Abrupt Stiffness Research Articles

Interaction-performance-driven design of negative-stiffness friction pendulum systems for aboveground structure–connected underground structure–soil system with ground motion effects

Within the transit-oriented development framework, aboveground structure–connected underground structures (ASUS) have been widely constructed in urban areas; however, abrupt stiffness changes and complex soil–structure interactions could cause structural damage or business disruption after earthquakes. In this study, to address these challenges, a novel approach is proposed that employs negative stiffness, damping elements, and friction pendulum bearings to enhance the overall performance of ASUS. An interaction-performance-driven design procedure and parameter selection methodology are developed to simultaneously upgrade multiple performance aspects of ASUS. A mechanical model of the negative stiffness amplification system-enabled friction pendulum system (NSAS-FPS) is constructed. The theoretical basis of the equivalent negative stiffness and enhanced energy dissipation effects is elucidated, and a finite element model of the NSAS-FPS-incorporated soil–ASUS interaction system is established. Extensive parametric, robustness, and correlation analyses against short/long-period ground motions are conducted to provide a comprehensive performance assessment framework. Then, an interaction-performance-driven design principle aimed at multiperformance upgrading of aboveground and underground structures is developed with proposed parameter selections and applied in a case study. These results indicate a significant improvement in vibration control for both aboveground and underground structures when utilizing NSAS-FPS compared to utilizing conventional FPSs with the same design. By following the proposed design procedure and parameters, the NSAS-FPS demonstrates enhanced efficiency in isolating energy dissipation and robustness in seismic isolation, as well as resistance against overturning, irrespective of variations in structural masses and functionalities. While the advantages of the NSAS-FPS include its ability to mitigate the effects of stochastic earthquakes, the extent of the performance improvement may decrease during long-period earthquakes. Therefore, the velocity characteristics of seismic excitations need to be carefully incorporated into the NSAS-FPS design, particularly when targeting specific demands for the isolation-layer performance within ASUS.

Study on the analytical model of bending deformation for spliced glass beams with stainless steel bolts

To deal with the problems of high cost in super long glass manufacturing, which restricts their applications and development in glass structures, spliced glass beams (SGB) with stainless steel bolts connections was developed. The bending deformation of the SGB with stainless steel bolts have not been elucidated because it is difficult to achieve full beam equal stiffness in the splicing part. In view of this, the conjugate beam method was utilized to calculate the bending deformation of the SGB with stainless steel bolts. The bending deformation of the SGB with stainless steel bolts was investigated by the bending performance test, while the location of abrupt stiffness change and the actual correction coefficient were determined. It is verified by finite element analysis, on the basis of which the influence law of the height-to-span ratio and the height-to-thickness ratio of glass and stainless steel plate on the ultimate load and maximum deflection of SGB with stainless steel bolts were studied. The results confirmed that SGB composed of as few stainless steel bolts as possible can fully utilize the bending capacity of glass. This study provides a simplified calculation method for the engineering design of SGB, and opens up an idea for the design of glass structures.

Time-varying damage detection in beam structures using variational mode decomposition and continuous wavelet transform

Civil engineering structures in operation are likely to suffer damage. During the service life, structural damage evolves gradually from minor to severe. However, most current studies focus on damage localization and quantification of damage severity, and hence little attention has been paid to the detection of time-varying damage. This paper aims to propose a new approach for tracking the damage evolution of beam structures. In this approach, the wavelet threshold method is used at first to denoise the response signal. After that, the variational mode decomposition (VMD) is introduced to decompose the denoised response signal into several mono-components adaptively. A proposed index of wavelet total energy change (WTEC) is then applied to the new decomposed signals to localize damages of beam structures. On a basis of this, a time-varying damage index called wavelet energy change ratio (WECR) is established via the continuous wavelet transform and time window techniques and then applied to the response at the damaged position for tracking damage evolution. The proposed method is verified via a numerical example of a simply supported beam (its length and area of cross section are 5 m and 0.04 m2, respectively) with a sudden and a linear stiffness reduction under 1940 El Centro ground acceleration record. In addition, an experiment on a 10-meters-long steel bridge with abrupt stiffness reduction under a moving load is investigated to demonstrate the effectiveness and accuracy of the proposed time-varying damage detection method. The results show that the index of WTEC is able to localize damages of beam structures effectively whatever they are a single damage position or multiple damage positions. Moreover, the damage evolution can be tracked by the proposed index of WECR accurately even though random noises and end effects pose a great impact on the time-varying damage detection results.

In Situ Investigation of the Dynamic Response and Settlement in the Expressway Culvert–Subgrade Transition Section Using a Vibration Exciter

During the operational phase of the expressway, a significant challenge arises concerning substantial differential settlement in the transition zone connecting the culvert and the general subgrade, affecting its smoothness. In order to address the issue of abrupt stiffness variations within the transition section and to mitigate the occurrence of differential settlement, a gradient pile–reinforced-concrete slab composite foundation was implemented for the first time within an expressway culvert–subgrade transition section. At the same time, an in situ vibration test was conducted through the SBZ30 vibration exciter to comprehensively understand the vertical dynamic responses in the culvert–subgrade transition section under various axle loads and speed conditions. Furthermore, continuous monitoring was conducted to track the long-term settlement of the roadbed. The findings indicate that the utilization of gradient pile–reinforced-concrete slab composite foundations can significantly mitigate the amplitude of the dynamic response parameters. Moreover, dynamic parameters and attenuation coefficients exhibit a gradual reduction as the depth increases. Dynamic stresses, acceleration, and displacements on the roadbed surface exhibited positive correlations with both the axle weight and vehicle speed. However, at deeper depths, the load weight exerted a more pronounced influence. As the speed rose, acceleration decayed faster, affecting a shallower depth. Conversely, the increased load slowed the acceleration decay. The cumulative deformation of the roadbed and the number of excitations followed exponential function characteristics. Settlement values progressively increased while the settlement rate gradually diminished, eventually reaching a stable state, ultimately stabilizing within 4.7 mm. These research outcomes offer valuable guidance and serve as a reference for the implementation of gradient pile–reinforced-concrete slab composite foundations within the culvert–subgrade transition section.

Performance Evaluation of a Combined Transition System in Slab-Ballasted Railway Track Using a Vehicle-Track-Substructure Interaction Model

Abrupt stiffness variations along the railway track may increase the geometrical and mechanical defects of railway lines. The conjunction points of a railway track with concrete and ballast pavements, which are called slab-ballasted track transitions, are one of the main areas where vertical track stiffness changes sharply. Therefore, the potential benefits of a combined transition system along the slab-ballasted transition, made of an approach slab and additional rails, are studied in this paper. For this purpose, a vehicle-track-substructure interaction model, which included three main segments of the railway track (slab track, transition zone, and ballasted track) was programmed based on the finite element method. A test line with the mentioned combined transition system was built to measure the railway track responses through field study. Then, the three-dimensional (3D) numerical model was validated using the results obtained from the experimental tests. Afterwards, a number of parametric studies were performed to analyze the dynamic responses of the combined transition zone. The results indicated that this type of transition system promotes a smoother stiffness transition between the slab track segment and the ballasted track segment by making the transition in three gradual steps. The track displacements in the analyzed case-study gradually increased by about 22%, 28%, and 34% along the combined transition zone in the junction points of the slab and ballasted tracks.

A Computational Approach to Smoothen the Abrupt Stiffness Variation along Railway Transitions

A Computational Approach to Smoothen the Abrupt Stiffness Variation along Railway Transitions

Investigations on Guided Ultrasonic Wave Dispersion Behavior in Fiber Metal Laminates Using Finite Element Eigenvalue Analysis

AbstractComposite materials such as fiber metal laminates combine the advantages of metallic materials and fiber‐reinforced polymers. Hence, these materials are of great interest for thin‐walled structures in lightweight engineering. Due to the structure of these materials, damage to fiber metal laminate components occur more frequently inside the structure than with conventional materials. Since the detection of interlaminar damage is more complicated compared to external damage, it is one of the biggest challenges in the use of fiber metal laminates. One approach to detect this kinds of damage, is the use of guided ultrasonic waves, for example Lamb waves. To be able to perform such damage detection, knowledge about the propagation behavior of this kind of waves in fiber metal laminates is fundamental. Abrupt stiffness variations across the thickness of fiber metal laminates, resulting from the different material layers, lead to the question whether the known approaches for the propagation of guided ultrasonic waves in isotropic and transversely isotropic materials are applicable here. Therefore, the objective of this work is to investigate the propagation behavior of these guided ultrasonic waves in fiber‐metal laminates over large frequency ranges. For this purpose, dispersion relations from finite element simulations are compared with experimental data and numerical solutions based on the analytical framework. The investigations are carried out using a fiber metal laminate consisting of steel and carbon fiber‐reinforced polymers. Due to the orthotropy of the laminate, wave propagation in the fiber direction and perpendicular to it is considered. For the finite element simulations a linear two dimensional eigenvalue analysis is used. This method is especially suitable because it offers a very efficient modeling approach for this kind of application. The experimental data are based on measurements contained in previous publications by the authors. The comparison of the finite element simulations with the experimental data and the data from the analytical framework show that they are in good agreement. The results shown in this work serve to validate the numerical approach presented and allow for further, more complex simulations.

Input-state-parameter-noise identification and virtual sensing in dynamical systems: A Bayesian expectation-maximization (BEM) perspective

Structural identification and damage detection can be generalized as the simultaneous estimation of input forces, physical parameters, and dynamical states. Although Kalman-type filters are efficient tools to address this problem, the calibration of noise covariance matrices is cumbersome. For instance, calibration of input noise covariance matrix in augmented or dual Kalman filters is a critical task since a slight variation in its value can adversely affect estimations. The present study develops a Bayesian Expectation-Maximization (BEM) methodology for the uncertainty quantification and propagation in coupled input-state-parameter-noise identification problems. It also proposes the incorporation of input dummy observations for stabilizing low-frequency components of the latent states and mitigating potential drifts. In this respect, the covariance matrix of the dummy observations is also calibrated based on the measured data. Additionally, an explicit formulation is provided to study the theoretical observability of the Bayesian estimators, which helps characterize the minimum sensor requirements. Ultimately, the BEM is tested and verified through numerical and experimental examples, wherein sensor configurations, multiple input forces, and abrupt stiffness changes are investigated. It is confirmed that the BEM provides accurate estimations of states, input, and parameters while characterizing the degree of belief in these estimations based on the posterior uncertainties driven by applying a Bayesian perspective.

Bistable sound insulator with an abrupt stiffness shift using magnetic-coupled dielectric elastomer actuator

Aiming at noise isolation in low frequency range, this paper presents a novel kind of membrane sound insulator featuring a bistable actuation, by combining magnets and multilayer dielectric elastomer actuator (DEA). With a critical applied voltage on DEA, it deforms and the magnets attract in terms of a bistable snapping, which leads to an abrupt stiffness shift, and consequently regulates the sound transmission loss peak frequency. An electromechanical model is established to reveal the bistable characteristics and to study the effect of voltage and structure parameters for design optimization. The sound-insulation measurement experiment verifies the tunable acoustic performance. The sound-insulation peak frequency has a maximum shift of 142, 130, and 141 Hz under voltages of 2000, 2500, and 3000 V, respectively, showing an advancing figure of merit compared with the existed acoustic metamaterial based on dielectric elastomer.

Identification and semi-active control of structures with abrupt stiffness degradations

This paper presents for variable stiffness tuned mass dampers (VS-TMDs) a vibration control algorithm combined with a nonlinear system identification method. The objective of the proposed approach is the control of multistory shear frame structures, which exhibit abrupt stiffness degradations. A stiffness variable control (SVC) algorithm is developed to control the stiffness of the VS-TMD, which is based on the mitigation of the potential energy of the structure. For the identification of the system parameters, an adaptive unscented Kalman filter (A-UKF) scheme is utilized. The paper describes the theoretical background of the proposed approach with its governing equations and conducts performance studies on a semi-actively controlled 2-story shear frame structure. Harmonic, white noise and earthquake excitation scenarios including seismic aftershock effects are investigated. Sensitivity studies are conducted. With the proposed approach, the abrupt stiffness changes of the structure are detected and the damper stiffness is adapted successfully. The results show that the SVC together with the A-UKF clearly outperforms the passive TMD control.

Amplification Factor for Wood-Concrete Hybrid Structures Based on Dynamic Numerical Simulation

Extensive concerns on environmental protection have provoked low-carbon buildings to be the mainstream of building construction worldwide, and wooden structures in this sense outperform other structural forms. Wooden-concrete hybrid structures featuring distinct wooden and concrete stories typically exhibit uneven stiffness distribution along the structure height; in particular, abrupt stiffness changes occur at the wood-concrete transition stories. Therefore, structural designing of such hybrid structures must consider a stiffness amplification effect in the static structural calculation as well as complicated procedures in the dynamic analysis. To determine an appropriate amplification factor for design purpose, this study employed a dynamic numerical approach to determine the displacement response of wooden-concrete hybrid buildings and compared the results with the displacement response obtained from static analyses. According to the results, it is found that the appropriate amplification factor should beα= f (x) = 0.47x + 1.00.αcan be valued 1.94 at 2nd floor, 2.41 at 3rd floor and 2.88 at 4th floor. The results may serve as a reference for seismic designing of wooden-concrete hybrid structures.

Test and evaluation of modified TADAS devices with different grades of steel

Triangular-plate added damping and stiffness (TADAS) devices are reliable metallic energy dissipaters for seismic upgrading used in design and retrofitting of civil structures. Conventional TADAS devices are designed with closed-ended slots. In this study, a modified form of the TADAS device is proposed with open-ended slots in order to reduce the manufacture cost, facilitate the assembling and avoid abrupt stiffness increase. Cyclic and monotonic loading tests are then conducted to investigate the mechanical characteristics of the modified TADAS devices with regular Q345 steel and low-yield point LY160 steel triangular plates. The test results show that although the hysteresis performances are stable, the cyclic hardening behavior is different between the TADAS specimens with different grades of steel. The TADAS specimen with LY160 triangular plates exhibits more significant overstrength behavior than the one with Q345 triangular plates in cyclic loading, which is unsuitable to be described by the classic Bouc-Wen model. Therefore, a modified Bouc-Wen model is proposed to describe such overstrength behavior. It is shown that the modified model is able to simulate different extent of overstrength behavior in cyclic loading, based on which the cyclic hardening behavior of the TADAS specimen with LY160 triangular plates can be well described.

Identification of abrupt stiffness changes of structures with tuned mass dampers under sudden events

This paper presents a recursive system identification method for multi-degree-of-freedom (MDoF) structures with tuned mass dampers (TMDs) considering abrupt stiffness changes in case of sudden events, such as earthquakes. Due to supplementary non-classical damping of the TMDs, the system identification of MDoF+TMD systems disposes a challenge, in particular, in case of sudden events. This identification methods may be helpful for structural health monitoring of MDoF structures controlled by TMDs. A new adaptation formulation of the unscented Kalman filter allows the identification method to track abrupt stiffness changes. The paper, firstly, describes the theoretical background of the proposed system identification method and afterwards presents three parametric studies regarding the performance of the method. The first study shows the augmented state identification by the presented system identification method applied on a MDoF+TMD system. In this study, the abrupt stiffness changes of the system are successfully detected and localized under earthquake, impulse and white noise excitations. The second study investigates the effects of the state covariance and its relevance for the system identification of MDoF+TMD systems. The results of this study show the necessity of an adaptive definition of the state covariance as applied in the proposed method. The third study investigates the effects of modeling on the performance of the identification method. Mathematical models with discretization of different orders of convergence and system noise levels are studied. The results show that, in particular, MDoF+TMD systems require higher order mathematical models for an accurate identification of abrupt changes.

Biomechanical pathways of dentoalveolar fibrous joints in health and disease.

Spatial and temporal adaptations within periodontal tissues and their interfaces result from functional loads. Functional loads can be physiologic and/or pathologic in nature. The prolonged effect of these loads can alter the overall biomechanics of a dentoalveolar fibrous joint (dentoalveolar joint) by changing the form of the tooth root and its socket. This "sculpting" of the tooth root and alveolar bony socket is a consequence of several mechano-biological changes that occur within the periodontal complex of a load-bearing dentoalveolar joint. These include changes in biochemical expressions, structure, elemental composition, and mechanical properties of alveolar bone, the underlying tissues of the roots of teeth, and their interfaces. These physicochemical changes in tissues continue to prompt mechano-responsive biochemical activities at the attachment sites of periodontal ligament (soft) with bone (hard), and ligament with cementum (hard), which are the entheses of a load-bearing dentoalveolar joint. Forces at soft-hard tissue attachment sites between disparate materials with different stiffness values theoretically generate strain singularities or discontinuities. These discontinuities under prolonged functional loading increase the probability for failure to occur specifically at the enthesial zones. However, in a normal dentoalveolar joint, gradual stiffness gradients exist from ligament to bone, and from ligament to cementum. The gradual transitions in stiffness from softer ligament (lower stiffness) to harder bone or cementum (higher stiffness) or vice versa optimize tissue and interfacial strains. Optimization of tissue and ligament-enthesial physical and chemical properties facilitates transmission of cyclic forces of varying magnitudes and frequencies that collectively maintain the overall biomechanics of a dentoalveolar joint. The objectives of this review are 3-fold: (i) to illustrate physicochemical adaptations at the periodontal ligament entheses of a human periodontal complex affected by subgingival calculus; (ii) to demonstrate how to "program" the hallmarks of periodontitis in small-scale vertebrates in vivo to generate spatiotemporal maps of physicochemical adaptations in a diseased dentoalveolar joint; and (iii) to correlate dentoalveolar joint biomechanics in healthy and diseased states to spatiotemporal maps of physicochemical adaptations within respective periodontal tissues. This interdisciplinary approach demonstrates that physicochemical adaptations within periodontal tissues using the mechanics of materials (tissue mechanics), materials science (tissue composition), and mechano-biology (matrix molecules) can help explain the mechano-adaptation of dentoalveolar joints in normal and diseased functional states. Multiscale biomechanics and mechano-biology approaches can provide insights into the functional competence of a diseased relative to a normal dentoalveolar joint. Insights gathered from interdisciplinary and multiscale biomechanics approaches include the following: (i) physiologic loads related to chewing maintain a balance between mineral-forming and-resorbing biochemical cellular events, resulting in gradual stiffness gradients at the periodontal ligament entheses, and, in turn, sustain the overall biomechanics of a normal "healthy" dentoalveolar joint; (ii) pathologic loads resulting from tissue degradation and physical changes to the periodontal complex promote an abrupt stiffness gradient at the periodontal ligament entheses. The shift from gradual to an abrupt stiffness gradient could prompt a shift in the biochemical cascades, exacerbate mechano-responsive biochemical expressions at periodontal ligament entheses farther away from the site of insult, and culminate in joint degradation; (iii) sustained pathologic function on periodontally diseased joints exacerbates degradation of periodontal ligament entheses providing insights into "rescue therapy", such as the use of an adequate "mechanocal dose" to regain joint function; and (iv) spatiotemporal maps of changes in biochemical expressions, and physicochemical properties of strain-dominated affected sites, including the periodontal ligament entheses, can guide anatomy-specific therapeutics for tissue regeneration and/or disease control with the purpose of regaining dentoalveolar joint function. Modulation of occlusal loads could minimize disease progression and potentially assist in regaining functional attachment of ligament to bone and/or ligament to cementum of the dentoalveolar joint. Elucidating mechanisms that drive the breakdown of the functionally active periodontal complex burdened with microbes will provide the required critical insights into regenerative medicine and/or biomimetic approaches that would facilitate rescue/regain of dentoalveolar joint function.

Thickness-Dependent In-Plane Polarization and Structural Phase Transition in van der Waals Ferroelectric CuInP2 S6.

van der Waals (vdW) layered materials have rather weaker interlayer bonding than the intralayer bonding, therefore the exfoliation along the stacking direction enables the achievement of monolayer or few layers vdW materials with emerging novel physical properties and functionalities. The ferroelectricity in vdW materials recently attracts renewed interest for the potential use in high-density storage devices. With the thickness becoming thinner, the competition between the surface energy, depolarization field, and interfacial chemical bonds may give rise to the modification of ferroelectricity and crystalline structure, which has limited investigations. In this work, combining the piezoresponse force microscope scanning, contact resonance imaging, the existence of the intrinsic in-plane polarization in vdW ferroelectrics CuInP2 S6 single crystals is reported, whereas below a critical thickness between 90 and 100 nm, the in-plane polarization disappears. The Young's modulus also shows an abrupt stiffness at the critical thickness. Based on the density functional theory calculations, these behaviors are ascribed to a structural phase transition from monoclinic to trigonal structure, which is further verified by transmission electron microscope technique. These findings demonstrate the foundational importance of structural phase transition for enhancing the rich functionality and broad utility of vdW ferroelectrics.

Flexural damage behavior of CF/PA6 plain woven laminates with different layers

This study investigated the flexural properties and failure behavior of CF/PA6 plain woven laminates with different layers (i.e., 2, 4, 10 and 16 plies) fabricated by the hot compression technique. Step-by-step interrupted three-point flexural tests and optical observation were performed to study the failure mechanisms of CF/PA6 plain woven laminates with different layers. Incremental cyclic flexural loading tests were carried out to investigate cyclic cumulative damage. The results indicate that the flexural strength of various CF/PA6 plain woven laminates follows the Weibull distribution and that 16-layer laminates show a higher Weibull modulus than the other types of laminates. The flexural initial fracture point (matrix cracking), flexural knee point (intralaminar cracking) have also been identified based on the observation of about 50 specimens for each type. The knee point plays a critical role in determining the flexural properties of composites whereas initial fracture is not a critical factor for the flexural properties. The typical three stages (i.e., initial stage, smooth stage and damage stage) of a fatigue degradation process of various CF/PA6 plain woven laminates during incremental cyclic loading flexural tests were observed. The flexural knee point stress is near the abrupt stiffness degradation limit stress in the present study.

A wavelet transform and substructure algorithm for tracking the abrupt stiffness degradation of shear structure

Time-varying parameter identification is an important research topic for structural health monitoring, performance evaluation, damage diagnosis, and maintenance. Practical civil engineering structures usually contain multiple degrees of freedom; however, damage often locally occurs. In this study, a discrete wavelet transform and substructure algorithm is presented for tracking the abrupt stiffness degradation of shear structures. A substructure model is built by the extraction of the local structure which may contain damaged region. Time-varying stiffness and damping are expanded into multi-scales using discrete wavelet analysis. An optimization method based on Akaike information criterion is introduced to select the decomposition scale. The expanded scale coefficients are evaluated using least square method, then the original time-varying stiffness or damping parameter is identified by reconstructing from the scale coefficients. To validate the proposed method, a numerical example of seven-story shear structure with time-varying stiffness and damping is proposed. Experiment for a three-story shear-type structure with abrupt stiffness degradation is also tested in the laboratory. Both numerical and experimental results indicate that the proposed method can effectively identify the abrupt degradation of stiffness parameter with a satisfactory accuracy.

Effect of vehicle speed on the dynamics of track transitions

When a railway track presents an abrupt discontinuity of vertical stiffness (e.g., due to the presence of a structure), an amplification of the dynamic forces acting on both the vehicle and the track may be expected. Therefore, diverse solutions—generally known as track transitions—have been proposed in the literature to provide a smoother stiffness change between different track sections. An extensive research has been performed in recent years in order to better understand the dynamics of track transitions as well as the processes involved. However, to the best of the authors’ knowledge, no research has fully studied the effect of vehicle speed and only one value is generally used instead of considering a wider range. Hence, this paper explicitly analyzes the effect of train speed on the vibrational performance of four transition typologies: a concrete wedge; a hot mixed asphalt wedge; a geogrid; and a soil reinforcement. The results show that mitigation capacity of all the alternatives increases with train speed, the concrete wedge being the most effective solution. Moreover, the effects on vertical vibrations of the abrupt stiffness change are found to be significant only for high train speeds (220–300 km/h). Finally, an amplification effect due to resonance has been found for the concrete transition when a vehicle speed of 100 km/h is considered.

Smoothed reduction of fracture mechanics solutions to 1D cracked models

Abstract In the framework of fracture mechanics 2 or 3 dimensional modelling approaches are mostly employed in order to simulate cracks. However, in many applications 1D models that represent cracked structural members can be proved to be very useful. A crack contributes to abrupt stiffness reduction , causing “jump” in the displacement field close to the crack, in the present work the observation that the presence of cracks causes also stress and strain redistribution at some distance from the crack tips as resulted from fracture mechanics solutions is underlined. An appropriate “smoothed” stiffness reduction is introduced as a function from the distance from the crack consistent energetically with the Linear Elastic Fracture Mechanics (LEFM) solutions. These smoothed 1D solutions capture the strain variations in some distance from the crack(s) achieving very good accuracy. Some modelling examples in static and dynamic (eigenfrequencies, mode shapes) cases are examined and compared to existing 1D models, 3D FEM simulation and experimental data.

TADAS dampers in very large deformations

Triangular-plate Added Damping and Stiffness (TADAS) dampers are special kinds of passive control devices that can be used in seismic design and retrofitting of structural systems. However, when exposed to large deformations, primary members of a structure can be in danger of serious damage due to improper geometric characteristics of these dampers. In this study, response of a one bay frame equipped with a TADAS device, previously tested in the laboratory, was simulated using a detailed FE model in ABAQUS. A monotonic analysis was then conducted on the TADAS damper alone, which indicated that in large deformations, TADAS damper pins hit the top of the holes, resulting in an abrupt stiffness increase in the damper. Seismic analysis of a six story moment resisting frame with TADAS dampers, using a series of twelve scaled earthquake ground motions, was also conducted in OpenSees which indicated that with sudden stiffness increase in dampers, the value of moments in beams as well as axial forces in braces will increase, causing possible damages in these areas. At the end, a method for calculating the optimal height for the holes in the damper was proposed, which is shown to be in good agreement with detailed ABAQUS models.