Elastomeric Pads Research Articles

A compliant tuned liquid damper for controlling seismic vibration of short period structures

Abstract Tuning of sloshing frequency of liquid to short period structures possess challenges in Tuned Liquid Dampers (TLD). However, seismic vulnerability of short period structures cannot be overemphasized. In such instances, frequency tuning is facilitated by inserting a spring between the structure and the TLD. An implementation of this is presented herein by mounting the TLD on an array of compliant elastomeric pads, referred herein as compliant TLD. The effectiveness of compliant TLD is demonstrated through simulation that involve numerical solution of the derived equation of motion. The nonlinear sloshing, wave breaking and resulting dissipation are described by Sun's model. The infeasibility of tuning of conventional TLD to short period structures and consequent inefficiency are shown to be largely eliminated by the proposed implementation. Significant reductions in the peak and root mean square (r.m.s) floor accelerations and storey displacements are observed while (the structures are) subjected to a suite of ground motions pertaining to varying hazard level. The parameters for the proposed system are chosen based on the parametric variations of the controlled responses. The performances of the compliant TLD are also verified with experimental investigations using shake table test on scaled model of a building-TLD system. The experimental results corroborate with the trends observed from simulation. The tuning invoked by the compliant mechanism is observed to largely retain the sloshing and dissipation through wave breaking. Further, the design of the compliant TLD is presented and enumerated with an example of realistic building frame.

Seismic behaviour of rocking bridge pier supported by elastomeric pads on pile foundation

Life line structures such as elevated flyovers and rail over bridges should remain functional after an earthquake event to avoid possible traffic delays and risk to general public. Generally, restraining the structure by reducing the degrees of freedom often cause serious damages that occurs during a seismic event through yielding of the structural components. By allowing the structure to rock through uplift using suitable arrangements can be a plausible seismic resilient technique. In this context, this article proposes a novel seismic resilient pile supported bridge pier foundation, which uses elastomeric pads installed at top of pile cap. The effect of pile soil interaction along with ground response analysis is also incorporated in the full bridge model adopted for the study. One dimensional equivalent linear site response analyses were performed to arrive at the amplified/attenuated ground motions along the depth of soil.The seismic performance of the proposed bridge with new rocking isolation concept is compared with existing bridge located in medium seismic zone of India. With the help of non-linear dynamic time history analysis and nonlinear static pushover analysis, the bridge modelled using the proposed novel rocking isolation technique shows good re-centering capability during earthquakes with negligible residual drifts and uniform distribution of ductility demand along the piers of the bridge considered in this study.

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 Modeling and Experimental Characterization of Elastomeric Pads Bonded in a Conical Spring under Multiaxial Loads and Pre-Compression

Elastomeric components are widely used in the engineering field since their mechanical properties can vary according to a specific condition, enabling their applications under large deformations and multiaxial loading. In this context, the present study seeks to investigate the main challenges involved in the finite element hyperelasticity simulation of rubber-like material components under different cases of multiaxial loading and precompression. The complex geometry of a conical rubber spring was chosen to deal with several deformation modes; this component is in the suspension system placed between the frame and the axle for railway vehicles. The framework of this study provides the correlation between axial and radial stiffness under precompression obtained by experimental tests in prototypes and virtual modeling obtained through a curve fitting procedure. Since the material approaches incompressibility, different shape functions were adopted to describe the fields of pressure and displacements according to the finite element hybrid formulation. The material parameters were accurately adjusted through an optimization algorithm implemented in Python program language which calibrates the finite element model according to the prototype test data. However, as an initial guess, the proper constitutive model and its parameters were first defined based only on the uniaxial tensile test data, since this test is easy to perform and well understood. The validation of the simulation results in comparison with the experimental data demonstrated that care should be given when the same component is subjected to different multiaxial loading cases.

Vibration Protection of Historical Buildings Located near the Lines of Urban Rail Transport

Besides the underground, the second common type of public transport is the tram. Tram lines in Moscow city center, as well as in other cities in Russia, are being renovated and reconstructed. Vibration of the railway track travels through the ground to the foundation of buildings adjacent to tram lines, causing high vibration and structure-borne noise levels inside them. The article presents result of a vibration isolation system analysis and design for a building, located in 37m of the two-lanes tram line. Prior to design procedure, field measurements were made and vibration levels inside the building were recorded. The vibration isolation system design included calculation of soil pressure on the isolation pad and subsequent estimation of the elastomeric pad dynamic modulus. Using this data, the eigenfrequecny of vibration isolation system was derived and its efficiency calculated. After the system maintenance, measurements were made to check the system’s performance. During the measurements acceleration of isolated part of the building and the ground surface were synchronously measured and transfer function derived.

Comparison between Elastomeric Passive Isolators and LQR Active Control in Stone Cutting process: Modelling and Simulation

Abstract This paper focuses on the problem of mechanical vibrations induced in the cutting process of stone and marble in stone cutting machines. The study leads to sustainable stone cutting operations by saving energy, further finishing and providing noise clean environment. This periodic force induced in the cutting area is reduced passively by using an elastomeric pad that isolates the base of the machine from the head and the table. Adding less than 2.5% of passive damping ratio to the isolator could reduce the level of vibration on the saw blade and on the table. To reduce the propagation of these vibrations through the base into the floor, another elastomeric pad is mounted under the machine. This pad reduces the propagation of oscillations through the floor to the other places in the factory. Another solution is presented to reduce the vibrations in the whole structure significantly by regulating the input force this one is controlled by the LQR method. The controller has the capability to regulate the vibrations in the structure by solving the Riccati equation to compute the optimal response for the input force to perform the required tasks.

Numerical analysis of long-haul structure laying on nonlinear foundation subjected to moving load

The article deals with a long structure laying on nonlinear foundation subjected to moving load. Such problems often arise due to design of an upper-track structure in railroad engineering, specifically due to design of floating slab track structures in tunnels. The design procedure aims at calculating static and dynamic parameters of a floating slab track structure, that consist of reinforced concrete track slab and a number of nonlinear-elastic elastomeric pads, that supports the track slab. In order to get detailed analysis of the floating slab track structure, the analysis is performed using FE-model in MSC Patran/Nastran software package. FE-model includes rails, railway fastenings, track slab, elastomeric pads and supports. The results of the static analysis are the deflections of the upper-track structure and stress-strain state of the floating slab. The results of the dynamic analysis include transfer-function of the floating slab and evaluation of insertion loss under excitation frequencies of moving trains over different speed.

Seismic fragility assessment of highway bridges using D-vine copulas

Seismic vulnerability of highway bridges is crucial to the seismic risk assessment of highway transportation networks. A new framework for developing the fragility function at the system level utilizing the D-vine copula theory is proposed. In this methodology, first, the joint probabilistic seismic demand model (JPSDM), which represents the conditional joint distribution of various engineering demand parameters (EDPs) under each intensity measure (IM) level, is constructed using the D-vine approach; then, sample realizations of both the established JPSDM and capacity models of these considered components are compared to derive the system-level fragility curves. This methodology is illustrated in a typical two-span RC continuous girder-box bridge case, where pier columns, elastomeric pad bearings, the sliding bearings, and the abutments in both passive and active directions are considered as the major components. The results demonstrate that the performance of the optimal D-vine for characterizing the dependence structure among various EDPs is relatively superior in comparison with commonly-utilized multivariate standard copulas. The combination of the quantitatively-identified optimal D-vine copula and their conditional lognormal marginal distributions is adequate to construct the JPSDM of these five EDPs. Furthermore, the effects of different copula selections on the overall system vulnerability are well captured, which highlight the necessity for quantitative identification of the optimal D-vine copula for modeling the correlations among various EDPs.

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.

Analytical solutions for rollover instability of concrete beams on elastomeric bearing pads

During construction, concrete beams are susceptible to rollover failure when unbraced and supported by elastomeric bearing pads. This failure occurs mainly due to the presence of initial horizontal curvature of the beam and the low torsional restraint provided by the supports. Besides, the uncertainties and variability about modulus of elasticity, initial imperfections and supports conditions can increase the risk of collapse of such elements. In contrast, there is a lack in analytical equations to predict the few published experimental results in this field that present different loading conditions from self-weight. Also, another lack is about recommendations of required pad stiffness for beam stability during construction. Thus, the current research focuses on presenting closed-form analytical solutions to predict the rollover load of beams supported by bearing pads and subjected to different loading conditions. Furthermore, this paper presents recommendations about required pad stiffness for the standard AASHTO bulb-tee beams subjected to self-weight. The variational Rayleigh-Ritz method enabled to determine the analytical solutions, and furthermore, the classical Southwell equation allowed to consider the effect of initial sweep on the beam stability. With this, the required pad stiffness was determined through Monte Carlo simulations. The proposed equations accurately predicted the experimental results available in the literature. The analytical and experimental rollover loads differed by 4.37% and 13.6% for the two studied cases. Besides, Monte Carlo simulations were performed to determine tolerances for initial imperfections.

On a coupling between the Finite Element (FE) and the Wave Finite Element (WFE) method to study the effect of a local heterogeneity within a railway track

Railway rolling noise is the main source of noise from trains at speeds below about 300 km/h. At the wheel–rail contact area, the track and the wheel are dynamically excited and vibrate together to emit the well-known rolling noise. The rail lies on elastomeric pads, which are essential parts concerning wave propagation. Stiff pads are advantageous as they increase the track decay rate and perform better acoustically.The Wave Finite Element Method (WFEM), based on the theory of periodicity, has been widely used to compute the response of infinite periodically supported railway tracks. However, the track should not always be regarded as a perfect infinite periodic system: a breakdown of the periodicity can be due to a local increase of the stiffness of the supports due to the wheel load, a transition area, geometric irregularities of the track, or to the use anti-vibration supports.The goal of this paper is to compute the dynamic response of an infinite railway track including a heterogeneous part. This zone is made of supports whose stiffness is different from the ones in the homogeneous part. To compute the dynamic response of the track, an extended Finite Element (FE) – Wave Finite Element (WFE) coupling method is proposed. It consists in dividing the heterogeneous part into several FE different supports linked with internal WFE wave-guides. This part is then coupled with semi-infinite WFE wave-guides. The proposed method is validated with experimental data of a track on uniform supports. Then, the dynamic response of the track with different supports is computed. Finally, the performances of an anti-vibration support is evaluated and discussed in terms of the drive point mobility and the track decay rates.

New horizons in selective laser sintering surface roughness characterization

Powder-based additive manufacturing of polymers and metals has evolved from a prototyping technology to an industrial process for the fabrication of small to medium series of complex geometry parts. Unfortunately due to the processing of powder as a basis material and the successive addition of layers to produce components, a significant surface roughness inherent to the process has been observed since the first use of such technologies. A novel characterization method based on an elastomeric pad coated with a reflective layer, the Gelsight, was found to be reliable and fast to characterize surfaces processed by selective laser sintering (SLS) of polymers. With help of this method, a qualitative and quantitative investigation of SLS surfaces is feasible. Repeatability and reproducibility investigations are performed for both 2D and 3D areal roughness parameters. Based on the good results, the Gelsight is used for the optimization of vertical SLS surfaces. A model built on laser scanning parameters is proposed and after confirmation could achieve a roughness reduction of 10% based on the Sq parameter. The Gelsight could be successfully identified as a fast, reliable and versatile surface topography characterization method as it applies to all kind of surfaces.

Rollover stability of precast concrete beams supported by elastomeric bearing pads

Abstract During construction of precast girder bridges, there is the concern on rollover instability of the beams when exclusively supported by elastomeric bearing pads. This type of failure has been the focus of recent research due several accidents reported. However, these studies have not considered the nonlinear behavior of elastomeric bearing pads and the lift-off effect. Therefore, this paper presents a parametric study with a finite element model calibrated with experimental results, reported in the literature, through a nonlinear geometrical analysis and considering that concrete behaves linearly. Besides, the experimental results are compared to simplified approaches which account the pad nonlinear behavior and the lift-off effect by utilizing its secant rotational stiffness. From the results, the difference between the instability load from nonlinear geometrical analysis and experimental results was 8.7 %, and the simplified eigenvalue solution and experimental was 11.4 %, which was the best fit compared to the other existing analytical models. From the parametrical analysis, the instability load was considerably decreased by varying the initial lateral deflection, the skewed pad rotation, top flange width and the span of the beam.

Thermal stability of the elastomeric anti-trauma pad

Abstract The elastomeric anti-trauma pad (EA-TP) based on shear thickening fluid (STF) has been developed. Dynamic oscillatory shear experiment was conducted at constant strain amplitude of 5%. STF composed of 25% of volume fraction of 7 nm Fumed Silica, dispersed in polypropylene glycol with molar mass 400 gmol−1 shows elastic properties in entire investigated range of the frequency. Ballistic tests of EA-TP with 7.62 mm × 39 mm PS bullets were performed according to the PN-V-87000:2011 standard. The studies revealed about 60% reduction of the average backface signature depth (BSD) for the EA-TP, when compared to the nowadays commonly used soft insert. The ATR-FTIR analysis confirmed slight impact of the elevated temperature and air (oxygen) on the chemical degradation of the EA-TP surface. The UV-VIS spectroscopy has allowed to notice colour deviation of the aged samples towards green and yellow, as well as lack of dye resistance to accelerated aging process. Thermographic analysis has shown no visible changes of the EA-TP surface and sub-surface during accelerated aging process. The aforementioned small changes on the surface of EA-TP did not affect the ballistic properties of composite armour. EA-TP insert maintains ballistic properties after accelerated aging process which was simulating the period of 6 years according to ASTM F1980 – 07:2002 standard.

Moment-Rotation Response of Beam-Column Connections in Precast Concrete Structures

This paper provides an experimental investigation on the moment-rotation response of typical moment resisting beam-column connections, employing continuous negative bars consolidated with cast in place concrete over the precast beam and passing through grouted corrugated sleeves into an intermediate column. According to [1], the relative beam-column rotation is highly dependent on the elongation mechanism of the negative bars related to both the embedment length into the grouted sleeves and the development length over the beam end, being also inversely dependent on the vertical distance between the position of the top bars and the centre of rotation at end beam section. The flexural secant stiffness of the moment-rotation response is caused by a sum of the joint opening mechanisms at the beam-column interface and crack propagation within the connection zone, wherein the bond-slip at crack positions occurs prior to the first yielding of the negative bars. Therefore, the semi-rigid behaviour of the beam-column connections is associated with deformation mechanisms that occur at the SLS, but which also affects the global behaviour and stability analysis of precast frames at the ULS.Cruciform tests of full scale beam-column connections were carried out at the Precast Research Centre of the Federal University of Sao Carlos (Brazil), where 6 prototypes were studied varying the detailing of the positive connectors over the concrete corbel. The first pair of connectors employed elastomeric bearing pads with 2 vertical dowel bars, the second pair of connectors employed horizontal joints filled with grout with 2 vertical dowel bars and the last pair of connectors employed positive welded plates. The comparison between the experimental results showed that the smallest secant stiffness, which was obtained from the connector with elastomeric bearing pad, was corresponded to 89% and to 82% of the highest secant stiffness obtained for the connectors with welded plates and grouted joint, respectively. Therefore, the experimental results indicate that the major deformation mechanism within the beam-column connections is mostly dependent on the elongation of the top bars. Finally, a simplified analytical equation has been calibrated against the experimental results of the studied beam-column connections.

Evaluation of the lateral stability of precast beams on an elastic bearing support with a consideration of the initial sweep

This study assessed the lateral behavior and stability of precast concrete beams under elastomeric bearing pad conditions. The lateral instability failure of the beam occurs due to the lateral displacement induced by the self-weight and rotation along the beam combined with a rigid body rotation at the support. Therefore, accounting for all the components of the lateral displacement, an analytical equation that can calculate the critical weight of a beam related to the lateral instability of the beam was derived. Furthermore, this study evaluated the critical lateral movements, including the displacement and rotation, with a variation in the initial sweep in the beam. Finally, an analytical procedure was also developed to evaluate the safety of the precast concrete beam against the lateral instability of the beam with a consideration of the initial sweep. The critical values obtained from the proposed method would be used to establish control values for retaining the lateral and torsional stability of a precast concrete beam on the elastic bearing support.

Numerical investigation of the resistance of precast RC pinned beam‐to‐column connections under shear loading

SummaryIn precast technology, the effective design and construction are related to the behaviour of the connections between the structural members in order to cater for all service, environmental and earthquake load conditions. Therefore, the design and detailing of the connections should be undertaken consistently and with awareness of the desired structural response. In the research presented herein, an analytical expression is proposed for the prediction of the resistance of precast pinned connections under shear monotonic and cyclic loading. The proposed formula addresses the case where the failure of the connection occurs with simultaneous flexural failure of the dowel and compression failure of the concrete around the dowel, expected to occur either when (i) adequate concrete cover of the dowels is provided (d > 6 D) or (ii) adequate confining reinforcement (as defined in the article) is foreseen around the dowels in the case of small concrete covers (d < 6 D). The expression is calibrated against available experimental data and numerical results derived from a nonlinear numerical investigation. Emphasis is given to identifying the effect of several parameters on the horizontal shear resistance of the connection such as: the number and diameter of the dowels; the strength of materials (concrete, grout, steel); the concrete cover of the dowels; the thickness of the elastomeric pad; the type of shear loading (monotonic or cyclic); the pre‐existing axial stress in the dowels; and the rotation of the joint. In addition, recommendations for the design of precast pinned beam‐to‐column connections are given, especially when the connections are utilised in earthquake resistant structures. Copyright © 2017 John Wiley & Sons, Ltd.

Effect of Material Mismatch on Static behavior of Flex Seal

A flex seal in a rocket nozzle provides required flexibility for smooth functioning of directional change of the rocket and acts as a pressure tight seal to prevent hot gases from the rocket motor. Flex seal consists of four different components, i) Elastomeric pads, ii) shims, iii) fore end ring and iv) aft end ring. Elastomeric pads are made of hyper elastic material like rubber to provide required flexibility in the system. Shims are made of either metals are composite materials to provides required stiffness to the flex seal. Fore end and Aft end rings are connected to the flex nozzle system and motor respectively. The objective of present work is to study the effect of mismatch in materials of shim and elastomeric pads. In the analysis, ground test conditions of flex seal system are simulated using 2D finite element models. From the analysis it is observed that there is no influence of the Poisson's ratio mismatch. Reduction in deflection and increase in stresses is observed with increase Young‘s modulus mismatch, which is varied by changing the Young‘s modulus of shims.

Rollover instability of precast girders subjected to wind load

The use of longer and deeper precast concrete girders has created concern regarding their rollover instability, particularly during construction. Current design and construction specifications do not provide any specific guidelines that can be used to evaluate the rollover instability of a girder. Therefore, analytical and simplified numerical studies were performed to evaluate the critical wind load, lateral displacement and rotational angle that would induce rollover instability of a girder supported on an elastomeric bearing pad. The influence of the length and section properties of the girder on rollover instability was also investigated. The analytical method proposed in this study can be effectively used for evaluating the lateral behaviour and rollover instability of bridge girders and can also provide management values for securing the lateral stability of girders. The paper also provides a worked problem for a long-span typical European girder to determine critical values with application of the proposed method.

Oil bleed from elastomeric thermal silicone conductive pads

Oil bleed is a serious problem in elastomeric thermal silicone conductive pads. The components of the oil bleed and the effect of the silicone chemical parameters on the amount of oil bleed have been determined. The main components of oil bleeds are the uncrosslinked silicones in the cured resins, which include the unreacted silicone materials and the macromolecular substances produced by the hydrosilylation reaction. Cured resins with a high crosslinking density and a high molecular weight of vinyl silicone residues had a lower amount of oil bleed. In addition, a low Si-H content also reduced the amount of oil bleed. Open image in new window