Due to the shift in paradigm from passive control to adaptive control, smart tuned mass dampers (STMDs) have received considerable attention for vibration control in tall buildings and bridges. STMDs are superior to tuned mass dampers (TMDs) in reducing the response of the primary structure. Unlike TMDs, STMDs are capable of accommodating the changes in primary structure properties, due to damage or deterioration, by tuning in real time based on a local feedback. In this paper, a novel adaptive-length pendulum (ALP) damper is developed and experimentally verified. Length of the pendulum is adjusted in real time using a shape memory alloy (SMA) wire actuator. This can be achieved in two ways i) by changing the amount of current in the SMA wire actuator or ii) by changing the effective length of current carrying SMA wire. Using an instantaneous frequency tracking algorithm, the dominant frequency of the structure can be tracked from a local feedback signal, then the length of pendulum is adjusted to match the dominant frequency. Effectiveness of the proposed ALP-STMD mechanism, combined with the STFT frequency tracking control algorithm, is verified experimentally on a prototype two-storey shear frame. It has been observed through experimental studies that the ALP-STMD absorbs most of the input energy associated in the vicinity of tuned frequency of the pendulum damper. The reduction of storey displacements up to 80 % when subjected to forced excitation (harmonic and chirp-signal) and a faster decay rate during free vibration is observed in the experiments.
This special issue focuses on Smart Tuned Mass Dampers (STMD) that are either active or smart or semi-active in nature. Active tuned mass dampers or active mass dampers have found wide acceptance and have been implemented in many tall buildings and long span bridges. Recently researchers have developed a new class of smart tuned mass dampers using either variable stiffness and/or variable damping to effect the change in instantaneous frequency and damping. Since tuning plays a central role in STMDs it is of great current interest thus the topic of this special issue. Discussions of recent active and smart TMD implementations in tall buildings and bridges are also included.
Summary Tuned mass dampers (TMDs) are used to control wind‐excited responses of high‐rise building as traditional vibration control devices. A TMD will have an excellent control effect when it is well tuned. However, a traditional passive TMD is sensitive to the frequency deviation; the mistuning in frequency and damping ratio both will decrease its control effect. In the previous research, an adaptive‐passive variable pendulum TMD (APVP‐TMD) is proposed, which can identify the TMD optimal frequency and retune itself through varying its pendulum length. However, it is found that the frequency variation will change the TMD damping ratio, and an unreasonable damping ratio will lead to a decrement in the robustness of a TMD. In this study, an adaptive‐passive eddy current pendulum TMD (APEC‐PTMD) is presented, which can retune the frequency through varying the pendulum length, and retune the damping ratio through adjusting the air gap between permanent magnets and conductive plates. An adjustable eddy current pendulum TMD (PTMD) is tested, and then, a single‐degree‐of‐freedom (SDOF) primary model with an APEC‐PTMD is built, and functions of frequency and damping ratio retuning are verified. The 76‐story wind‐sensitive benchmark model is proposed in the case study. The original model without uncertainty and ±15% stiffness uncertainty models are considered, and response control effects of different controllers are compared. Results show that because the APEC‐PTMD can both retune its frequency and damping ratio; it is more robust and effective than a passive TMD. It is also found that the APEC‐PTMD has a similar control effect with the active TMD, with little power consumption and better stability.
This article presents a novel semiactive independently variable stiffness (SAIVS) device, proposed for seismic response control of sliding base-isolated bridges. As a first step, force–displacement characteristics of the new SAIVS device are analytically and experimentally studied. It is demonstrated that the SAIVS device is capable of varying the stiffness, continuously and smoothly between minimum and maximum stiffnesses. This device is then incorporated into the sliding isolation system. In bridges, sliding isolation systems reduce pier drifts, but with increased bearing displacements. Such increased bearing displacements can be problematic under near-fault, large-velocity pulse-type earthquakes. To reduce bearing displacements, passive dampers are often incorporated into the isolation system. However, passive systems may result in increased pier drifts and isolation level forces. Semiactive variable stiffness systems, which can vary the period of the sliding isolated bridge in real-time, may reduce the bearing displacements and isolation level forces further than the passive systems; and hence, deserve investigation. In this study, the performance of a 1: 20-scaled sliding base-isolated bridge model equipped with the new SAIVS device is analytically and experimentally studied under several near-fault earthquakes. A new control algorithm for the control of the SAIVS device is developed and implemented in shake table tests. It is shown that the semiactive SAIVS device reduces bearing displacements further than the passive cases, while maintaining isolation level forces at the same level as in the minimum stiffness case.
Summary In this study, the coupled horizontal–vertical behavior of elastomeric bearings subjected to dynamic loading is studied in detail. Under extreme dynamic loading, elastomeric bearings exhibit unstable behavior and an instantaneous loss of horizontal stiffness that is recoverable. Building on an earlier study where the authors developed an analytical model for the horizontal behavior of bearings under dynamic loads, in this study, a new analytical model for the coupled horizontal–vertical behavior of the bearings is developed. The coupled behavior of the bearing is first studied for quasi‐static loading, and later, the behavior of the bearings under dynamic loading is studied. A clear distinction is made between different types of deformation the bearing undergoes in the vertical direction. Based on experimental results, it is observed that the behavior of the bearings under dynamic loading differs markedly from that observed under static loading. A new analytical model is proposed that can account for the coupled horizontal–vertical behavior of the bearings under dynamic loading. The proposed analytical model for predicting the post‐stability vertical behavior of the bearings is verified using experimental results. The model proposed is found to successfully predict the coupled horizontal–vertical behavior of elastomeric bearings. Copyright © 2015 John Wiley & Sons, Ltd.
The base-isolated Fire Command and Control (FCC) building in Los Angeles experienced strong motion during the 1994 Northridge earthquake. The California Strong Motion Instrumentation Program has instrumented the building and recorded the data during the Northridge earthquake; these data are available for performance evaluation. Impact was observed in the base-isolated FCC building during the Northridge earthquake. The objective of this study is to evaluate the seismic performance of the base-isolated FCC building during the 1994 Northridge earthquake and the effect of impact. New analytical modeling techniques are developed to analyze the base-isolated FCC building with impact and are verified using system identification. The response computed, using the developed analytical modeling techniques, is verified using recorded data. The response with and without impact is presented. The effects of impact on the structural response are evaluated. The seismic performance evaluations, comparing the response of the base-isolated building with the response if the building were fixed base, are presented. It is shown that the seismic performance of the FCC building in the Northridge earthquake was satisfactory, except for increased shear and drift due to impact. Impact should be avoided in base-isolated structures as it can cause damage.
