Elastomeric Bearing Pads Research Articles

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.

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.

Impact of rail joints on the local stresses in crane runway girders

Vertically acting wheel loads from overhead bridge cranes and potential additional horizontal crane loads induce global stresses due to bi-axial bending and torsion and local stresses in crane runway girders 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 used for moderate to high wheel loads. They are usually connected to the top flange with rail clips. 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 numerical parametric studies based on finite element calculations, both for rails with and without elastomeric bearing pads. The aim of the investigations is to develop a better understanding of the mechanical behaviour and to quantify the increase factor for maximum local stresses in order to avoid future fatigue damage due to an unexpected increase of local stresses at a rail joint.

Local vertical compressive stress in the crane runway beam web

In this paper, the authors analysed several variants of connections between a block rail (60 mm × 60 mm) and a crane runway beam (IKS 800-6). They compared local vertical compressive stress in the crane runway beam web, calculated using an analytical approach and numerical simulations. In the case of the continuous block rail rigidly fixed to the beam flange, satisfactory convergence was obtained. For the remaining types of connections the results based on the analytical method were different from the results of the numerical simulations. The difference resulted from the fact that the analytical method did not take into account the crane rail joint. Furthermore, the impact of the elastomeric bearing pad on the local stress value was taken into account in a simplified manner in the analytical method by increasing the effective length by approximately 30%. The local vertical compressive stress in the crane runway beam web was significantly affected by the connection between the rail and the crane runway beam, the crane rail joint type, the use of the elastomeric bearing pad, the length of the elastomeric bearing pad, and the crane rail wear.

Compression behavior of perforated steel laminated elastomeric bearing

Elastomeric bearing pads have been the economical and maintenance-free, widely used component of bridges for more than decades. Research has been ongoing for years to increase the versatility of elastomeric bearings. Recently, fibre fabrics like glass and carbon reinforced with elastomers have substantiated a lead to traditional steel reinforced elastomeric bearings by a reduction in cost and weight. This paper deals with an experimental investigation into the compressive behavior of elastomeric bearing pads reinforced with perforated steel shims of various geometries placed between traditional solid steel shims. The compressive behavior of modified elastomeric bearings was determined and compared with that of traditional steel-reinforced elastomeric bearings.

Application and analysis of elastomeric supporting style for topside modules of a spread mooring FPSO

The offshore elastomeric supporting style via steel reinforced elastomeric bearing pads (SREBPs) has been in use gradually. In this study, the elastomeric supporting style used for the interfaces between topsides and stools is adopted by a spread mooring FPSO to analyze the responses of SREBPs and evaluate the applicability. Firstly, the motion responses of target FPSO are numerically simulated to check if the mooring system is safe. Then, the hydrodynamic responses are taken as the boundary conditions of hull for the multibody dynamic simulations. In the simulation, a compression spring model is proposed to equivalently replace the SREBPs. The stiffness of equivalent compression springs is obtained by linear fitting of the stiffness data from finite element analysis of SREBPs. Finally, the multibody numerical results show that the SREBPs can reach into yield state, but if there are assistant devices helping to limit the deformations, the SREBPs would work well. The largest deformations of SREBPs are observed to be sensitive to the hydrodynamic responses, so the SREBPs can still reach into yield state in extreme case. In that condition, it is recommended to bond the topsides to the stools and the numerical results confirm that it is available.

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.

Fatigue life analysis of laminated elastomeric bearing pad

The elastomeric bearing pads playing an important role by transforming the loads from bridge superstructure to its substructure. The fatigue life estimation of these elements is necessary to avoid any problems resulting from deterioration of such elements. To do so, the current study is devoted to develop a three-dimensional model for steel-laminated bearing pad subjected to different designated applied loads. The Ogden model, one of the built-in constitutive models in ABAQUS software, was used to fit the experimental load-deformation curve and to obtain the coefficients of the rubber material used in the pad to feed the ABAQUS software. The pad was modelled with elements C3D8R, C3D8RH, and M3D4R to represent the steel, rubber, and rubber skin respectively. Four loads with three frequencies for each load were selected to applied on modelled pad. Fe-safe, one of ABAQUS software package, was used to find the fatigue life for modelled pad. The results showed a good agreement with previous experimental studies on this field.

Finite element analysis for three-dimensional hyper-elastic problems

Hyper-elastic materials are special elastic material that the stress can be derived by the strain energy density function. The most attractive property of these rubber-like materials is their ability to undergo large strains with small loads and recover their initial shape after unloading. Hyper-elastic materials are widely used in engineering such as tire, elastomeric bearing pad, belt drives, rail pad and so on. Due to the large strain state in most of application of this type of material, the behavior of hyper-elastic is often considered in finite deformation analysis. In comparison with linear material, analysis for hyper-elastic material which have nonlinearities is more complicated because both material nonlinearity and geometric nonlinearity should be considered. Along with the development of computer and numerical methods, the finite element method (FEM) is known as a powerful numerical computation tool that can helps to solve engineering problems in many fields such as structural, thermal, electronic, and biomedical analyses. Actually, most of practical engineering problems appear in three-dimensional (3D) state, especially in nonlinear analyses. So, the development for an effective numerical method for 3D nonlinear problems is very necessary. In this study, a finite element approach with 8-node hexahedron element is presented for analyses of large deformation problems of hyper-elastic material. The compressible neo-Hookean is used as the constitutive model for 3D hyper-elastic problems and the total Lagrange formulation is applied for the discretization of large deformation problems. To obtain the nonlinear solutions, the standard Newton-Raphson algorithm with constant load step is chosen as the iteration method. The computing programs are built with Matlab language. To verify the accuracy of the present approach, the obtained results are compared with the reference solutions given by Ansys program.

Simplified Analytical Nonlinear Model for Contact Problem between Precast Concrete Beams and Elastomeric Bearing Pads

AbstractThis paper presents an advance in the analytical prediction of the contact interaction between bearing pads and precast beams. Contact problems are typically nonlinear, and until recently, ...

Using the uniaxial tension test to satisfy the hyperelastic material simulation in ABAQUS

Since, hyperelastic materials, such rubber, are widely used in different life fields principally in engineering of elastomeric bearing pads. The present study aims to determine a suitable constitutive model dependent on strain energy potential which can characterize hyperelastic material behavior through uniaxial tension test only. Built-in ABAQUS software constitutive hyperelastic models are used to fit the experimental results of the uniaxial tension test, check the stability and obtain the material coefficients. The used models are that of Mooney-Rivlin, Polynomial, Neo-Hookean, Yeoh and Ogden. The results revealed that Polynomial, Ogden and then Yeoh models are convenient to fit the hyperelastic behavior of the rubber material while Mooney-Rivlin and Neo-Hookean models have a slight ability of fitting limited to the early stage of the linear behavior of the material.

Seismic Performance of Composite Simply Supported Bridge Decks during Real Earthquake

This study investigates the overall response of traditional bridge decks in Iraq under real earthquake excitation already happened in the area. The bridge deck under investigation is of Al Bathah overpass expressway located in the south of Iraq at Al Nasiriya city. Al Bathah Bridge deck is a composite simply supported consist of seven built-up steel girders and reinforced concrete slab. Three-dimensional finite element models of composite simply supported bridge deck was created using CSI Bridge and ABAQUS software. Time history analysis conducted using the Halabja earthquake hit the Iraq-Iran border on 12 Nov. 2017. The finding of this study revealed that the typical bridge deck in Iraq will fail to withstand the transverse earthquake excitation under intensity already happened. The connection epoxy layers between the elastomeric bearing pads and girders will fail due to the excessive transverse displacement at bearings. Consequently, the girders slip from their position and the deck will fail.

Seismic performance of highway bridges considering sacrificial abutment: a case study in Afghanistan

The effect of skewness on the sacrificial seat-type abutment and abutment interaction with the skew deck is quite well known. Unlike the simplified approach, this study focuses on the effect of skewness on the seating width of seat-type abutment by providing a rigorous deck model in the analysis while the sacrificial seat-type abutment interacts with the straight deck. This effect is investigated by comparing the seismic performance of two case study bridges, the bridge with elastomeric bearing pad as a bearing mechanism, namely the conventional bridge and the bridge with lead rubber bearing, as an isolated bridge. Realistic seismic response behaviors of these bridges were simulated by nonlinear 3D models. The models are capable of simulating the flexural yielding of piers, the bilinear behavior of isolation bearings, the elastic perfect plastic behavior of elastomeric bearings of the conventional bridge and the other important nonlinear behaviors of these structures. The results highlight the effectiveness of isolation bearing on seismic performance of the isolated bridge, and it was revealed that in the early pounding frequencies, passive forces on the sacrificial backwall springs are uniformly distributed. Whereas for the last pounding frequencies, the passive forces on the backwall are not uniform anymore, this implies that the increase in the pounding frequency leads to an increase in the possibility of deck rotation in the straight deck. Moreover, the result confirms that the earthquake energy absorbed by the fusing backwall could significantly lead to a reduction in dissipation energy by the pier. These results suggest recommendations to improve the seismic performance of the conventional bridge system in the country.

Numerical analysis of the effective stiffness of elastomeric bearing pads under precast beams for the limit load of lateral instability

Abstract Precast concrete girders on bearing pads are subjected to instability depending on several variables such as span length, initial imperfections and bearing pads behavior. On this paper, numerical models are developed in order to assess the instability limit loads and the rotational stiffnesses of the pads in many combinations of span length, cross section of the girder and lateral sweep. The lift off phenomenon is considered in each analysis by a bearing pad model composed by springs with compression only behavior, with good results in comparison with the experimental values of the technical literature. The increase in spans and initial imperfections causes a decrease in the rollover limit load. The lift off effect is aggravated as the lateral eccentricities increase. In the analyzed combinations, the reduction of the rotational stiffness is about 37% for the critical situation, which span length about 40 m and lateral sweep of L/300, with loss of contact between 50% and 60%.

Numerical analysis of an elastomeric bearing pad by hyperelastic models

Elastomeric bearing pads are responsible for transferring loads at the junction between beams and columns of bridges and viaducts, providing restrict freedom of movement in the superstructure. The elastomeric material of the bearing pad is a synthetic rubber reinforced with carbon black particles and subjected to a process of vulcanization, also represented by hyperelastic material models based on strain energy density functions. The objective of the present paper is to use the finite element analysis software Abaqus® to select the most appropriate hyperelastic model, as well as its constants, applying them in a bearing pad installed in an existing viaduct, evaluating its behavior and displacements resulting from the application of usual loads. The proposed methodology presents results coherent with technical specifications limits for available bearing pads products.

Design of Elastomeric Bridge Bearing Pad Compound Formula Based on Hydrogenated Natural Rubber

Laminated elastomeric bearing pad which is commonly produced by natural or chloroprene rubber is functioned as isolation system in bridge or flyover structures. In the research, hydrogenated natural rubber (HNR) was evaluated its feasibility to be used as base elastomer on steel-laminated bearing pad production by designing rubber compound formula. The compounding procedures of HNR applied various vulcanization system and carbon black filler types. The physical and mechanical tests result showed that only hardness parameter could fill the standar quality requirement of commercial elastomeric bearing pad as stated in AASHTO M251 in the range of 50 "“ 70 Shore A scale. The tensile property and compression set value of the HNR vulcanizates were under the requirement. This was due to low rubber-filler interaction and rigidity of crosslink network. The low interaction was more evident with increasing carbon filler particle size. By adjusting semi efficient vulcanization system and used N220 as carbon filler in designing compound formula,HNR was regarded as alternative promosing base elastomer for elastomeric bridge bearing pad manufacture. Nevertheless, it was necessary to improve the procedure to achieve better tesile property and compression set parameter.

Seismic Behavior of Composite Simply Supported Bridge Decks supported on Elastomeric Bearings

This paper studies the behavior of bridges’ superstructure under seismic action. The bridge under investigation is one of the typical bridges usually used in overpasses in Iraq, which is made of simply supported steel built up girders and reinforced concrete deck slab isolated from the substructure by elastomeric bearing pads. A three-dimensional finite element model was developed using CSI Bridge Software. Time history analysis was carried out using true-recorded earthquake took place in Iraq near the city of Halabja in 2017. The results of the analysis show that the displacements of the elastomeric bearing pads under transverse seismic loading are much higher than the permissible displacements’ limit which will produce failure of these bearings and potential failure of the bridge superstructure.

Preparation of natural rubber elastomeric bridge bearing pad compound formula on various curing systems

Commercial elastomeric bridge bearing (EBB) pad is dominated by the laminated type. Laminated EBB pad comprises of rubber composite layers which are arranged intermittently among the thin steel plates. The rubber composite uses natural rubber or chloroprene synthetic rubber as the base elastomer. Local EBB pad industries mostly produce natural rubber bridge bearing pad type due to the enormous availability of natural rubber in Indonesia. However, the quality of natural rubber bridge bearing pad product often cannot fulfil the standard requirement in compression set and accelerated aging parameters. The research studied the design of EBB pad compound formula based on natural rubber type. The EBB compound formulas were prepared by varring the curing system such as sulphur (efficient and semi-efficient) and peroxide curing system. Designing the compound formula was in accordance to the methods required in improving the compression set and accelerating aging quality of natural rubber bridge bearing pad. The result of curing characteristic of the natural rubber bridge bearing pad compound showed that peroxide curing system gave the longest optimum curing time. Further, sulphur curing system produced high crosslink density followed with good mechanical properties of natural rubber bridge bearing pad vulcanizate. The compression set value of natural rubber bridge bearing pad vulcanizates which were obtained by efficient and semi-efficient curing systems as 14.09% and 24.81%, respectively were regarded to be below the maximum requirement (25%). The peroxide curing system was not recommended due to the high compression set value of 40.68%. Meanwhile, maximum percent changes of tensile properties and retention values which indicated accelerated aging parameter of natural rubber bridge bearing pads were formed either by sulphur and peroxide curing system could fulfilled the standard requirement of EBB Duro 70 refered to SNI 3967:2013.

Hydrocarbon Fire Performance of Reinforced Elastomeric Bridge Bearing Pads

AbstractElastomeric bearing pads are commonly used to support precast prestressed bridge girders. Previous studies on such pads have been conducted only at ambient temperatures. Bridges are suscept...

Numerical studies on vibration propagation and damping test V1

Earthquakes and aircraft impacts induce vibrations that propagate throughout the entire building and they need to be considered in designing SSCs (Structures, Systems and Components). Mainly linear calculation methods have been in use in design practice and the codes and standards consider damping ratios only for linear structural analyses. Induced vibrations, especially in damaged concrete structures, have not been studied extensively enough for optimization of structural frameworks and/or qualified systems and components. Experimental data on damping properties of damaged reinforced concrete are needed also for benchmarking analysis programs and methods.
 Recently, within IMPACT project, a new type of test series considering vibration propagation has been carried out at VTT. The test target is a reinforced concrete structure with two parallel walls connected to a floor slab. The front wall is additionally supported by triangular shaped side walls which are connected to the floor slab too. The test structure is supported on elastomeric bearing pads, with back pipes effective mainly in compression and with bars effective in tension. In order to obtain information on vibration propagation in damaged concrete structure at different levels of damage grades the same structure was tested six times. At each time the mass of the deformable stainless steel missile was 50 kg. The hit point located in the middle of the front wall. The impact velocity was about 110 m/s in the first four tests (V1A-D) and about 60 m/s in the remaining two tests (V1E and F). In this paper, numerical results on tests V1A and V1F are compared with the corresponding experimental ones.
 The calculated results, such as accelerations, displacements, their response spectra and strains, are compared with experimental measurements. Five finite element (FE) programs are used in computations: Abaqus, Europlexus, LS-DYNA, SOFiSTiK and an in-house code (IHC).
 Most of the FE-codes in the present study use shell elements. In Abaqus and SOFiSTiK non-linear behaviour of shell section is modelled by dividing the cross section into layers. Reinforcements are also modelled as layers. In Europlexus and IHC, an alternative approach is adopted in which the non-linear behaviour of concrete and reinforcement is homogenized beforehand in the shell thickness direction obtaining relations between stress resultants and generalized strains valid for the shell section. In LS-DYNA, 3D solid elements for modelling concrete and beam elements for modelling reinforcements are used.
 Equations of motion are integrated with explicit central difference time integration method, except in SOFiSTiK implicit integration method is used. Modelling and computations with the mentioned FE-programs are made independently of each other. Computations with LS-DYNA are carried out as blind exercises.
 Consideration of the results from benchmarking point of view is still on-going. However it is evident that analysed results follow reasonable well test results in main design parameter level such as maximum displacements, accelerations and strains. Also frequency spectra are estimated reasonably well.