Elastomeric Bearings Research Articles

Bridge assessment: A case study of Ajaokuta-Itobe Bridge, Kogi State

This report summarizes the assessment carried out as a result of the public uproar on the degree of safety of the Ajaokuta/Itobe Bridge in Kogi state. The public outcry was as a result of a severe damaged expansion joints of the bridge. Visual inspection and concrete strength test were carried out to ascertain the safety condition of Itobe Bridge. Seven out of the total number of eight expansion joint covers were damaged and out of place while all the elastomeric bearings were in good working condition. The scouring of the river bed was not visually pronounced except little at the abutment side of the Abuja-Ayingba approach which is attributed to change of water course. Farming activities within the vicinity of the bridge embankment has no effects on the bridge foundation. The compressive strength test result of some bridge elements selected shows that the values are within the satisfactory range. The assessment recommended the lengthening and desilting of the drainage pipes to prevent further corrosion of the concrete and steel members. The use of sand blasting and repainting of the steel beams was also recommended to protect them from further corrosion. Maintenance of cracks on the reinforced concrete abutment and piers should be carried out. The use of sheet piles filled with compacted sand or gabions around the exposed piles caps to protect the foundation was recommended. Shoreline protection measures should be used in protecting the bridge eroded embankment. Seven out of eight expansion joint devices were damaged therefore exposing the elements of the structure that are otherwise protected by the joint devices. The openings about 47cm-53cm becomes a conduit by which moisture, abrasives, chemicals, and other debris are deposited on the superstructure and substructure below the opening, thereby causing extensive damage. The expansion joints devices should be fixed with proper elastomeric strip seal to protect the bridge from further deterioration.

Finite Element Analysis for Nonlinear Unbonded Circular Fiber-Reinforced Elastomeric Bearings

In recent years, interest in low-cost seismic isolation systems has increased. The replacement of the steel reinforcement in conventional elastomeric bearings for a carbon fiber reinforcement is a possible solution and has garnered increasing attention. To investigate the response of fiber-reinforced elastomeric bearings (FREBs) under seismic loads, it is fundamental to understand its mechanical behavior under combined vertical and horizontal loads. An experimental investigation of the components presents complexities due to the high loads and displacements tested. The use of a finite element analysis can save time and resources by avoiding partially expensive experimental campaigns and by extending the number of geometries and topologies to be analyzed. In this work, a numerical model for carbon fiber-reinforced bearings is implemented, calibrated, and validated and a set of virtual experiments is designed to investigate the behavior of the bearings under combined compressive and lateral loading. Special focus is paid to detailed modeling of the constituent materials. The elastomeric matrix is modeled using a phenomenological rheological model based on the hyperelastic formulation developed by Yeoh and nonlinear viscoelasticity. The model aims to account for the hysteretic nonlinear hyper-viscoelastic behavior using a rheological formulation that takes into consideration hyperelasticity and nonlinear viscoelasticity and is calibrated using a series of experiments, including uniaxial tension tests, planar tests, and relaxation tests. Special interest is paid to capturing the energy dissipated in the unbonded fiber-reinforced elastomeric bearing in an accurate manner. The agreement between the numerical results and the experimental data is assessed, and the influence of parameters such as shape factor, aspect ratio, vertical pressure, and fiber reinforcement orientation on stress distribution in the bearings as well as in the mechanical properties is discussed.

Influence of Bearing Types and Design Code Advances on Seismic Vulnerability of Simply Supported Highway Bridges

ABSTRACT Multi-span simply supported (MSSS) highway bridges are one of the most common bridge types across the world and have several vulnerable components, including bearings, piers, and abutments. Although several past studies have evaluated the seismic response and fragility of common multi-span simply supported bridges, there is negligible research that explores the influence of bearing types, and non-ductile failure modes of bridge piers on the performance of older non-seismically designed simply supported bridges. Additionally, a better understanding of seismic risk to highway transportation systems necessitates the exploration of design code advances and subsequent impact on the seismic vulnerability of MSSS highway bridges. Consequently, this study also focuses on developing and comparing fragility curves for the older design era non-seismically designed, and modern era seismically designed MSSS bridges. High-fidelity three-dimensional (3-D) analytical models, which account for the nonlinear behavior of different components, including non-ductile failure modes of bridge piers, are developed. Deterministic seismic response assessment reveals a higher seismic demand on bridge pier for MSSS bridges with steel bearings as compared to those with elastomeric bearings. The bridge component and system fragility curves are developed with a suite of ground motions representative of the seismic hazard of the case-study region. Results reveal the significant vulnerability of older non-seismically designed MSSS bridge with steel bearings due to the non-ductile failure of the bridge pier. The vulnerability of the bridge is significantly reduced with the adoption of modern seismic design and detailing practices.

Investigating Importance of Friction between Elastomer Bearing and Its Support on the Seismic Performance of Skew Seat-type Bridges

Investigating Importance of Friction between Elastomer Bearing and Its Support on the Seismic Performance of Skew Seat-type Bridges

Stretchable Semiconducting Composite Films Fabricated via Blending Polythiophene with an Elastomer Bearing Pendant Dopant

Stretchable Semiconducting Composite Films Fabricated via Blending Polythiophene with an Elastomer Bearing Pendant Dopant

Study of curved surface sliding isolated structure with multiple bearings

Earthquake is one of the most devastating natural disasters in the world. Elastomeric bearings are costly for the low-rise residential buildings of developing countries. Thus, it is necessary to research low-cost and highly efficient frictional bearings. A dynamic model of Curved Surface Sliding Isolated Structure (CSSIS) will be studied under horizontal earthquakes. Theoretical derivation concentrates on identifying the design parameters that affect the accelerations, displacements and lift-off forces of seismic isolation bearings. Key factors consist of radius of curvature, coefficient of friction, and damping ratio of the superstructure. Sensitivity analysis is performed by the numerical simulation, followed by comparing the results of the analysis with the shaking table tests. As the curvature radius increases, the displacements of the superstructure enlarge, the accelerations remain stable and the reaction forces of seismic isolation bearings decrease simultaneously. On the other hand, if the friction coefficient increases, the displacements of the superstructure decreases, but the accelerations of the superstructure and the reaction forces get enlarged. Results prove that CSSIS can effectively control the sliding displacement, superstructure recovery and lift-off forces of seismic isolation layer. The current finding will have a broad application of low-rise residential buildings, especially in the developing countries.

Comparison of the Shear Modulus of an Offshore Elastomeric Bearing between Numerical Simulation and Experiment

The most important item when indicating the mechanical properties of offshore elastomeric bearings is the shear modulus, and the method of measuring this is shown in EN 1337-3, a regulation related to offshore elastomeric bearings. In this work, we conducted an experimental and numerical study on an offshore elastomeric bearing to find its shear modulus. Shear modulus tests were conducted according to the procedure specified in EN 1337-3 Annex F, while simulations were performed using the finite element analysis (FEA) software, ANSYS. The main objective of this research work is to determine optimum analysis conditions for the simulation method that considers a nonlinear model for the elastomer material and predicts the experimental results accurately. We considered the Mooney–Rivlin (M-R) model that has two-parameter (2P), five-parameter (5P), and nine-parameter (9P) forms, depending on the number of terms in the series. We observed that the load-displacement graph is linear, and the percentage error between the results obtained with 2P and 5P M-R models is around 2.23% in the compression and 0.38% in the shear. The simulation results from 2P M-R model showed a good agreement with the experimental results with the correlation coefficient (R2) being 0.999 with an average error of about 2%. However, the deviation between the experimental and simulation results from the 9P M-R model is very high, with about 7%. Based on this study, we can say that the 2P M-R model can accurately predict the nonlinear behavior of hyperelastic material used in elastomer bearing. In addition, the shear modulus of elastic bearings for Class 3 Shore hardness was verified by comparing the numerical simulation values with those presented in EN 1337-3 Annex D.

Behavior of torsionally coupled buildings isolated by super-elastic bearing subjected to earthquakes

Performance of torsionally coupled buildings isolated by Shape Memory Alloy based Super-elastic isolation bearing is presented considering stochastic and recorded seismic excitations. The stochastic responses of isolated buildings are analyzed considering random earthquakes. The optimal choice of the pertinent isolator parameters are obtained through a bi-objective optimization that minimizes the angular acceleration of the building and the base displacement of the isolator simultaneously. Effectiveness of the Super-elastic bearing is also verified against recorded ground motions considering possible variations in eccentricity, ratio of uncoupled rotational to translational frequencies of the superstructure (frequency ratio) and the isolator. The super-elastic bearings are observed to be less efficient for isolating torsionally coupled building but helps in eliminating residual deformations in the isolators when compared with the conventional elastomeric bearing.

High-order finite element model of bridge rubber bearings for the prediction of buckling and shear failure

Performance-based design is becoming the main design method for highway bridge seismic design. This design method requires a good knowledge of the damage mechanisms of each component of the bridge. Rubber bearings and isolators represent a key component of the earthquake-resistance system of bridges that can experience large lateral displacements while supporting high axial loads. Rubber bearings and isolators can thus experience lateral instabilities under seismic loading, resulting in ultimate limit states by buckling or by shear failure depending on the geometry of the bearing. This paper investigates the development of a general numerical 3D finite element model for layered elastomeric bridge bearings and isolators that is able to accurately predict both limit states under shear-compression loadings at very large deformations. Such a model is aimed at subsequent utilization in large numerical and parametrical studies to develop practical and accurate design guidelines for the limit states of bridge rubber isolators. In this study, the accuracy of several rubber finite element formula tions has been studied, including the often used low-order and easy-to-calibrate Mooney-Rivlin and Neo-Hookean models and the two high-order Arruda-Boyce and 6-parameter Ogden models. For the latter model, a calibration procedure is proposed based on three simple standard characterization tests of the material that circumvents the much higher difficulty of calibration of the Ogden model compared to the others. The calibration results for the four considered models show that the 6-parameter Ogden model surpasses the ability of the three other models to accurately represent the material behavior in the different deformation modes experienced by rubber bearings under shear compression at large deformations. The four models are then compared for their ability to predict the force–displacement curves of some experimentally tested isolators. The Ogden model showed again higher accuracy compared to the other models that are mostly used in literature. The finite element model based on the Ogden formulation is finally completely validated by using extensive experimental results obtained from tests performed on real-scale rubber bearings and isolators of various shape factors and slenderness values. Finally, for nonslender bearings that experience shear failure at large deformation, a numerical material failure criterion is proposed and validated by comparing the critical displacement predictions of the model to the available experimental results.

Shear stress distribution of unbonded reinforced elastomeric bearings after lift-off occurs

Reinforced elastomeric bearings (REBs) are widely used to accommodate displacements in bridges as well as for seismic isolation applications. For unbonded REBs, lift-off (i.e. separation between the superstructure and the bearings) could occur under certain combinations of large rotations and relatively low axial stress. Canadian and American bridge design codes (i.e. CSA S6 and AASHTO) have inconsistent requirements in the regulation of lift-off. The objective of this study is to validate the existing analytical solution of the moment-rotation relationship for unbonded REBs considering lift-off by finite element analysis (FEA). The analytical solution, which accounts for the compressibility of the elastomer and extensibility of the reinforcement, has not yet been validated. The shear strain distribution in the elastomeric layers of unbonded REBs is derived and validated by FEA. Eight infinite strip-shaped bearings with different number of layers are investigated. The results show that the numerical curves fit well with the analytical curves in terms of the overall tendency. The analytical solutions could be used to predict the behaviour of unbonded REBs subjected to lift-off. The numerical results of the moment-rotation relationship were more agreeable to the analytical solutions for the unbonded bearings with fewer number of layers and under smaller loads.

A nonlinear plane strain finite element analysis for multilayer elastomeric bearings

The purpose of this paper is the prediction of the behaviour of multilayer elastomeric bearings by the finite element analysis. First, the finite element formulation of equilibrium equations of incompressible elasticity problem is presented. This approach is based on the modified potential energy taking into account the incompressibility. The linearized system obtained is solved by the Newton–Raphson iterative method with the total lagrangian formulation. A large plane strain element is developed for the analysis of elastomeric materials under large strain deformation. This element is then integrated into our software. After validating the plane strain element using examples with known exact solutions, an industrial case study made of laminated (metal-rubber) elastomeric component is examined. The stress distribution study is limited to the elastomeric layers, possible sources of crack appearance.

Seismic fragility and uncertainty mitigation of cable restrainer retrofit for isolated highway bridges incorporated with deteriorated elastomeric bearings

Overcoming the deterioration of aging infrastructure has aroused increasing concern in recent years, particularly, problem of deteriorated elastomeric bearings has emerged as one of the greatest challenges in maintenance and reliability strategies for isolated highway bridges. Though the abundant applications of cable restrainers to provide alternative measure against bearing deterioration and reduce the risk of bridge collapse due to deck unseating, the performance of cable restrainer retrofit is not well understood because of the complicated and nonuniform deterioration process of elastomeric bearings. This paper presents an in-depth seismic fragility and variation analysis to evaluate cable restrainer retrofit for isolated highway bridges, with a special emphasis on the introduction and mitigation of structural response uncertainty caused by the deteriorated lead rubber bearings (LRBs) and cable restrainer retrofit. Firstly, the mechanical properties of deteriorated LRBs and cable restrainers including the associated parameter uncertainty were modeled based on the consideration of past relevant researches. Subsequently, seismic response of a simplified model of a typical continuous girder isolated highway bridge subjected to various scaled earthquake ground motions was computed to statistically evaluate the effect of typical uncertainties of the mechanical behavior of deteriorated LRBs and cable restrainers upon the risk of global seismic failure of the bridge. Finally, the contribution of cable restrainer retrofit in mitigating the vulnerability and response uncertainty of structural components is quantitatively assessed by comparing the cases with and without the application of cable restrainers. The statistical assessments not only reveal the effect of restrainer cable retrofit at the earthquake levels for design standards, but also consider the levels of seismic events greater than consideration in the design, incorporating the seismic performance uncertainty introduced and enlarged by the aging deterioration of LRBs.

Experimental investigation of unbonded ordinary steel reinforced elastomeric bearings as an isolation system in bridges

Reduction of large tensile stresses and cost-efficiency has made unbonded isolators an attractive option as an isolation system. Following this idea and the results obtained by various researchers, it is shown that unbonded steel-reinforced elastomeric bearings (SREBs), which are used and designed for non-seismic actions, have inherently acceptable characteristics in tolerating large shear deformations for a cost-effective isolation system and can provide improved structural performance. However, this capacity is neglected in the design process. The current article presents an experimental program to analyze the mechanical properties of steel-reinforced natural rubber bearings without the upper and lower endplates when subjected to large shear displacements and to assess how they can be used and what are the limitations. The overall behavior of the bearing is explained and the affecting variables including the level of axial load, rate of loading, and contact conditions are discussed. A full-scale test setup using a pair of bearings sandwiched between three concrete platens is utilized which considers the interaction of compressive and cyclic shear loading. Even though it is costly and difficult, this setup provides a realistic approach for testing bearings while they are in contact with concrete on both sides. The test results reveal that under different vertical loading levels, all bearings exhibited stable hysteretic response. In presence of adequate axial load, the specimens were capable of tolerating shear strains more than 125% without slippage of the bearings. It was shown that albeit demonstrating low damping characteristics, these bearings provide adequate flexibility and shear displacement capacity which indicates they can be a proper choice for substitution as costly isolators in low to moderate seismic zones or for low-risk short span bridges in developing countries.

Parametric studies on the behaviour of reinforced elastomeric bearings considering the compressibility and extensibility index, shape factor, and lift-off

Reinforced elastomeric bearings (REBs) are widely used in bridges as well as for seismic isolation applications. Analytical solutions for the critical design properties of REBs (e.g. compression and bending modulus, stress distributions) have been derived based on the assumptions of the pressure solution. In all cases, the analytical solutions can be expressed as functions of the dimensionless compressibility and extensibility index. This parameter accounts for the influence of the compressibility of the elastomer and the extensibility of the reinforcement. Together with the shape factor, these variables are highly influential on REB design. The objective of this study is to investigate mechanical behaviour of bonded and unbonded REBs with the same compressibility and extensibility index but different other parameters and the influence of the shape factor by finite element analysis (FEA) including lift-off. For unbonded REBs, lift-off (i.e. the separation between the superstructure and the bearings) can occur under certain combinations of large rotations and relatively low axial stress. Three different loading cases (pure compression, pure bending and the combined case) are considered. The results show that REBs with the same compressibility and extensibility index but different other parameters have similar behaviour under the same loading condition. Available analytical solutions have good agreement with numerical results provided an appropriate shear modulus is selected and the level of rotation is reasonable for structural applications.

Dynamic Analysis of Ballastless Rail Superstructure on a Track Switch

Proposed article presents design procedure and dynamic analysis of a ballastless rail superstructure used to decrease the vibration from the moving trains in underground tunnels located adjacent to residential and commercial buildings. The rail superstructure features a floating slab consisting of a reinforced concrete (RC) slab with direct fixation of railway fastenings and elastomeric bearings, that transfer the loads from the floating slab to the tunnel casing. A track switch is mounted on a FST. The aim of the design procedure is to select required static and dynamic properties of elastomeric bearings made of cellurar polyurethane as well as the amount of reinforcement taking into account deteriorating properties of both materials. FE-model created in MSC Patran/Nastran software package is used to get an insight on stress-strain state of this floating slab track structure. Proposed FE-model consists of switch track with direct fixation railway fastenings, RC track slab, elastomeric supports. Static analysis is performed to get the upper-track structure elements’ deflections as well as stress-strain state of RC slab under moving trains. Dynamic interaction of the ballastless rail superstructure is investigated using derived from FE-analysis transfer-function between the superstructure and tunnel invert. Vibration isolation efficiency under excitation frequencies of moving trains over different speed is obtained from the transfer function.

Effect of Taper on Shear Stiffness of Steel-Reinforced Neoprene Bearing Pads

Steel-reinforced elastomeric bearing pads are widely used in bridge construction to vertically support girders on piers while also accommodating translational and rotational girder deformations caused by live loads and temperature changes. To support sloped girders, flat bearing pads of uniform thicknesses are typically used with either tapered steel shim plates or an inclined concrete bearing seat. The use of tapered pads has the potential to reduce both construction time and cost by eliminating the need for tapered plates or seats to match the girder slope. However, limited research has been performed to investigate the effect of introducing taper on relevant design properties of bearing pads. In this paper, results are presented from experimental testing that was performed to quantify the effect of taper on shear stiffnesses of pads having varied geometric characteristics (plan view dimensions, elastomer thicknesses, and slope angles). An experimental bearing pad test device was designed and utilized to impose shear loads in accordance with ASTM standards, while simultaneously maintaining a constant axial load. Bearing pads chosen for testing were tapered variations of standard flat bridge bearing pads used in the state of Florida, U.S. Results obtained from the study revealed that shear stiffness was not significantly influenced by the introduction of taper angle, the direction of shear along the length of pads, or axial load level. The shear stiffness of tapered pads remained within approximately 10% of the shear stiffness of corresponding flat pads.

Most suitable types of seismic isolation for use in old mosques in Syria

The article discusses the most suitable base
 isolation bearings from the author's point of view for use in the buildings of
 old mosques in Syria, which are designed to protect such buildings from the
 effects of earthquakes that can occur at any time. Especially since many of
 such buildings have an architectural and cultural value, and are included in
 the world heritage list of UNESCO. Elastomeric
 bearings with high energy dissipation capacity (HDRB), elastomeric bearings
 with lead cores (LDRB), single friction pendulum, double friction pendulum and
 triple friction pendulum sliding (FPS) bearings are considered. What they
 consist of, their characteristics. Three, mosques in Syria that are of a great
 value from the point of view of architecture and cultural heritage are listed
 and described, and conclusions are drawn.

Experimental investigation and seismic fragility analysis of isolated highway bridges considering the coupled effects of pier height and elastomeric bearings

Elastomeric bearings are widely utilized in highway bridges and attracting a great deal of attention, although their mechanical behavior has been clearly recognized, the coupled effects of critical bridge structural components and complex mechanical behavior of elastomeric bearings are yet to be well characterized. In this study, experimental investigation and seismic fragility analysis were conducted to evaluate the seismic performance of isolated highway bridges, with a special emphasis on considering the coupled effects of pier height and rate-dependent behavior of elastomeric bearings on the bridge response. To this end, real-time hybrid simulation (RTHS) tests featured by a velocity loading control were performed on a typical highway bridge. Two pier heights and two common types of elastomeric bearings including low damping rubber bearing and high damping rubber bearing were paired and tested. The effects of pier height and elastomeric bearings were illustrated by comparing and analyzing a wide range of response quantities of the bridge. The test results indicated that pier height and rate-dependent behavior of elastomeric bearings could remarkably influence the seismic response of the bridge in both individual and combined ways. Subsequently, a hyper-viscoelastic model of elastomeric bearings was proposed to capture their mechanical behavior, then, both the proposed and conventional bilinear models were implemented in the numerical simulation to evaluate the seismic fragility of the bridge. Fragility curves for two bridge components including piers and elastomeric bearings as well as for the bridge system were developed and discussed. The study reveals crucial effects of pier height and mechanical behavior of elastomeric bearings on both the component and system fragility curves of the bridge, it is found that an optimal combination of pier height and elastomeric bearings should be considered to improve the seismic performance of isolated highway bridges.

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 ...

Nonlinear Dynamic Analysis of Seismically Base-Isolated Structures by a Novel OpenSees Hysteretic Material Model

The complex response characterizing elastomeric isolation bearings is reproduced by employing a novel uniaxial hysteretic model that has been recently formulated and successfully implemented in OpenSees. Such a novel OpenSees material model offers several advantages with respect to differential models typically available in commercial software products for structural analysis, such as 3D-BASIS and CSi programs. Firstly, it is based on a set of only five model parameters that have a clear mechanical significance; such a property not only allows one to drastically simplify the parameters identification process, but it also allows the model to be used in practice. In addition, the model does not require numerical methods for the evaluation of the restoring force since the latter is computed by solving an algebraic equation. To encourage researchers and designers to adopt the proposed model for research and practical purposes, we demonstrate its accuracy by performing some numerical tests in OpenSees. In particular, we first employ the recently implemented model to compute the nonlinear dynamic response of a seismically base-isolated structure with elastomeric bearings and, subsequently, we compare the results with those obtained by modeling the seismic isolators with the OpenSees BoucWen uniaxial material model, that is one of the most popular and accurate hysteretic models currently available in OpenSees.