High Damping Rubber Research Articles

Seismic performance of structure equipped with a new rubber bracing damper system

Nowadays, vibration energy absorption devices are widely implemented in many buildings subjected to severe vibration due to natural hazards, such as earthquakes, strong winds, and typhoons. Recently, viscous dampers have been commonly used in many structures as the most conventional damper type. However, the high maintenance cost resulting from oil leakage from cylinder seals has prompted researchers to seek an alternative system to viscous damper systems. Therefore, the main aim of this research is to develop a new rubber bracing damper (RBD) system by implementing high damping rubber material as a viscoelastic material to be installed in framed structures as diagonal bracing members. This will help dissipate vibration effects on the structure. To achieve this, the initial design for the RBD device has been developed, and finite-element simulation has been conducted to evaluate the behavior of the proposed RBD under various dynamic loading conditions. To define the viscoelastic material properties in finite-element modeling, high damping rubber material has been produced and experimentally tested to determine the numerical model of the material. Subsequently, the test data were utilized to develop the analytical model of the RBD device, and its performance was evaluated by applying cyclic loads and conducting nonlinear analysis. Furthermore, a series of cyclic dynamic tests with various displacement amplitudes and frequencies have been conducted on the prototype of the RBD device based on the finite-element results. Finally, to analyze the dynamic behavior of the structure equipped with RBD, a finite-element model of a three-story reinforced concrete frame structure furnished with RBD dampers has been developed. The response of the structure has been evaluated under seismic loads, and a parametric study has been conducted to investigate the response of the structures with various rubber properties. The numerical analysis results indicated that the implementation of the RBD device leads to a reduction in the occurrence of plastic hinges and lateral displacements of the structure by up to 69%. This demonstrates the efficiency of the RBD device in diminishing the seismic load effect on the structure’s response.

Experimental Study and Seismic Response Evaluation of Chlorobutyl Rubber-Based Viscoelastic Dampers

Conventional viscoelastic devices often use high-damping elastomeric pads, typically made of patented formulations, that are bonded to steel plates. The response properties of these pads under cyclic shear deformations directly influence the load-deformation hysteretic response of the device. Chlorobutyl (CIIR) is a high-damping rubber commonly used in industrial applications. However, this study found that the damping properties of a typical CIIR rubber compound are insufficient for effective structural seismic mitigation at ambient temperatures above 0°C. The goal of this study was to develop a new composite of CIIR, referred to as modified CIIR, with improved damping properties and to compare its performance with that of the reference CIIR rubber. In the first phase of the experimental studies, the viscoelastic characteristics of the reference and modified CIIR rubber materials were evaluated using dynamic mechanical thermal analysis (DMTA) in tension mode. Prototype viscoelastic damper devices were then fabricated from both the reference and modified CIIR rubber materials and subjected to cyclic shear tests at room temperature and various loading frequencies. The results showed that the modified CIIR rubber exhibited significantly improved effective damping compared to the reference CIIR. The final component of this study involved investigating the seismic response of a 2D frame structure equipped with prototype dampers made from both reference and modified CIIR materials, using nonlinear time-history analyses. The analysis results indicated that the modified CIIR rubber can be effectively utilized in the seismic response mitigation of structures.

Dynamic behavior of high damping rubber bearings and lead rubber bearings under near-fault earthquakes

Civil engineering structures are susceptible to natural calamities such as earthquakes, floods, and strong winds. Base isolation is a proven method for protecting structures during earthquakes. It involves inserting a flexible layer between the foundation and superstructure to isolate the structure from earthquakes, thereby changing the system's dynamic characteristics. The present study compares the dynamic performance of passive base isolators, specifically High Damping Rubber Bearings (HDRBs) and Lead Rubber Bearings (LRBs), under near-fault ground motion conditions to assess their effectiveness in reducing seismic impact on structures. The isolator is first analyzed using a static general approach and validated against existing literature before undergoing dynamic analysis. In this research, the LRB isolation system is analyzed using a dynamic explicit approach in ABAQUS, while the HDRB is analyzed using a dynamic implicit approach. The behavior of these isolators is studied under seismic events such as those from the Imperial Valley, Managua, Loma Prieta, Northridge, and Kocaeli ground motions. The results indicate that LRBs significantly reduce acceleration at the top of the bearing compared to HDRBs. The maximum reductions in response are 68.42% for the Kocaeli earthquake in case of LRBs and 61.80% for the Northridge earthquake in case of HDRBs. The LRB shows a minimum acceleration response reduction of 57.24%, while for HDRB, it is 24.47% for the Imperial Valley records in both cases.

Seismic resilient performance of code-designed, base-isolated slender steel buildings in firm soils

The seismic response of slender base-isolated structures can be significantly compromised during strong earthquakes, as significant tensional forces or uplifts can be demanded to exterior and corner base isolators. Nevertheless, there are few studies published in the literature where the expected seismic response of fully-designed base-isolated buildings according to a given base-isolation code or standard is shown and discussed when subjected to ground motions records related to the design earthquake scenario. In this paper, the authors present the results obtained from the cases of study of four code-designed base-isolated buildings, from 8 to 24 stories in height, with different global slenderness ratios H/L: 2.0, 2.5, 4.0 and 6.0. Subject buildings were assumed to be located at the city of Puebla, Mexico, in firm soil sites. Buildings were designed according to current base-isolation guidelines for the Manual of Civil Works (MOC) using the modal response spectrum analysis method while neglecting the vertical component in the design process. The base isolation system was composed of high-damping rubber bearings (HDRB). The considered structural system above the isolation system was a dual system composed of special concentrically steel braced frames (SCBFs) and special moment steel frames (SMFs). The resulting base-isolated (TI) to fixed-base (Tfb) natural periods ratio for the designed buildings was within the range 2.55 ≤ TI/Tfb ≤ 3.02. Nonlinear dynamic analyses were conducted for the designed buildings when subjected to five strongest pairs of orthogonal ground motions recorded during the September 19, 2017 Puebla-Morelos earthquake, which correspond to the design earthquake scenarios considered in MOC. In addition, the impact of the vertical ground motion component was evaluated for the most critical station. From the obtained results, it can be concluded that for the studied buildings, the modal response spectrum design method was safe enough to achieve resilient seismic designs. Nevertheless, net tensile forces and uplifts were triggered in corner base isolators, particularly for ground motion records which corresponding displacement spectra was close to the code displacement spectra for the target design base-isolated period TI. Tensile forces and uplifts in base isolators were slightly increased when considering the action of the vertical ground motion component of the critical station. In addition, peak accelerations at the floor levels were moderately increased when considering the vertical component, which may have detrimental effects in acceleration-sensitive non-structural components and the shear capacity of floor systems.

Performance of High-Damping Rubber Bearings for Seismic Isolation – Case Study of Nayumi Sam Tower Malang Apartment

Performance of High-Damping Rubber Bearings for Seismic Isolation – Case Study of Nayumi Sam Tower Malang Apartment

Hybrid simulation tests evaluating the seismic performance of lead high-damping rubber bearings at low temperatures

As a hybrid rubber isolation bearing, the lead high-damping rubber bearing (LHB) exhibits enhanced seismic isolation and energy dissipation performance by combining lead cores and high-damping rubber (HDR) in a single device. However, at low temperatures, the LHB exhibits the same hardening and self-heating problems as conventional lead rubber bearings (LRBs) and HDR bearings. The complicated thermo–mechanical coupled behavior of the LHB is difficult to predict and is an obstacle for designing and applying it in cold earthquake-prone areas. In this study, the mechanical characteristic variations of the LHB owing to a low temperature were evaluated in the cyclic loading tests, and the low temperature effect on the seismic behavior of a bridge isolated with LHBs was investigated in hybrid simulation tests using a loading system that can control the ambient temperature of the bearing.

A multi‐layer thermo‐mechanical coupling hysteretic model for high damping rubber bearings at low temperature

AbstractHigh damping rubber (HDR) bearings have been widely applied in seismic isolation of structures. However, the complex behavior of HDR bearings is influenced by thermal mechanism coupled with the seismic response of the structure, particularly at low ambient temperatures. In order to express the hysteretic restoring force behavior of HDR bearings involving temperature dependence, heating effect, and heat transfer with an improved accuracy, a multi‐layer thermo‐mechanical coupling model was developed. The thermal mechanism was illustrated by considering the heating effect and heat transfer in the multi‐layer thermal‐coupled model. A nonlinear hysteretic model including the temperature dependence of the stress‐strain relationship of rubber was incorporated. Quasi‐static cyclic loading was conducted for parameter identification and real‐time hybrid simulation tests were carried out for model validation. The model accurately represented the time‐dependent thermal mechanism within the bearing, considering the non‐uniform distribution of internal temperature. Numerical results exhibited good agreement with the experimental results, including the hysteresis curve, temperature history, and temperature distribution. The model demonstrated improved accuracy in computing the hysteretic behavior compared with an existing simple model.

High-damping fiber-reinforced elastomeric seismic isolator in different boundary conditions: An experimental insight

Seismic isolation reduces structural vulnerability and is an effective retrofitting solution. The commonly used steel-reinforced elastomeric isolators (SREIs) consist of several rubber pads interspersed with steel laminas for vertical reinforcement. However, SREIs are expensive, making them economically-unjustified for ordinary residential buildings, especially in developing countries. Fiber-reinforced elastomeric isolators (FREIs) offer a lighter alternative with thin fiber layers instead of steel laminas. FREIs can be applied to the structure in bonded (traditional), unbonded, or partially bonded configurations. Unbonded FREIs (UFREIs) are cost-effective as they are not bonded or fastened to thick connection steel plates. Furthermore, they are inherently more flexible in lateral directions and thus require relatively less rubber material to offer the same seismic isolation performance as traditional elastomeric isolators. However, UFREIs cannot resist tensile forces and may slip under certain loads, limiting their use in situations with overturning or high vertical accelerations. To address these limitations, partially bonded applications (PBFREIs) bond only a reduced area of the rubber device to the connection steel plates. PBFREIs retain beneficial characteristics of both unbonded and bonded applications, such as improved lateral flexibility, and resistance to uplift forces and slip. The possibility of UFREI applications remains promising, particularly in developing countries, due to their low cost, ease of fabrication and installation. This paper proposes a FREI made of high-damping rubber and glass fiber fabrics, and examines its performance in bonded, partially bonded, and unbonded applications. As a unique feature, the material and geometrical characteristics of the FREIs are identical. A comparative analysis, including experimental testing, highlights the strengths and weaknesses of each application typology. The paper also provides a detailed explanation of the design process, encompassing rubber compound development, fabrication, and experimental characterization of the device.

Mechanical properties and analytical model of a novel dissipative angle bracket for CLT structures

The connections are essential in providing the strength, stiffness, ductility, and energy-dissipating capacity for CLT structures. In this paper, a novel dissipative angle bracket for CLT structures was proposed, which combines the benefits of soft-steel brackets and high-damping rubber to offer great energy-dissipating capacity and high ductility. Both quasi-static monotonic and reversed cyclic loading tests were conducted to evaluate the failure mechanisms and mechanical properties of this connection. Failure modes, including the rupture of steel ribs, fracture of the CLT wall, and debonding of the CLT slab, were observed during the tests. The rupture of steel ribs is the controlled failure mode, but the connection can still work as a whole to resist applied load after the steel ribs’ failures thanks to the rubber that is effectively bonded to the steel bracket. The tested connections’ load-displacement curves exhibit a bi-linear form, with the yielding point resulting from the yielding of steel ribs. Almost all the tested specimens have a ductility larger than 9.0 and an equivalent viscous damping ratio of around 10%–22%, indicating high ductility and energy-dissipating capacity. Furthermore, a simplified analytical model of the novel dissipative angle bracket was established. Comparison with test results demonstrates that the proposed model can reasonably estimate the initial stiffness, post-yield stiffness, and yield force. The outcomes of this study are expected to provide valuable references for future research and potential applications of the novel dissipative angle bracket for CLT structures.

Development of novel high damping rubber damper under axial compression dynamic load for energy-dissipation application

High Damping Rubber (HDR) has been a reliable and durable material used in bearings as seismic isolation devices for several decades. However, there has been no development of HDR as dampers to mitigate structural response caused by earthquake excitations, specifically by dissipating the induced energy applied to structures under direct axial load. This paper aims to address this gap by developing a novel HDR damper utilizing Hyper Elastic Composite Material (HECM) and conducting experimental investigations to determine its damping ratio, compressibility, and elasticity behaviour under axial dynamic compression load for effective dissipation of dynamic loads. The research methodology involved performing response spectrum analysis (RSA) on a model of actual building structures, following the guidelines of National Annex to MS EN 1998–2017. Subsequently, the dampers were incorporated into the model to achieve a seismic base shear value without seismic actions, as determined by the RSA. Full-scale dampers were then developed using three different HECM variants (NR- A, B and C), selected based on their achievement of a damping ratio of more than 10% as bearing isolators using the shear method according to EN 15129:2009 cl. 8.2.4.1.5. The developed dampers underwent testing for damping and wind load in accordance with EN 15129 cl. 7.4.2.7 and cl. 7.4.2.8, respectively, incorporating the testing parameters derived from the model's RSA. Finite element models (FEM) were developed and accurately simulating the hysteresis curves and damping properties of the HDR damper. The properties of HECM in the FEM were derived from the simulation results and can be utilized for future damper design, ensuring compliance with industry requirements. Additionally, an empirical formula will be developed to enable structural designers to estimate the mechanical properties of the tested damper. The testing shows that NR-C HECM damper is able to achieve 10.46% under 1.8 Hz requirement and able to exceed more than10% damping ratio up to frequency 2.3 Hz, thus providing an alternative energy dissipation damper in the building industry.

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.

Damping in stay cable with damper: Practical universal damping curve and full-scale measurement

This paper includes two main parts which are the development of a universal damping curve for cables of cable-stayed bridges with dampers and a full-scale measurement of cable damping. In the first part, the universal damping curve is derived for cables with viscous dampers or High Damping Rubber (HDR) dampers. The proposed damping curve is a single curve which incorporates several cable-damper parameters like cable bending stiffness, boundary conditions at cable ends (hinged, fixed or restraint ends), damper stiffness, damper support stiffness and added negative stiffness. A numerical approach by a finite difference method (FDM) is also developed to verify the proposed universal damping curve. In addition to FDM, the accuracy of the proposed curve was confirmed with damping formulations in literature over ten different damper types. The results showed a good agreement of estimated damping between proposed damping curve and others. Additionally, a significant improvement in estimating cable damping was observed through two available full-scale tests, which compared the results between proposed curve and current curve. The second part in this study presents a full-scale measurement of cable vibration and a real application of the proposed damping curve for the identification of damping in cables of Shinminato Bridge (cable lengths from 100 to 200 m). Both HDR and viscous dampers were used for the cable vibration control of the bridge. The results of damping analysis indicated that the HDR damper effectiveness was higher than 0.7 whereas this effectiveness was smaller than 0.4 for the viscous damper.

Analysis of seismic damage mechanism of simply supported girder bridges at near‐fault liquefaction sites

AbstractThis work uses the Yematan Bridge as an example to explore the seismic damage mechanism of simply supported girder bridges at near‐fault liquefaction site. It analyzes the bridge from the local portion to the complete bridge, considering the effects of the near‐fault and liquefied soil layers. First, a three‐dimensional model of the pile‐soil seismic action of Pier No.17 was created using simulated near‐field ground motion, and analysis was performed to simulate the action of the liquefied soil layers on the pile foundation, getting pile‐soil dynamic p‐y curves. After that, the accuracy of the pile spring parameters was verification by doing an equivalent static analysis. Finally, to identify the seismic damage mechanism of high‐damping rubber (HDR) bearings and the dynamic unseating process of the Yematan Bridge, a finite element model of the complete bridge was developed. During this procedure, the near‐field ground motion amplitude and soil spring parameters were iterated and optimized continually, such that the simulated earthquake damage was identical to the real one. The findings suggest that the bridge was destroyed by significant structural vibration. The near‐fault impulse effect and lack of equivalent limiting measures induced the entire collapsing girders to move consistently and destroyed the HDR bearings. Liquefied soil can cause some damage to pile foundations, and lateral spreading can cause the piers of the same span to perform differently.

Development of hybrid rubber damper-restrainer (HRDR) system for structures under sever dynamic excitation

Nowadays, high damping rubber materials are extensively implementing in various types of structure to mitigate harmful effect of imposed vibration and dynamic force to the structure. Although, the rubbers exhibit noticeable damping in the shear action, however, de-bounding, shear rupture and delamination of rubber layers under cyclic loads, undermine the load-bearing capacity of the rubber dampers and increase their maintenance costs. Hence, the action of the rubbers is considerably high under applied compression to generate resistant force to restrain the deformation.For this reason, in this research, a new hybrid rubber damper-restrainer (HRDR) system is proposed. The system comprises a high-damping rubber component designed to dissipate applied vibrations, along with a pair of hyper-elastic rubbers intended to restrain displacement. Therefore, the developed HRDR device is capable of dissipating vibrations while restraining large movements to prevent any damage and debounding of the rubber layers and also, protect the structure from excessive displacements.To examine the performance of the proposed device, the numerical model of a HRDR was developed using the finite element simulation and subsequently, nonlinear dynamic analyses were conducted for the 6 storey prototype steel structure furnished with HRDR device. The findings revealed that the structure equipped with the HRDR device exhibited outstanding response against applied earthquake excitation which is proving high efficiency of HRDR device to diminish vibration effect on structure and prevent any excessive deformations. The HRDR device is applicable to any types of framed structures through installing via chevron brace system in steel structures or short wall in reinforced concrete structures. Furthermore, the developed HRDR device can be implemented in bridge structures, between the deck and pier of bridge to effectively dissipate vibrations and restrain the movement of the bridge span under traffic loads.

Seismic performance assessment of steel plate shear walls equipped with passive dampers

The main objective of the current study is to improve the structural resilience and damage control of steel plate shear walls (SPSWs) equipped with a unique passive visco-plastic damper. The proposed damper is made of a high-damping rubber layer with self-centering characteristics and ductile steel bolts. The seismic response of the novel SPSW system equipped with the aforementioned visco-plastic damper is evaluated using a three-dimensional nonlinear finite element analysis validated with experimental data. Furthermore, a parametric study is conducted to see the effect of different parameters such as the bolt diameter-to-height ratio, rubber thickness, number of bolts, number of dampers, location of the damper connection, and bolt material on the behavior of SPSW equipped with visco-plastic dampers under cyclic loading. Results showed that the suggested damper could concentrate most of the damages merely in itself and preserve the primary structural components in the undamaged elastic range, which acted as a structural fuse. The results indicated that to obtain the research objective, the bolt diameter-to-height ratio needs to be 0.2 or less, which in this case, more than 85% of the total input energy is absorbed by merely the damper and steel boundary columns and beam remained elastic and undamaged, while the infill plate had a relatively low energy absorption rate of roughly 10%. On the contrary, the infill plate of the conventional SPSW absorbed the highest energy, accounting for more than 75% of the total input energy. The beam also had a relatively high energy absorption rate of around 24%. In addition, the self-centering behavior of the proposed system could reduce nearly 36% of the residual lateral displacement compared with the conventional SPSW.

A hybrid inter-module connection for steel modular building systems with SMA and high-damping rubber components

The recent technological advancements achieved in modular construction have accelerated the trend of building taller self-standing steel modular building systems (MBSs), leading to a consensus among researchers regarding the vital role that inter-module connections (IMCs) play in the structural performance of MBSs subjected to extreme lateral loading. However, existing IMCs are typically designed such that the global structural system heavily relies on the hysteresis of the steel framing members, leading to severe sustained damage and costly, impractical retrofitting programmes. To unlock the full “disassembly and reuse” potential of steel MBSs, IMCs can be designed to contribute more effectively to the global damage distribution mechanism, by engaging specific “fuse” components which are easy to replace, improving the reuse prospects of volumetric modules. In this regard, the present study proposes a novel, hybrid IMC using custom corner fittings, a high-damping rubber (HDR) core and a shape-memory alloy (SMA) bolt. Calibrated and validated material models using data from experimental material characterisation tests have facilitated the full characterisation of the hybrid mechanical response, determining the deformation modes, stress states, hysteresis loops and mechanical parameters. The parametric FEA included the variation of bolt preload, endplate thickness, axial load magnitude and the vertical layout of the HDR core. The study represents a preliminary, proof-of-concept investigation, showcasing the favourable cyclic performance of the proposed IMC under the main deformation modes expected in tall self-standing MBSs during lateral loading. Due to the effective contribution of each component to the combined hybrid response, the connection succeeds in preventing the formation of significant plastic damage in the MBS’s corner fittings to facilitate reusability of modules.

A numerical model for non-linear shear behavior of high damping rubber bearings

The dynamic behavior of isolated structures is strongly controlled by the force–deformation constitutive behavior of the isolators. Among the different types of existing isolation devices, High Damping Rubber Bearings (HDRBs) are commonly used in practice, which behavior is highly non-linear and difficult to model analytically. Consequently, this article proposes a simple, but sufficiently accurate, mathematical model for simulating the non-linear shear behavior of HDRBs under large deformations, and an estimation procedure for its parameter values using the geometrical features and mechanical characteristics of the device. First, we briefly describe the phenomena observed in the experimental test data, as well as other phenomena not observed within the range of experimental deformations. Then, the mathematical formulation is presented, which is based on the consideration of two components connected in parallel, a hyperelastic spring and a dissipative component. The governing equation for the former is derived from the expanded formulation of the Mooney–Rivlin model for isotropic hyperelastic materials, and the latter from a Bouc-Wen model with hardening. A novel model is included to account for stiffness degradation, including scragging and Mullins effects, which is developed from experimental data of 924 tested devices. The proposed model fits well the experimental test results of HDRBs with different geometric features and material properties. Based on the evolution laws for the different variables, the model can be successfully used in structural dynamic analysis. To facilitate model calibration, a statistical estimation procedure is proposed to reduce the 17 force–deformation constitutive model parameters of the isolator to 9 unknown parameters, which are computed from the geometric features of the device and mechanical characteristics of the rubber material. This makes the calibration of the force–deformation constitutive model parameters feasible. The estimation procedure successfully predicts the behavior of an average device within a batch of HDRBs, showing good agreement with two different experimental datasets.

λ-Factors for the Upper and Lower Bound Analyses of Base-Isolated Structures: Historical Review of Code Provisions for Elastomeric Bearings

The seismic response of base-isolated structures is notably influenced by mechanical properties of isolation devices due to their essential role in structural behavior. Consequently, the variability of such properties should be accounted for in the design process. The current seismic codes prescribe a simplified approach based on structural analyses in two extreme situations resulting from the upper and lower bound design properties of bearings (upper and lower bound analyses). In the case that experimental data are not provided by manufacturers, seismic codes provide the so-called “property modification factors” or “λ-factors”, i.e., modification coefficients to be applied to the nominal dynamic properties of bearings to obtain their upper or lower design properties. The aim of this paper is to provide a historical review of values provided for such factors by the main seismic codes by highlighting the limits, as well as some clerical errors, present in some codes. In particular, the European seismic codes are illustrated in detail, i.e., the Eurocode for bridges (EN 1998-2) and product standard on anti-seismic devices (EN 15129). Both these codes account for different sources of variability, such as the bearings production and the environmental and behavioral effects. For all these effects, the same λ-factor values are provided by the two codes, deriving from the second version of the AASHTO guide specifications for seismic isolation of bridges (AASHTO 1999), which are based on limited and/or old data, especially for high damping rubber bearings (HDRBs), and were never updated in the successive versions. More recent standards are also illustrated, providing different perspectives that deserve attention, even though they require further investigations to be applied in the design practice.

Formulation and Performance of NBR/CR-Based High-Damping Rubber Composites for Soundproof Using Orthogonal Test.

Multiple functional-material-filled nitrile butadiene rubber/chloroprene rubber (NBR/CR) acoustic composites were extensively studied and prepared. According to the orthogonal test table L25 (56), 25 groups of samples were prepared by using a low-temperature one-time rubber mixing process. With tensile strength, average transmission loss, and damping peak as indexes, the influence degree of different factors and levels on the properties of acoustic composites was quantitatively discussed and analyzed. The matrix weight analysis was employed to optimize the material formula of rubber composites, and the corresponding influence weight was given. Results showed that the acoustic composite with blending ratio of 70/30 for NBR/CR matrix had preferable mechanical and acoustic properties; adding mica powder (MP) and montmorillonite (MMT) in matrix contributed to improve all above three indexes owing to their specific lamellar structures; hollow glass beads (HGB) had a positive influence on improving acoustic property due to its hollow microcavities, however, it had a negative impact on damping property because of the smooth spherical surfaces. Accordingly, the optimal formulation was found to be NBR/CR blending ratio of 70/30, MP of 10 phr (per hundred rubber), HGB of 4 phr, and MMT of 10 phr.

Practical negative stiffness device with viscoelastic damper in parallel or series configuration for cable damping improvement

Negative stiffness mechanism has been found able to improve damping performance of dampers on a stay cable which otherwise is limited by the damper installation distance from a cable end. This study provides a practical negative stiffness device (NSD) with adjustable negative stiffness and experiments are performed to validate the negative stiffness effect. The NSD is then combined with a viscoelastic damper in parallel or series for cable damping improvement. Explicit design formulas are derived for optimal design with a target enhancement effect in damping considering the damper described respectively using the Kelvin model and the linear hysteretic damping model. The formulas are verified by analytical and numerical solutions. Parametric analyses show damping enhancement effects of the NSD and it is found more efficient when combined with a damper in series because both deformation amplitudes of the damper and the NSD are further increased in this configuration. Subsequently, case studies are carried out based on two cables of the Sutong Bridge respectively with a shear-type viscous damper and a high damping rubber damper. The results show that the designed NSD can fulfill practical requirements. Particularly, a 100% increase in damping can be achieved by the presented NSD when combined with the damper installed on a cable of 546.9 m long.