bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparative assessment of stabilizing techniques for joint input-state estimation via Augmented Kalman Filter
Authors: Caglio Luigi , Stang Henrik , Katsanos Evangelos
Published: June 2024

In the context of Structural Health Monitoring, the accurate estimation of the state of a structural system subjected to various sources of dynamic loads can be beneficial for assessing the current structural performance and for predicting the future one. In case of linear systems, for example, the estimation of the state can provide valuable information about unmeasured strains and corresponding stresses that, in turn, can favor the prediction of fatigue damage. Additionally, state estimation of structural systems responding in the nonlinear regime can facilitate the identification of damages that occurred during an extreme event (e.g., excessive wave, earthquake and strong wind). A major challenge in the state estimation task stems from the unavailability of the external input loads. Therefore, several joint input-state estimation techniques have already been developed to address this issue; among them, the Augmented Kalman Filter (AKF) is one of the most commonly employed. Despite the advantages of the AKF, a critical aspect of this joint input-state estimation technique is associated with the instability that the estimation can experience when only noisy acceleration time series are available. Heretofore, several approaches have been proposed aiming to stabilize the estimation in case of linear systems. In this work, some of the most commonly employed approaches for stabilizing the AKF-based joint-input state estimation (e.g., dummy displacement measurements, dummy load measurements, and Gaussian process latent force model) are adopted and thoroughly compared. Two five-DOF linear systems subjected to dynamic loads are simulated, while the calculated responses are used to assess and compare the performance of various existing techniques for stabilizing the estimation.
Convolution models for output only linear structural system identification and the problem of identifiability.
Authors: Mclean J.H. , Dervilis N , Rogers T.J.
Published: June 2024

This paper investigates the use of the Gaussian Process Convolution Model (GPCM) as an output only system identification tool for structural systems. The form of the model assumes a priori that the observed data arise as the result of a convolution between an unknown linear filter and an unobserved white noise process, where each of these are modelled as a GP. The GPCM infers both the linear time filter (which is the impulse response function, i.e. Green’s function, of the system) and driving white noise process in a Bayesian probabilistic fashion with an approximate variational posterior over both signals. It will be shown that although the model structure is intuitive and sensible priors are applied, the GPCM falls short in recovering the linear impulse response of interest response due to the problem of identifiability. This is an interesting result indicating that physically informed kernel structures alone are not enough to recover the true impulse response in similar non-parametric probabilistic models. Despite this, the avenue of research remains highly promising, and several ideas are proposed to improve the model as a system identification tool.
Unsupported machining fixture layout optimisation
Authors: Soto C , Sims N D , Ozturk E , Weekes B
Published: June 2024

It is well established that excessive vibrations in machining operations hinder productivity and quality of the components being made. In these environments it is common to encounter self-excited vibrations due to the dynamic response characteristics of the cutting tool and workpiece; referred to as regenerative chatter. To suppress these effects, conventional practices provide the workpiece with as much support as possible and therefore commonly require custom-built fixturing bases and several manual intervention stages. In contrast, for modern reduced fixturing approaches, the workpiece is minimally-held, with the benefits of reduced setup times, lower fixturing and inventory costs, and improved access to the workpiece thereby avoiding multi-stage setups. However, minimal fixturing reduces support of the workpiece, and so vibration becomes a greater challenge, along with the subsequent detrimental effects to part quality and material removal rate (mrr). This paper sets out to determine an optimisation methodology for layout configurations that maximise milling depths of cut whilst achieving dynamic stability; by means of FEA model-based simulations and particle swarm optimisation (pso) methods. The optimisation algorithm is then tested on simplified setups and compared to exhaustive searches. It is shown that optimal results can differ from standard practice, and despite the comparative reduction in workpiece stiffness to a traditional approach is mostly unavoidable, careful placement of workholding elements can reportedly improve cutting conditions and increase dynamic stability within an unsupported environment.
Sensor placement optimal for the precision of modal parameter estimation with subspace methods
Authors: Greś Szymon , Döhler Michael , Dertimanis Vasilis , Chatzi Eleni
Published: June 2024

In this paper we focus on sensor placement for output-only modal analysis, where the objective is to choose those sensor locations yielding a minimal variance in the identification of modal parameters from measurement data. It is heuristically shown that the variance of modal parameters estimated with data-driven subspace identification can be approximated solely based on the process and the measurement noise properties with the Kalman filter and the underlying system model, and is independent of data which are not available at the experimental design stage. The performance of the proposed approach is illustrated on an extensive Monte Carlo simulation for an illustrative example of a mechanical chain system.
Vibration-based assessment of the structural integrity of a masonry wall system with single opening subjected to progressive damage induced by out-of-plane loading conditions
Authors: Meoni A , D’Alessandro A , García-Macías E , Saviano F , Parisi F , Lignola G P , Ubertini F
Published: June 2024

Existing masonry constructions often develop a complex mechanical response due to considerable material heterogeneity of the ancient masonry and presence of structural pathologies. The occurrence of severe loading conditions, such as those caused by differential soil settlements and seismic events, can also induce brittle collapse mechanisms in ancient masonry constructions. Operational Modal Analysis (OMA) methods are particularly well-suited Structural Health Monitoring (SHM) approaches for historical masonry constructions. Despite their benefits, low sensitivity of OMA methods to localized damage is often indicated in the literature as major limitation. This paper presents preliminary results of vibration-based structural integrity assessment of a masonry wall system with single opening. Specifically, the wall specimen was subjected to progressive damage induced by increasing out-of-plane displacements. The modal identification of the structure was performed at different steps of the test sequence. Similarly, visual inspections were carried out on the wall specimen to detect the development of damage. Changes in the identified modal features were computed for every step of the test. The obtained preliminary results show clear variations in modal features, consistently with the damage level suffered by the tested structure. Interestingly, mode shapes were found particularly sensitive to damage even under initial levels of out-of-plane deformation.
Damage detection of a typical historic masonry tower using control charts
Authors: Testa F , Barontini A , Lourenço P B
Published: June 2024

Control charts have become a common method for damage detection within vibration-based structural health monitoring. Successful applications have been implemented including for historical buildings preservation. Nonetheless, their performance is affected by several algorithm parameters that should be properly set and more research is needed to optimise such tools. To this end, the present work discusses the preliminary results of a project that focuses on the development of a cost-effective damage detection strategy based on control charts for masonry towers in seismic prone areas. Here, a prototype of historic tower is defined based on an extensive documentary search, a methodology to simulate realistic long-term monitoring data is developed and, finally, different parameters that may affect the damage detection performance are analysed and compared against small-extent damage scenarios. The importance of normalising the features to account for seasonal fluctuations and setting a correct threshold for detection clearly emerged and drives the future scope of the work.
Dynamic characterization of a modern heritage structure: the Palazzetto dello Sport by Pier Luigi Nervi
Authors: Ciambella Jacopo , Ranzi Gianluca , Romeo Francesco
Published: June 2024

This paper focuses on the dynamic characterization and monitoring of the Palazzetto dello Sport in Rome, a reinforced concrete structure built in 1957 by Pier Luigi Nervi. The study employs an experimental dynamic testing campaign to identify the structure’s modal properties via Operational Modal Analysis (OMA) and to develop an accurate 3D numerical model of the structure. The analysis of the dynamic features associated with the axial symmetry of the dome reveals the presence of axisymmetric and non-axisymmetric modes with identical frequencies. The repeated modes analysis is performed using the MAC criterion validation. The selection of suitable dynamic structural characterization strategies for monitoring the exemplary twentieth-century concrete structure considered is eventually discussed. The extracted information can be used for effective structural condition assessment.
An investigation into wave propagation in hanging chains
Authors: Cleante V G , Gonçalves P J P , Waters T , Brennan M J , Carneiro J P , Rade D A
Published: June 2024

The study introduced in this work is motivated by the prospect of using a hanging chain as an Acoustic Black Hole (ABH) for passive vibration control. An ABH is effectively a waveguide in which a wave slows progressively as it propagates away from the source enabling it to be extinguished with modest damping. The effect can be achieved by engineering inhomogeneity into a structure’s geometry or material, the most common realisation being a beam of tapered thickness. This paper proposes an alternative realisation, that of a chain hanging under its own weight. Such a system has a wave speed that naturally decreases to zero, owing to its linear variation in tension, thus overcoming the challenges of constructing precisely shaped beams with vanishingly thin tips. The study of transverse vibration of hanging chains is a classical problem in structural dynamics. The motion of the chain can be described in terms of Bessel or Hankel functions, which are needed to account for the variation in tension along the chain. In this work, the hanging chain problem is revisited from a wave propagation perspective. An expression is derived for the amplitude of the waves in an infinite chain due a point excitation. From which, the spatial behaviour and the receptances of the waves are evaluated, revealing differing characteristics of upward and downward propagating waves. Some experimental results are presented to support the theoretical analysis.
A three-dimensional model of an air bubble curtain in offshore pile driving
Authors: Peng Yaxi , Tsouvalas Apostolos
Published: June 2024

With the growing demand for renewable energy, an increased number of offshore wind farms are planned to be constructed in the coming decades. The monopile is the main foundation of offshore wind turbines in shallow waters while the installation process itself takes place with large hydraulic impact hammers. This process is accompanied by significant underwater noise pollution which can hinder the life of mammals and fish. To protect the marine ecosystem, strict sound thresholds are imposed by regulators in many countries. Among the various noise mitigation systems available, the air-bubble curtain is the most widely applied one. While several models exist which aim to describe the mitigation performance of air-bubble curtains, they all assume a cylindrically symmetric wave field. However, it is well known that the performance of the air-bubble curtains can vary significantly in azimuth due to the inherent variations in the airflow circulation through the perforated pipes positioned on the seabed surface. This paper presents a new model which is based on a multi-physics approach and considers the three-dimensional behavior of the air-bubble curtain system. The complete model consists of three modules: (i) a hydrodynamic model for capturing the characteristics of bubble clouds in varying development phases through depth; (ii) an acoustic model for predicting the sound insertion loss of the air-bubble curtain; and (iii) a vibroacoustic model for the prediction of underwater noise from pile driving which is coupled to the acoustic model in (iii) through a three-dimensional boundary integral formulation. The boundary integral model is validated against a finite element model. The model allows for a comparison of various mitigation scenarios including the perfectly deployed air bubble curtain system, i.e.no azimuth-dependent field, and an imperfect system due to possible leakage in the bubbly sound barrier along the circumference of the hose.
Acoustic streaming in porous media – homogenization based two-scale modelling
Authors: Rohan Eduard , Moravcová Fanny
Published: June 2024

A homogenized model of the acoustic streaming (AS) in rigid porous periodic structure is presented. Using the classical perturbation approach, the first and the second order subproblems arising from the N-S equations governing the fluid dynamics in the pores are obtained and further homogenized. The driving force of the permanent flow is obtained due to the time average of the nonlinear advection terms expressed using the first order acoustic harmonic fluctuations. Homogenization of the 1st order problem yields the dynamic Darcy flow mode governing the wave response. This is employed to constitute the streaming source term involved in the 2nd order homogenized problem for time-averaged pressure field. The AS can be observed at both the macroscopic and the microscopic levels. While the acoustics-driven microflows are observed for any microstructure, the macroscopic AS depends on the porous microstructure geometry and boundary conditions. We propose a solution method based on the spectral analysis of the characteristic microscopic dynamic Stokes flow. The AS phenomenon in the homogenized medium is illustrated using 2D examples of periodic porous microstructures.
A comparison of high frequency force balance mode shape correction approaches for predicting wind effects on a high-rise building
Authors: Mahdi Salehinejad M. , Fai Li Yin , Ma Quincy , Flay Richard George James
Published: June 2024

The wind loads on high-rise buildings can be predicted from the high frequency force balance (HFFB) technique. This experimental technique is widely accepted among wind and structural engineers due to its simplicity and adaptability to obtain wind-induced loads and dynamic response of tall buildings. But, for the general case of non-linear and combined sway and twist mode shapes, analysis of HFFB measurements gives rise to serious challenges and various techniques have been developed using significant assumptions. In this study, a 1:300 scale model of Building A, a benchmark tall building geometry has been chosen to perform HFFB tests in a closed-circuit boundary layer wind tunnel. It has complex 3D mode shapes combining sway and twist motions. First, the base shears, overturning moments and torques for different wind directions were measured. Subsequently, different HFFB mode shape correction approaches were examined for estimating the dynamic wind effects using modal analysis in the time domain. Furthermore, the high frequency pressure integration (HFPI) wind tunnel technique was utilised to measure surface pressure information in separate tests to obtain the more precise wind effects results for validation of the HFFB predictions. The power spectral densities (PSDs) of aerodynamic base overturning moments and torques determined from both techniques are compared. The PSDs and variance coefficients of generalised wind forces for the first three modes are calculated and compared to each other to investigate the accuracy of the different HFFB-based analysis approaches. Also, the statistical properties including standard deviations and peaks of tip acceleration and tip displacement time histories are computed for comparison. The results show that the HFFB approaches overestimate the dynamic wind-induced responses and have some weakness for twist prediction. It is found that the HFFB methods with same wind loading correlation state generally seem to perform in a similar manner.
A probabilistic approach to the Poffenberger-Swart bending stress of conductors subject to aeolian vibrations
Authors: Foti F. , Denoël V. , Martinelli L. , Perotti F.
Published: June 2024

Overhead electrical transmission line conductors are prone to aeolian vibrations, resulting from the alternate shedding of vortices in the wake of the cable. Aeolian vibrations are characterized by small-amplitude high-frequency flexural oscillations and, whenever not properly controlled, can induce wear damage and fatigue failures of the conductor. The standard technical approach to the assessment of aeolian vibrations and residual life of overhead conductors is based on the Energy Balance Method (EBM) and the Poffenberger-Swart formula for bending stresses. This approach relies on the main simplifying assumption of mono-modal oscillations. Typical aeolian vibration records, however, clearly show that several modes can be simultaneously excited due to wind variations in time and along the span. In this work a new approach is proposed for the prediction of aeolian vibrations of conductors within a probabilistic framework. The proposed approach allows to account both for non-linearities typical of internal damping of metallic cables and multi-modal contributions to aeolian vibrations in a straightforward and mechanically sound way. The proposed approach paves the way to a full probabilistic description of the Poffenberger-Swart bending stresses, making a further step towards a more refined methodology to define of the expected life of overhead conductors.
Mechanical behavior of ship to shore container crane subjected to different stochastic wind actions.
Authors: Solazzi L , Zrnić N
Published: June 2024

This research aims to evaluate and compare the mechanical behaviour of a real crane subjected to wind actions. These are schematized in three different ways, i.e. considering wind velocity variable in time (two models) and the second one considering constant in time (as defined in the standards for designing the cranes). The fluctuation was estimated by adopting two power spectral models: Eurocode and the IEC Kaimal turbulence mode. The wind velocity and the resulting forces were determined by developing a specific Mathcad program. Through a crane solid model, it was possible to make a finite element model and then perform the numerical analyses by Ansys software. The elaboration of the numerical results shows, especially in terms of maximum displacement, that the two spectral models show very similar results, which are greater concerning the one obtained considering constant velocity; the displacement increment is approximately of three times. The research was extended also to the crane supports reaction. By adopting a variable wind action, the constraint reaction also takes on negative magnitudes, demonstrating the real possibility of crane overturning. The research is still under development especially to assess whether the results are extendable by adopting other wind turbulence models.
Comparative study of experimental assessment methodologies for the dynamic characterization of elastic elements
Authors: Liravi Hassan , Arcos Robert , Clot Arnau , Conto Kenny F.
Published: June 2024

In this paper, four distinct methods for the experimental assessment of the dynamic stiffness of elastic elements in a laboratory environment are compared. The comparison has been done experimentally in a simple mass-element-mass-isolator test rig based on the proposals presented in ISO 10846 by testing an elastomeric mat specimen. The four existing experimental approaches compared are the direct and indirect methods proposed by ISO 10846, a frequency-independent characterization method based on the transmissibility peak, and an existing methodology for in situ applications that in this work has been proposed to be used for laboratory assessments. In order to compare these methodologies, the vertical stiffness of the under-ballast mat sample has been obtained through the four methods proposed. The application of the approach also showed that the rotational degrees of freedom test rig massive elements must be considered in the characterization of elastic elements using this particular test rig configuration, especially when their rotational stiffness is low. Results show that the in situ method applied to laboratory-based setups allows for obtaining accurate results for a wide range of frequencies with a simple experimental setup.
Regression-based Evaluation of Novel Intensity Measures under Alternative Ground Motion Record Sets
Authors: Kadas K , Yakut A
Published: June 2024

Intensity measures are generally considered as the fundamental properties of strong ground motion records and are widely utilized in performance-based seismic design methodology to relate the seismic hazard levels to the structural damages, or seismic response in general. Recent two decades have exhibited several studies proposing new alternatives that have intended to reduce the variability in seismic demand predictions. Although there exist several simple-to-advanced scalar and vector ground motion intensity measures; the literature is limited in the number of comparative studies investigating the efficiency of these parameters, especially in the entire response range of structures. This study aims at evaluating the correlation of major engineering demand parameters with novel simple-to-advanced intensity parameters following a regression-based approach to calculate efficiency metrics. For a group of low-to relatively high-rise reinforced concrete frames, alternative ground motion record sets have been formed considering different simple scalar intensity measures including peak ground acceleration, peak ground velocity, acceleration spectrum intensity, velocity spectrum intensity and spectral acceleration at the fundamental period of the structure of consideration, and utilizing these record sets, nonlinear time history analyses have been performed using OpenSees software to obtain key engineering demand parameters of the multi-degree-of-freedom systems. The correlation performance of novel scalar and vector intensity parameters have been quantified by evaluating regression models formed in between demand parameters and intensity measures. The regression-based approach has assisted to rank the ground motion intensity parameters according to their efficiency in terms of reducing the variability in response. The results of this comprehensive study display the relative correlation performance of scalar and vector forms together and mark particular scalar parameters as ‘best candidates’ for reliable loss estimation studies, despite their simplicity.
Sensitivity Analysis of the Seismic Response of Steel Moment Frames Under Different Earthquake Scenarios
Authors: Torres-Rodas Pablo , Fayaz Jawad , Medalla-Riquelme Miguel
Published: June 2024

This research examines the influence of the two main types of earthquake mechanisms (i.e., subduction and crustal) on the seismic response of steel moment frames (SMFs). Nonlinear time history analyses are conducted on five archetype SMFs using two suites of selected unscaled recorded ground motions. The first suite consists of records from subduction earthquakes, while the second suite consists of unscaled crustal ground motions that are spectrally equivalent to the subduction ground motion suite. The differences between the two seismic environments are analyzed by conducting a sensitivity analysis of the seismic response of the SMFs against ground motion intensity measures. The results indicate that peak floor accelerations and inter-story drift ratios under subduction earthquakes are statistically higher than their counterparts from crustal earthquakes. On average, peak floor accelerations and inter-story drifts of the SMFs are amplified by 1.43 and 1.13, respectively, when subjected to ground motions from subduction sources.
In-situ characterization of Soil Structure Interaction through measurement of Impedance Functions
Authors: Clément J , Lancieri M , Bouhjiti D , Semblat J F , Richard B
Published: June 2024

In situ characterization of structural behaviour under seismic hazard provides an opportunity to acquire experimental data that improve our understanding of soil-structure interaction (SSI). Experimental programs such as Lotung and Hualien in Taiwan, EuroProteas in Greece and NUPEC in Japan, are amongst the most known. Such investigations aim at studying a structure with a rigid shallow raft and measuring the seismic impedance functions at soil-foundation interface. Indeed, impedance functions are by far the most widely used tools to study SSI. In this paper, considering feedbacks from these in situ tests, we aim at assessing the feasibility to acquire measurements of the seismic impedance functions for any structure with a rigid shallow foundation. To test the proposed methodology, we carry out a laboratory test with a small-scale device: the soil is represented by a model material (silicon rubber block) and the foundation by a cylindrical shaker inducing monitored harmonic vertical forces on the silicon rubber block. Experimental tests are paired with numerical simulations to identify, by inverse analysis, unknown parameters and to compute the order of magnitude of displacements and forces within the system. This paper presents the laboratory test setup, the experimental design, and the results of the associated simulations.
Model of coordinated crowd dynamics
Authors: Racic V. , Gazzola F.
Published: June 2024

This paper presents a mathematical model of synchronisation of multiple people during cyclic activities such as walking, running, jumping and bouncing. Providing that quality models of individual loading for these activities do exist, the sync model is the key component towards an urgently needed yet reliable model of artificial dynamic loading due to multiple active occupants. A model proposed here describes the effect of external and internal factors on the crowd dynamics. The former includes periodic external stimuli on the body motion of individuals, such as perceptible vibration of the ground and music beats. The later addresses the mutual interaction between individuals, such as possibility to see, hear or touch each other. Modelling approach is inspired by the existing models of coupled pendulums while the governing equations feature Mathieu-type behaviour. For the sake of simplicity and efficiency, the model is kept linear and deterministic. All modelling parameters have a physical interpretation and their values can be calibrated to match experimental measurements.
Dimensioning and realistic design of a novel based negative stiffness seismic isolator
Authors: Florakis Georgios I. , Kapasakalis Konstantinos A. , Antoniadis Ioannis A. , Sapountzakis Evangelos J.
Published: June 2024

Seismic isolation, which at first used only for special applications, is nowadays gaining increased popularity in the field of protecting existing structures from seismic loading and it even constitutes one of the standard methods for seismic upgrade. This method can be achieved with various devices, with elastomeric bearings being the most commonly used. The main drawback of these devices is that they permit large horizontal displacements in every direction. An effective approach to mitigate these responses under earthquake events is an advanced negative stiffness damped system, termed as KDamper, which its dynamic performance has been demonstrated in recent studies. In this paper, an extension of the initial device, the Extended KDamper (or EKD), is presented. The structural form and its negative stiffness mechanism are introduced with special emphasis placed on its dimensioning and its indicative design. More specifically, for a reference SDOF system with a mass of 1tn, the components of the EKD are realistically designed and a detailed assembly of the device is presented. The final model proves that the proposed device is realistic and within reasonable technological capabilities. To verify and evaluate the feasibility of this device, a numerical case study is also conducted on the SDOF system subjected to 30 artificial accelerograms. The results and the comparison with conventional and high damped elastomeric isolators demonstrate that the Extended KDamper can reduce both structural displacements and accelerations, proving its effectiveness and superiority over the other isolation techniques.
System identification based appraisal of soil structure interaction in elevated water tank for various reservoir conditions
Authors: Gautam Dipendra , Rimal Hariram , Olafsson Simon , Rupakhety Rajesh
Published: June 2024

Due to the lack of information regarding structural details and construction technology, finite element analysis based results may be dubious for aging structures. The results will not confirm the effect of soil structure interaction either since back analysis based assumptions may not exactly represent the behavior of soil and structure accurately. To this end, realistic material properties as well as dynamic characteristics are required for a reliable numerical model. This study reports the dynamic characteristics of a 50-year-old pre-code overhead water tank constructed with smooth bars. Ambient vibration records were taken for empty, half, and full reservoir conditions. Parametric identification using the numerical algorithm for subspace state space system identification (N4SID) is performed to estimate the modal properties of the 14.43 m tall water tank. The fundamental vibration frequencies of the tank for empty, half, and full reservoir conditions are estimated as 1.1 Hz, 0.93 Hz, and 0.77 Hz, respectively. We also created the numerical model of the tank with and without soil structure interaction. The fixed base analysis resulted in the fundamental vibration frequencies of 1.21 Hz, 1.02 Hz, and 0.86 Hz, respectively for empty, half, and full reservoir conditions. Similarly, the fundamental vibration frequencies are estimated as 1.08 Hz, 0.91 Hz, and 0.78 Hz, respectively for empty, half, and full reservoir conditions when soil flexibility is considered. The results highlight that system identification-based fundamental vibration frequencies are better captured by the model created incorporating soil flexibility. We conclude that soil structure interaction is vital to be considered for special structures such as water tanks in active seismic regions with loose soil deposits.
SHM approach with indirect load measurements and Kalman update of state and model parameters
Authors: Kähler Philipp , Petryna Yuri
Published: June 2024

The present contribution is dedicated to the development of advanced approaches for structural health monitoring (SHM) of civil engineering structures. The approach consists of two principal parts, a continuous load monitoring system (LMS) and a continuous state and condition monitoring system based on Kalman Filter update. The overall approach can serve as a kind of Digital Twin for SHM. The measurement data assimilation with a physically based structural model by use of Kalman Filters can provide reliable state predictions if the actual load history is known. To overcome this problem, the present work proposes a two-step update procedure. The first step contains a cluster of Convolutional Neural Networks for the traffic load identification, including its magnitude, mixture, position and velocity. The obtained numerical results show a very good correlation between predicted and reference data. In the second step the identified loads are used as input for the Kalman Filter updates. The results of a second numerical example show that the model parameters like stiffness, damping and mass can be continuously predicted even in presence of sudden changes and permanent uncertainties.
Reusable Miniature Piezo-Magnetic Sensor for Rapid Application of Electro-Mechanical Impedance Technique on Steel Structures
Authors: Gupta Ashok , Aulakh Dattar Singh , Rawat Divya Singh , Bhalla Suresh
Published: June 2024

In the last two decades, the electro-mechanical impedance (EMI) approach has been established as an effective technique for structural health monitoring (SHM) of civil structures. When employed in the EMI technique, piezo sensors exhibit extremely high sensitivity towards structural damage. However, the instrumentation of piezo sensors to a structure requires permanent bonding, which increases the complexity and possibility of deterioration over time. Additionally, large structures require numerous sensors, which disturb the monitoring economics. This demands an urgent development of reusable piezo sensors for an economical and effective monitoring setup. Accordingly, this paper focuses on developing magnetic reusable piezo sensors for damage monitoring using the EMI technique. In this study, three variants of the advanced reusable piezo sensor using a magnet is fabricated and investigated for damage detection and localisation on the steel plate specimen. The repeatability of all the piezo-magnetic sensors is evaluated by estimating the coefficient of correlation. Root mean square deviation (RMSD) is estimated between the healthy and damaged states to locate the damage. All the variants of piezo magnetic sensor are effectively able to capture the damage with good sensitivity.
Structural mitigation measures to archaeological wooden Viking age sledges based on calibrated FEM models using advanced vibration measurements
Authors: Ellingsen Ståle , Hauer David , Carioti Mattia , Kosche Florian , Vedholm Kjetil , Brekke Arild , Gjestvang Morten
Published: June 2024

The Viking Ship Museum in Oslo, Norway, houses the world’s largest collections of artefacts from the Viking era and holds the best-preserved Viking ships in the world. It is being expanded to provide new exhibition areas, improving both the visitor experience and the physical conditions for the objects on display. Three extremely fragile alum treated sledges are secured onsite as they are considered too fragile to move off the premisses. Finite element models are developed as a tool for understanding the sledges’ static and dynamic behaviour and the models are used to design effective mitigation measures applied to the sledges’ existing support systems. The models are established using highly detailed geometry 3D scans. They are dynamically calibrated using advanced vibration measurements identifying the sledges’ eigenfrequencies with corresponding mode shapes. The models are also calibrated using load deformation measurements with controlled loads applied to the sledges’ support systems.
Effects of wind-induced vibrations in tall buildings on cognitive work performance, comfort, and wellbeing of the occupants
Authors: Heshmati K , Shahabpoor E , Darby A , Walker I , Ghanbari S
Published: June 2024

Tall buildings inherently have low natural frequencies, excitable by wind loading through buffeting and vortex shedding. Such vibrations can cause discomfort or even fear in the occupants which is a design failure from vibration serviceability standpoint. Current wind-induced vibration serviceability guidelines such as ISO10137-2007, have proposed their acceptability criteria based on human perception of vibrations. However, recent studies suggest that such perception thresholds may not be an appropriate measure of vibration acceptability. Rather, more direct factors such as influence on work (both cognitive and physical) performance, health and wellbeing, and the emergence of mild motion sickness (sopite syndrome), should be used to assess ‘acceptability’.

This study provides experimental evidence of the effects of wind-induced vibrations on cognitive work performance, comfort, and wellbeing of the occupants. The state-of-the-art motion simulator facility, located at the University of Bath (VSimulator) was used to simulate bidirectional random vibrations, typical of tall building response due to wind loading. Under fully controlled conditions, research participants were exposed to six different motion conditions, as a cross-product of two frequencies and three peak accelerations, five of which were deemed acceptable for office buildings according to ISO-10137. Both objective and subjective psychological measurements were carried out to evaluate work performance, comfort, and wellbeing of participants subjected to these different motion characteristics. The results showed that both peak acceleration and frequency of motion had adverse effects on work performance, comfort and wellbeing of participants and showed evidence of the onset of sopite syndrome symptoms during even relatively short (∼2 hour) exposures. It was concluded that even for motion conditions with peak acceleration magnitudes below the threshold of conscious perception, there were negative consequences, especially as exposure to such motions caused participants to experience sopite syndrome. The data here suggests that buildings constructed to current standards might lead to negative consequences for wellbeing and work performance even when people are not consciously aware of any motion. Current serviceability criteria might be insufficient to address acceptable levels of wind-induced vibrations in tall buildings and future design criteria could be based on how vibrations affect health, wellbeing and performance rather than simply on the perceptibility of vibrations.
Retrofitting of typical existing school buildings through seismic vulnerability assessment
Authors: Tabernero Rodrigo , Ambrosini Daniel , Curadelli Oscar
Published: June 2024

Extensive damage to school buildings has been observed around the world during past earthquakes and their potential vulnerability and seismic retrofit alternatives need to be assessed. In regions of moderate and high seismic risk, there is a probability of structural damage and even collapse of school buildings, resulting in the loss of life of hundreds of children. In this work, seismic performance of standardized existing school buildings, lacking proper seismic design, is assessed by means of a numerical study. A 3D nonlinear finite element model is developed, and failure analyses are performed using a set of 10 seismic records scaled at increasing values of peak ground acceleration (PGA). Four seismic retrofit alternatives are proposed and evaluated following two major design approaches, stiffening and flexibilization. For each considered case, seismic fragility curves are derived, and seismic risk is assessed as limit state probability in 50 years, considering PGA as a random variable. Results obtained from this work allow the identification of the contribution of each proposed alternative to the reduction of seismic risk of the school buildings. A very simple and low-cost alternative, such as flexibilization by decoupling the facades from the lower floors, was found to produce excellent results.
A study on the effects of torsional spillover on an ideally controlled three dimensional structure
Authors: Abhishek S , Pilakkat Deepthi , Chakraborty Sanjukta
Published: June 2024

In this study, the adverse effect of an inadequately designed input control force was experimentally investigated in view of the excitation of the torsional modes of a structural system. The initial formulation was developed based on a generalized symmetric structural system under PD, PI, and PID control strategies that aimed at controlling the lateral modes of the structural system. Based on the control design, an experimental investigation was carried out on a single-story symmetric frame structure under the three designed control conditions using an Arduino-based data acquisition system. The structure was subjected to sinusoidal excitation with different frequency ratios and white noise excitation. In the next step, the system was perturbed by reducing the column stiffness in a way, that made the center of mass and the center of stiffness different. The perturbed structural system was also provided with the same initially designed input control forces under the same set of external excitations. Responses of the different control algorithms were recorded and analyzed considering the excitation of the torsional mode of the perturbed system. A significant excitation of the torsional mode was noticed in the study, particularly for an excitation near the resonating frequency of the lateral mode of the system.
Magnetic Control of a Simple Pendulum with a Moving Pivot Point
Authors: Atzampou Panagiota , Meijers Peter , Tsouvalas Apostolos , Metrikine Andrei
Published: June 2024

The present study introduces a magnetic PD control technique for the case of a simple pendulum driven by a sinusoidal motion of its pivot. The results attained demonstrate a good control performance for all the excitation cases of pivot point motion considered. The motion of the mass of the pendulum is successfully attenuated even when the pivot excitation is at the natural frequency of the pendulum. Furthermore, a fixed desired position can be achieved with small error and no saturation of the actuation present at steady-state. The initial distance between the magnet and the mass that ensures an efficient motion control is derived analytically and is validated by numerical simulations. The magnetic control method proposed serves as promising foundation for a non-contact position control technique for offshore wind turbine installation purposes.
Optimal design of pendulum-tuned mass damper for the vibration control of offshore wind turbines with a flexible monopile foundation
Authors: Colherinhas G B , Petrini F , de Morais M V G
Published: June 2024

This paper presents an optimal design of a passive-adaptive Pendulum-Tuned Mass Damper (PTMD) to mitigate the structural vibrations of an Offshore Wind Turbine (OWT) with a flexible monopile foundation considering the Pile-Soil Interaction (PSI). The OWT is based on the 5-MW baseline proposed by the National Renewable Energy Lab. The PSI is designed by a pile modeled as beam-column elements supported by nonlinear springs for lateral loads (p-y curves) and axial loads (t-z and Q-z curves), applied at the nodal points between the elements. The estimation of wind and wave spectra, as well as the hydrodynamic and aerodynamic loads, are conducted by using an in-house built MATLAB® routine working together with an ANSYS® 3-D finite element global model for evaluating the resultant peak displacement response at the OWT hub by a power spectral density analysis. Optimum design cases of PTMD parameters are obtained by a parametric analysis evaluating the dynamic response along and across directions at the hub and the resultant stress at the base of the tower. These responses and stress are evaluated as a function of the wind velocity at the hub.
Frequency-amplitude decoupling in the Gentle Driving of Piles (GDP) method: shaker design and experiments
Authors: Gómez Sergio S. , Tsetas Athanasios , Middelplaats Lennart N. M. , Metrikine Andrei
Published: June 2024

This paper presents a new shaker design for the Gentle Driving of Piles method. Specifically, a lab-scale vibratory device has been developed that can simultaneously apply axial and torsional vibrations, both possessing frequency-amplitude decoupling. This design was implemented and tested in a lab-scale experimental campaign, where both pile and soil were extensively instrumented. The monitoring of the dynamic pile and soil behaviours during driving with various installation settings is of utmost importance to comprehend the governing mechanisms of the process. In that manner, the optimization of pile installation may be realized both for axial vibratory driving and GDP. In this work, the frequency-amplitude decoupling is pivotal, as it is showcased that both enhanced installation performance and reduced power consumption can be attained with proper selection of the installation settings and exploitation of high-frequency torsion.
Optimization Problem of the size-scale for a Foldable Chain Scissors Structure based on Stress Analysis
Authors: Yoshida Keigo , Ario Ichiro , Zawidzki Machi , Hama Yuta
Published: June 2024

Emergency bridges are used to restore the lifeline of damaged bridges after disasters. However, the design specification of existing emergency bridges do not afford rapid bridging. Therefore, a trial deployable bridge (Scissors Bridge) using a scissors structure that folds compactly has been experimentally produced. But, the assembly process for the bridge has not been considered and there are no practical design examples or design methods for scissors bridges. In this paper, as for existing bridges, we established a design method of scissors bridges when considering the live load. In addition, a general-purpose member cross-sectional dimension optimization method, aimed at minimizing weight, was developed and proposed. Considering the problem of insufficient strength of the scissors bridge, the optimum reinforcing pattern and its cross-sectional dimensions were determined through two methods of reinforcement and optimization of the cross-sectional dimension of the member. Finally, a trial of practical design calculation was performed using the results of the study to determine whether a scissors bridge satisfying the standard of the Specifications for Highway Bridges can be designed.
mechanical bridge machineries: phenomenological modelling and experiments
Authors: Sektani K. , Tsouvalas A. , Metrikine A.
Published: June 2024

The reassessment of existing mechanical bridge machineries in The Netherlands has prompted the development of acceptance/rejection criteria for evaluating their structural safety. The current design code in The Netherlands [1, 2] establishes an ultimate limit state, primarily intended for the design of new machineries, employing a conservative approach with upper bounds on maximum loads. However, to reassess existing bridges and prevent unnecessary replacements, a more accurate prediction of the dynamic response is essential. The current code relies on a linear single degree of freedom (SDOF) dynamical system [3], which is found to inadequately predict the dynamic response of existing machineries across all load cases [4]. This discrepancy can be attributed to, for instance, the neglect of time-dependent and discontinuous model parameters of the machineries [5, 6, 7].

Given that each movable bridge possesses a unique set of fixed parameters, on-site measurements of a single bridge do not provide the generic information required for the design and/or reassessment of existing structures in general terms. In this paper, a novel experimental setup is presented which allows the investigation of a wide range of variations in order to capture the dynamics of the powertrain in a class of bridge machineries. Additionally, a modelling methodology is developed to overcome the limitations of existing calculation rules, by incorporating base excitations, damping, and other relevant variables of the physical system, which are currently neglected by the code. A subsequent comparison with measured data, demonstrating the accuracy of the proposed methodology for different driveline compositions, machinery configurations and braking systems is included in the thesis of this research, due to page limitations.