Seismic Response Mitigation Research Articles

Optimal Design and Performance Evaluation of Lightweight Inerter Systems (LwIS) for Seismic Response Mitigation

Optimal Design and Performance Evaluation of Lightweight Inerter Systems (LwIS) for Seismic Response Mitigation

Low temperature effect on cyclic behavior of shape memory alloy U-shaped dampers

Although Nickel-Titanium (NiTi) shape memory alloys (SMAs) have been widely studied as seismic response mitigation devices in civil structures, their temperature sensitivity due to the coupled thermo-mechanical behavior prevents their practical implementation in cold temperature environments. This paper investigated the effects of varying ambient temperatures (particularly low ambient temperature) on the hysteretic behavior and self-centering (SC) ability of shape memory alloy U-shaped dampers (SMAUDs) that were made of NiTi showing superelasticity (SE) at room temperature. Thermo-mechanical properties of SMAUDs were identified through differential scanning calorimetry (DSC) tests. Cyclic loading experiments on SMAUDs were conducted at a wide ambient temperature range from −40 °C to 20 °C. The variations in the hysteretic characteristics of the SMAUDs, including partial superelasticity (SE), strength, stiffness, SC, and energy dissipation capabilities, at different ambient temperatures were investigated. In general, the decreasing ambient temperature leads to the degradation of the SC ability. At ambient temperatures below the phase transformation temperature, the SMAUDs lose the SE but still maintain certain levels of strength and energy dissipation, which is different from common axial-type SMA elements. Meanwhile, the SMAUDs can restore their SC ability and strength after the recovery from low temperatures to room temperature, making them suitable for use in a cold environment.

Dual-Demand-Based Optimal Design of Lightweight Tuned Viscous Mass Damper (LwTVMD) for Seismic Response Mitigation

Dual-Demand-Based Optimal Design of Lightweight Tuned Viscous Mass Damper (LwTVMD) for Seismic Response Mitigation

A novel design strategy of track‐based asymmetric nonlinear energy sink for seismic response mitigation of structures

AbstractMass dampers, whether linear or nonlinear, rely on resonance with the structure to achieve optimal control performance. However, linear mass dampers require frequency tuning, while nonlinear mass dampers are sensitive to input energy levels, rendering both inadequate for control problems that involve frequency and energy uncertainties. To address this issue, the track asymmetric nonlinear energy sink (TANES) has been developed as a robust mass damper against frequency and energy changes. In this study, a novel design strategy consisting of physical and parameter design was proposed for TANESs. First, TANESs with inverted tracks as the auxiliary mass were proposed, resulting in a significant reduction in the dimensions and weight of the device. The new physical design was then realized, and the mathematical descriptions of the TANES system were validated through experiments on a two‐story frame structure. Subsequently, a parameter design method was proposed to match the frequency variation pattern of the TANES with the given structural and load conditions. Following the design procedure, three TANESs with markedly different track shapes were obtained and compared with existing mass dampers under different types of excitations. Results showed that the frequency responses of the TANES systems subjected to harmonic ground excitations shared great similarity with those of a well‐tuned TMD system at small‐to‐moderate energy levels. As the energy level increased, nonlinear responses such as strongly modulated responses were observed in the TANES systems with decrease structural frequencies, which significantly reduced the resonant peak in the frequency responses. The frequency responses of the TANES systems were consistent with the design objective and could be used to quantitatively predict the robustness performance of the devices under impulsive and seismic excitations. With the reduced dimensions and weight resulting from the inverted‐track configuration and the robustness performance in line with common structural and load conditions, the proposed design strategy of TANESs demonstrated great potential in the seismic response mitigation of engineering structures.

A Novel Dual Self-Centering Friction Damper for Seismic Responses Control of Steel Frame

Due to their weight, the seismic response control of buildings needs a large-scale damper. To reduce the consumption of shape memory alloys (SMAs), this study proposed a dual self-centering pattern accomplished by the coil springs and SMA, which could drive the energy dissipation device to recenter. Combined with the friction energy dissipation device (FD), the dual self-centering friction damper (D-SCFD) was designed, and the motivation and parameters were described. The mechanical properties of D-SCFD, including the simplified D-SCFD mechanical model, theoretical index calculations of recentering, and energy dissipation performance, were then investigated. The seismic response mitigation of the steel frame adopting the D-SCFDs under consecutive strong earthquakes was finally analyzed. The results showed that a decrease in the consumption of SMA by the dual self-centering pattern was feasible, especially in the case of low demand for the recentering performance. Reducing the D-SCFD’s recentering performance hardly affected the steel frame’s residual inter-story drift ratios when the residual deformation rate was less than 50%, which can help strengthen the controls on the steel frame’s peak seismic responses. It is recommended to utilize the D-SCFD with not too high a recentering performance to mitigate the seismic response of the structure.

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.

Simplified optimization of inerter-enabled tuned mass damper for lightweight-oriented seismic response mitigation of long-span domes

Suspending tuned mass dampers (TMDs) from long-span domes has been studied to mitigate seismic responses of long-span domes. However, the strict weight limitations on the suspension mass in conventional tuned mass dampers (TMDs) hinder their widespread adoption. To address this issue, we introduce the inerter-enabled tuned mass damper (IeTMD) that consists of a suspension mass, tuning spring, and a tuned viscous mass damper (TVMD) sub-system into the seismic vibration mitigation of long-span domes. Under the assumption that long-span domes remain within the elastic range and adhere to the small deformation hypothesis, we have proposed simplified design formulae for IeTMDs, guided by the lightweight-based seismic vibration control criterion. Parametric studies are conducted to illustrate the degree to which an IeTMD can improve the performance of the long-span dome when its key parameters change within certain ranges. The effectiveness of the design strategy in exploiting the damping enhancement effect is confirmed. Time history responses of a benchmark long-span dome demonstrate that the IeTMD has high control efficiency, as bi-directional displacements, accelerations, and base shear are significantly reduced. Comparative analyses between the proposed IeTMD and conventional TMD are conducted. Results show that the IeTMD designed by the simplified design formulae can achieve the target control performance with less suspension mass. Furthermore, the frequency analysis shows that the proposed IeTMD contains a wider control frequency band than conventional TMD, illustrating the promising approach for long-span domes.

An Analytical Study on Using Maxwell-Coulomb Friction Damper to Mitigate Quasi-Static Response of SDOF Systems

Excessive cumulative stroke in the longitudinal movement of long-span suspension bridge can led to premature fatigue damage in the bridge's connecting components. However, existing control devices, like viscous damper, remain suboptimal. This paper aims to reveal the underlying mechanism of cumulative stroke control and find an effective control method to address this issue. Firstly, the statistical and frequency characteristics of longitudinal displacement were analyzed based on a 24-hour field measured data set. Secondly, the cumulative stroke control performance of nonlinear viscous damper was evaluated with a SDOF system, uncovering the reasons for their low efficiency in controlling cumulative stroke. Thirdly, the Maxwell-Coulomb friction damper was introduced to control the excessive cumulative stroke, and its effective control performance was validated. Finally, a novel parallel model combining viscous dampers and friction dampers was proposed to leverage the superior performance of friction damper in controlling the cumulative stroke under daily operation condition, while also harnessing the seismic response mitigation capacity of the viscous damper. This research enhances the understanding of cumulative stroke control in long-span suspension bridges and presents an innovative control method by introducing the Maxwell-Coulomb friction damper, highlighting its potential for practical application in bridge engineering.

Seismic control of adaptive variable stiffness intelligent structures using fuzzy control strategy combined with LSTM

A novel semi-active control algorithm for adaptive variable stiffness intelligent structures that combines the fuzzy control strategy with Long Short-Term Memory (LSTM) is proposed in this study, with the aim of mitigating structural responses under earthquake excitations. The combined Fuzzy-LSTM strategy utilizes an LSTM neural network to predict the displacement and velocity responses of the structure at the next moment, and uses the predicted results as input for fuzzy control to obtain active control forces. Due to the difference between the displacement-velocity response and the fuzzy control domain, the genetic algorithm is used to optimize scaling factors of displacement and velocity responses and the control force, which is implemented by exploiting stiffness variability and structural inter-shift. The Fuzzy-LSTM strategy can compensate for the time delay effect on active control caused by stiffness variations, algorithmic computations and sensor measurements, and therefore achieves a better control effect through prediction. The semi-active independently variable stiffness (SAIVS) device is used to implement the presented control algorithm, which is a diamond device consisting of four linear springs and an electromagnetic actuator. The SAIVS device can achieve a continuous and smooth stiffness variation and meet the application requirements of the developed algorithm. Therefore, active control forces can be obtained through structural stiffness variations and interlayer displacements under seismic excitation, to achieve an approximate active control effect through a semi-active method. A 10-story building is presented as a case study for numerical simulations. Results show that the Fuzzy-LSTM strategy can significantly improve the control effect compared to the conventional fuzzy control strategy, and therefore achieve a better seismic response mitigation performance.

A novel nonlinear isolated rooftop tuned mass damper-inerter (IR-TMDI) system for seismic response mitigation of buildings

A novel nonlinear isolated rooftop tuned mass damper-inerter (IR-TMDI) system for seismic response mitigation of buildings

Seismic response mitigation of prefabricated industrial equipment structural frames through a hybrid isolation system

For reducing the excessive acceleration response of the critical equipment in a type of industrial equipment structural frames under strong earthquakes, a hybrid isolation system (HIS), incorporating linear natural rubber (LNR) and lead rubber (LR) bearings, is proposed. The efficiency and reliability of the HIS are verified through a series of full-scale shaking table tests on two prefabricated industrial moment resisting frames (MRFs), with respect to a corresponding fixed-base system (FBS). The structural dynamic characteristic and seismic performance of the two types of MRFs, i.e., reinforced concrete structure (RCS) and composite concrete-filled steel tube structure (CCFSTS), are examined both with the HIS and FBS subjected to a range of seismic intensities. The test results demonstrate the superior performance of the HIS in controlling transient acceleration response under near-fault, far-field and artificial ground motions. The average peak acceleration reduction coefficients (PARCs) of the HIS range between 75.60% and 79.51% in the two considered MRFs along two horizontal directions, with a strict satisfaction on the peak acceleration response for normal operation of the critical equipment. Also, the hysteretic behavior of the HIS is stable and controllable during the earthquake excitations. The peak transient displacement of the HIS is satisfactory, and the residual deformation is negligible even under the maximum considered earthquake (MCE) excitations. Besides, components of the two MRFs are undamaged during the whole test. Thus, with the capacity of protecting the acceleration-sensitive equipment and structural components, the proposed HIS possesses a great prospect in enhancing the structural resilience.

Effects of shear panel dampers on seismic response mitigation of high-speed railway simply supported bridge-track system under far-field and near-field ground motions

Effects of shear panel dampers on seismic response mitigation of high-speed railway simply supported bridge-track system under far-field and near-field ground motions

Dual-Demand-Based Optimal Design of Grounded Tuned Mass Damper Inerter for Seismic Response Mitigation

Dual-Demand-Based Optimal Design of Grounded Tuned Mass Damper Inerter for Seismic Response Mitigation

Experimental validation, analytical investigation, and design method of tuned mass damper‐clutching inerter for robust control of structures

AbstractInerters have significantly uplifted the cost‐effectiveness of structural control technologies. A recently proposed tuned mass damper‐clutching inerter (TMDCI) takes advantage of both mass amplification effect and energy absorption capacity of inerter which is more effective and practical than its predecessors. However, the existing study only provided numerical demonstrations while experimental evidence and analytical explanation are still lacking for in‐depth understanding of the dynamic properties and working principles of TMDCIs. In this study, the mathematical descriptions of TMDCIs are first developed and experimentally validated on a three‐story structure. The validated model is then used to analyze the influences of inerter arrangement and total inertance in inerter‐enhanced devices. With an appropriate inerter arrangement and inertance, the TMDCI shows excellent control performance regardless of the changes in the structural frequency. The reason for the strong robustness of TMDCIs is then revealed via analytical investigation of standalone TMDCIs; the harmonically forced steady‐state responses manifest that the TMDCI can be linearized as equivalent tuned mass damper‐inerters with variable parameters whose natural frequency increases with the increase of excitation frequency. Based on the analytical findings, a design method with robustness consideration is subsequently proposed and draws satisfactory TMDCI designs for both single‐degree‐of‐freedom and multi‐degree‐of‐freedom structures. The designed TMDCI outperforms the comparable devices for both impulsive and seismic response mitigation. The study provides analytical insight into the control capacity of TMDCIs and lays the groundwork for practical design of TMDCIs as an effective and robust control strategy for engineering structures.

Optimum design of a tuned‐mass damper with negative stiffness device subjected to ground excitation

In this study, a negative stiffness device based on the magnetic principle is presented and experimentally tested. Then, a tuned mass damper with a negative stiffness device (denoted as TMD_NSD) subjected to harmonic support excitation is optimized in terms of H∞ optimization criterion, H2 optimization criterion, and stability maximization criterion (SMC). Closed-form expressions for the optimal tuning parameters are derived in terms of both H∞ criterion and SMC, while the optimal tuning parameters are numerically determined in terms of H2 criterion. The control performance of the TMD_NSD is compared with the classical TMD in terms of maximum dynamic amplification factor (DAFmax). It is found that the performance of the TMD_NSD based on these three optimization methods is superior to that of the classical TMD. Besides, the performance based on H∞ and H2 optimization is almost similar, while the performance based on SMC is less than the first two methods. Compared with the classical TMD, the TMD_NSD could significantly reduce the primary system's peak value and broaden the efficient frequency range of vibration mitigation. However, surprisingly, the DAFmax decreases with the increase in the mass ratio of the classical TMD, while the DAFmax for the TMD_NSD increases with the increase in mass ratio. Finally, the effectiveness of optimization methods in seismic response control is examined via time history analyses (THA) under 20 real earthquake excitations. The THA findings suggest that the TMD_NSD is superior to the TMD for seismic response mitigation for the three optimization methods. However, it is noted that the displacement response of TMD_NSD based on H∞ and H2 optimization is comparable but slightly better than that of the SMC method. Nevertheless, in terms of absolute acceleration control, it is shown that TMD_NSD performance based on the SMC method is better than that of the H∞ and H2 methods. Overall, the three optimization methods are validated to be effective for seismic mitigation of the un-damped single-degree-of-freedom (SDOF) primary structure subjected to real seismic excitations.

Seismic Response Mitigation of Extra-Large LNG Storage Tanks

The paper investigates the effectiveness of a smart base-isolation system for seismic response mitigation of extra-large liquified natural gas (LNG) storage tanks. The mathematical model of the base-isolated LNG tank with smart dampers, the magneto-rheological (MR) dampers, is presented. The governing equations of motion of the smart system are derived and solved by the classical transition matrix method in the time domain. The linear quadratic regulator (LQR) control scheme is employed to command MR dampers. The LNG tank system is analyzed under six artificial accelerograms, compatible with operational basis earthquake (OBE) and safe shutdown earthquake (SSE) response spectrum, generated using a method of a random set of phase angles with amplitudes obtained from power spectral density function. A time-delay compensation procedure based on the Taylor series expansion is applied to reduce the deterioration of control performance due to time delay. To investigate the effectiveness of smart base-isolation, the responses are compared with the fixed-base tank, base-isolated tank, and tank with passive MR damper. The results show that the smart base-isolation is effective in reducing the seismic response of extra-large LNG tanks, especially the displacement at the isolation level without much altering other responses. The passive MR damper is also found effective and showed fail-safe behavior even under the failure of the control algorithm. Moreover, the application of time-delay compensation using the Taylor series increased the performance and overall efficiency of the LNG tank system.

Study on Parameters’ Influence and Optimal Design of Tuned Inerter Dampers for Seismic Response Mitigation

In this paper, parameter analyses of a tuned inerter damper (TID) are carried out based on the displacement mitigation ratio. The optimal design of TID based on the closed-form solution method is carried out and compared with the fixed-point method. Meanwhile, applicable conditions of two methods are discussed in wider range of values of objective function under different inherent damping ratios. Finally, seismic responses of SDOF system with TID are carried out, which verifies the feasibility of the closed-form solution optimization method. Compared with the fixed-point method, the inherent damping ratio of the original structure is considered in the closed-form solution method, and the optimal damping ratio of a TID is smaller than that of the fixed-point method under same displacement mitigation ratio. The parameters’ combination of a TID designed by the fixed-point method obtains a vibration mitigation effect with a larger damping ratio by cooperating with the deformation enhancement effect of the inerter, which may make the vibration mitigation effect of the TID lower than that of the VD in structures with large inherent damping ratios. However, the deformation enhancement effect on the damping element of the inerter can be fully used by using the closed-form solution method. Better applicability and robustness are shown in closed-form solution method. Under the same displacement mitigation ratio, the damping ratio of a TID obtained by using the closed-form solution method is about one tenth of that obtained by using the fixed-point method, which can realize the lightweight design of the TID.

Seismic response mitigation of buildings with an active inerter damper system

Seismic response mitigation of buildings with an active inerter damper system

Seismic response mitigation of girder displacement of cable-stayed bridge using inerter systems

Cable-stayed bridges have been widely utilized as transportation hubs in mountainous and coastal areas. Once these bridges are damaged during earthquakes, the routine for rescue operations will be interrupted, leading to enormous life and financial loss. Since damage of cable-stayed bridges are mainly caused by excessive displacement of main girders, this paper considers mitigating the displacement demands by implementing inerter systems between tower and main girder. Following brief introduction of inerter systems, a simplified three degree-of-freedom (DOF) dynamic model of a cable-stayed bridge prototype is established and verified by refined finite element (FE) model. Then the design parameters of inerter systems are optimized based on the dynamic amplification factor (DMF) method, while the influence of each parameter on the performance is discussed in detail. To further investigate the efficiency of these systems, the seismic responses of cable-stayed bridge with different inerter devices are computed and compared with the prototype, as well as system with conventional viscous dampers (VD). From the analytical results, the inerter systems are demonstrated effective in alleviating displacement demands of main girder of cable-stayed bridges and outperforming the commonly used VD. This study is believed able to provide basis for engineering application of inerter systems on cable-stayed bridges to improve the seismic performance and reliability against earthquakes.

Multi-location seismic isolation approach and design for underground structures employing the negative-stiffness amplification system

Underground structures are vulnerable to strong earthquakes, with their central columns being prone to damage owing to their insufficient resistance capacity. In this study, an effective, hybrid, and multi-location seismic isolation approach was proposed for multi-floor and multi-span underground structures using several negative-stiffness amplification system-based isolation systems (NSAS-ISs). The NSAS-IS originated from the incorporation of an NSAS and an isolation bearing, which was proposed as a flexible connection installed at either the top or bottom of the central columns. The mechanical model as well as physical realization of the NSAS-IS was explored, and an improved damping mechanism was introduced. Subsequently, a multi-location isolation method was proposed with the NSAS-ISs installed at the top or bottom of the columns (corresponding to the 1-end-based isolation method) and at both the top and bottom of the columns (corresponding to the 2-end-based isolation method). The effectiveness and robustness of the proposed NSAS-IS pertaining to the structural seismic response mitigation of typical underground structures under different isolation methods were investigated, focusing on the underground structures buried at different depths subject to various seismic excitations at multiple intensities. The obtained results indicated the effectiveness of both the 1-end- and 2-end-based isolation methods for NSAS-IS in improving the seismic performance of multi-floor and multi-span underground structures, with significant improvement being observed in the damping and isolation effects. In particular, the 2-end isolation method was found to be considerably effective in multi-performance control for multi-intensity excitations and is thus suggested for underground structures with limited space for installation and isolation layers. Consequently, the plastic energy-dissipation burden of the primary structures can be significantly relieved, and the residual deformation of the columns can be avoided owing to their excellent isolation ability.