Passive Protection of Structures using Innovative Rotational Inertia Dampers and Rotational Energy Conversion Devices

Civil structures, including bridges, buildings, roads, railways, and utility networks, are vital parts of modern life; therefore, it is essential to protect these structures and systems against natural and artificial hazards. Some hazards, such as earthquake or extreme winds, can put structures in danger of damage or destruction. In some cases, even moderate amplitude vibrations decrease the serviceability of structures. Considerable research has been conducted for the purpose of reducing the effects of dynamic loads on structures due to external natural and artificial excitation. Accordingly, many different structural control technologies have been developed and utilized in civil structures in recent decades. Active, semi–active, and passive control strategies have been proposed, developed, and utilized for the purpose of protecting structures against various types of excitations and ensuring occupant safety and structural serviceability. Unlike semi-active and active control devices, passive control devices can adjust the dynamic properties of a structure and improve its energy dissipation potential without relying on a controller, sensor, and power. Because of these advantages, passive control systems are, in general, more accepted by the construction industry and have been increasingly utilized by practicing structural engineers. Significant research efforts have been made in the past and are currently ongoing to develop and improve these passive control systems including systems exploiting rotational inertial devices

Vibration performance of in situ cross-laminated timber (CLT) floors in medium-rise buildings

Det finnes begrenset med informasjon angående vibrasjonsegenskapene til CLT-gulvsystemer installert i konstruksjoner. Ingeniører som ønsker å anvende CLT sin utmerkede styrke til masse forhold støter ofte på et bruksgrensetilstand problem. På grunn av et relativt lavt forhold mellom masse og stivhet blir systemet lett satt i bevegelse og vibrasjoner blir et problem. Helt siden introduksjonen av CLT har det blitt arbeidet med å utforme retningslinjer som skiller mellom akseptabelt og ikke-akseptabelt design. De fleste av disse retningslinjene tar ikke hensyn til betydningen av ikke-bærende konstruksjoner. Denne avhandlingen anvender OMA for å belyse hvordan in-situ gulv blir påvirket av omkringliggende elementer. Et omfattende studie har blitt utført på syv ulike gulv ved Ås videregående skole i løpet av prosjektperioden. Totalt ble tretten forskjellige tester utført for å samle inn feltdata.Innhentede data ble analysert for å bestemme gulvenes vibrasjonsegenskaper og for grundig å dokumentere effekten av in-situ elementer. Overføring av bevegelse på tvers av ikke-bærende skillevegger er gitt spesiell oppmerksomhet for å forklare oppdaget modusformer. Fordelingen av bevegelse er dokumenter gjennom VDV og arms konturkart. En analytisk del er inkludert for å vurdere hvor nøyaktig oppdatert Eurokode 5 kan forutsi fundamental egenfrekvens og kvadratisk gjennomsnitt for akselerasjon. Den aksepterte antagelsen om at ikke-bærende skillevegger kan ignoreres i design fasen utfordres. Gjennom detaljerte in-situ eksperimenter er det demonstrert at de har innflytelse på modale egenskaper. Spesielt er modusformen til den fundamentale egenfrekvensen påvirket av omkringliggende skillevegger. Integrasjon av CLT-gulvsystemer i konstruksjoner øker raskt kompleksiteten, noe som redusere antall identifiserbare modusformer. Fordeling av bevegelse på gulvet er vist til å følge lav frekvens modusformer via VDV og arms. Konsekvensen av dette er at skillevegger spiller en viktig rolle i å bestemme kritiske aksjelerasjonspunkter. Den reviderte EC5 systematisk undervurder av gulvenes grunnfrekvenser, mens den overestimerer gulvenes akselerasjons egenskaper. En slik unøyaktigheten reduseres byggekodens egenskap til å skille mellom akseptabelt og ikke-akseptable design.There is limited information regarding the vibration characteristics of CLT floor systems within superstructures. As designers utilise the excellent strength-to-mass ratio of CLT, they are often faced with a serviceability problem. Due to the relatively low mass-to-stiffness ratio, the system is prone to oscillation, and vibration becomes a major issue. In recent years, there have been a lot of efforts to establish guidelines for distinguishing between acceptable and unacceptable design. However, many of these guidelines do not consider the importance of non-bearing structures. This thesis utilises OMA to highlight how in-situ floors are affected by surrounding elements. A comprehensive study was conducted on seven floors within Ås High School during the thesis project. In total thirteen distinct tests were carried out to gather field data, which was then analysed to determine modal characteristics. By determining modal characteristics, the effects of in-situ elements are thoroughly documented. Transfer of motion across non-bearing partitions is given special attention to explain detected mode shapes. The distribution of motion is documented through VDV and arms contour maps. An analytical component has been incorporated to assess the accuracy of the updatedEurocode 5 in calculating the fundamental natural frequency and root-mean-square acceleration. The standing assumption that non-bearing partition walls can be ignored during design is challenged. Through detailed in-situ experiments, it becomes clear that they play an essential role in determining the modal characteristics of the floors. It has been found that partition walls have a significant impact on all modal characteristics. The configuration of surrounding partition walls especially impacts the fundamental mode shape. As the CLT floor system is integrated into the superstructure, its complexity rapidly increases, decreasing the number of identifiable modes. Distribution of motion across floors documented with VDV and arms is shown to follow low-frequency mode shapes. The consequence is that partition walls play an important role in determining critical acceleration spots. The revised EC5 underestimates the fundamental frequencies performance of the floors while overestimating its arms performance. This inaccuracy reduces its effectiveness in discriminating between acceptable and unacceptable design

Seismic control of rocking structures using inerters

When subjected to lateral excitations, a variety of structures, such as museum artefacts, historical buildings, bridge piers and post-tensioned walled buildings, might uplift and set into rocking motion. Although this mechanism can efficiently limit the internal forces at their base, the possibility of overturning or experiencing increased lateral deformations and accelerations may severely affect the functionality of rocking structures. Nevertheless, suitable seismic control strategies are presently limited and consist mostly in preventing rocking motion altogether, which may induce undesirable stress concentrations and lead to impractical interventions. This thesis examines the alternative of using supplemental rotational inertia devices to control the seismic response of rocking structures. The newly proposed strategy employs inerters, which are mechanical devices that develop resisting forces proportional to the relative acceleration between their terminals and can be combined with a clutch to ensure they act only in opposition to the motion. The fundamental dynamic behaviour of the system is firstly examined considering a free-standing rigid block model. By deriving the corresponding equations of motion, it is demonstrated that the inclusion of the inerter effectively reduces the frequency parameter of the block, resulting in lower seismic demands and enhanced stability due to the well‐known size effects of the rocking behaviour. In subsequent chapters, this simplified single-degree-of-freedom model is gradually extended in order to incorporate the effects of post-tensioned tendons, structural flexibility and higher modes on the response. Overall, the analyses conducted under coherent pulses and real ground motion records show that inerter-equipped structures experience reduced seismic demands and lower probabilities of exceeding limit states usually associated with structural and non-structural damage. The fundamental knowledge acquired in the first part of this thesis is finally applied to control the seismic response of rocking timber buildings. To this end, a set of three post-tensioned rocking walled buildings, comprising 3, 6 and 9 storeys, is designed following direct-displacement-based design guidelines. Additionally, a set of clutched and non-clutched ball-screw and gear inerters is designed using a newly proposed pre-dimensioning procedure. The performance of bare and protected structures with different levels of apparent mass ratios is then compared in terms of peak inter-storey drifts and floor accelerations. Special attention is paid to the resisting forces developed in the inerters and the mechanism to transfer them to the structural diaphragm. Likewise, the ability of the inerters to control higher-mode effects is closely examined. Finally, a performance-based assessment with particular emphasis on non-structural and contents damage is conducted considering a database of 202 pulse-like ground motion records. Overall, the results of this assessments confirm the trends observed in the analytical examinations of the earlier chapters.Open Acces

Vibration control of frame structure using multiple tuned mass dampers

Need for taller structure in construction and real estate industry is increasing all over the world. These structures are flexible and constructed as light as possible (as seismic load acts on a structure is a function of self-weight), which have low value of damping, makes them vulnerable to unwanted vibration. This vibration creates problem to serviceability requirement of the structure and also reduce structural integrity with possibilities of failure. Current trends use several techniques to reduce wind and earthquake induced structural vibration. Passive tuned mass damper (TMD) is widely used to control structural vibration under wind load but its effectiveness to reduce earthquake induced vibration is an emerging technique. Here a numerical study is proposed on the effectiveness of tuned mass damper to reduce translation structural vibration. Total three type of models, i.e., shear building with single TMD, 2D frame with single TMD and 2D frame with double TMD are considered. Total five numbers of loading conditions are considered named sinusoidal ground acceleration, EW component of 1940 El-Centro earthquake (PGA=0.2144g), compatible time history as per spectra of IS-1893 (Part -1):2002 for 5% damping at rocky soil (PGA=1.0g), Sakaria earthquake (PGA=1.238g), The Landers earthquake (1992) (PGA=1.029g) for time history analysis of considered model.The effectiveness of single TMD to reduce frame vibration is studied for variation of mass ratio of TMD to frame. Also the effect of double tuned mass damper on the frame response is studied for uniform, non uniform distribution of mass ratio and variation of damping ratio of damper.From the study it is found that effectiveness of TMD increases with increase in mass ratio. Use of double TMD is much more effective than single TMD of same mass ratio for vibration mitigation under earthquake as well as sinusoidal acceleration

Dynamic range implications for the effectiveness of semi-active tuned mass dampers

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 159-164).The response of tall buildings subjected to dynamic wind loads has been widely studied. For excitations approaching the resonant frequencies of the structure, ensuring serviceability is a significant concern. One traditional solution is the implementation of a tuned mass damper (TMD), which acts as a passive damping device in the region of the tuned frequency. However, TMDs exhibit a limited bandwidth and often require a significant mass. Active systems, such as the active mass driver, have been utilized to improve the effectiveness of the TMD concept, but these systems require significant power and bring the inherent risk of instability. Hybrid semi-active schemes with variable damping devices have been proposed. They are stable, require low power, and are controllable, thus providing a broader range of applicability. The concept of a semi-active tuned mass damper (STMD) has been investigated, but the influence of the dynamic range of the semi-active damping device has not been documented. This analysis assesses the effectiveness of STMD systems using a variable-orifice damper and a magnetorheological damper with varying dynamic ranges. Results demonstrate a performance dependence on the dynamic range and also elucidate the superiority of non-linear damping devices. It is shown that the prescribed TMD mass may be reduced by a factor of two when semi-active control is implemented, thereby making the STMD an attractive and feasible option when space and weight concerns govern design.by Cory W. Lindh.S.M

마찰도입 비선형 다중동조질량감쇠기의 최적설계

학위논문 (박사)-- 서울대학교 대학원 공과대학 건축학과, 2017. 8. 이철호.Modern development of design techniques and material science in architectural engineering contributes to increase in demand for buildings with longer span and light weight structure. In spite of its advantageous aspects, such advances in technologies often leads to problems with undesired discomfort caused by excessive vibration. In order to help dampen the unwanted excessive vibration, a variety of relevant techniques have been investigated, among which tuned mass damper (TMD) is one of the most widely used techniques so as to control the problematic vibration. This study first investigates the optimal solution of linear multiple tuned mass dampers (linear MTMDs, LMTMDs) of various configurations. The configurations considered in this study include the cases where the frequency ratios are linearly distributed, the damping coefficients are uniformly distributed, the mass distributions are linearly distributed, or these constraints are combined in some ways. Two different optimization techniques are employed: Nominal Performance Optimization (NPO) and Robust Performance Optimization (RPO). The NPO searches a solution that minimizes the objective function deterministically, while the RPO minimizes the mean value of the objective function, assuming that the associated structural parameters are probabilistic rather than deterministic. Further, this study provides contour maps for the root-mean-square (RMS) displacement of main structure and the largest RMS displacement of LMTMDs, which can be useful in the design process. Next, this study seeks the optimal solution of frictional multiple tuned mass dampers (FMTMDs) in which the Coulomb-type frictional force is incorporated in either purposefully or unintentionally. In this study, four of the feasible FMTMD configurations are formulated and comparably analyzed. The investigated configurations involve: 1) no constraint on either the frequency ratios or the coefficient of friction (COF) is imposed2) the frequency ratios are linearly distributed and equally spaced3) the COFs are identically distributed4) the frequency ratios are equally spaced and the COFs are identical. In order to cope with the difficulties inherent in nonlinearity of the problem, this study adopts a statistical linearization technique, which enables the complicated nonlinear force terms to be linearized in a statistical sense. Some miscellaneous considerations such as stroke limitations and design procedure are also aptly included. This study mainly addresses RMS responses and extreme value distributions for the frictional multiple tuned mass dampers (FMTMDs). In designing of optimal FMTMD, the original nonlinear system arising from the frictional elements is replaced with an equivalent linear system by means of statistical linearization. In order to improve the accuracy for the estimation of peak distribution of MTMDs, this study exploits a statistical nonlinearization technique which replaces the nonlinear system at hand with a class of other nonlinear systems whose exact solution has been already explicitly derived. A correction factor that defines the ratio of RMS displacement between nonlinear and linear system is derived based on the results of statistical nonlinearization technique. This study also provides an explicit formula for evaluating a peak factor for frictional TMDs. The correction factor and the peak factor proposed are validated with Monte Carlo Simulation. Several application examples of MTMDs are included in this thesis. of multiple tuned mass dampers (MTMDs). In the first section, a mechanism-based frictional pendulum tuned mass damper (FPTMD) is proposed, which contributes to overcome some shortcomings of conventional translational TMDs with viscous damping. In the second section, a numerical study is carried out to provide a design procedure of MTMDs, which covered modal analysis based on finite element method, optimal design of tuned mass dampers, and evaluating their control performance and robustness under the frequency-perturbed states. The final section presents a project in an attempt to mitigate an excessive vibration of a problematic structure. The overall process of the project includes the vibration performance evaluation, modal analysis based on finite element method and optimal design and manufacturing of tuned mass dampers.Chapter 1 Introduction 1 1.1 Background 1 1.2 Scope and Objectives 4 1.3 Outline of Dissertation 5 Chapter 2 Literature Review 9 2.1 Optimization Criteria and Techniques 10 2.1.1 H∞ optimization 10 2.1.2 H2 optimization 12 2.1.3 Stability maximization 13 2.2 Multiple Tuned Mass Dampers 14 2.3 TMDs on Nonlinear Structures 23 2.4 Nonlinear Tuned Mass Dampers 24 2.5 Applications and Structural Implementations 29 2.5.1 Wind-induced vibration attenuation 29 2.5.2 Seismic response mitigation 30 2.5.3 Floor vibration control 35 2.6 Other Issues 38 2.6.1 Stroke limitations 38 2.6.2 Reliability-based optimization 39 Chapter 3 Linear Multiple Tuned Mass Dampers 43 3.1 Introduction 44 3.2 Model Formulation 46 3.2.1 Governing Equations of motion 46 3.2.2 LMTMD configurations 51 3.3 Optimization Strategies 58 3.3.1 Nominal performance optimization 58 3.3.2 Robust performance optimization 60 3.4 Results and Discussion 63 3.4.1 LMTMDs designed by NPO 63 3.4.2 LMTMDs designed by RPO 72 3.4.3 Approximate solution for LMTMDγζ 78 3.5 Stroke Consideration and Design Procedure 82 3.5.1 Stroke consideration 82 3.5.2 Design procedure 84 3.6 Concluding Remarks 85 Chapter 4 Frictional Multiple Tuned Mass Dampers 87 4.1 Introduction 88 4.2 Model Formulation 91 4.2.1 Governing equations of motion 91 4.2.2 FMTMD configurations 95 4.2.3 Statistical linearization 98 4.3 Optimization Strategies 101 4.3.1 Set 1: FMTMDo and FMTMDγ 103 4.3.2 Set 2: FMTMDτ and FMTMDγτ 104 4.4 Results and Discussion 105 4.4.1 Optimal parameters 105 4.4.2 Frequency responses with optimal parameters 112 4.4.3 Input-intensity sensitivity analysis 114 4.4.4 Approximate solution for FMTMDγτ 117 4.5 Design Procedure 122 4.6 Concluding Remarks 123 Chapter 5 Extreme Value Analysis for Frictional MTMDs 125 5.1 Introduction 126 5.2 FMTMD Optimization 128 5.2.1 Governine equations of motion 128 5.2.2 Statistical linearization 132 5.2.3 Optimization strategy 135 5.3 Improved Estimation of Peak Distribution 137 5.3.1 Statistical nonlinearization 137 5.3.2 Correction factor 142 5.3.3 Peak factors 144 5.4 Model Evaluation 147 5.5 Concluding Remarks 148 Chapter 6 Applications of MTMDs 155 6.1 Frictional Pendulum Tuned Mass Dampers 156 6.1.1 Introduction 156 6.1.2 FPTMD proposed and equations of motion 158 6.1.3 Statistical linearization 165 6.1.4 Gradient-based optimization 167 6.1.5 Numerical example 171 6.1.6 Summary and conclusions 181 6.2 Vibration Attenuation of Hallway 183 6.2.1 Description of examined hallway 184 6.2.2 Design of multiple tuned mass dampers 187 6.2.3 Numerical investigation 187 6.2.4 Results and discussion 195 6.3 Project: Vibration Mitigation of Floating Café 196 6.3.1 Introduction 196 6.3.2 Description of floating café 197 6.3.3 Design of multiple tuned mass dampers 199 6.3.4 Vibration serviceability assessment 200 6.3.5 Results and discussion 202 Chapter 7 Summary and Conclusions 203 Appendices 209 Chapter A Point Estimation Method 211 Chapter B Statistical Linearization 217 B.1 Formulation 217 B.2 Solution Procedure 219 B.2.1 Error minimization 219 B.2.2 Response evaluation 221 B.3 Examples of Systems with Power-Law Damping 222 Chapter C Applying Pre-Filters 227 Bibliography 231 Abstract (in Korean) 247Docto

Characterising the dynamic response of ultrasonic cutting devices

The current work begins by considering a range of common high power ultrasonic components in order to establish a standardised approach to tool design for optimum performance. The vibration behaviour of tuned components resonating longitudinally at ultrasonic frequencies around 35 kHz is modelled via finite element analysis and measured by experimental model analysis. Significant improvements in experimental validation of the models are achieved by the use of a 3D LDV, which allows modal analysis from both in-plane and out-of-plane measurement, which is critical in proposing alternative designs. The vibration characteristics of complex multiple-component systems used in ultrasonic cutting of food products are also investigated. Commonly, the design approach for ultrasonic systems neglects to account for the mutual effects of physically-coupled components in the system vibration. The design of systems also neglects the nonlinear dynamic effects which are inherent in high power systems due to the nonlinearities of piezoelectric transducers. The first issue is tackled by considering the vibration behaviour of the whole system and the influence of individual components and, particularly, offers design improvements via modification of block horns and cutting blade components, which are modelled and validated. The issue of nonlinearity is addresses by identifying the mechanisms of energy leakage into audible frequencies and characterising the common multimodal responses. For this study, design modifications focused on reducing the number of system modes occurring at frequencies below the tuned system frequency. As a consequence of these approaches, insights for the design of multiple-component systems in general are provided

Seismic Behaviour and Design of Steel Frames Incorporating Tubular Members

This thesis deals with the seismic behaviour of steel frames with particular focus on structures that employ tubular members as either columns or bracing elements. It addresses a number of design and assessment issues at the local (connection), frame, and overall (system interaction) levels. At the connection level, two experimental investigations on: (i) blind-bolted and angle connections, and (ii) combined channel/angle connections, are presented. The main behavioural patterns and the effects of key design parameters on the connection performance are examined. Refined mechanical models able to estimate the response of these connecting details are developed. These mechanical models are subsequently employed to perform parametric studies based on which simplified design-oriented expressions for the estimation of stiffness, strength and ductility are suggested. The susceptibility to low-cycle fatigue within critical connection components and the predictions of available fatigue damage models are also assessed. At the frame level, an evaluation of the inelastic demands on moment-resisting, partially-restrained and concentrically-braced steel structures is performed and equivalent linear models for the estimation of peak deformations are proposed. Particular attention is given to the influence of a number of scalar ground-motion frequency content parameters on the estimation of peak displacements. Additionally, simplified models based on rigid-plastic dynamics, and implemented within response history analysis, are proposed. It is shown that such rigid-plastic models can predict global deformations with reasonable accuracy. At the system interaction level, a comparative assessment of the peak response of one-way, two-way and mixed framing configurations under bi-directional earthquake loading is studied by means of idealized 3D simplifications and refined 2D models. This enables a detailed quantification of the contribution of gravity frames to the reduction of seismic risk and highlights the benefits of proper secondary frame design in mitigating the probabilities of dynamic instability. Finally, the findings of the thesis are summarized and future research areas are identified