Self-centering Damper Research Articles

A hybrid self-centering building toward seismic resilient structures: Design procedure and fragility analysis

The current paper presents the development and seismic assessment of the Smart Hybrid Resilient building (SHR). This novel building is comprised of self-centering dampers in parallel with Pall friction dampers. The design methodology and equations are first introduced with aim of creating the seismic resilience feature in structures. The designed SHR systems have the capability to adjust and control the residual drift of each story (covers the disadvantage of Pall system) in addition to high energy-dissipating capacity (covers the downside of expensive shape memory alloy-based system). Based on FEMA P-58 recommendation, 0.2% and 0.5% drift ratios are considered as the economical residual drift limitations of specimens. Limiting the story residual drift to these thresholds makes the decision of repairing structure after earthquake occurrence more rational rather than rebuilding the new one. In order to the comprehensive assessment of SHR system performance and precision of design equations, some specimens with diverse heights and various consumed shape memory alloy materials are modeled in OpenSees. Afterwards, all the SHR specimens in comparison with purely Self-Center systems are subjected to quasi-static cyclic loading analysis and incremental dynamic analysis. Fragility curves are also used to evaluate the efficiency of seismic performance of the SHR system in a probabilistic framework. The results demonstrate that the SHR buildings designed with suggested design methods are conservatively and precisely satisfied the seismic resilience criterion.

Analytical and numerical study on the cyclic behavior of buckling-restrained SMA-based self-centering damper

Owing to the unique superelasticity and satisfactory energy dissipation capacity, shape memory alloys (SMAs) show great potential in earthquake engineering. This study focused on establishing analytical method and finite element (FE) model for the buckling-restrained SMA (BRSMA) based self-centering (SC) dampers. For the BRSMA-based SC damper, the lateral deformation of the slender SMA component is constrained by the surrounding buckling-restrained plates (BRPs). Hence, the SMA component avoids buckling induced instability and the damper accordingly exhibits stable cyclic behavior under tension–compression loadings. Although the compressive behavior has been obtained through cyclic loading tests, an in-depth understanding on the corresponding force-displacement relationship is required. As such, a simple analytical method was proposed for estimating the compressive strength capacity of the BRSMA-based SC damper. Besides, the FE model was built to provide additional information that was difficult to obtain in physical model tests. The accuracy of the analytical method and FE model was confirmed by the testing results. The verified FE model was further used to conduct the parametric analysis. The parameters of interest included the shape of the reduced section, the dimension of the BRSMA components, the gap between the BRSMA components and BRPs and the number of bolts. The findings of this paper not only promote understanding on the cyclic behavior of this new damper, but also provide suggestions and guidelines for future design.

HYSTERESIS MODEL AND EXPERIMENTAL INVESTIGATION OF ASSEMBLED SELF-CENTERING BUCKLING-RESTRAINED BRACES

To reduce the large residual deformation of buckling-restrained braces after strong earthquake, and facilitate structural repair, an assembled self-centering buckling restrained brace with combined disc springs (SC-BRB) is invented. The characteristics of the hysteretic curve can be effectively controlled by the yield force of the energy dissipation system and the pre-pressure of the self-centering system. The construction and mechanism of the novel SC-BRB were described, and the theoretical hysteretic model under cyclic loading was derived. Three different types of SC-BRBs were designed and fabricated. The residual displacement and hysteretic energy dissipation were analyzed through the quasi-static tests, and self-centering effect and failure mode were discussed. The experimental results show that the SC-BRB has flag shaped hysteretic curve and stable energy dissipation capacity. The combined disc spring self-centering system greatly reduces the residual deformation. The theoretical hysteretic model proposed in this paper agrees well with the experimental results. The novel SC-BRB is an effective self-centering damper with stable energy dissipation capacity.

An experimental study on a self-centering damper based on shape-memory alloy wires

This experimental study investigates the behavior of a proposed damper based on austenite Nitinol wires. The damper’s design is so that the wires are always in tension under both tensile and compressive forces. Also, the damper can employ steel wires as a hybrid to enhance the performance of the damper. Steel wires can be employed in parallel with the SMA wires and in the same manner. Therefore, SMA and steel wires are stretched simultaneously in the hybrid damper state. This experimental study includes the process of training the wires and the main cyclic tests with different strain rates which leads to the extraction of the hysteresis curves of the proposed damper. A thermal study is also conducted on the employed shape-memory alloy (SMA) wires during the cyclic loadings. The results indicate that the increase of loading frequency causes the SMA wires to heat; thus, the inner area of the hysteresis curve decreases, resulting in diminished damping capacity. Also, the damper stiffness and the residual strain are increased by using the steel wires. The proposed SMA damper is employed for seismic control of a three-story steel frame to evaluate its efficiency. The results reveal that the residual drift ratios of the controlled structure are significantly decreased.

Development of a high-performance hybrid self-centering building for seismic resilience

In the present paper, a novel hybrid self-centering system is introduced. This system, called the Hybrid Self-centering Pall friction (HSP) system, consists of Self-Centering Dampers (SCDs) and Pall Friction Dampers (PFDs). The design methodology of HSP systems is developed and some examples of the designed HSP are presented. HSP systems not only have the capability of dissipating energy but can also remove or arrange residual drifts of structures. In fact, HSP systems are comprised of a combination of SCDs and PFDs that can maintain design target residual drifts (zero or any) during lateral loading similar to SCD and have the benefits of high capacity energy dissipation of PFDs. The HSP system is developed for seismic resilience in terms of economic benefits, ready-to-use after the earthquake event, and practical fabrication. To evaluate the proposed design method, different low- to high-rise buildings equipped with SCDs are selected from the literature, redesigned based on the proposed method, and then subjected to cyclic loading. Results are presented in terms of the cyclic response, residual drift, maximum story drift, and maximum floor acceleration of structures. Results indicate that the proposed design equations precisely meet the target structural performance of the HSP system and the HSPs system is obviously a superior system compared to the SCDs or PFDs.

DEVELOPMENT AND EXPERIMENTAL INVESTIGATION OF SELF-CENTERING DAMPERS WITH PARALLEL HIGH STRENGTH STEEL RING SPRING GROUPS

Based on the self-centering damper with high-strength steel ring spring, a self-centering damper with parallel high-strength steel ring spring is proposed. The seismic performance of the parallel ring spring self-centering damper under multiple seismic conditions was verified by a hysteretic test. The test results show that the parallel high-strength steel ring spring self-centering damper has good self-centering ability, and will not experience performance degradation after multi-time earthquakes. It does not need to be replaced after the earthquake. Compared with the self-centering damper with a single group of ring springs, the damper bearing capacity can be effectively improved under the same size, and the damper internal space can be fully utilized. The different frictional conditions of the annular spring contact surface have a certain influence on the performance of the self-centering damper. The theoretical prediction model proposed is in a good agreement with the experimental results.

Seismic Performance Evaluation of Building-Damper System under Near-Fault Earthquake

The building-damper system designed by a seismic code is usually considered to be able to withstand the attack of strong earthquakes. However, near-fault earthquakes, especially those with the forward-directivity effect, might cause early and unexpected failure of code-designed dampers and consequent severe structural damage. In this paper, by taking into account near-fault earthquakes, seismic performance of the building-damper system and damper failure’s influence are evaluated systematically. A 9-storey steel building is designed by the Chinese seismic code as the benchmark model, and five typical dampers, including buckling-restrained brace damper (BRB), friction damper (FD), self-centering damper (SCD), viscous damper (VD), and viscoelastic damper (VED), are adopted. It was found that the building-damper systems show a large response and possible damper failure under the near-fault earthquake excitations. Then, the influence of damper failure is investigated, which reveals that damper failure would significantly affect seismic performance of the building-damper system, especially for the building-SCD system. Subsequently, by introducing the artificial near-fault earthquake excitation, the influences of different pulse parameters, such as pulse velocity amplitude, pulse period, and the number of significant pulses, are studied. It shows that the pulse velocity amplitude and pulse period obviously affect the seismic performance, while the number of significant pulses presents little influence.

Seismic vibration control of an innovative self-centering damper using confined SMA core

Using confined shape memory alloy (SMA) bar or plate, this study proposes an innovative self-centering damper. The damper is essentially properly machined SMA core, i.e., bar or plate, that encased in buckling-restrained device. To prove the design concept, cyclic loading tests were carried out. According to the test results, the damper exhibited desired flag-shape hysteretic behaviors upon both tension and compression actions, although asymmetric behavior is noted. Based on the experimental data, the hysteretic parameters that interested by seismic applications, such as the strength, stiffness, equivalent damping ratio and recentering capacity, are quantified. Processed in the Matlab/Simulink environment, a preliminary evaluation of the seismic control effect for this damper was conducted. The proposed damper was placed at the first story of a multi-story frame and then the original and controlled structures were subjected to earthquake excitations. The numerical outcome indicated the damper is effective in controlling seismic deformation demands. Besides, a companion SMA damper which represents a popular type in previous studies is also introduced in the analysis to further reveal the seismic control characteristics of the newly proposed damper. In current case, it was found that although the current SMA damper shows asymmetric tension-compression behavior, it successfully contributes comparable seismic control effect as those having symmetrical cyclic behavior. Additionally, the proposed damper even shows better global performance in controlling acceleration demands. Thus, this paper reduces the concern of using SMA dampers with asymmetric cyclic behavior to a certain degree.

Behavior and application of self-centering dampers equipped with buckling-restrained SMA bars

This study proposes a new type of self-centering damper equipped with novel buckling-restrained superelastic shape memory alloy (SMA) bars. The new solution aims to address some critical issues related to degradation and loss of superelasticity observed in existing tension-only SMA-based self-centering devices, and in addition, to encourage enhanced material utilization efficiency. The cyclic tension-compression behavior of individual SMA bars is experimentally studied first, and subsequently, two proof-of-concept self-centering dampers are manufactured and tested. A simple yet effective numerical model capturing the flag-shaped response of the dampers is then established, and a preliminary system-level analysis is finally conducted to demonstrate the effectiveness of the proposed damper in structural seismic control. The individual SMA bar specimens show asymmetrical flag-shaped hysteretic responses with satisfactory self-centering capability and moderate energy dissipation. Through a specially designed configuration, the proposed damper shows desirable symmetrical and stable hysteretic behavior, and maintains excellent self-centering capability at 6% bar strain. The system-level dynamic analysis indicates that the dampers, as a means of retrofitting, could effectively reduce both the peak and residual inter-story drift ratios of a six-story steel frame. In particular, the mean residual inter-story drift ratio is reduced from over 0.5% to below 0.2% under the maximum considered earthquake, implying elimination of necessary structural realignment even after strong earthquakes.

Aftershock fragility assessment of steel moment frames with self-centering dampers

This study explores the aftershock collapse performance of steel buildings designed with superelastic viscous dampers (SVDs) under seismic sequences. The SVD strategically combines shape memory alloy (SMA) cables and a viscoelastic compound to provide good self-centering and damping capabilities. A nine-story steel special moment resisting frame (SMRF) is first designed with or without SVDs to satisfy modern seismic design requirements. A mainshock incremental dynamic analysis (IDA) is conducted for the SMRF and SVD frames using a total of ten as-recorded seismic sequences. The specific levels of post-mainshock interstory drift ratios are then induced in both frames and an aftershock IDA analysis is conducted for the mainshock-damaged buildings. The maximum interstory drift and residual drift IDA curves are developed and compared for both frames at different mainshock damage levels. The results are analyzed in terms of aftershock collapse capacity, collapse fragility, and collapse capacity at demolition. The effect of aftershock ground motion polarity on the performance of both frames is also explored. The study reveals that the SMRF has increased vulnerability to aftershocks when higher damages are induced during mainshock, while the aftershock collapse performance of the SVD frame is not affected from the intensity of mainshock event. It is also shown that the SVD frame significantly improves the aftershock capacity associated to a residual story drift that leads to major alignment or demolition.

Experimental investigations on seismic control of cable-stayed bridges using shape memory alloy self-centering dampers

This paper presents the experimental investigations of a novel self-centering damper (SCD) for controlling seismic responses of cable-stayed bridges. The damper is fabricated employing the super-elasticity effect and energy dissipation characteristics of shape memory alloy wires. Within super-elastic range, a damping force model is derived and verified based on the constitutive model of shape memory alloy wires. One reduced-scale cable-stayed bridge model is designed to investigate its seismic control performance. Two different system configurations of the cable-stayed bridge model are considered, including the without control state and incorporating with the SCD between the tower and the deck. Seismic behavior of different cable-stayed bridge systems is then evaluated via shaking table tests under different ground excitations. Experimental results show the effectiveness of the SCD. The accelerations and the relative displacements of the tower reduce obviously due to the energy dissipation of the SCD. Relative displacements of the deck decline dramatically because of the connection of the SCD. Moreover, the strain responses also indicate the drop of the bending moment in the tower.

Design, analysis, and manufacture of a tension–compression self-centering damper based on energy dissipation of pre-stretched superelastic shape memory alloy wires

Superelastic shape memory alloys dissipate significant amount of energy since they recover large transformation strains upon mechanical unloading. Due to their dissipation properties, shape memory alloys can be effectively employed as dampers. Design, simulation, and fabrication of a newly developed superelastic shape memory alloy damper are discussed in this article. To enhance the stroke and dissipation capacity of the proposed damper, a system is implemented which operates more efficiently than a single shape memory alloy wire. Although shape memory alloy wires can only undergo tension, the new system enables the damper to be loaded in both tension and compression. Two damping groups are employed in this mechanism: one of which is activated during tension and the other is activated during compression of the damper. Each damping group consists of two shape memory alloy wires acting in the opposite directions to increase the damping capacity of the system. The mechanical responses of the individual components as well as the assembled damper are simulated. The predicted performance of the damper is then validated through tension/compression tests on the fabricated sample. Numerical and experimental force–displacement curves are also shown to be in a good agreement. The effect of different parameters on damping ratio and dissipated energy of the presented damper is investigated.

Development of a novel combined system of deformation amplification and added stiffness and damping: Analytical result and full scale pseudo-dynamic tests

This research presents the theoretical and experimental development of a new system called: Amplified Added Stiffness and Damping (AASD), which is a combination of an amplifying mechanism and a frictional self-centering damper capable to support large deformations. The operation of the damper is based on the well-known straps with friction principle. A first conceptual single acting device used for validating this principle and comparing the behavior of commercial straps (polyamide, aramid and carbon fiber) was built. Subsequently, two double acting prototypes with carbon fiber straps were built, since this material showed the best performance. Both, the conceptual device and the two prototypes (named as I and II) have shown very stable constitutive relations. Because of its greater simplicity, the “prototype II” represents a technically and economically attractive solution. Furthermore, due to its ability to accommodate large deformation in both directions, it is an ideal device to combine with amplifying mechanisms. A parametric numerical analysis performed on a single-story structure with AASD, showed a wide range of parameters of AASD leading to reductions greater than 40% on displacement response. A full-scale asymmetric one-story steel structure equipped with one AASD was built. The structure was subjected to a variety of tests using a multi-axis pseudo-dynamic equipment recently installed in the Laboratory of Structural Engineering of the Pontificia Universidad Católica de Chile. So far, the authors didn’t find references of a full scale pseudo-dynamic test of this nature. The structure without AASD presented a non-linear behavior mainly due to sliding of the bolted connections of the beams. Pseudo-dynamic seismic response tests were performed considering an artificial ground motion acting in one direction. As expected, and due to the mass eccentricity (20% of its plan length), high concentration of deformations in the flexible edge of the structure without AASD was observed. Conversely, the structure with AASD showed a great plan deformation uniformity (torsional balance), with reductions of nearly 40% in maximum edge deformation, which is consistent with the parametric analysis results. The eccentric lever arm used as amplifying mechanism, which have large amplifying ratio α=11, worked in great accordance with numerical simulations.