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Nyawako D.S.,University of Exeter | Reynolds P.,University of Exeter | Reynolds P.,Full Scale Dynamics Ltd
JVC/Journal of Vibration and Control | Year: 2017

This study presents the results of vibration suppression of a walkway bridge structure with a single actuator and sensor pair by using a proportional-integral (PI) controller and observer-based pole-placement controllers. From the results of experimental modal analysis, reduced-order models of the walkway are identified. These are used for the design of a PI controller as well as for state estimation procedures that are necessary for the development of reduced-order observer controllers. The respective orders of the latter are dependent on the number of plant modes used for their designs. They are formulated from plant and observer feedback gains that are obtained from the specification of desired floor closed-loop eigenvalues and observer eigenvalues. There are numerous solutions possible with the observer-based controller design procedures whereas the PI controller defaults to a particular solution. There is also the flexibility for isolation and control of target vibration modes with the observer-based controllers for higher controller orders from a purely single-input single-output controller scheme as demonstrated in the analytical and experimental studies presented. Further, in this work, a design space of potential feedback gains is specified, where only a single plant mode has been used for the observer-based controller design process, and a multi-objective genetic algorithm optimization scheme is used to search for an optimal solution within some pre-defined constraint conditions. The best solution here is regarded as one that offers the greatest vibration mitigation performance amongst the solutions identified. © The Author(s) 2015.

Brownjohn J.M.W.,University of Exeter | Brownjohn J.M.W.,Full Scale Dynamics Ltd | Reynolds P.,Full Scale Dynamics Ltd | Reynolds P.,University of Exeter | Fok P.,Civil Land Transport Authority
Proceedings of the Institution of Civil Engineers: Structures and Buildings | Year: 2016

Helix Bridge is a key feature of the iconic Marina Bay Sands development in Singapore. It usually functions as a pedestrian link between the Esplanade and Sands Casino/Hotel, but is occasionally used as a viewing platform for events in Marina Bay that have centred on a small purpose-built stadium opposite the bridge. To supplement the stadium capacity, integral cantilevered ‘pods’ have been built into the bridge. Because of its dual role, the Land Transport Authority of Singapore commissioned a vibration serviceability evaluation of Helix Bridge following a specification developed by Arup Australia. This evaluation was carried out in three stages. First, an experimental campaign comprising multi-shaker modal testing was used to estimate modal properties. Next, limited pedestrian and crowd testing directly evaluated the dynamic response to individuals and small groups walking, running or jumping. Finally, modal properties were utilised, with bespoke simulation software, to predict the performance of the bridge under extreme crowd loading using models specified in the most up-to-date design guidance on crowd loading for pedestrian bridges and stadia. The bridge performance proved to be acceptable, both in direct testing with small groups and in the simulations of large crowds. © ICE Publishing: All rights reserved.

Agency: European Commission | Branch: H2020 | Program: MSCA-ITN-ETN | Phase: MSCA-ITN-2014-ETN | Award Amount: 3.70M | Year: 2015

The growth of cities, impacts of climate change and the massive cost of providing new infrastructure provide the impetus for this proposal entitled Training in Reducing Uncertainty in Structural Safety (TRUSS) which will maximize the potential of infrastructure that already exists. If flaws in a structure can be identified early, the cost of repair will be vastly reduced, and here an effective monitoring system would allow identifying the optimum time to repair as well as improving structural safety. But safety is difficult to quantify and requires a deep understanding of the uncertainty associated to measurements and models for the structure and the loads. TRUSS will gather this understanding by bringing together an intersectoral and multidisciplinary collaboration between 4 Universities, 11 Industry participants and 1 research institute from 6 European countries. The consortium will combine and share expertise to offer training at an advanced level as new concepts for monitoring, modelling and reliability analysis of structures are emerging all the time. TRUSS will make knowledge of structural safety grow by incorporating these emerging technologies (hi-tech monitoring and manufacturing, computing, etc.) into the training programme and it will support job creation by enabling a wider talent pool of skilled and accredited engineering graduates with business, entrepreneurship, communication, project management and other transferrable skills. The training programme will be structured into taught modules combined with original research supported by secondments that will expose 14 fellows to both academia and industry. While developing tools that will reduce uncertainty in structural safety and improve infrastructure management, TRUSS will lay the basis for an advanced doctoral programme that will qualify graduates for dealing with the challenges of an aging European infrastructure stock, thereby enhancing their career prospects in both industry and academia.

Pereira E.,University of Alcalá | Diaz I.M.,Technical University of Madrid | Hudson E.J.,University of Exeter | Reynolds P.,University of Exeter | Reynolds P.,Full Scale Dynamics Ltd
Engineering Structures | Year: 2014

Civil structures such as floor systems with open-plan layouts or lightweight footbridges can be susceptible to excessive levels of vibrations caused by human activities. Active vibration control (AVC) via inertial-mass actuators has been shown to be a viable technique to mitigate vibrations, allowing structures to satisfy vibration serviceability limits. It is generally considered that the determination of the optimal placement of sensors and actuators together with the output feedback gains leads to a tradeoff between the regulation performance and the control effort. However, the "optimal" settings may not have the desired effect when implemented because simplifications assumed in the control scheme components may not be valid and/or the actuator/sensor limitations are not considered. This work proposes a design methodology for multi-input multi-output vibration control of pedestrian structures to simultaneously obtain the sensor/actuator placement and the control law. This novel methodology consists of minimising a performance index that includes all the significant practical issues involved when inertial-mass actuators and accelerometers are used to implement a direct velocity feedback in practice. Experimental results obtained on an in-service indoor walkway confirm the viability of the proposed methodology. © 2014 Elsevier Ltd.

Diaz I.M.,University of Castilla - La Mancha | Pereira E.,University of Alcalá | Hudson M.J.,University of Sheffield | Reynolds P.,University of Sheffield | Reynolds P.,Full Scale Dynamics Ltd
Engineering Structures | Year: 2012

Active vibration control (AVC) via inertial actuators is considered a viable technique for the mitigation of excessive vibrations in civil engineering structures. In particular, several recent field trials have shown that this technique has the potential to be effective for the cancellation of human-induced vibrations in pedestrian structures. However, prior to the implementation of AVC using inertial actuators, several drawbacks have to be dealt with. The main disadvantages come from the dynamic behaviour of the inertial actuators employed for this application, which are: (i) their low frequency dynamics (that might interact with the structure dynamics), and (ii) their nonlinearities (stroke and force saturation). Thus, any control technique to be implemented has to tackle stability problems (caused by the low frequency response of the actuators) and stroke and force saturation, which might lead to poor vibration cancellation performance. To alleviate such drawbacks, this work proposes to use an AVC strategy based on two control loops: (i) a loop, closed within the actuator, designed to artificially modify the actuator frequency response according to its maximum stroke and force and the structure dynamics, and (ii) a loop designed to impart damping to the structure. This work focuses on the design process such that stability and actuator saturations are taken into account to improve the efficiency of a given inertial actuator when the AVC system is based upon velocity feedback. Experimental results on a full-scale concrete laboratory structure using a commercial actuator are presented to illustrate the performance of the AVC strategy proposed, which ensures adaptability to a given structure without requiring hardware modifications. © 2012 Elsevier Ltd.

Brownjohn J.,University of Exeter | Brownjohn J.,Full Scale Dynamics Ltd | Racic V.,University of Sheffield | Racic V.,Polytechnic of Milan | Chen J.,Tongji University
Mechanical Systems and Signal Processing | Year: 2016

Floor vibrations caused by people walking are an important serviceability problem both for human occupants and vibration-sensitive equipment. Present design methodologies available for prediction of vibration response due to footfall loading are complex and suffer from division between low and high frequency floors. In order to simplify the design process and to avoid the problem of floor classification, this paper presents a methodology for predicting vibration response metrics due to pedestrian footfalls for any floor type having natural frequency in the range 1-20 Hz. Using a response spectrum approach, a database of 852 weight-normalised vertical ground reaction force (GRF) time histories recorded for more than 60 individuals walking on an instrumented treadmill was used to calculate response metrics. Chosen metrics were peak values of 1 s peak root-mean-square (RMS) acceleration and peak envelope one-third octave velocities. These were evaluated by weight-normalising the GRFs and applying to unit-mass single degree of freedom oscillators having natural frequencies in the range 1-20 Hz and damping ratios in the range 0.5-5%. Moreover, to account for effect of mode shape and duration of crossing (i.e. duration of dynamic loading), the recorded GRFs were applied for three most typical mode shapes and floor spans from 5 m to 40 m. The resulting peak values as functions of frequency i.e. spectra are condensed to statistical representations for chosen probability of being exceeded over a wide range of applications. RMS (acceleration) spectra show strong peaks corresponding to the first harmonic of pacing rate followed by clear minima at approximately 3.5 Hz, a second much smaller peak corresponding to the second harmonic and a steady decline with increasing frequency beginning around 5 Hz. One-third octave spectra show asymptotic trends with frequency, span and damping. A comprehensive validation exercise focusing on the acceleration RMS spectra was based on a representative range of floor samples for which modal properties had been identified and walking response studied during experimental campaigns of vibration serviceability evaluation. Due to the statistical approach an exact validation would not be possible, hence measured peak RMS values were matched to distributions for the equivalent idealised structure. In the vast majority of cases the measured values, intended to represent worst-case conditions, fitted the upper decile of the corresponding simulated spectra indicating consistency with the proposed approach. © 2015 Elsevier Ltd. All rights reserved.

Fernandez P.,University of Oviedo | Reynolds P.,University of Sheffield | Reynolds P.,Full Scale Dynamics Ltd | Lopez-Aenlle M.,University of Oviedo
Experimental Mechanics | Year: 2011

In operational modal analysis (OMA) mode shapes can be obtained only with arbitrary normalization. There are many applications where mass normalized mode shapes are required, such as response prediction and stress analysis. A method to scale the mode shapes in OMA is to modify the dynamic behaviour of the structure by adding masses and then to use the modal parameters of both the original and modified structure. Several mass change methods have been proposed in recent years for estimating the scaling factors, where a distributed array of added masses are needed to obtain good results. In this work a new mass change approach based on performing several individual mass changes is presented. This approach requires only a small number of masses that are located at different points in each individual experiment. The results of the individual tests are then combined to estimate the scaling factors. The approach is developed and validated by measurements carried out on a 15-tonne prestressed concrete slab strip and a steel cantilever beam. The results show that a good accuracy can be obtained by this method when a proper mass change strategy is used. © 2010 Society for Experimental Mechanics.

Brownjohn J.M.W.,University of Exeter | Brownjohn J.M.W.,Full Scale Dynamics Ltd | Zanardo G.,Main Roads | Brown D.G.,Atomic Weapons Establishment | Prichard S.,BuroHappold Engineering
Proceedings of the Institution of Civil Engineers: Structures and Buildings | Year: 2016

In 2005 the UK Ministry of Defence awarded a contract for construction of the Orion laser facility at the Atomic Weapons Establishment (AWE). Orion delivers a power density of 1021 W/cm2 on a 5 μm target, making it a worldclass facility for the study of high energy density physics. The ability to target to such high precision depends on the ‘stability’ of the building and internal structures with respect to thermal expansion and vibration. This paper concerns experimental activities supporting the prediction and evaluation of the minute vibrations against a ‘budget’ comprising the effects of all vibration sources, internal and external, and the sequence of experimental campaigns and signal evaluation that fed into this process. This involved a sequence of dynamics-based measurements of foundation pile stiffness, vibration propagation from both controlled and uncontrolled sources at stages during the construction and, finally, evaluation of vibration levels in the as-built facility due to internal machinery and the few external vibration sources passing through the sophisticated vibration barrier. The approach focused on time series of vibrations in the design phase and on the evaluation of statistical properties of displacement power spectral density functions. © ICE Publishing: All rights reserved.

Diaz I.M.,University of Castilla - La Mancha | Pereira E.,University of Castilla - La Mancha | Reynolds P.,University of Sheffield | Reynolds P.,Full Scale Dynamics Ltd
Structural Control and Health Monitoring | Year: 2012

SUMMARY Integral resonant control (IRC) has been recently introduced as a simple, robust and high-performance technique for vibration control of smart structures instrumented with collocated piezoelectric actuator-sensor pairs. This work deals with the design and implementation of an active vibration control (AVC) system based on an IRC strategy for the mitigation of human-induced vibrations in light-weight civil engineering structures, such as floors and footbridges, via proof-mass actuators. This work presents a new AVC strategy that combines an approximate inversion of the proof-mass actuator dynamics with an IRC-based strategy. The result is a control scheme with the following desirable characteristics: (i) the closed-loop system exhibits very high stability margins, (ii) the risk of stroke saturation at low frequencies is significantly reduced so that the saturation nonlinearity, which has to be included to keep the system hardware safe, can be designed to account only for force saturation (i.e. the actuator performance is enhanced), (iii) rigorous stability analysis and systematic design can be proposed and (iv) it is not necessary to measure the actuator force. The stability analysis is carried out using the recently developed stability theorem based on the positive feedback interconnection of systems with negative imaginary frequency response. The control scheme is validated on a full-scale prestressed concrete laboratory structure. Excellent vibration reduction performance is reported for frequency-response-function-based tests and for walking excitations. Copyright © 2010 John Wiley & Sons, Ltd.

Reynolds P.,University of Sheffield | Reynolds P.,Full Scale Dynamics Ltd
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

The vibration serviceability of civil engineering structures under human dynamic excitation is becoming ever more critical with the design and redevelopment of structures with reduced mass, stiffness and damping. A large number of problems have been reported in floors, footbridges, sports stadia, staircases and other structures. Unfortunately, the range of options available to fix such problems are very limited and are primarily limited to structural modification or the implementation of passive vibration control measures, such as tuned mass dampers. This paper presents the initial development of a new framework for advanced methods of control of humaninduced vibrations in civil engineering structures. This framework includes both existing passive methods of vibration control and more advanced active, semi-active and hybrid control techniques, which may be further developed as practical solutions for these problems. Through the use of this framework, rational decisions as to the most appropriate technologies for particular human vibration problems may be made and pursued further. This framework is also intended to be used in the design of new civil engineering structures, where advanced control technologies may be used both to increase the achievable slenderness and to reduce the amount of construction materials used and hence their embodied energy. This will be an ever more important consideration with the current drive for structures with reduced environmental impact. © 2012 SPIE.

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