Seismic Isolation Devices Research Articles

Seismic Response of Simply Supported Base-Isolated Bridge with Different Isolators

The seismic response of simply supported base-isolated bridge with different isolators is presented. The isolated bridge deck is idealized using simplified model of a simply supported rigid deck with three degrees-of-freedom, two lateral translational, mutually orthogonal and one rotational. The rotational degree-of-freedom of the bridge deck may arise because of the dissimilarity in properties of different seismic isolation devices such as elastomeric and sliding systems supporting the bridge deck. The sources of dissimilarity in the isolators considered here are the isolation stiffness and the yield force. The flexibility of abutments and bridge deck is ignored and two horizontal components of earthquake ground motion are applied, considering bi-directional interaction of the seismic response. The governing equations of motion for the uncoupled and torsionally coupled bridge are derived and solved using Newmark's method of integration to obtain the seismic response. The parametric studies are conducted for different system configurations, isolation systems and frequency ratios during torsionally coupled and uncoupled conditions. The seismic response of base-isolated bridge is seen to be considerably altered due to the dissimilarity in the isolator properties. The eccentricity arose due to the isolation stiffness affects more than that due to the isolator yield forces. The effectiveness of isolation reduces at higher eccentricities and the torsionally coupled response diminishes with the increase of uncoupled torsional to lateral frequency ratio.

Experimental and Analytical Studies on the Horizontal Behavior of Elastomeric Bearings under Support Rotation

AbstractLaminated elastomeric bearings are used widely as seismic isolation devices. Most previous studies on the horizontal behavior of elastomeric bearings have assumed that the rotations of the ...

Improvement of the polyurethane spring isolation device for HV post insulators and its evaluation by fragility curves

A novel seismic base isolation system has been developed for high-voltage (HV) porcelain post insulators. The seismic isolation device consists of two steel plates, four polyurethane springs, and a steel rod, which are low-cost components compared to the post insulators. Two alternative designs of the device are experimentally and numerically assessed in this article. A simple and robust numerical model consisting of linear line elements and nonlinear springs was generated, and subsequently validated using the experimental results. Incremental dynamic analyses (IDAs) were then performed to obtain fragility curves. Ten historical earthquake profiles, scaled to intensities between 0.1 and 2.0 g, were then applied to the numerical models. The fragility curves, generated according to the latest version of IEEE-693, demonstrate that the seismic isolation devices are highly effective in diminishing the base moment of the porcelain insulator. It should be noted that relatively large displacements at the top of the pole must be accounted for by ensuring adequate slackness in the flexible conductors.

Study on Seismic Isolation Device with Magnetic Damper for Long Period Ground Motion

Study on Seismic Isolation Device with Magnetic Damper for Long Period Ground Motion

Development of Seismic Isolation Device for Long Period Ground Motion Using Non-linear Spring

Development of Seismic Isolation Device for Long Period Ground Motion Using Non-linear Spring

Semi-active control for seismic isolation device using acceleration response spectrum derived from seismic motion observed at the nearest monitoring station

Semi-active control for seismic isolation device using acceleration response spectrum derived from seismic motion observed at the nearest monitoring station

Evaluation and analysis of response reduction effect of seismic isolation device using air floating technology

Evaluation and analysis of response reduction effect of seismic isolation device using air floating technology

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.

DEVELOPMENT AND APPLICATION OF ISOLATION BEARING ELEMENT CONSIDERING BI-DIRECATIONAL COUPLED INTERACTION

Base isolation technology, which introduces isolated bearings between the top of foundation and upper structure, is regarded as an effective method to reduce seismic energy absorbed by the upper structure. Lead rubber bearing (LRB), that is, a representative seismic isolation device, has been widely used in isolated structural systems. An isolation bearing element for simulating the behavior of LRB was developed with the user element subroutine (UEL) feature of ABAQUS, which was further introduced into seismic analysis of the base-isolated structure with LRB. The Bouc-Wen bi-directional coupled restoring force model was adopted in the developed element to describe the nonlinear hysteric characteristics for LRB in the lateral direction. Meanwhile, the strength differences of LRB in the vertical direction were also included in the element. The accuracy of the isolation bearing element was verified by close agreement between numerically predicted hysteresis curves and experimental counterparts. Moreover, the nonlinear earthquake responses of a four-story reinforced concrete structure isolated by LRB with and without the bi-directional coupled interaction of bearing restoring forces were separately explored, and it was revealed that the bi-directional coupled interaction had considerable effects on the seismic responses of the isolated buildings. Once these coupled interaction effects were not taken into account, the displacement of LRB was underestimated while the bearing capacity would be over-predicted, which had a detrimental effect on the design of isolated buildings.

Graphic Procedure for the Optimum Design of Elastomeric Isolators

A simple graphic procedure for the optimum design of elastomeric seismic isolation devices is proposed. Starting from the design requirements concerning a base-isolated building, such as the device’s stiffness, maximum displacement, and vertical load, as well as the code checks on the device, the procedure allows defining the optimum values of the mechanical and geometrical parameters, such as rubber shear modulus, diameter, and thickness, and the number of rubber and steel layers. In more detail, the procedure allows for first identifying the ranges of the geometrical characteristics through a graphic representation of code checks in terms of the rubber’s diameter and volume, and then their specific values that allow one to obtain the optimum solution according to the design requirements for any fixed values of the mechanical characteristics of the materials. The graphic representation represents a suitable tool to better understand the role and influence of the different checks. The procedure can be easily automated by means of a computer code.

Modeling and design of tuned mass dampers using sliding variable friction pendulum bearings

An effective vibration control device, the pendulum tuned mass damper (P-TMD), can be easily realized as a mass supported on rolling or sliding pendulum bearings. While the bearings’ concavity provides the desired gravitational restoring force, the necessary dissipative force can be obtained either from additional dampers installed in parallel with the bearings or from the same friction resistance developing within each bearing between the roller/slider and the rolling/sliding surface. The latter solution may prove cheaper and more compact but implies that the P-TMD effectiveness will be amplitude dependent if the friction coefficient is kept uniform along the rolling/sliding surface, as in conventional friction bearings. In this case, the friction P-TMD will be as efficient as a viscous P-TMD only at a given vibration level, with large performance reductions at other levels. To avoid this inconvenience, this paper proposes a new type of sliding variable friction pendulum (VFP) TMD, called the VFP-TMD, in which the sliding surface is divided into two concentric regions: a circular inner region, having the lowest possible friction coefficient and the same dimensions of the slider, and an annular outer region, having a friction coefficient set to an optimal value. A similar arrangement has been recently proposed to realize adaptive seismic isolation devices, but no specific application to TMDs is reported. To assess the VFP-TMD performance, first its analytical model is derived, rigorously accounting for geometric nonlinearities as well as for the variable (in time and space) pressure distribution along the contact area, and then, an optimal design methodology is presented. Finally, numerical simulations show the influence of the main design parameters on the device behavior and demonstrate that the VFP-TMD can achieve nearly the same effectiveness of viscous P-TMDs, while considerably outperforming conventional uniform-friction P-TMDs. The proposed analytical model can be used to enhance or validate existing models of VFP isolators that assume a constant and uniform contact pressure distribution.

Rubber compounds made of reactivated EPDM for fiber-reinforced elastomeric isolators: an experimental study

Rubber recycling technology is a popular issue in many research fields, considering the huge amount of rubber waste in the environment. This paper discusses an application of regenerated ethylene propylene diene monomer (EPDM) to produce vulcanized items such as fiber-reinforced elastomeric isolators (FREIs), which are nowadays considered efficient low-cost seismic protection devices for low rise buildings (e.g., made by masonry) in developing countries. Two types of regenerated EPDM are studies and blended with two different virgin rubbers, Vistalon 3666 and Dutral 4038. The first virgin rubber is used to produce a compound with a hardness of around 30 Shore A, while the latter exhibits 60 Shore A. The present study, which is part of a wider research project aimed at the production of low cost un-bonded seismic isolation devices, focuses exclusively on the determination of both crosslinking degree through rheometer tests and elasticity/mechanical properties of the rubber pads, before and after ageing (hardness, tensile strength, elongation-at-break, stretch-stress behavior before and after ageing). The results show that the compounds with the second reactivated EPDM (type B) exhibit the most satisfactory performance, before and after ageing. This paper discusses also the method of fabrication of FREIs, obtained by the interposition of pads made by the selected recycled rubber and dry glass fiber-reinforced polymer (GFRP) textiles. The hardness tests performed on the sliced FREI specimen indicate that the vulcanization temperature used in the production is roughly suitable to obtain the expected rubber properties.

Dynamic analysis of a multi-span simply supported prestressed concrete bridge with restrainers and seismic isolation devices

The Nonlinear F.E. code Structural Analysis Program (SAP) in which the primary nonlinear characteristics of bearings, impact elements and steel restrainer cables considered herein in order to investigate the dynamic analysis of a multi-span simply supported MSSS prestressed concrete bridge, equipped with steel restrainer cables and Lead Rubber Bearings LRB devices including Soil Structure Interaction (SSI) effects. A MSSS bridge with restrainer cables and lead rubber bearings at the two abutments and intermediate bents located in North Algeria is selected according to RPOA for seismic design category 1 is considered in this study. A detailed 3D nonlinear analytical model of study bridge subjected to three components identical seismic excitation including pounding elements, restrainer cables and bearing devices at expansion joints is developed. The nonlinear characteristics of theses boundary elements are represented by bilinear hysteretic models. Under strong seismic excitations, the large longitudinal displacements result the collision between bridge decks or even unseating of these decks at expansion joints of MSSS bridge. Finally, the study reveals among others that in order to prevent deck unseating resulting from restrainer failures and subsequent bridge collapse, particular attention should also be given to proper design of nonlinear characteristics of restrainers and bearing devices.

Editorial: Recent Advances and Applications of Seismic Isolation and Energy Dissipation Devices

Editorial: Recent Advances and Applications of Seismic Isolation and Energy Dissipation Devices

Risk-informed sensitivity analysis and optimization of seismic mitigation strategy using Gaussian process surrogate model

This work aims to develop a method to derive the optimal parameters of seismic mitigation devices for achieving the minimum system seismic risk, which is derived by accounting for the correlation between each individual components risk. Gaussian process surrogate model (GPSM) is used to illustrate the functional relationship between seismic risk and the variables of the mitigation devices, and then both sensitivity analysis and parameter optimization are carried out. Specifically, global sensitivity analysis (GSA), which is powerful for assessing the relative importance of parameters of the isolation devices, is achieved through the use of GPSM; the parameter optimization can be efficiently conducted to find the minimum seismic risk. A cable-stayed bridge model is established to demonstrate the application of the proposed GPSM-based method of sensitivity analysis and optimization of seismic isolation devices. The fluid viscous damper (FVD) which provides additional damper and stiffness is selected to illustrate the procedure of the multi-object optimization of seismic isolation devices on cable-stayed bridges. The seismic risk is calculated by integrating probabilistic seismic hazard analysis (PSHA), probabilistic seismic demand analysis (PADA), and probabilistic damage states, incorporating important sources of nonlinearity and uncertainties. Component-level objectives and one system-level object are considered, and the optimal parameters (damping coefficient Cd and exponent α) are determined. The results demonstrate that the GPSM-based is effective and efficient for sensitivity analysis and optimization of seismic isolation devices.

Dynamic analysis of a multi-span simply supported prestressed concrete bridge with restrainers and seismic isolation devices

Dynamic analysis of a multi-span simply supported prestressed concrete bridge with restrainers and seismic isolation devices

Effects of the long-term aging of glass-fiber reinforced bearings (FRBs) on the seismic response of a base-isolated residential building

Rubber based devices for seismic isolation have been adopted worldwide to protect buildings and bridges from seismic events. Very recently, a significant research effort has been dedicated to the study of Fiber Reinforced Bearings (FRBs), a low cost rubber based device for seismic hazard mitigation. In some applications, FRBs could be preferred over traditional steel reinforced isolators as: (i) they are lighter than conventional devices, (ii) FRBs can be produced with an easy manufacturing process where each bearing is cut to size and shape from a pad of large dimensions, (iii) FRBs require materials with low mechanical properties and cost. This is because FRBs are generally adopted in unbounded configurations and they are free to roll off from the supports. While these devices have shown to be an effective passive protection strategy in many applications, the effects of aging and other environmental conditions on the mechanical properties of these bearings are still to be addressed. With this consideration in mind, the aims of this work are those of: (i) studying the long-term performance and durability of FRBs through experimental testing, (ii) verifying the effects of aging on the response of FRBs both in compression and shear, (iii) determining the effects of aging of the bearings on the seismic response of a benchmark base isolated building, while (iv) comparing the as new and aged response of neoprene FRBs against that of conventional steel reinforced bearings. This work contributes toward determining the viability of FRBs as base isolation devices for residential buildings and toward determining the effects of their aging on the seismic response of a typical residential building.

The pulse effect on the isolation device optimization of simply supported bridges in near-fault regions

Seismic isolation devices serve as an important measure to reduce hazards or mitigate structure damage subject to earthquakes. It’s of great necessity to select the optimal parameters of isolation devices to achieve a good performance especially for structures near the fault. In this paper, a risk-based approach is proposed to identify the optimal parameters of isolation devices particularly considering the pulse effect. The seismic risk is convolved combining the near-fault seismic hazard and seismic fragility results. Seismic hazard analysis is performed for the selected IM and seismic fragility analysis is conducted using the probabilistic seismic demand anaylsis (PSDA) method for ordinary bridges which are common in transportation networks with a set of far-field ground motions and a set of pulse-like ground motions. The objective parameters include the elastic stiffness (K1), characteristic strength (Q) and post-yielding stiffness (K2) to model the seismic behavior of isolation devies subject to ground motions. Especially, the damage criteria of piers and isolation devices are combined to derive the system-level damage of bridges. The results shows that the damage probability of isolated bridges is significantly influenced by the mechanical properties of isolation devices and pulse effect. With the discrete seismic risk points, Kriging interpolation method is used to obtain the object functions which describe the relationship between the near-fault risk and the parameters of isolation devices. With the help of optimization index, the optimal parameters of isolation devices are identified as a function of structural properties and damage states. Additionally, the pulse effect on the optimal parameters of isolation devices is quantified and the relationship between the optimized results and the source-to-site distance is established. The result can provide effective and practical guidance for design and retrofitting of near-field bridges.

New structural seismic protection for high-rise building structures

Presented Structural Seismic Isolation Method (SSIM) aims to provide high safety for Highly Reliable Structures (HRS) against strong earthquakes including near-fault and long-period ground motions. The examined structure is converted to Structural Seismic Isolation System (SSIS) by the SSIM method which exhibited inverse pendulum behaviour. For this purpose, structure foot base and foundation contact surfaces have been designed as any curved surfaces (spherical, elliptical, etc.) depending on the earthquake-soil-superstructure parameters and this contact surfaces have been separated by elastomeric (lead core rubber or laminated rubber bearings) seismic isolation devices. It would allow the structure foot base to turn around gyration centre through rubber bearing contact and maintains similar behaviour to the super-structure. SSIS system provides the possibility of keeping the natural-period of the structure in a larger interval, which is greater than the predominant-period of the majority of possible earthquakes (including near-fault pulse) using currently existing conventional elastomeric isolators with up to 4 second period. Thus, the structure can sustain its serviceability after strong and long-period earthquakes. In this study SSIS system’s performance is presented for high-rise building structures, for this aim, the finite element model of the building (Bg) structure with SSIS system (SSIS-Bg) has been prepared and the nonlinear dynamic analysis of the model has been conducted using strong and long-period ground motions. Results indicate that the base and top accelerations, base shear and base moment responses of the SSIS-Bg structure is 23.21 %, 75.47 % and 85.74 % in average lower than the Conventional Application Method of Seismic Base Isolation Devices for Building (CAMSBID-Bg) structures respectively and it is not prone to resonant vibrations under long-period earthquakes related with the excessive deformation in the isolation layers in case of using CAMSBID-Bg structures. It should be noted that in this study with the presented SSIM method and SSIS system, it is aimed to protect only the Highly Reliable Structures(HRS) from the effects of strong and long-period ground motions and these structures (HRS) are classified as follows: 1) Nuclear Containment Structures; 2) High-rise buildings that contain information, operating systems, sensitive instruments, communication systems, routing systems, bank operating systems, databases, management systems and other similar facilities that are linked to the security and economy of a country; 3) High-rise hospitals etc.

Comparative analysis of ways to protect bridge structures from external influences

Due to the fact that modern bridge construction sets itself the task of building new bridge structures in seismically active areas where earthquakes or other external impacts are permanent, there is an urgent question of protecting the structure from these impacts. This article is devoted to the analysis of ways to protect the bridge structure from external influences. The author analyzes these methods on the basis of publicly available data from companies engaged in the production of structures that prevent external influences, as well as on the basis of modern regulatory documents. The article presents such methods of protection as: deformation seams, support parts, dampers of various modifications and vibration dampers of shrouds. To choose the optimal method, both from the economic side and from the technical side, it is necessary to make verification calculations for static, dynamic and seismic effects, study the geological characteristics of the construction site, conduct mandatory tests of the structures used, as well as use regulatory documents and guidelines for testing and using seismic isolation devices. Also, the author of the article emphasizes that it is important to study ways to protect bridge structures not only in domestic practice, but also in foreign practice.