Optimal Control of Adaptive/Smart Bridge Structures

Through the use of active controllers, a structure can modify its behavior during dynamic loadings. A computational model and efficient and robust parallel-vector algorithms have been developed on shared-memory multiprocessor machines for the active control of large adaptive structures subjected to dynamic loadings such as impact, wind or earthquake loadings. The computational model and the algorithms have been applied to large bridge and high-rise building structures. This paper is a brief overview of our recent research in this area.

Active vibration control of large flexible space structure is a challenging topic in the system dynamics and control of spacecraft. This paper proposes a novel approach for vibration control on a large hoop truss structure, typically used as mesh satellite antenna. First, to suppress the first-order bending modal response of the hoop truss structure with an initial disturbance, a piezoelectric bending actuator with excellent bending actuation performance was carefully designed as a key component of an active vibration control system. Then, the actuating characteristics of the actuator and the dynamic equations of the active structure were analyzed and formulated based on a finite element method. In order to improve the vibration-attenuating effect of the control system, a Mamdani-type fuzzy logic algorithm was employed in a closed-loop control system. Finally, simulations and experiments were implemented to validate the effectiveness of the proposed active control approach and structure. The experimental results showed that the decay time of first-order bending modal response (around 0.34 Hz) of control system reduces by 75% compared with that of the uncontrolled system. The results demonstrate that the proposed active vibration control system has good application potential in controlling the bending modes of a large flexible spacecraft.

Consideration of site specific lateral loading due to wind or earthquake loads along with vertical gravity loads is important for finding the behavior of the tall buildings. As the height of a building becomes taller, the amount of structural material required to resist lateral loads increases drastically. The design of tall buildings essentially involves a conceptual design, approximate analysis, preliminary design and optimization, to safely carry gravity and lateral loads. The design criteria are strength, serviceability and human comfort. The aim of the structural engineer is to arrive at suitable structural schemes, to satisfy these criteria. In the present study, the limit state method of analysis and design of a 3B+G+40-storey reinforced concrete high rise building under wind and seismic loads as per IS codes of practice is described. Safety of the structure is checked against allowable limits prescribed for base shear, roof displacements, inter-storey drifts, accelerations prescribed in codes of practice and other relevant references in literature on effects of earthquake and wind loads on buildings.

A structure with a building plane 7.75 × 8.35 m, 47.8 m high, and having a height/width aspect ratio exceeding 6 has a building response that is difficult to control in both seismic and wind loading. We therefore changed the vibration mode from rocking to swaying by softening first-story translation stiffness and concentrating building deformation to make the first story energy-absorbing. The soft first-story structure we introduce involves (1) stiffening the structure above the second story, (2) making first-story columns laterally flexible and axially rigid, and (3) developing a response-hardening oil damper. The sections below detail these structural elements and dynamic response control performance against wind and seismic loading through time-history response analysis.

With the advancement in material science, construction technology and structural analysis, a new building code was essential to keep pace with technological advantages. Recently introduced BNBC 2020 bridges the gap largely. A very basic change in lateral loading provision has occurred in the new code, which accounts for several newly defined parameters. For wind analysis, the new code introduces 3-second gust velocity as basic wind speed, wind pressure application in four cases that accounts for eccentricity. It considers topographic and internal pressure effect. A new seismic zoning is introduced in BNBC 2020 with revised PGA values and spectral acceleration. The code also introduces seismic design category and revised response reduction factor. All these changes will affect the design practice. To understand and compare lateral loading in different zones, a FEA of 20 storied RC building with and without core shear wall was analyzed using ETABS V18. The comparison shows that Rajshahi (Zone I) has lowest wind and seismic loading, Chattogram (Zone III) has highest seismic and wind loading while, Dhaka (Zone II) has moderate seismic and wind loading. Wall frame building has slightly larger seismic base shear while shear wall resists major portion of base shear and reduces top story displacement and story drift greatly. The cost of construction in zone III is significantly larger than in zone I and II. In all zones shear wall building imparts economic structural solution compared to bare frame against lateral loading for 20 storied buildings and the margin of economy increases with increasing lateral loading.

In this study, the effects of wind and seismic loads on 5, 10, and 15 story steel buildings with different bracing systems were investigated. Linear static and nonlinear dynamic analyses were performed to assess the base shear, base moment, and story drift for all bracing systems. In addition, the cost analysis was taken into consideration. Five structural configurations were used: V-bracing, inverted V-bracing, one-story X-bracing, and multistory X-bracing. One of the most important features of a building is lateral stiffness, which defines the resistance to displacement under seismic and wind loads, at the same time, the lateral stiffness has a major impact on the natural time of the structure. Reducing displacement and cost in the structures indicates that the design is safe and economical. Therefore, the purpose of this article is to find the best bracing system that causes minimum displacement, which indicates maximum lateral stiffness. From this point of view, the behavior of bracing systems exposed to wind and seismic loads in buildings with different stories was investigated. Static linear analysis results showed that the best bracing systems to reduce lateral displacement were the one-story X-bracing system for 5 and 15 story buildings and the V-bracing system for 10 story buildings. On the other hand, nonlinear dynamic analysis results showed that lateral displacement was minimum in unbraced, V-bracing, and one-story X-bracing systems for 5, 10, and 15 stories, respectively.

High-rise buildings and wind turbines under dynamic environmental loads experience excessive vibrations. Excessive vibration in tall buildings can exceed both strength and serviceability limit states, leading to structural damage and occupant discomfort. In contrast, unwanted vibration in wind turbines can have adverse effects on energy generation, fatigue life, and initial cost. The current research investigates two high-rise buildings and a 5 MW wind turbine from the National Renewable Energy Laboratory (NREL) numerically and experimentally to single out the optimal vibration mitigation techniques under diverse environmental loads. A performance-based design of viscous dampers with magnifying mechanism was employed to mitigate the vibration in 76 story benchmarks building under seismic and wind loads. Displacement, acceleration, inter-story drift ratio, shear force, and base bending moment are considered along with other concise sets of system-level performance criteria that are easily understood by decision-makers and/or stakeholders of diverse technical backgrounds. The results suggest viscous dampers as a viable solution for vibration attenuation in high-rise buildings. Viscous dampers can reduce structural and nonstructural damage by counteracting multi-hazard forces in real-time. We proposed a robust pendulum-pounding tuned mass damper (PTMD) to attenuate vibration in wind turbines. The NREL wind turbine equipped with the pendulum PTMD was modeled following the Lagrangian method to facilitate the numerical study. The results reveal that the optimum frequency ratio of the pendulum PTMD can be far different from the corresponding tuned mass damper (TMD) frequency ratio. The pendulum PTMD exhibits higher performance over the corresponding TMD, in terms of robustness and capabilities to reduce maximum accelerations and displacements under earthquakes. We verified the numerical results using a shake table experiment under several earthquake excitations. We carried out dynamic analysis investigations of a 42-story timber-hybrid building, along with a comparative control performance study of three mass dampers: (1) pendulum pounding tuned mass damper (PTMD), (2) tuned mass damper inerter (TMDI), and (3) tuned mass damper (TMD) under the earthquake excitations. Coupling the inerter with TMD to form TMDI can impact the optimal frequency ratio and damping ratio of TMD, resulting in reduced performance. Compared to TMD/TMDI, the pendulum PTMD was more robust, with a higher potential to reduce building responses under seismic loads. We performed aerodynamic investigations of a large-scale high-rise building model at a high Reynolds number (~1 million) to evaluate wind pressure distribution and wind loads. To demonstrate, aerodynamic testing of a 1:50 scale test model was executed with two aspect

This paper studies the feasibility of self-powered active vibration control of structures with Tuned Mass Dampers (TMDs). Without consuming external energy, the proposed self-powered vibration control strategy can provide better performance than the passive TMD in mitigating the vibration of buildings induced by wind load. the vibration-dissipative element of TMD is replaced with an electromagnetic machine, which serves as actuator and harvester at the same time. First, the desired force is obtained by adopting Linear Quadratic Regulator (LQG) optimal control. Then, the self-powered active control strategy is designed based on the essence of the desired force, which can be passive or active types. The energy of the vibration can be harvested as electricity in energy harvesting mode, and pumped back into the mechanical system when instant active force is required. Switch based circuits with capability of bi-directional power flow are presented for the implementation of self-powered active TMDs. With taking the efficiency of the harvesting and driving circuits into account, numerical simulations are carried out based on a tall building with a TMD under random and harmonic excitations. The results indicate the feasibility and effectiveness of self-powered active TMDs.

A new method is proposed for measuring interstory drift, the shifting of floors relative to one another when a building undergoes wind or earthquake loading. A free-space crosshair beam is projected from ceiling to floor onto a square of four position-sensitive photodetectors. Every lateral position and torsional angle gives a unique set of voltages at the photodetector outputs; thus, as the floors shift with respect to one another under load, detector voltages vary, the new beam axis location is determined, and the 2-D interstory drift is obtained. The theory of operation and a quasi-static verification of the method using micropositioning stages to provide input displacements are reported. Lateral positions, including translational and rotational components, are calculated from the photodetector outputs, and show excellent agreement with input displacements. The overall performance of the sensor system is extremely linear and predictable, and appears robust enough for field deployment. It is envisioned that some day it could serve as the input to an active control system used to stabilize smart buildings experiencing earthquake and wind loads.

Active control of structures has been under intensive development for the last ten years. Reference 2 reviews much of the identification and control technology for structural control developed during this time. The technology was initially focused on space structure and weapon applications; however, recently the technology is also being directed toward applications in manufacturing and transportation. Much of this technology focused on multiple-input/multiple-output (MIMO) identification and control methodology because many of the applications require a coordinated control involving multiple disturbances and control objectives where multiple actuators and sensors are necessary for high performance. There have been many optimal robust control methods developed for the design of MIMO robust control laws; however, there appears to be a significant gap between the theoretical development and experimental evaluation of control and identification methods to address structural control applications. Many methods have been developed for MIMO identification and control of structures, such as the Eigensystem Realization Algorithm (ERA), Q-Markov Covariance Equivalent Realization (Q-Markov COVER) for identification; and, Linear Quadratic Gaussian (LQG), Frequency Weighted LQG and H-/ii-synthesis methods for control. Upon implementation, many of the identification and control methods have shown limitations such as the excitation of unmodelled dynamics and sensitivity to system parameter variations. As a result, research on methods which address these problems have been conducted.

China’s western alpine regions are rich in mineral resources. However, factors such as freeze-thaw erosion, earthquakes, rainfall, and mining disturbances have weakened the strength of rock masses in alpine mine slopes, leading to structural weathering. These issues severely compromise the safety and stability of rock slopes and hinder the safe, efficient production of mineral resources. Both impact loads (such as blasting) and seismic loads can induce instantaneous deformation in structures and their components, sharing similar mechanisms of action. Therefore, this study conducts dynamic impact tests on sandstone based on the research context of impact loads including seismic events and excavation blasting. This study focuses on the Lanping Lead-Zinc Mine. First, through freeze-thaw cycle tests, SHPB (Split Hopkinson Pressure Bar) impact tests, and DIC (Digital Image Correlation) technology, the impact mechanical responses and failure characteristics of sandstone specimens under different freeze-thaw cycles were investigated. The dynamic mechanical properties and crack propagation patterns of sandstone under impact loading at various freeze-thaw cycles were revealed. The findings indicate that the strain rate ε´-t curve of sandstone specimens under dynamic impact is characterized by “increasing-stabilizing-accelerating decrease”. The strain (ε-t) curve initially increases before stabilizing, and the peak strain rises with the number of freeze-thaw cycles. The stress-strain response of sandstone under impact loading can generally be divided into three stages: linear elastic, nonlinear hardening, and strain softening. The slope of the stress-strain curve in the elastic stage decreases as the number of freeze-thaw cycles increases. The dynamic peak stress and dynamic elastic modulus of sandstone gradually decrease with increasing freeze-thaw cycles. Analysis of the dynamic evolution of Y-directional strain in sandstone specimens under impact loading using DIC technology reveals that crack propagation is closely linked to strain concentration zones on the specimen surface. The distribution of axial strain concentration zones determines the initiation and expansion of primary and secondary cracks during specimen failure. The conclusions of this study provide theoretical insights for disaster prevention and control (e.g., frost heave and dynamic loading) in rock slope engineering in alpine mining regions.

Tuned Mass Dampers (TMD) have been widely used in the passive vibration control of engineering structures, both under wind and seismic loads. Under wind loads, a proper frequency tuning ensures a significant response reduction of the primary structure. While under wind loads the structure is likely to remain in the elastic range of behaviour, when large earthquakes occur it can experience inelastic deformations and damage, with a consequent de-tuning effect. In this paper, nonconventional TMDs with large mass ratios, realized through Inter-story Isolation Systems (IIS), are considered and the influence of the inelastic behaviour of the primary system on the overall structure response is analysed. In detail, IIS is employed for retrofitting existing masonry buildings through a vertical extension, isolated at its base and built up on the roof of the existing structure. Pivot-type hysteretic models are used to grasp the mechanical behaviour of the masonry structure. Based on a case-study building, time history analyses on 3D Finite Element models are implemented. The results of nonlinear time history analyses show that in the building with the vertical extension both displacements and hysteretic energy dissipated by the masonry piers, are lower than in the as-is building, confirming that, although a de-tuning effect can occur, the inelastic engagement of the original structure is significantly reduced.KeywordsNonconventional TMDMasonry structureMasonry nonlinearitiesSteel vertical additionSeismic retrofit

This review presents an up-to-date account of research in multi-hazard assessment and vibration control of engineering structures. A general discussion of the importance of multi-hazard consideration in structural engineering, as well as recent advances in this area, is presented as a background. In terms of performance assessment and vibration control, various hazards are considered with an emphasis on seismic and wind loads. Although multi-hazard problems in civil engineering structures are generally discussed to some extent, the emphasis is placed on buildings, bridges, and wind turbine towers. The scientific literature in this area is vast with rapidly growing innovations. The literature is, therefore, classified by the structure type, and then, subsequently, by the hazard. Main contributions and conclusions from the reported studies are presented in summarized tables intended to provide readers with a quick reference and convenient navigation to related publications for further research. Finally, a summary of the literature review is provided with some insights on knowledge gaps and research needs.

A new class of materials known as ‘functionally graded materials’ (FGMs) has emerged recently, in which the material properties are graded but continuous particularly along the thickness direction. In an effort to develop the super heat resistant materials, Koizumi [1] first proposed the concept of FGM. These materials are microscopically heterogeneous and are typically made from isotropic components, such as metals and ceramics. In the quest for developing lightweight high performing flexible structures, a concept emerged to develop structures with self-controlling and self-monitoring capabilities. Expediently, these capabilities of a structure were achieved by exploiting the converse and direct piezoelectric effects of the piezoelectric materials as distributed actuators or sensors, which are mounted or embedded in the structure [2, 3]. Such structures having built-in mechanisms are customarily known as ‘smart structures’. The concept of developing smart structures has been extensively used for active control of flexible structures during the past decade [4]. Recently considerable interest has also been focused on investigating the performance of FG plates integrated with piezoelectric actuators. For example, Ootao and Tanigawa [5] theoretically investigated the simply supported FG plate integrated with a piezoelectric plate subjected to transient thermal loading. A 3-D solution for FG plates coupled with a piezoelectric actuator layer was proposed by Reddy and Cheng [6] using transfer matrix and asymptotic expansion techniques. Wang and Noda [7] analyzed a smart FG compositestructure composed of a layer of metal, a layer of piezoelectric and a FG layer in between, while in [8] a finite element model was developed for studying the shape and vibration control of FG plates integrated with piezoelectric sensors and actuators. Yang et al. [9] investigated the nonlinear thermo-electro-mechanical bending response of FG rectangular plates covered with monolithic piezoelectric actuator layers; most recently, Huang and Shen [10] investigated the dynamics of a FG plate coupled with two monolithic piezoelectric layers undergoing nonlinear vibrations in thermal environments. All the aforementioned studies focused on the rectangular-shaped plate structures. However, to the authors’ best knowledge, no researches dealing with the free vibration characteristics of the circular FGM plate integrated with the piezoelectric layers has been reported. Therefore, the present work attempts to solve the problem of providing analytical solution for free vibration of thin circular FG plates with two full size surface-bonded piezoelectric layers on the top and the bottom of the FG plate. The formulations are based

This study provides a method of vibration control of large space structures by simultaneously integrating the structure and control design to reduce the structural response from a disturbance. The formulation of the design scheme is obtained by the structural modification of some nominal finite element model, which is controlled in an optimal fashion by a linear regulator, to increase the active modal damping factor beyond that of the nominal structure. The structural modifications are achieved by using a nonlinear mathematical optimization technique. The objective function is the weight of the structure with a constraint on the damping parameter of the closedloop system. The application of the algorithm is illustrated by designing an ACOSS-FOUR model with different constraint values.