Elastomeric Bearings Research Articles

Deep learning-based condition assessment for bridge elastomeric bearings

Deep learning-based condition assessment for bridge elastomeric bearings

Nondestructive Assessment of Elastomeric Bridge Bearings Using 3D Digital Image Correlation

Elastomeric bridge bearings are installed between the bridge superstructure and substructure to accommodate translational and rotational deformations. The manufacturing quality of elastomeric bridge bearings is of high significance because manufacturing defects (such as variations in rubber layer thickness and nonparallel steel laminates) may jeopardize their short- and long-term structural behavior and integrity. Current quality control procedures involve destructive testing of samples of bearings from a lot. This type of testing is time consuming and costly, and thus limited to a relatively small sample size, which may undermine confidence in the quality of remaining bearings in the lot. This paper presents an alternative, vision-based assessment methodology for the nondestructive identification of the internal structure of elastomeric bridge bearings. The methodology capitalizes on the high deformability of rubber and the near inextensibility of the steel laminates, which together result in a unique deformation pattern on the vertical surfaces of a bearing when it is subjected to axial load. This deformation pattern features local extrema in in-plane strain and horizontal displacement fields on the vertical surfaces. These local extrema are analyzed to deduce the thicknesses of the rubber layers and rubber side covers. The methodology is developed based on three-dimensional finite-element analyses (3D-FEA). Then, three-dimensional digital image correlation (3D-DIC) is used in experimental tests to evaluate its capability to identify manufacturing defects in elastomeric bridge bearings. Finally, the methodology is validated against destructive tests. The nondestructive method presented in this study is conducted in conjunction with compressive tests that departments of transportation carry out routinely and is therefore expected to facilitate rapid and cost-effective qualification of elastomeric bridge bearings.

Shear Characteristic Changes in Blended Rubber of Elastomeric Bearings due to Aging

Rubber bearings are widely used for seismic retrofit of bridges because they reduce the seismic force by making the vibration period of the bridge longer and distributing the seismic force to all the piers. However, they have the disadvantage of being easily aged compared to steel bearings as well as having variations in the shear stiffness. The shear characteristic changes in the blended rubber for the rubber bearings were analyzed, specifically, the aging accelerated by heat. The higher the aging temperature and longer the exposure time, the greater is the maximum stress and strain at that time, and the greater is the shear stiffness. This implies that the seismic performance gradually deteriorates due to aging as the service period becomes longer. This can provide the basis for the mechanical model of the aging bearing.

Differences in Shear Characteristics by Rubber Types for Elastomeric Bearing According to Aging Promotion Level

Differences in Shear Characteristics by Rubber Types for Elastomeric Bearing According to Aging Promotion Level

Assessment of the Suitability of Elastomeric Bearings Modeling Using the Hyperelasticity and the Finite Element Method.

The paper presents modeling of bridge elastomeric bearings using large deformation theory and hyperelastic constitutive relations. In this work, the simplest neo-Hookean model was compared with the Yeoh model. The parameters of the models were determined from the elastomer uniaxial tensile test and then verified with the results from experimental bearing compression tests. For verification, bearing compression tests were modeled and executed using the finite element method (FEM) in ABAQUS software. Additionally, the parameters of the constitutive models were determined using the inverse analysis method, for which the simulation results were as close as possible to those recorded during the experimental tests. The overall assessment of the suitability of elastomer bearings modeling with neo-Hookean and Yeoh hyperelasticity models is presented in detail.

Parameterized models for prediction of lifetime bearing demands

A good replacement and maintenance policy for bridge bearings is essential for bridge integrity and functionality. This requires proper estimation of the bearing life expectancy which in turn is dependent on the working condition demands. The lifetime travel and peak displacement demands are highly sensitive to the loading, bridge geometry, and bearing properties. Hence, predicting when bearings should be replaced is difficult. To facilitate the decision making process, this study proposes prediction models for the annual demands of elastomeric bridge bearings. First, random bridge configurations (e.g. elements geometry, deck type, and number of spans) and random loading conditions (e.g. temperature profiles, earthquake records, and traffic loading scenarios) are generated using Monte Carlo simulation combined with Latin hypercube sampling, and the bearing demands are computed. Bearing demand prediction models are then developed via regression analysis and used to create a general fatigue loading protocol. This protocol can be used for testing and rating sample bearings. This would aid in predicting the bearing life expectancy, allowing for better replacement scheduling, and budget estimation. The application of the proposed demand prediction models for generating fatigue loading protocols is demonstrated through a case study.

Modeling and analysis of a prestressed girder bridge prior to diagnostic load testing

Progressive deterioration is a problem that affects road infrastructure, especially bridges. This requires the development of methods for its adequate detection and revision, one of them being load testing. Within load testing, finite element analysis (FEA) models provide initial information to understand the behavior of a structure and plan accordingly, which represents a fundamental step towards a precise structural evaluation of a bridge. This study focused on the modeling and analysis of the static response of the bridge over the river Lili in Cali, Colombia, a prestressed girder bridge programmed to undergo a diagnostic load test. A linear FEA model was created with information from a manual survey and from other bridges’ plans designed and built under the regulations in force at the time. Due to the absence of plans and design specifications for the bridge, variations were applied to certain model parameters (stiffness of diaphragms and elastomeric bearings), to quantify their effect on the overall behavior of the bridge. The analysis included obtaining the critical position for the design vehicles, the transversal distribution of stresses and determining the influence of the variation parameters in the response of the structure. Results showed that the critical combinations for bending moment and shear were when the loads were the closest to the exterior girders, being these elements the most affected. The variation on the modulus of elasticity for the diaphragms and the stiffness of the elastomeric bearings did not significantly influence the results for bending moment and shear, nor the critical position. Girder distribution factors (GDF) from the model were compared to previous research, finding similarities in shape and value with other FEA models and experimental results. Finally, an instrumentation plan focused on the girders of the bridge was proposed based on the zones where the maximum effects are expected. The findings in this study show how linear FEA models provide initial but relevant information regarding the critical position of design vehicles, the distribution of stresses and the expected values for bending moment and shear under design loads.

Bi-directional loading of unbonded rectangular fiber-reinforced elastomeric isolators

Elastomers are ideal for application as base isolators due to their ability to accommodate large recoverable strains. The formation of a composite with reinforcement, either steel or fibers, takes advantage of the near incompressibility of the elastomer to enhance the vertical and bending properties of the bearing. Although the conceptual design of a fiber-reinforced and steel-reinforced elastomeric bearing is similar, the lack of flexural rigidity of the fiber reinforcement results in unique performance characteristics, especially in the lateral direction. In this paper, an experimental program is conducted to evaluate the effect of lateral coupling in rectangular unbonded fiber-reinforced elastomeric isolators (UFREIs). An apparatus with six degrees of freedom was used to apply a vertical load with simultaneous displacement in both primary lateral directions, whereas previous experimental programs are mostly based on a two degree of freedom analysis (vertical and lateral). The UFREI specimen was subjected to cyclic lateral displacements including tests with initial lateral offsets in the secondary lateral direction, in directions angled off the principal lateral axis, and in a circular motion. This experimental program is the first to investigate lateral coupling in rectangular UFREIs. A comparison was conducted based on the effective lateral stiffness, equivalent viscous damping, and energy dissipation characteristics. The considered rectangular UFREIs were found to exhibit lateral coupling but the degree of coupling and the impact on the structural performance under bidirectional loading require further investigation. Residual displacement was observed in the experimental program and is discussed in depth. Also, a theoretical equation is derived to calculate the lateral stiffness based on the angle of loading and lateral displacement. Theoretical values are compared with experimental results to verify the equation.

The role of shear modulus on the mechanical behavior of elastomeric bearings when subjected to combined axial and shear loads

Multi-layered elastomeric bearings (EB) are used extensively in civil structures and infrastructures, due to their ability to mitigate the movements that structures such as buildings, bridges and nuclear power plants may experience when they are subjected to vibrations, earthquakes and other natural hazards. During large movements, EBs may experience both axial and shear loads and consequently displacements which have been investigated in several studies based on analytical, experimental and numerical approaches. This study investigates the role of the shear modulus, Gb, on the mechanical behavior of EBs when combined axial and shear loads are applied, by performing numerical simulations. The main objective is a closed-form solution that describes the non-linear relationship between the vertical axial load, the relative rotation and the shear modulus of the EBs. The presented formulation constitutes a proposal for potential applications to numerical platforms in order to reproduce the combined axial – shear macroscopic behavior of the EBs.

Seismic fragility assessment of Chilean skewed highway bridges

The 2010 Maule, Chile earthquake demonstrated that many bridges were highly vulnerable to seismic demands. Among these bridges, skewed multi-span prestressed concrete girder bridges supported on non-anchored elastomeric bearings were the most vulnerable ones. After the 2010 Maule earthquake, several damaged skewed bridges were repaired and retrofitted using an updated seismic design criterion. Therefore, this study aims to compare the seismic performance of typical Chilean skewed highway bridges in their original design (prior to 2010) and in their repaired condition (post 2010). With this aim, three-dimensional (3D) nonlinear finite element models of four skewed bridges, which were damaged during the 2010 Maule earthquake, are developed and analyzed. Nonlinear static and incremental dynamic analyses (IDAs) are conducted, and fragility curves are obtained to evaluate the short-term evolution of the Chilean design practices. Additionally, the influence of the skew angle, vertical seismic bars, modelling assumptions and anchorage of elastomeric bearings, on the seismic performance of Chilean skewed highway bridges is analyzed through IDAs and fragility curves. The results of this study show that repair measures considered after the 2010 Maule earthquake improve the seismic performance of skewed bridges and effectively prevent span unseating. However, the adopted measures do not significantly improve the performance at slight to moderate damage states. It is also demonstrated that the skew angle and deck-abutment pounding have significant influence on the seismic performance. Finally, the results show that an adequate modelling of vertical elements, such as elastomeric bearings, must be considered to avoid underestimating displacement demands.

Base isolation for mid-rise buildings in presence of soil-structure interaction

Base isolation has been commonly used for seismic protection of lowrise (short period) buildings on firm ground. For taller buildings on soft soil, however, the following concerns arise: soil-structure interaction (SSI) alters the resonant characteristics of the whole system and its dynamic response. The efficiency of base-isolation depends on the dynamic properties of the system and the shape of the site response spectrum. In this work, SSI effects on the dynamic response of base-isolated mid-rise buildings are examined. A discrete shear-building model with linear elastic elastomeric bearings and flexible foundation is analyzed by a suitable method for systems with non-classical damping. The model is applied to evaluate the feasibility of using seismic isolation at soft-soil sites of Mexico City, where typical buildings of 10–15 stories were the most damaged during the great 1985 Michoacán earthquake. It is concluded that base isolation can be effectively used to control the detrimental SSI effects anticipated for these buildings located at sites with dominant period longer than the fundamental fixed-base period of the superstructure.

Geometric Attention Regularization Enhancing Convolutional Neural Networks for Bridge Rubber Bearing Damage Assessment

Rubber bearing condition evaluation is crucial for bridge inspection, and the current practice heavily relies on human-vision inspection. Convolutional neural networks (CNNs) have shown great potential for structured damage recognition tasks in recent years; however, this method usually requires a large training data set, which is difficult to collect in practice for rubber bearings. Therefore, methods to improve the performance of CNN for condition classification for elastomeric bearings are necessary. In this paper, a geometric attention regularization (GAR) method is proposed to enhance the performance of CNN for the condition evaluation of rubber bearings. Firstly, the data set of bearings contains different damages that are collected and labeled where the location of the rubber bearing is presented as a bounding box. Then, the location information is utilized to enhance the loss function of CNN in two aspects. On one hand, the bearing location worked as an attention mechanism to indicate the important part of the input image. Besides, it worked as a regularization method to mitigate the effect of overfitting. Experiments using two CNN architectures, including VGG-11 and ResNet-18 trained with transfer learning techniques, are used to evaluate the efficacy of the proposed method. The results show the proposed method is effective to enhance the performance of the CNN model.

Mitigation of Earthquake Responses Using SMA Supplemented Base-Isolation Devices for Benchmark Building

The efficiency of traditional isolation bearings is doubted for near-field earthquakes because these bearings undergo large displacement. A comparative study of different base isolation systems of base-isolated benchmark building is carried out in the present study. The study is based on assumption that buildings are bi-directionally acted upon by near-field earthquakes for assessing their relative performance in seismic control of the benchmark building. The time history variations of important response parameters and evaluation criteria of the benchmark building has been studied for assessing the effectiveness of the isolation systems. The Shape Memory Alloy (SMA) is utilized with elastomeric bearings and friction bearings to study the effectiveness of SMA wires with different isolators. The benchmark building is modelled as a discrete linear elastic shear structure having three degrees of- freedom at each floor level. Time domain dynamic analysis of this building has been carried out with the help of constant average acceleration Newmark’s method and equilibrium of non-linear forces has been taken care by fourth order Runge-Kutta method. The comparative performance of various isolation systems has been studied with uniform and hybrid combinations. The hybrid combination of SMA supplemented bearings works out the better isolation system keeping in view of the percentage reduction in evaluation criteria for smart base-isolated benchmark building. Furthermore, it is shown that, the functionality of SMA wire is not efficient with Lead Rubber Bearing system, as it is able to control displacement but increases the acceleration, base shear, story drift and isolation forces.

Probabilistic seismic performance assessment of optimally designed highway bridge isolated by ordinary unbonded elastomeric bearings

Following the idea of using unbonded isolators to eliminate the tensile stress and providing a cost-effective isolation system, recent experimental research has shown ordinary unbonded steel reinforced elastomeric bearings (SREBs) as an attractive option for seismic isolation of highway bridges. The focus of current research work is on the evaluation of the seismic vulnerability of a highway bridge isolated by unbonded SREBs through developing fragility curves of the structure. This assessment considers parameters playing a key role in the isolation system behavior, namely the friction coefficient, as well as the isolator aging effects. In this regard, a typical three-span highway bridge is considered and designed with the rubber bearing isolation system by applying a multi-objective optimization procedure to reduce the seismic isolation deformation as well as the base shear simultaneously. The nonlinear models for bridge piers and isolation devices are incorporated. An Incremental Dynamic Analysis (IDA) method is applied to generate the fragility functions using a suite of 20 ground motion records. The results show that this type of base isolation system is well capable of mitigating earthquake excitation. Additionally, the overall performance of the bridge is not sensitive to the friction coefficient, while the aging of the isolator units caused an increase in the bridge vulnerability.

Self-Healing, Reprocessable, and Degradable Bio-Based Epoxy Elastomer Bearing Aromatic Disulfide Bonds and Its Application in Strain Sensors

A dicarboxylic acids functional aromatic disulfide (DTSA) and a dimer aliphatic acid (DAA) were used to crosslink epoxidized soybean oil (ESO) to obtain a bio-based epoxy elastomer with comprehensive properties of toughness and stretchability. This work addresses some urgent needs for epoxy networks, such as recyclability, degradability, and mechanical properties. Ratios of permanent and dynamic crosslinks were tuned to yield epoxy elastomers with various characteristics. The bio-based epoxy elastomer in this work took advantages of dynamic aromatic disulfide bonds which can rapidly exchange even at room temperature without external stimuli. Therefore, the epoxy elastomer reported here presented almost quantitative self-healing efficiency and high recovery in terms of mechanical properties after being reprocessed for many times. Besides, incorporation of permanent chemical crosslinks with DAA caused low hysteresis, which made them suitable for fabricating sensitive and durable strain sensor against cyclic strain.

Validation of an elastomeric bearing characterized with finite element hyperelastic models

Elastomeric bearing is a crucial element of a structure. To study these elements' behavior under different loads, a correct strain energy function should be selected to predict the nonlinear hyperelastic behavior accurately. Physical compression test performed on a sample of a steel laminated elastomeric bearing, which is originally used on structure foundation to resist seismic forces. A finite element software was used to simulate physical test for seven different hyperelastic models. Error percentages were also calculated and compared between all models with the experimental data. The results of these seven models were validated in order to select the most fitted form. Multiple models gave an accurate prediction of this element behavior. Reduced Polynomial form was the best choice to model compression tests and the finite element simulation showed an accurate prediction for bearing behavior, the model curve is perfectly fitted with the physical test curve and the maximum error percentage was less than 7% and less than 2% minimum error.

Seismic Risk Assessment of Optimally Designed Highway Bridge Isolated by Ordinary Unbounded Elastomeric Bearings

Seismic Risk Assessment of Optimally Designed Highway Bridge Isolated by Ordinary Unbounded Elastomeric Bearings

Evaluation of Design Equations for Critical Properties of Reinforced Elastomeric Bearings and Recommended Revisions

AbstractGlobal interest in seismic isolation technology continues to increase due to the satisfactory performance of isolated structures in recent earthquake events. In addition to the overall resp...

Accuracy of analytical models to predict primary and secondary system response in seismically isolated buildings

Seismic isolation is generally considered an effective earthquake protection strategy. As application of seismic isolation increases, decisions on the use of one particular isolator versus another isolator increasingly depend on computed responses with complex analytical models. Accordingly, validation of analytical models to predict primary (structural) and secondary system (non-structural component) response in seismically isolated buildings becomes very important. This paper presents comparisons of experimental and analytical results on the primary and secondary system response of a building model in order to provide information on the accuracy of the predicted response. The tested model was configured as a 6-story building at quarter length scale in a moment-frame configuration, and with the following seismic isolation systems: a) Low damping elastomeric bearings with and without linear or nonlinear viscous dampers, b) Single Friction Pendulum (FP) bearings with and without linear or nonlinear viscous dampers, and c) Lead-rubber bearings. Response quantities compared include story drifts and isolator shear forces and displacements for the primary system, and peak floor total velocities and floor response spectra that relate to secondary system response. This paper presents samples results out of a total of 288 comparisons of experimental and analytical results presented in an MCEER report. It is shown that the primary and secondary system response is computed with sufficient accuracy by the analytical models but some response quantities may be underestimated or overestimated by significant amounts.

A simplified and versatile element model for elastomeric seismic isolation bearings

A novel approach for two-dimensional modeling of elastomeric bearings using three springs in parallel is presented. This simplified element model considers as follows: (1) an elastoplastic spring with a smooth transition between branches; (2) a linear elastic spring; and (3) a non-linear elastic spring, and is fully defined by only six parameters. The main advantages of the simplified model are twofold: (1) versatility, as a single model is capable of accurately reproducing the main characteristics of the hysteretic behavior of different types of rubber-based seismic isolators, including low damping rubber bearings (LDRBs), high damping rubber bearings (HDRBs), and lead-core rubber bearings (LRBs) and (2) simplicity, as it requires fewer parameters and it is easier to calibrate from experimental cyclic test results than most currently available models. Model parameters’ identification is illustrated using quasi-static cyclic and earthquake simulator tests of HDRBs and LRBs, demonstrating that the model shows a good agreement between the test-measured and model-predicted hysteretic behavior. Different objective functions are evaluated in the optimization procedure, and their effect on the identified parameters is studied and discussed. This practitioner-oriented model is particularly amenable for implementation in general-purpose structural analysis software. Its usage is strongly recommended as an initial-stage design tool to select the optimal isolation system for a specific project.