Tuned mass dampers (TMD), active mass dampers (AMD) and hybrid mass dampers (HMD) have been widely applied for vibration control of tall buildings and bridges in the past decade. Recently, the first author and his coworkers have developed semiactive or smart tuned mass dampers (STMD) using semiactive variable stiffness systems. STMD's are superior then TMD's in reducing the response of the primary structure. In case the fundamental frequency of the primary structure changes due to damage or deterioration, then the TMD will be off-tune; hence, it will lose its effectiveness significantly, whereas the STMD is robust against such changes as it is always tuned. The author and his coworkers have shown that STMD can provide performance similar to AMD/HMD, but with an order of magnitude less power consumption. This paper presents the development of a new STMD to reduce the vibrations of structures. The new STMD is an adaptive length pendulum (ALP) damper. It is essentially an Adaptive Stiffness Device (ASD); wherein, the length of the pendulum is varied in real time to achieve the change in frequency or stiffness (with mass remaining constant) of the pendulum. The Two different control approaches to adjust the length of pendulum of the ALP-STMD are developed (1) a shape memory alloy (SMA) actuator, and (2) servomotor. In both the mechanisms the length of the pendulum is adjusted semi-actively based on the feedback signal displacement of the top floor of the structure. Experimental studies are carried on a two-storey scaled model building with ALP-STMD. Effectiveness of the proposed ALP-STMD in controlling the fundamental mode of the structure is validated experimentally using both the SMA and servomotor to change its length. Off-tuned ALP-STMD results are presented to demonstrate the importance of tuning the length of pendulum.
In recent years, considerable attention has been paid to research and development of structural control devices, with particular emphasis on alleviation of wind and seismic response of buildings and bridges. In both areas, serious efforts have been undertaken in the last two decades to develop the structural control concept into a workable technology. Full-scale implementation of active control systems have been accomplished in several structures, mainly in Japan; however, cost effectiveness and reliability considerations have limited their wide spread acceptance. Because of their mechanical simplicity, low power requirements, and large, controllable force capacity, semiactive systems provide an attractive alternative to active and hybrid control systems for structural vibration reduction. In this paper we review the recent and rapid developments in semiactive structural control and its implementation in full-scale structures.
Risers are the conduits between the subsea wellhead and the drilling/production platform for development, production, gas lift or water injection purposes, which are also one of the most important and the most vulnerable components for deepwater floating platforms. To address the lack of appropriate global structural health monitoring (SHM) system for deepwater risers, this paper proposes a time-frequency domain approach using a wavelet modified second order blind identification (WMSOBI) method and combined distributed force change (CDFC) index. WMSOBI provides a reliable time-frequency domain identified modal properties of riser systems, even with large damping and under-determinate conditions. In addition, CDFC index generated from modal properties extracted by WMSOBI can accurately identify the damage location and damage level for both single and multiple crack scenarios. Details of experiments conducted on suspended pipe are presented. Both numerical and experimental verification are presented to validate the effectiveness of the proposed WMSOBI/CFDC algorithm and SHM system.
In civil, mechanical, and aerospace structures, full-field measurement has become necessary to estimate the precise location of precise damage and controlling purposes. Conventional full-field sensing requires dense installation of contact-based sensors, which is uneconomical and mostly impractical in a real-life scenario. Recent developments in computer vision-based measurement instruments have the ability to measure full-field responses, but implementation for long-term sensing could be impractical and sometimes uneconomical. To circumvent this issue, in this paper, we propose a technique to accurately estimate the full-field responses of the structural system from a few contact/non-contact sensors randomly placed on the system. We adopt the Compressive Sensing technique in the spatial domain to estimate the full-field spatial vibration profile from the few actual sensors placed on the structure for a particular time instant, and executing this procedure repeatedly for all the temporal instances will result in real-time estimation of full-field response. The basis function in the Compressive Sensing framework is obtained from the closed-form solution of the generalized partial differential equation of the system; hence, partial knowledge of the system/model dynamics is needed, which makes this framework physics-guided. The accuracy of reconstruction in the proposed full-field sensing method demonstrates significant potential in the domain of health monitoring and control of civil, mechanical, and aerospace engineering systems.
In base‐isolated structures specially designed isolation systems provide the needed flexibility and energy dissipation capacity. The isolation systems, which can be either elastomeric or sliding systems, exhibit highly nonlinear behavior. The existing algorithms cannot analyze base‐isolated structures with sliding isolation systems accurately. This paper presents an analytical model and a solution algorithm developed for nonlinear dynamic analysis of three‐dimensional‐base‐isolated structures with elastomeric and/or sliding isolation systems. The novelty of the analytical model and solution algorithm is its capability to capture the highly nonlinear frictional behavior of sliding isolation systems in plane motion. Nonlinear behavior is restricted to the base and the superstructure is considered to be elastic at all times. Biaxial and uniaxial models, which can represent both elastomeric and sliding isolation bearings, are presented. The solution algorithm consisting of the pseudoforce method with iteration is presented. Comparison of computed results with experimental results is presented for verification. A six‐story‐reinforced‐concrete‐base‐isolated structure is analyzed.
A newly developed structural damage monitoring technique is presented. The study focuses on capturing the initiation of multiple damages as they occur in a structure, which is similar to the concept of the fault detection filter. Previously, it has been shown that modified interaction matrix formulation provides a series of input error functions that generate a nonzero residual signal when the system experiences erroneous inputs. Error functions for each individual structural member are developed from the analogy between actuator failure and damageinduced residual force. When each individual error function is monitored, multiple damages as they occur in a structure can be simultaneously detected and isolated. Because the technique does not require frequency-domain measurements, it is readily applicable to online monitoring systems. This real-time technique also accommodates nonlinear breathing cracks and works for any type of excitation. A numerical simulation using a spring‐mass system and truss structure successfully demonstrates the proposed method.
This paper addresses tracking-control of hysteretic systems using a gain-scheduled (GS) controller. Hysteretic system with variable stiffness and damping is represented as a quasi linear parameter varying (LPV) system. Designed controller is scheduled on the measured/estimated stiffness and damping in real-time. GS controller is constructed from the parameter dependent Lyapunov matrices, which are obtained as optimal solutions of linear matrix inequalities (LMIs) that ensures the feasibility solution for closed loop system performance. The proposed method is worked on semiactive independently variable stiffness (SAIVS) device. It is shown that the gain-scheduled controller developed for the quasi-LPV system results in excellent tracking performance even in the cases where robust-H∞ controller failed to function.
A new output only modal analysis method is developed in this paper. This method uses continuous wavelet transform to modify a popular blind source separation algorithm, second order blind identification (SOBI). The wavelet modified SOBI (WMSOBI) method replaces original time domain signal with selected time-frequency domain wavelet coefficients, which overcomes the shortcomings of SOBI. Both numerical and experimental studies on bridge models are carried out when there are limited number of sensors. Identified modal properties from WMSOBI are analyzed and compared with fast Fourier transform (FFT), SOBI and eigensystem realization algorithm (ERA). The comparison shows WMSOBI can identify as many results as FFT and ERA. Further case study of structural health monitoring (SHM) on an arch bridge verifies the capability to detect damages by combining WMSOBI with incomplete flexibility difference method.
Benchmark problems in structural response control have served the international structural controls community as virtual test beds to compare different control algorithms since the first benchmark problem was proposed in 1996 through the sponsorship of the ASCE Structural Control Committee and Task Group on Benchmark Problems, the U.S. Panel on structural control, and International Association of Structural Control and Monitoring (IASCM). These problems offer well-developed models of structural system focusing on the response control of seismic and wind-excited buildings, seismically excited long-span cable-stayed bridges and seismically excited base-isolated buildings using prescribed earthquakes and standard set of evaluation criteria. They have been used by the entire community of researchers, educators, students and practitioners to investigate numerous control devices and algorithms. In 2004, the authors, in collaboration with Professor Ping Tan of Guangzhou University in China and Professor Jian Zhang of the University of California, Los Angeles, developed the benchmark structural control problem for a seismically excited highway bridge through the sponsorship of the ASCE committee on Structural Control and Task Group on Benchmark Problems, the U.S. Panel on structural control and International Association of Structural Control and Monitoring (IASCM). This special issue focuses on contributions to this benchmark structural control problem for a seismically excited highway bridge. Copyright © 2009 John Wiley & Sons, Ltd.
