Elastomeric Pads Research Articles

Application of controlled-rocking isolation with shape memory alloys for an overpass bridge

Resilience of bridges in seismic zones can be realised by taking the advantage of rocking isolation which aims at reducing the permanent drifts after a seismic event. The seismic forces at the base of the bridge can be reduced by allowing uplift in the foundation when subjected to ground shaking. Conventional monolithic connection of bridge pier to the foundation often leads to severe damages (or even collapse) during high magnitude earthquakes. In this context, this article proposes a novel seismically resilient pier footing which rocks on elastomeric pads and external restrainers (provided by shape memory alloy bars). Seismic performance of a typical existing overpass motorway bridge is compared with the proposed rocking isolation concept. The proposed technique shows good re-centring capability during earthquakes with negligible residual drifts. Furthermore, it is also observed that forces in the pier and size of pier footing are reduced as compared with the reference bridge considered in this study.

Influence of the Testing Procedure on the Value of the Impact Attenuation of Rail Fastening Systems: an Experimental Study

Railway superstructure components are subject to impact forces caused by irregularities in the rail and wheel or variations in the support stiffness. These imperfections lead to the premature and accelerated deterioration of the track and increase maintenance costs. Generally, to mitigate these dynamic loads, elastomeric rail pads are interposed between rails and sleepers. For each track section, the pad choice is made according to its stiffness, impact attenuation and cost. In this experimental study, eight types of rail pads were characterized using two procedures from EN 13146–3. The results revealed that the rail pad material and geometry affect the impact attenuation ability of the pad and the testing procedure affect the results. It was found that the preload applied is one of the parameters that most affects the impact attenuation value. Appling a preload of 50 kN during the impact attenuation test, which is suggested by the standard, affected this parameter by ranging from between ~2 and ~ 20, depending on the rail pad. Based on these results it is considered that EN 13146–3 should be updated.

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.

Rocking isolation of bridge pier using shape memory alloy

The conventional design philosophy of bridges allows damage in the pier through yielding. A fuse-like action is achieved if the bridge piers are designed to develop substantial inelastic deformations when subjected to earthquake excitations. Such a design can avoid collapse of the bridge but not damage. The damage is the plastic hinge formation formed at location of maximum moments and stresses that can lead to permanent lateral displacement which can impair traffic flow and cause time consuming repairs. Rocking can act as a form of isolation by means of foundation uplifting which act as a mechanical fuse, limiting the forces transferred to the base of the structure. In this context, this paper proposes a novel resilient controlled rocking bridge pier foundation, which uses elastomeric pads incorporated beneath the footing of the bridge piers and external restrainer in the form of shape memory alloy bar (SMA). The rocking mechanism is achieved by restricting the horizontal movement of footing by providing stoppers at all sides of footing. The pads are designed to remain elastic without allowing their shearing. The pier, the footing and the elastomeric pads are assumed to be supported on firm rigid concrete sub base resting on hard rock. By performing nonlinear dynamic time history analysis in the traffic direction of the bridge, the proposed pier with the novel resilient foundation is compared against a fixed-based pier and classical rocking pier (CC). The proposed pier rocking on elastomeric pads and external restrainer (CP+SMA) has good re-centering capability during earthquakes with negligible residual drift and footing uplift. In this new rocking isolation technique, the forces in the piers are also reduced and thus leading to reduced construction cost with enhanced post-earthquake serviceability.

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.

A system for simulating the kinematics and measuring the impact force from riding whips used in Thoroughbred horseracing

Thirty horse racing whips of four different designs were tested to measure dynamic impact force and compared using a specially designed mechanical testing device to simulate the whipping action of a jockey during racing. The whips tested included designs used in Thoroughbred horse racing in North America, which meet the design criteria established by the Association of Racing Commissioners International (ARCI) model rules, as well as the most common whip used in British horse racing. The objective of the device was to allow comparisons to be made between peak impact loads resulting from different whip designs. A high peak dynamic force on a horse’s shoulder or hind quarter may result in injuries, such as welts. The testing device contains a planar three-bar, open mechanical linkage loaded by torsion springs to model the arm motion of a jockey. The whip strikes a flat plate covered by an elastomeric pad. The energy input is replicated during the simulated impact. A single axis dynamic load cell under the loading plate and three single-turn precision potentiometers located at each joint of the three-arm mechanical system measure impact forces and relative angular positions, respectively. Force measurements are compared from the face of each whip and the edge or seam where applicable. In addition to the flap design, other physical differences between whip designs included mass, shaft length, shaft stiffness, flap cushion thickness/compression factor, flap surface area, and flap seam area. Statistically significant impact force differences were found between flap face and flap seam impact orientations, with higher impact forces delivered by the flap face. Significant differences were also found in impact forces between the three whip styles with seams.

Implementation of anisotropic soft pads in a surgical gripper for secure and gentle grip on vulnerable tissues.

Current surgical grippers rely on friction grip, where normal loads (i.e. pinch forces) are translated into friction forces. Operating errors with surgical grippers are often force-related, including tissue slipping out of the gripper because of too low pinch forces and tissue damaging due to too high pinch forces. Here, we prototyped a modular surgical gripper with elastomeric soft pads reinforced in the shear direction with a carbon-fiber fabric. The elastomeric component provides low normal stiffness to maximize contact formation without the need of applying high normal loads (i.e. pinch forces), whereas the carbon-fiber fabric offers high shear stiffness to preserve the formed contact under the lateral loads (i.e. shear forces) that occur during tissue lifting. Additionally, we patterned the pads with a sub-surface micropattern, to further reduce the normal stiffness and increase shear stiffness. The body of the prototype gripper, including shaft, joints, and gripper tips, was fabricated in a single step using 3D printing, followed by manual attachment of the soft pads to the gripper. The gripping performance of the newly developed soft gripper on soft tissues was experimentally compared to reference grippers equipped with metal patterned pads. The soft-pad gripper generated similar gripping forces but significantly lower pinch forces than metal-pad grippers. We conclude that grippers with anisotropic-stiffness pads are promising for secure and gentle tissue grip.

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.

Determination of wheel loads from runway cranes based on rail strain measurement

The knowledge of the actual wheel loads resulting from the runway cranes in service is of major importance for the fatigue assessment of existing crane runway girders. Once the wheel loads are known, the global and local stress fields can be calculated based on well-known procedures.Within this paper a methodology is developed to quantify the wheel loads based on strain measurements on the rail. For cases without rail pad, only two vertical strain gauges are sufficient to calculate the wheel load, while two additional horizontal strain gauges are necessary for cases with rail pad.Experimental tests with different rail types are presented and compared with numerical calculations. Both, the borderline case of rails with ridged support and cases of rails on crane runway girders, with and without elastomeric pads, are studied in detail.

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.

Impact of aluminum oxide nanopowder on thermal, optical and surface properties of polysiloxane-aluminum oxide composites as elastomeric thermal pad for light emitting diode application

ABSTRACTVirgin polysiloxane and aluminum oxide nanopowder (10%–50%) reinforced polysiloxane composite films were prepared and its thermal, optical, surface properties were investigated. Polysiloxane/aluminum oxide (Al2O3) (50%–50%) composite film sample exhibit high thermal conductivity (k – 0.26 W/mK) and UV absorption, decreased junction temperature (ΔTJ = 25.69°C at 700 mA) and thermal resistance (∆Rth-tot = 12.41 K/W at 700 mA) compared to virgin polysiloxane film. Overall, the prepared composites can be used as an alternate elastomer thermal pad for efficient thermal management as well as UV blocking encapsulant for future UV-free LED application development.

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.

Effect of Different Constraint Systems on the Seismic Response of Double-Deck Curved Girder Bridges

Double-deck curved girder bridges can achieve large climb in a short distance, and their seismic response differs from that of regular bridges due to their special structural form. The constraint system of bridges, which consists of bearings and shear keys, has a key influence on the seismic response of the bridge structure. Accordingly, this research aims to develop a reasonable constraint system for double-deck curved girder bridges. A finite element simulation of a double-layer curved steel box girder bridge is also conducted to compare some indexes, which are the displacement of bearings with the curvature of the pier section. The shear bolt is selected as the limit device to study the influence of shear bolts and different bearings on the seismic response of the double-deck curved girder bridge structure. Under the influence of ground motion, the displacement of the upper bearings of double-layer curved girder bridges is generally larger than that of the lower bearings. The double-layer constraint system makes the section curvature and ductility in the middle of the pier smaller than that at the top and bottom of the pier. The spherical steel bearings have a small displacement, whereas the pier has a large internal force. After setting the shear bolts, the displacement of the spherical steel bearings decreases, whereas the damage to bridge piers does not show obvious changes. When the displacement of elastomeric pad bearings increases, sliding occurs under a low ground motion intensity, thereby reducing the degree of damage to the bridge pier. Moreover, the application of shear bolts limits the displacement of bearings and subsequently increases the seismic force being transmitted to the pier whose damage is the most serious. However, the displacement of pot bearings is relatively small, and the displacements of the upper and lower layers are close. In addition, the seismic inertial force of the superstructure is relatively uniform, thereby protecting the piers to a certain extent. After setting the shear bolts, the deformation falls within an allowable range, whereas the damage to the bridge piers slightly increases. Therefore, combining pot bearings with shear bolts creates a reasonable constraint system for double-deck curved girder bridges.

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.

A feasibility study on pre-compressed partially bonded viscoelastic dampers

The conventional viscoelastic damper devices employ high damped elastomeric pads that are chemically bonded at their entire contact surfaces to the steel plates of the device. The hysteretic load-deformation characteristics of the device are governed by the inherent response properties of the elastomeric material under cyclic shear deformations. The high damped viscoelastic material of the device is typically made of a particular copolymer of patented formulation. The main objective of this paper is to improve the hysteretic characteristics of a viscoelastic damper by applying physical changes to the configuration of its viscoelastic pads. As such, innovative pre-compressed partially bonded viscoelastic damper devices have been introduced. The proposed dampers employ fiber-reinforced viscoelastic pads that are partially bonded to the inner and outer steel plates of the damper, and are subjected to a desired level of permanent pre-compression. A set of full scale prototype damper devices of different geometrical configurations have been examined experimentally. Results of cyclic shear tests indicate that the pre-compressed stresses increase the effective inherent damping of the viscoelastic material. Moreover, the fiber reinforcing layers provide an additional source of energy dissipation as the partially bonded pads exhibit rollover deformations under cyclic shear loads. Based on the results of this proof-of-concept study, the pre-compressed partially bounded viscoelastic dampers are found to be quite feasible.

Seismic evaluation of precast bridge columns with built-in elastomeric pads

A novel built-in elastomeric pad was incorporated into the plastic hinge zone of precast bridge columns with grouted corrugated duct connection to improve its seismic performance. Appropriate energy dissipation and minimal local concrete damage are expected in the innovative precast reinforced concrete (RC) columns. Four 1/4-scaled bridge column specimens were designed and tested under constant axial compression force and cyclic lateral loads to evaluate the feasibility and effectiveness of the proposed concept. Detailed experiment results were compared and discussed. The testing results showed that the main seismic index of precast RC bridge columns with grouted metal corrugated duct connection was similar to that of the cast-in-place bridge columns. It was also found that the precast RC column with a built-in elastomeric pad in the plastic hinge zone effectively minimized local concrete damage at the bottom of bridge columns and increased the energy dissipation capacity. The laminated elastomeric pad is recommended to be applied in the precast bridge column to maintain necessary initial stiffness and energy dissipation capacity and to avoid lateral bulge of single thick rubber. Excessive buckling and shear deformations of longitudinal rebars should be prevented by inserting a rectangular or square steel tube at the center of the elastomeric pad.

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.