Elastomeric Bearings Research Articles

Seismic fragility and risk assessment of Reinforced Concrete bridges undergoing elastomeric bearing deformations induced by landslide

The paper presents a study on the seismic fragility of Reinforced Concrete (RC) bridges isolated by elastomeric bearing devices subjected to differential displacements induced by slow-moving landslides. The seismic behaviour of isolated bridges is ruled by the performance of elastomeric bearings to reduce and dissipate earthquake actions. These bridges are subjected to service loads that usually are accounted for in design, but possible additional actions from the surrounding environment, such as landslides affecting substructure components, can seriously undermine the seismic response. The paper describes a practical approach to investigate the seismic fragility and risk of RC bridges isolated by elastomeric bearings, which may undergo early deformations induced by the differential displacements of substructure components. On the basis of previous existing studies, the proposed methodology is based on numerical modelling accounting for landslide-induced substructure displacements and proper modifications on the constitutive law and hysteretic response of the elastomeric bearings. Subsequently, after establishing specific limit-states, nonlinear time history analyses of the seismic response are used to estimate fragility curves and risk indicators. The study points out that it is possible to quantify the influence of landslide-induced effects on seismic fragility and risk by using only two numerical models, in order to provide decision support to transportation authority responsible for ensuring the safety of bridges and road networks. The proposed approach has been tested on a real-life case study, the Santo Stefano Viaduct in Italy, which was subjected in the past to relevant deformations of the elastomeric bearings due to an active landslide phenomenon.

The Seismic Response Evaluation of an Existing Multi-span Reinforced Concrete Highway Bridge in the Presence of Linear and Nonlinear Viscous Dampers

AbstractIt’s crucial to keep bridges safe and operational all the time. Before or after an earthquake, they may require immediate seismic retrofitting. In this situation, adopting both isolation systems and viscous dampers could be used as a solution. Therefore, the seismic performance of a RC bridge with linear and nonlinear viscous dampers at both pier tops and abutments is investigated. The selected bridge model is the Incesu Bridge in Artvin province in north–eastern Turkiye. In the bridge model, elastomer bearings (EBs) and viscous dampers (VDs) are added to the abutments and the tops of the piers (i.e., the bridge deck connection points). The results revealed that the maximum bending moment of two piers could be significantly reduced compared with the case where the pier’s tops are fixed to its deck. However, a large level of a viscous damper coefficient added to a bridge could cause structural damage to its deck under a strong design earthquake.

Performance of Novel Rectangular Partially Bonded Steel Mesh–Reinforced Elastomeric Bearings for Seismic Isolation of Bridges

Performance of Novel Rectangular Partially Bonded Steel Mesh–Reinforced Elastomeric Bearings for Seismic Isolation of Bridges

Critical behavior of thick rubber bearings under compression and shear

Thick rubber bearings (TRBs) are used for seismic isolation as well as for subway-induced vertical vibration mitigation. Under earthquake ground shaking, TRBs typically undergo large horizontal displacements that lead to a reduction of their vertical bearing capacity, which should be carefully evaluated during design. This study investigates the performance of TRBs under compression and compression-shear loading. Eight full-scale TRB specimens were designed and tested. The test results show that increasing the axial load increases the compressive stiffness of TRBs. During compression-shear loading, TRBs under design level axial loads failed due to rubber rupture at shear strain γ > 350 %, while under higher axial loads, they failed because of instability at γ ＜ 300 %. In addition, in cyclic shear deformation under axial loads larger than twice the design level axial load, the TRBs exhibited negative stiffness at the unloading branch of the F-u loop. The effective damping ratio significantly increased with increased axial load. Then, the test data were used to validate existing mechanical models for the prediction of the compression-shear behavior of elastomeric bearings. Existing analytical models were modified by accounting for the compressive stiffness change due to increased axial loads, leading to more accurate prediction. Finally, models for the critical load of TRBs under zero and lateral displacement were examined and improved.

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

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

Seismic fragility analysis of simply supported bridges considering uncertainty in scour condition

Bridges are vital infrastructures but face compounding risks from scouring and seismic events. Although recent studies have explored these individual and overlapping hazards, they often utilize deterministic approaches and focus on specific bridge types in limited geographical areas. This study addresses these gaps by introducing a probabilistic framework for assessing the seismic performance of multi-span reinforced concrete (RC) highway bridges in the presence of scour-related uncertainties. A time-dependent scour model, informed by a Bayesian approach and literature-based uncertainties, is integrated into the framework. Probabilistic Seismic Hazard Analysis (PSHA) and record selection strategies are employed to define the seismic demand probabilistically. Monte Carlo simulation (MCS) is utilized to propagate combined uncertainties during the analysis, considering different scour scenarios defined according to the discharge peak condition of the flood event at the specific location of the bridge. In the last step of the probabilistic framework, fragility analyses are conducted on individual components and the entire system by means of nonlinear dynamic models and multiple stripe analysis (MSA). An actual five-span bridge with simply supported prestressed concrete girders, located in Chile, is used as application example of the proposed approach, considering measured hydrological data and seismic hazard of the real location of the bridge. The study identifies distinct vulnerabilities across various bridge components under scour conditions. Elastomeric bearings are particularly susceptible in scenarios characterized by low scour depths (low discharge peak condition). Conversely, abutments display heightened vulnerabilities as scour depth increases (medium discharge peak condition). Piles also exhibit notable vulnerability, escalating in scenarios with great scour depth (medium discharge peak condition). Notably, piles tend to be more susceptible than columns to scour effects, especially in bents featuring shorter columns. These disparities in vulnerability are influenced by the bridge design philosophy, as well as the synergistic effects of seismic forces and varying scour depths. System fragility curves further elucidate that the likelihood of exceeding specific damage thresholds varies according to different scour scenarios, with the deeper scour depth scenario, displaying the higher vulnerabilities.

Design and numerical simulation of the elastomeric support for the topside modules of an FPSO

Elastomeric support utilizing steel-reinforced elastomeric bearing pads (SREBPs) has been applied to offshore structures gradually. This study presented a process for designing the offshore elastomeric support. And a specific numerical method was introduced to synchronously simulate the hydrodynamic responses and structural interactions between hull and topside modules of a spread-moored floating production storage and offloading (FPSO) unit with elastomeric-supporting topside modules. Furthermore, a model test of the target FPSO was conducted in a deepwater offshore basin to validate the numerical simulation, and the numerical results were consistent with the experimental outcomes overall. The numerical results demonstrated that both bearing force and stress of the SREBPs fell within the design scope, and the maximum bearing force on vertical SREBPs was found to be around 1.3 times the weight of a corresponding topside module, considering the dynamic effects resulted from motion responses of the FPSO. Additionally, the maximum bearing force acting on anti-uplift SREBPs can refer to the peak value of a vertical SREBP's dynamic force correspondingly. The horizontal interactions between hull and topsides mainly depend on inclination of the hull, so the bearing forces of horizontal SREBPs are closely related to the severity of rolling and pitching.

A Crown-Ether-Based Elastomer Bearing Loop Structures with Dissipating Characteristics and Enhanced Mechanical Performance.

Loops are prevalent topological structures in cross-linked polymer networks, resulting from the folding of polymer chains back onto themselves. Traditionally, they have been considered as defects that compromise the mechanical properties of the network, leading to extensive efforts in synthesis to prevent their formation. In this study, we introduce the inclusion of cyclic dibenzo-24-crown-8 (DB24C8) moieties within the polymer network strands to form CCNs, and surprisingly, these loops enhance the mechanical performances of the network, leading to tough elastomers. The toughening effect can be attributed to the unique cyclic structure of DB24C8. The relatively small size and the presence of rigid phenyl rings provide the loops with relatively stable conformations, allowing for substantial energy dissipation upon the application of force. Furthermore, the DB24C8 rings possess a broad range of potential conformations, imparting the materials with exceptional elasticity. The synergistic combination of these two features effectively toughens the materials, resulting in a remarkable 66-fold increase in toughness compared to the control sample of covalent networks. Moreover, the mechanical properties, particularly the recovery performance of the network, can be effectively tuned by introducing guests to bind with DB24C8, such as potassium ions and secondary ammonium salts.

A Crown‐Ether‐Based Elastomer Bearing Loop Structures with Dissipating Characteristics and Enhanced Mechanical Performance

AbstractLoops are prevalent topological structures in cross‐linked polymer networks, resulting from the folding of polymer chains back onto themselves. Traditionally, they have been considered as defects that compromise the mechanical properties of the network, leading to extensive efforts in synthesis to prevent their formation. In this study, we introduce the inclusion of cyclic dibenzo‐24‐crown‐8 (DB24C8) moieties within the polymer network strands to form CCNs, and surprisingly, these loops enhance the mechanical performances of the network, leading to tough elastomers. The toughening effect can be attributed to the unique cyclic structure of DB24C8. The relatively small size and the presence of rigid phenyl rings provide the loops with relatively stable conformations, allowing for substantial energy dissipation upon the application of force. Furthermore, the DB24C8 rings possess a broad range of potential conformations, imparting the materials with exceptional elasticity. The synergistic combination of these two features effectively toughens the materials, resulting in a remarkable 66‐fold increase in toughness compared to the control sample of covalent networks. Moreover, the mechanical properties, particularly the recovery performance of the network, can be effectively tuned by introducing guests to bind with DB24C8, such as potassium ions and secondary ammonium salts.

Air and Structural Loads Analysis of a 5-Ton Class Rotorcraft in a Pull-Up Maneuver Using CFD/CSD Coupled Approach

The air and structural loads of a 5-ton class light helicopter (LH) rotor in a 2.24 g pull-up maneuver are investigated using a coupling between the computational structural dynamics (CSD) and computational fluid dynamics (CFD) methods. The LH rotor is characterized by a five-bladed system with elastomeric bearings and inter-bladed dampers. The periodic trim solution along with the converged CFD/CSD delta airloads obtained in steady-level flight (advance ratio of 0.287) are used to perform the transient CSD maneuver analysis. The resulting vehicle attitude angles and velocity profiles of the aircraft are then prescribed in the quasi-static (QS) CFD maneuver analysis. It is demonstrated that the present QS approach provides an effective means for the maneuver loads’ analysis. The important flow behaviors such as BVI (blade–vortex interaction)-induced oscillations and the negative pitching moment peaks met in maneuver flight are captured nicely with the proposed method. Either the vortex trajectories or the surface pressure distributions are examined to identify the sources of the oscillations. A loose CFD/CSD coupling (LC) is used to predict the blade elastic motions, structural moments, and pitch link loads at the specified maneuver revolution of the rotor and also to correlate these with the transient CSD-based predictions. A reasonable correlation is obtained. The LC results show more pronounced 5P (five per revolution) oscillations on the structural response than those of the CSD-based methods.

Computationally-efficient high-fidelity nonlinear FEA of seismically isolated post-tensioned RC bridges

This study presents a novel computationally efficient high-fidelity nonlinear FEA (NLFEA) methodology for prestressed RC bridges constructed in the UAE and seismically isolated with elastomeric bearings. Specifically, the presented NLFEA methodology, using 3D solid brick elements, is shown to overcome traditional prohibitive numerical burdens. This is demonstrated without compromising accuracy or upscaling applicability and appropriateness. The proposed NLFEA approach is highlighted through detailed modeling of RC bridges’ non-traditional structural components and loading aspects (elastomeric bearings and post-tension prestressing cables). The mechanical behavior of elastomeric isolators and the RC continua, including cracking and other nonlinear phenomena, are captured via 3D solid brick elements. Moreover, the modeling procedure accurately represents the post-tension tendons’ prestressing forces and the associated effects on the RC elements. The prestressing forces are incorporated within the tendon elements via insightful manipulations of stepwise initial conditions and internal force adjustments. Additionally, load-carrying capacity determination for the elastomeric bearings was achieved by conducting a parametric investigation to capture their mechanical behavior adequately. Eventually, the analysis of a full-scale bridge is presented in this paper. The post-tensioned RC bridge understudy spans 100 m over eight elastomeric (natural rubber) seismic isolator bearings. Twelve post-tension prestressing cables are utilized to provide the bridge with continuous internal tension-balancing forces. A high-fidelity detailed FEA model of the complete bridge is developed and validated against a SAP2000 FEA model. It is shown that reasonable computational efforts can be expected without compromising the accuracy of the results.

Seismic fragility analysis of isolated bridges considering landslide-induced differential settlements

The structural safety of bridges and viaducts can be affected by the combination of different hazardous sources. This paper presents a study on the seismic fragility of continuous-deck bridges isolated through elastomeric bearings subjected to ground settlements induced by slow-moving landslides. In the investigated bridge typology, the relative differential displacement of bridge substructure components can involve significant strains of the bearing devices reducing their seismic deformation capacity and determining the increase of bridge fragility. Based on observations on a real case-study bridge, a parametric analysis is carried out to investigate the sensitivity of bridge fragility considering several realistic landslide-induced differential settlement scenarios and variable characteristics of the elastomeric bearings. Seismic fragility curves considering specific settlement scenarios are computed and compared to the undeformed condition to estimate the influence on fragility curves. Results show that a significant increase in fragility is registered for settlement scenarios inducing localized settlements of substructure components and for high-damping nonlinear seismic response.

Large Deformation Analysis of Hyperelastic Continuum with Hexahedral Adaptive Finite Elements

The use of hyperelastic materials capable of large deformations, such as elastomeric bearings used to reduce seismic effects, is quite common in civil engineering. Such environments are, in most cases, addressed by numerical solution techniques such as the finite element method. In case of large deformations, nonlinear analysis is used in the solution. In the study presented here, large deformations of a hyperelastic continuum expressed by the Mooney-Rivlin material model are calculated using hexahedral adaptive finite elements. A code was written in MATLAB using the total Lagrangian formulation for the nonlinear adaptive finite element solution. Comparisons were made with Abaqus software to check the consistency of the results obtained from this program. It has been observed that local refinements in the adaptive element mesh occur in the regions where they are needed. Considering the variation of maximum displacement and maximum stress with the number of elements, it has been observed that mesh refinement creates a convergent solution.

Сomputational approach to thermal-stressed state modeling of tire based on the algorithm of its self-heating analysis. Part 2 – Practical results of applying the approach

Elastomers and their composites are widely used in modern innovative technology: for the production of aviation and automobile tires, anti-vibration elements (rubber, rubber-metal springs), dampers, elastomeric bearings. Also they are used in shaft suspensions, as spacers between structural parts, supporting parts and fasteners. Elastomeric elements of structures have a high dynamic load, in particular of a cyclic nature, which is accompanied by the formation of hysteresis loops and, as a result, the occurrence of the phenomenon of self-heating. An increase in temperature in the middle of materials causes significant changes in their mechanical properties, reduces strength characteristics, accelerates aging and degradation processes, and has a significant impact on fatigue processes. In addition, an increase in temperature causes an additional thermal stress state, capable of significantly changing the qualitative picture of the structure's deformation characteristics' distribution. Thus, the purpose of this study is development of approach to assessing the thermal stress state of structures made of elastomeric materials for the possibility of further analysis of its influence on the structure work as a whole. The appropriate approach was built on the basis of numerical modeling of thermal and deformation processes which takes place into the structure during operation. The proposed approach includes several related calculations by using FEM and is based on the fundamental approaches of the theories of elasticity and viscoelasticity, thermal conductivity and thermo-elasticity. Thus, the article presents an approach to the analysis of the thermal stress state of structural elements under operating conditions. This approach was applied to determine the thermo-strain-stress characteristics of a pneumatic tire and corresponding pictures of its distribution were obtained.

Redesign of The Overpass Bridge Structure at Km 839+450 Toll Road Pasuruan-Probolinggo Using Parker Type Truss Bridge

The Overpass Bridge Km 839+450 Pasuruan - Probolinggo Toll Road which is located in Leces District, Probolinggo Regency, East Java has a total span length of 144 meters with a Girder I bridge type. This bridge has 5 spans with 4 pillars. The writer want to redesign the bridge into 2 spans to increase the free space under the bridge overpass. The Parker truss bridge type was chosen because it has the lightest self-weight compared to other types of steel truss bridges. This parker type steel truss bridge is planned with a length of 72 m, a width of 12 m, and a height of 13 m. The bridge is designed for 1 lane which has 2 main lanes and 1 emergency lane. From the analysis carried out, the thickness of the vehicle floor plate is 20 cm with concrete fc 30 MPa and reinforcement Fy 410 MPa. The steel structure uses BJ 41 steel quality with profile dimensions on longitudinal girders WF 300.300.10.15, transverse girder profile dimensions using WF 700.300.13.24, main frame girder dimensions using WF 552.500.50.50 & WF 552.475.25.30, transverse wind ties using WF 294.200.8.12, as well as cross wind ties using the L 250.250.35. For the connection, high-strength bolts of type A325 with Fy 820 MPa are used with a diameter of 24 mm and a connection plate which is L 100.100.10, L 120.120.12, and a 25 mm thick plate. on the main frame connection. The placement of the bridge uses the placement of Typer Elastomeric Bearings coated with steel plates with dimensions of 600x600x150 mm. Steel truss bridge parker type has the advantage that the upperstructure's own weight is lighter than the existing bridge, the difference in weight reaches 33,07 %.

Design and Analysis for Multi-Layered Elastomeric Bearing on Rotor Hub Considering Large Axial Load and Nonlinear Motion

This paper examines the initial sizing theory of elastomeric bearings. In addition, the manufacturing process of the elastomeric bearing was analyzed to define the essential contents necessary to manufacture reliable elastomeric bearings. Mooney-Rivlin parameters were presented based on the test results to predict the characteristics of metal materials and rubber stacked. Mooney-Rivlin parameters were inputted to determine whether the structure was abnormal, by constructing a finite element model for the elastomeric bearing. A modeling technique was established to meet the structural rigidity and strength requirements of full elastomeric bearings, critical components of the helicopter main rotor system. In addition, the flight situation in which the maximum load of an actual helicopter equipped with an elastomeric bearing can be applied was selected, and linear structural analysis and nonlinear analysis were performed to confirm the behavior of the elastomeric bearing. As a result of performing linear static analysis, a negative margin was generated, but when nonlinear analysis was performed again, it was confirmed that there was a sufficient safety margin. It was shown that design reliability for the molding and manufacturing process of elastomeric bearings could be improved in terms of strength.

Variability of Dynamic Properties of Rubber Compounds for Elastomeric Bearings

The λ-factors for stiffness and damping of rubber bearings should be experimentally assessed during the qualification process or deduced from tests performed on material specimens. Moreover, the λ-factors suggested in the informative annexes of EN 15129 and of EC8-part 2 can be also used as reference values. However, they are derived from outdated experimental campaigns and do not refer to all the sources of variability. In this paper, a statistical analysis on a significant set of rubber compounds, certified according to EN 15129 from different suppliers, is carried out to assess the current variability of the dynamic properties of such compounds. Different sources of variability may be identified by distinguishing between behavioural and environmental effects. For elastomeric bearings, especially high-damping rubber (HDR) ones, the main behavioural effects are strain amplitude, strain rate dependence, and cyclic degradation, whereas the environmental effects are due to temperature variation and ageing. All these sources of variability have been analysed in this paper. The results of the statistical analysis have been used to propose a new set of λ-factors for all the source of variability studied. Such new values have been compared with the ones suggested by the codes when available. The main inconsistencies found have been highlighted and commented in this paper. Finally, some considerations about the influence of such variability on the structural response of base-isolated structures have been drawn by focusing on both the isolation system and the superstructure.

Material Characterization of Elastomeric Bearing Elements in Wave Energy Converters

According to the European Council, 75% of the greenhouse emissions are caused by energy production and use. In order to decarbonize the energy sector, more research is focused towards the renewable energy sources. Among the many available resources, wave energy is one of the key resources to consider. As part of the research, KTH is developing a winch based point absorber wave energy converter. The winch consists of a chain link with elastomer bearings wound around a drum. The winding and unwinding motion of chain converts wave motion into electricity. A typical winch based wave energy converter undergoes around 80 million cycles in its lifetime. This calls for a durable system design requiring minimal service and maintenance. With an elastomer bearing, the winding and unwinding of the chain over the drum is realized as deformation of the elastomer thereby eliminating sliding. While the use of elastomer enables an efficient design, it also makes it more challenging due to its highly non-linear and viscoelastic behavior. A constitutive model is necessary to determine material characteristics of an elastomer for different loading conditions. In this work, a systematic design process is outlined and an attempt is made to determine a suitable hyperelastic material model for the elastomer. The study is focused on two materials – silicone and polyurethane. The test samples are compressed and followed by shear in deformation. For material model determination, the test data is curve fit and later verified using finite element method. The material is assumed incompressible.

Influence of eccentric load introduction during launching with rockers using an elastomeric bearing

AbstractDuring launching, the superstructure acts as a continuous beam supported by different launching bearings on the piers. Just before reaching the next pier, a part of the superstructure temporarily behaves as a long cantilever. As a result, a large bending moment and reaction force at the last bearing occur. The interaction of the internal forces results in a biaxial stress state in the cross‐section. This load case is usually determining for the buckling check and the structural design of the webs. Additionally, the webs of the superstructure and the launching bearing often fail to share the same center lines. This eccentricity can be caused by misalignments of the launching bearings, the necessary air gap to the lateral guide as well as the different thicknesses of the panels along the superstructure. These eccentricities are not considered in the buckling check according to EN 1993‐1‐5 [1]. It is often discussed how these eccentricities affect the buckling behaviour and whether they must be considered in the buckling check. In the case of launching bearings like a rocker system which includes an elastomeric bearing between the superstructure and the launching beam, the reaction forces of the nonlinear material behaviour are additionally discussed. In [2] the effects on the buckling resistance in dependence of load eccentricity for some parameters for the different types of launching bearings are presented. [3] shows the comparison of the buckling resistance with investigations from [4] and [5] with the buckling check according to [1]. A comprehensive summary and the new proposal for considering an eccentric load application and clamping effects in the buckling zone can be read in [6]. This paper shows first investigations of the influence of the elastomeric bearing and the problem of the reaction of the nonlinear material behaviour and its definition in the numerical model. The results have shown that load eccentricities in combination with elastomeric bearings have no impact on the buckling behaviour.

Stress increases in crane runway girders due to rail joints

AbstractVertically acting wheel loads from overhead bridge cranes and potential additional horizontal crane loads induce two types of stresses in crane runway girders: i) global stresses due to bi‐axial bending and torsion and ii) local stresses which mainly affect the girder's web. The latter typically represent one of the most decisive criteria for the fatigue design check of welded girders and are the focus of this paper. Crane rails with foot flange are typically connected to the top flange with rail clips. These clips maintain the position of the rail in vertical and horizontal transverse direction, but they generally allow for longitudinal movement of the rail. Rails with foot flange are used with and without elastomeric bearing pads between the rail and the top flange of the girder. The local stresses in the webs of crane runway girders are strongly affected by discontinuities of the crane rails. Such discontinuities can originate from unplanned rail cracks as well as planned rail expansion joints. The current mechanical models for concentric as well as eccentric wheel loading in relevant design standards assume continuous crane rails. However, rail joints are expected to significantly increase the local stresses in the region beneath rail joints. The present paper focuses on the impact of rail joints on the local stresses in crane runway girders. The research activities comprise experimental tests as well as finite element calculations. The aim of the investigations is to develop a better understanding of the mechanical behaviour in order to avoid future fatigue damage due to an unexpected increase of local stresses at a rail joint.