span seismic isolated continuous bridge is performed, and the principal of simplifying the bridge to an SDOF system is carefully explained and verified.

Applicability of Commercial Software for Bridge Design with Consideration of Seismic Loading Effects

The construction of bridges with use of seismic isolation is a less-used concept in Slovakia and the Czech Republic. The concept of seismic isolation of bridges is a way of protecting bridge construction without damaging the pillars and substructure unlike the currently used methodology of consideration and development of plastic joints. When using this concept correctly, it is possible to prevent serious damage of construction and greatly reduce economic losses. Creation of a FEM (Fine Element Method) model, that is capable of correct description of the bridge behavior during a seismic event is often problematic. In this paper, the features of designing and modeling of bridge constructions with use of seismic insulation based on elastomeric bearings are presented. Furthermore, the calculations of stiffness constants required for numerical modeling are presented as well. In this paper are described methods of modeling of seismic isolations in a commonly and commercially available FEM based software. The work also contains a comparison of possibilities as well as limits of these programs. We further present recommendations for correct modeling by use of nonlinear material properties or elastic bonds between elements.

The Strength Reduction Factors for Seismic-Isolated Bridges Characterized by SDOF Bilinear Systems in Far-Fault Areas

ABSTRACTThis article presents a statistical study on strength reduction factors for seismic-isolated bridges in far-fault areas. 1410 ground motions are selected and modified to be compatible with the recommended response spectra. Then, they are divided into 60 groups to investigate the effects of PGA/PGV ratios, soil conditions and post-to-pre-yield stiffness ratio. Results show that reduction factors are significantly affected by the PGA/PGV ratio, while the latter two items are not as important as the first one. Finally, an improved equation to estimate the reduction factor is proposed, and the accuracy of the equation is verified by additional records.

KDamper concept in seismic isolation of bridges with flexible piers

Contemporary seismic isolation systems for bridge applications provide (a) horizontal isolation from the effects of earthquake shaking, and (b) an energy dissipation mechanism to reduce displacements. Throughout the years many kinds of seismic isolation mechanisms have been developed, with two concepts being the most promising ones: the introduction of negative stiffness elements and the incorporation of an additional mass. The latter has led to the development of Tuned Mass Dampers (TMDs), engineering devices consisting of a mass, a spring and a viscous damper commonly used to suppress any undesirable vibrations induced by wind and earthquake loads. The negative stiffness behavior is primarily achieved by special mechanical designs involving conventional positive stiffness pre-stressed elastic mechanical elements, such as post-buckled beams, plates, shells and pre-compressed springs, arranged in appropriate geometrical configurations. Combining the beneficial characteristics of both concepts, a novel passive vibration isolation and damping concept is introduced, the KDamper. The KDamper is based on the optimal combination of appropriate stiffness elements, which include a negative stiffness element. The presence of the additional mass enables structural vibrating energy to be transferred from the structure to the device. The main advantage of the KDamper over other similar concepts including negative stiffness elements is that no reduction in the overall stiffness of the system is required.In this paper, an initial approach towards the implementation of the KDamper to the absorption of seismic excitation of structures is considered, by applying the KDamping concept to a typical single-pier bridge subjected to three different types of dynamic loading. The contribution of pier is taken into account during the analysis. A comparison with a non-isolated bridge with similar characteristics confirms that KDamper based seismic absorption designs can provide a promising alternative to the conventional seismic isolation bearings, offering numerous advantages, such as increased damping and simple technological implementations.

Nonlinear FE model updating and reconstruction of the response of an instrumented seismic isolated bridge to the 2010 Maule Chile earthquake

SummaryNonlinear finite element (FE) modeling has been widely used to investigate the effects of seismic isolation on the response of bridges to earthquakes. However, most FE models of seismic isolated bridges (SIB) have used seismic isolator models calibrated from component test data, while the prediction accuracy of nonlinear FE models of SIB is rarely addressed by using data recorded from instrumented bridges. In this paper, the accuracy of a state‐of‐the‐art FE model is studied through nonlinear FE model updating (FEMU) of an existing instrumented SIB, the Marga‐Marga Bridge located in Viña del Mar, Chile. The seismic isolator models are updated in 2 phases: component‐wise and system‐wise FEMU. The isolator model parameters obtained from 23 isolator component tests show large scatter, and poor goodness of fit of the FE‐predicted bridge response to the 2010 Mw 8.8 Maule, Chile Earthquake is obtained when most of those parameter sets are used for the isolator elements of the bridge model. In contrast, good agreement is obtained between the FE‐predicted and measured bridge response when the isolator model parameters are calibrated using the bridge response data recorded during the mega‐earthquake. Nonlinear FEMU is conducted by solving single‐ and multiobjective optimization problems using high‐throughput cloud computing. The updated FE model is then used to reconstruct response quantities not recorded during the earthquake, gaining more insight into the effects of seismic isolation on the response of the bridge during the strong earthquake.

Seismic Isolation of Bridges Using the Principle of Electromagnetic Attraction and Repulsion

Abstract This paper presents a new type of seismic isolator that uses the principle of electromagnetic attraction and repulsion, to control the friction force between two electromagnets during earthquakes. The two electromagnets are used in conjunction with a secondary high friction dissipating and damping mechanism composed from a 10mm thick neoprene ring layer and two steel surfaces coated with Si3N4 that are used to dissipate the kinetic energy in the bridge deck at some maximum ground accelerations. The isolator utilizes tri-axial accelerometers embedded in the abutments, high current rechargeable batteries and an automated controlling unit. The presented isolator was developed specifically for a concrete bridge deck with a span of 36 meters and simple supported on two abutments, using time history electromagnetic and structural analyses. The paper presents the advantages of using this active seismic isolation system, compared to classical passive devices and the important results obtained in terms of decreasing internal forces on the substructure elements cross sections together with the reduction of relative displacements between the two electromagnets.

Nonlinear FE model updating of seismic isolated bridge instrumented during the 2010 Mw 8.8 Maule-Chile Earthquake

In this paper, nonlinear finite element model updating (FEMU) is performed to study the prediction accuracy of a state-of-the-art finite element (FE) model of a seismic isolated bridge (SIB). The seismic isolator model parameters are updated in two phases: using component-wise and system-wise FEMU. The isolator model parameter values estimated from 23 isolator component tests show a large scatter, and a poor goodness-of-fit (GOF) of the bridge response to the 2010 Maule Earthquake is obtained when most of those parameter sets are used for the isolator elements of the bridge FE model. In contrast, good agreement between the FE predicted and measured bridge response is obtained when the isolator model parameters are calibrated using the bridge response data recorded during the 2010 Mw 8.8 Maule, Chile Earthquake. The updated FE model is then used to reconstruct response quantities not recorded to gain more insight into the effects of seismic isolation during a strong earthquake.

An equivalent linear model for shear pin fractures and its experimental verification

For bridges in seismically active areas, lower horizontal bearing stiffnesses are usually designed to reduce structural seismic responses and protect the piers and foundations against earthquake damage. But lower horizontal bearing stiffnesses are not preferred under normal service conditions. In the seismic designs of Chinese bridges, shear pins are extensively integrated into bearings to resist horizontal force and restrict the relative longitudinal displacement between the superstructure and the substructure under normal service conditions. Shear pins are designed to be sheared off in a certain earthquake to activate the seismic isolation mechanism. For lack of a proper constitutive model for shear pin fractures, effects of shear pin fractures have not been considered in current bridge seismic isolation designs yet. In order to establish a constitutive model of seismic isolation bearings considering shear pin fracture effects, shear fracture tests of shear pins were conducted and an equivalent linear model was established. Ultimate deformation and equivalent stiffness of the equivalent linear model are approximately proportional to the diameter of the shear pin, and load capacity is approximately proportional to the square of the diameter of the shear pin. A series of shaking table tests were conducted, and then test results were compared with numerical results calculated with the equivalent linear model. It was found the equivalent linear model was accurate enough and suggested to simulate the effects of shear pin fractures in bridge seismic designs.