bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure-to-human interaction during rhythmic jumping
Authors: Abraham Nimmy Mariam , Zivanovic Stana , Williams Genevieve
Published: June 2024

Rhythmic jumping is the largest human-induced load that occurs on assembly structures. It involves a repeated alternation between contact and flight phases at a given frequency. Human loading on the structure takes place during the contact phase while the load is zero during the flight phase. When a structure vibrates, the displacement profile of the structure interacts with human movement during the contact phase. This structure-to-human interaction could result in an alteration in the jump height and the contact duration, and thus the peak ground reaction force (GRF) attained. This paper presents an experimental study that investigates the influence of jump timing relative to the platform position in its vibration cycle on rhythmic jumping. The vertical harmonic vibrations of the platform had a magnitude of 2.0 m/s2 and a frequency of 2.8 Hz. Data were collected from a test subject who was instructed to jump at a frequency of 2.8 Hz in such a way as to land at four different instances of the vibration cycle. These were landing on the platform while at its (i) reference position and on the way down (mid-down), (ii) lowest position (trough), (iii) reference position and on the way up (mid-up), and (iv) highest position (peak) in the vibrating cycle. The timings were presented to the test subject through a metronome beat. The peak toe clearance, impact ratio, contact ratio and frequency of jumping were compared on a cycle-by-cycle basis between the four cases of target landing timing as well as on a non-vibrating platform. The impact ratio and the peak toe clearance were positively correlated with each other and negatively correlated with the contact ratio. Furthermore, the jump height and consequently the peak GRF were higher, and the contact ratio was lower for landing at the trough and the mid-up positions, compared to those on the non-vibrating platform. This is the result of the platform helping the test subject to perform jumps of greater impact in case of landing near the trough and the mid-up positions of the platform.
Experimental insight into human footfall loading for walking on vibrating surfaces
Authors: Zhang Sigong , Lin Bintian , Williams Genevieve , Živanović Stana
Published: June 2024

Current design methods for vibration serviceability assessment of pedestrian structures are generally based on footfall loading models representing walking over rigid level surfaces rather than vibrating surfaces that might modify the loading due to human-structure interaction. A two-year project was carried out to identify vertical vibration conditions under which the human-structure interaction occurs. As part of the testing program, participants were asked to walk over either an outdoor footbridge or a rigid ground surface at various step frequencies. Ground reaction forces were measured by using insole sensors, and the effects of vibration amplitudes and walking to vibration frequency ratios on these forces were examined. It was found that the vibrating surface has no discernible effect on the step-to-step variability. Comparison of dynamic load factors generated on the vibrating footbridge with those on the rigid-level ground revealed that while the vibrating surface increased the first dynamic load factor, it actually reduced it when the step frequency approached the fundamental frequency of the structure.
Application of empirical green function method for synthesis of response spectrum compatible time histories
Authors: Ji H Y , Lee S J , Kim J H
Published: June 2024

In recent seismic design codes, accelerograms recorded in areas with similar conditions to the target site are required for seismic analysis. When there are no available recorded ground motions of sufficiently large intensities, small intensity ground motions need to be appropriately amplified. In this study, the Empirical Green’s Functions (EGF) method by finite earthquake fault modeling was used for this purpose. The high frequency filter according to the distance between earthquake source to site was applied. The regression analysis of spectral acceleration amplifications by magnitude and hypocentral distance was performed. Finally, the methodology to determine an optimum condition for converting the recorded accelerogram into ground motion time histories compatible with the Design Response Spectrum (DRS) was suggested.
Development of an earthquake simulator for soft soils: Multidirectional Shear Testing Device
Authors: Chao C , Broere W , Jommi C
Published: June 2024

Testing soils for earthquake and dynamic loads requires advanced equipment able to assess the effects of hydromechanical coupling on the soil response. The majority of laboratory element tests are either “slow tests”, which intend to approach drained conditions throughout the soil sample in order to obtain reliable pore water pressure measurements, or “fast undrained tests”, where flow is prevented by closing the drainage lines. However, many natural loads, including earthquakes, impose a wide range of high loading frequencies, typically triggering a partially drained response in the field. Although the rate effect plays an important role in soil behaviour, its investigation is hindered by the limitations of existing equipment. In addition, the ability to apply multidirectional loading to soil elements in the laboratory is important to fully understand the soil response under earthquakes. Currently, multidirectional simple shear devices are used to study the soil behaviour under earthquake loadings. Nevertheless, many shear devices suffer from stresses and strains non-uniformities, which could potentially mislead data interpretation and constitutive models development. This paper presents an innovative multidirectional shear device developed in the section of Geoengineering at TU Delft, which can apply higher loading frequencies compared to previous equipment and a wider variety of multidirectional cyclic loading patterns. The apparatus is equipped with advanced sensors, also developed at TU Delft, to capture the local response of specimens. The sensors are installed to reduce a priori assumptions on the soil response, better interpret the element experimental results and further investigate the rate effect of applied loading. Preliminary performance test results are provided to illustrate the complex load conditions which can be achieved.
Bidirectional Real-Time Hybrid Test on a Steel Column Virtually Connected to a Reinforced Concrete Substructure
Authors: Bodnar B. , Titirla M. , Gatuingt F. , Ragueneau F. , Larbi W. , Deü J.-F.
Published: June 2024

This paper uses a hyper-reduced order model (HROM) to perform bidirectional Hardware-in-the-Loop (HiL) real-time hybrid tests on a steel column virtually connected to a two-story reinforced concrete (RC) substructure under earthquake conditions. Two hydraulic dynamic actuators apply the horizontal displacements at the top of the specimen. Nonlinear multi-fiber beam elements are used to model the numerical substructure. The computational cost of the finite element (FEM) analysis is reduced using a Proper Orthogonal Decomposition (POD) Unassembled Discrete Empirical Interpolation Method (UDEIM) with a non-iterative α-Operator Splitting (α-OS) time integration scheme. Data acquisition is carried out using a Linux® real-time (RT) target, while the dynamic analysis is performed on a Windows® host computer running custom procedures implemented in MATLAB® software. A LABVIEW® interface connects both systems via a lossless stream network. Results on the present case study show that: (1) using a HROM can accelerate costly nonlinear dynamic analyses so that they can be run above the sampling period of the ground motion during hybrid tests, and (2) using lossless stream networks calling a MATLAB® kernel efficiently combines the high data acquisition speed of RT targets (i.e., 10 µs per sample) with the computing power of host computers since the data exchange is quasi-instantaneous.
Robust adaptive compensation of force-based RTHS testing with uncertain compliance spring and force measurement noise
Authors: Araya Diego , Fermandois Gastón
Published: June 2024

This study proposes a force-based real-time hybrid simulation (RTHS) framework with robust compliance-based adaptive compensation. Adding a compliance spring between the loading actuator and a rigid specimen is an alternative to measure restoring forces through load cells with significant noise. But, we considered compliance spring and load cell properties to be uncertainties. Robust adaptive model-based compensation will be employed to overcome force-tracking errors between substructures. The proposed methodology will be verified in a virtual RTHS environment, where parametric studies will be considered to check the system’s robustness over uncertain compliance and specimen properties.
A territorial scale analysis based on a map-oriented database for the out-of-plane seismic behaviour of masonry structures
Authors: Yu Chenjie , Toshniwal Shubham , Meijers Sander
Published: June 2024

Since 1986, earthquakes have occurred in East Groningen, but most buildings made of unreinforced masonry have not been designed for earthquakes, which must now withstand magnitude 4 earthquakes. This has created an urgent need to assess large amounts of buildings in a fast but reliable manner.

The out-of-plane behaviour is important for seismic assessments of unreinforced masonry buildings. Although the most accurate analysis method to determine the out-of-plane response of such walls is non-linear time-history analysis (NLTH), non-linear kinematic analysis (NLKA) provides a simple, fast but still reliable solution due to the computational difficulties of NLTH for structures constructed of unreinforced masonry.

In this paper, the out-of-plane behaviours of masonry structures are up-scaled from a component scale to a provincial scale in a multi-scale manner. A map-oriented database is established to describe both local behaviours of walls and global behaviours of a province. The out-of-plane assessment by non-linear kinematic analysis (NLKA) is automated via the database without further calculations after the static analysis. The database provides a solid guidance to determine which detailed assessment methods will be adopted with limited data before a FEM model is built.
A novel approach for analyzing the dynamic properties of trees with fractal sympodial branching architecture: a group tree modeling
Authors: Loong Cheng Ning , Dimitrakopoulos Elias G.
Published: June 2024

It is remarkable that trees with high slenderness ratios are able to survive regular strong wind events. This phenomenon is motivating the exploration of the inherent vibration mitigation mechanisms of trees. This study examines the role of trees’ hierarchical branching architecture on their modal properties. Its particular focus is on the modal frequencies and mode shapes of sympodial trees. This study idealizes trees as fractal structures with sympodial branching architecture and proposes a new group tree modeling approach to analyze their modal properties. Analytical closed-form solutions are derived to estimate the modal properties of trees. The analysis shows that sympodial trees localize vibrations on higher order branches. Furthermore, the modal properties of trees with a specific fractal level could be self-similar, and repetitive and form recursive relations with that of the previous level. Overall, the results offer a possible explanation of how fractal branching architecture prevents trees from excessive vibration.
Application of dynamics inversion techniques to the force control of electrodynamic actuators used for active vibration absorption
Authors: Ramírez-Senent José , Díaz Iván M , García-Palacios Jaime H , Jiménez Alonso Javier F
Published: June 2024

The active vibration absorber has been successfully used, both in laboratory and actual facilities, to mitigate the human-induced vibrations taking place in lively, low-damping structures such as long-span floors or pedestrian footbridges. Nonetheless, the dynamic behavior of the electrodynamic proof-mass actuators employed for this purpose may negatively affect the overall vibration attenuation features due to the interaction with the motion of the structure under optimization. In this paper, the utilization of dynamic inversion techniques to improve the force control of electrodynamic proof-mass actuators is presented. The main idea behind this approach is to find an approximate inverse model of the actuator dynamics which, upon implementation on a real-time controller, leads to an approximate cancellation of actuator dynamics, making it behave closer to an ideal one. The selected way of proceeding also accounts for the actuator-structure interaction phenomenon. This approach may be employed to improve the performance of any force-based vibration control algorithm. Herein, the dynamic inversion techniques are applied to the well-known Direct Velocity Feedback algorithm which aims at emulating the behavior of a dashpot connected between the control point and the ground in its simplest version. The goodness of the proposed procedure has been assessed both by experimental tests performed over a full-scale composite material pedestrian footbridge existing at the School of Civil Engineering of the Technical University of Madrid. The test results show that the dynamic inversion approach improves the force tracking of the proof-mass actuator to a great extent, therefore yielding better attenuation results that those achieved with the classical Direct Velocity Feedback scheme.
Sliding TLCD for vibration control of base-isolation systems: experimental comparison with traditional TLCD and TMD
Authors: Masnata C , Di Matteo A , Adam C , Pirrotta A
Published: June 2024

In the context of hybrid passive vibration control, the effectiveness of the Tuned Liquid Column Damper (TLCD) for seismic protection of base-isolated (BI) systems has been demonstrated both numerically and experimentally. In contrast to the previous studies on TLCDs, the present study explores the possibility of equipping a BI system with a sliding model of TLCD (STLCD), until now introduced only for the suppression of wind-induced vibrations of fixed-base structures. Specifically, the proposed STLCD consists of a U-shaped tank partially filled with water, mounted on a roller support and connected to the BI system via a spring-dashpot system. The validity of the introduced mathematical model is assessed by means of an extensive shaking table testing campaign at the Laboratory of Experimental Dynamics at the University of Palermo, Italy. For the experimental tests, a small-scale model of a single-degree-of-freedom (SDOF) BI structure with the STLCD is constructed, and the effectiveness of the proposed combined control strategy is experimentally evaluated. Finally, comparisons with traditional TLCDs and TMDs are made and the control efficiency is discussed with emphasis on the reduction of the accelerations of the BI system.
Vibration Control of Wind Turbines through a Novel Reduced Column Section Approach: Numerical Application to the Onshore Wind Turbine in Sassoferrato, Italy
Authors: Rostami Rohollah , Tombari Alessandro
Published: June 2024

The Reduced Column Section (RCS) is a design approach recently proposed by the Authors to convert the transition piece of wind turbines into a passive vibration-control device. Featured with an hourglass shape and high-strength steel, the novel device combines the advantages of several approaches used in seismic engineering, such as the isolation system, the “rocking approach” design as well as the reduced beam section approach. Through proper tuning, the proposed device can be designed to modify the first natural frequency of the wind turbine and to localize the maximum stresses onto the device, protecting the remaining parts of the wind tower and foundation.

In this study, the seismic response of an onshore wind turbine subjected to earthquakes is investigated. The numerical model is developed to reproduce a real onshore wind turbine located in Italy. Operational modal analysis is performed, and the experimental modal frequencies are used to validate the numerical model. Code-compliant spectrum-compatible nonlinear analyses are performed to explore the benefits obtained by adopting the novel RCS approach. Furthermore, an incremental dynamic analysis is conducted to evaluate the dynamic mitigation induced by the proposed RCS device. Results show that the proposed device is able to efficiently mitigate the effective stresses on the wind tower wall by up to 70% compared to the stresses on the existing structure.
Influence of tuned inerter dampers on inelastic seismic performance of building frames
Authors: Sachdeva Rohit , Manohar C S
Published: June 2024

The paper aims to analyse the dynamic behaviour of frames fitted with tuned inerter dampers (TIDs), accounting for various aspects of inelastic frame behaviour, bending-torsion (B-T) coupling, irregularities in elevation, and transient nature of the ground motions. An inerter is a mechanical two-terminal device that creates a force proportional to the relative acceleration between its terminals. It has the potential to produce high dynamic mass while its static mass remains fixed. To gain understanding about its working, an inerter was fabricated and installed in a 3-storey shear-frame model for experimentation and numerical validation. Then, we focus on the behaviour of a 5-storeyed inelastic building frame model fitted with a TID on the ground floor and subject to transient earthquake support motion. The presence of TID is observed to be beneficial in terms of reducing response features such as the ductility demand, hysteretic energy absorbed, and measures of global damage. Finally, a one-story frame, asymmetric in plan, was subjected to two-component earthquake support motion to investigate the influence of the location and number of TIDs on the B-T coupled inelastic behaviour of the frame. The study established the beneficial aspects of incorporating TID(s), while also highlighting the need for further parametric study to design and determine the optimal position of TIDs for achieving best performance.
An approach to define the minimum detectable damage and the alarm thresholds in vibration-based SHM systems
Authors: Kamali Soroosh , Quqa Said , Palermo Antonio , Marzani Alessandro
Published: June 2024

This paper proposes an approach to defining the alarm thresholds for vibration-based structural health monitoring (SHM). The approach uses natural frequencies identified from the acceleration response of the monitored structure and is based on the concept of Minimum Detectable Damage (MDD), namely the smallest damage size in each structural element associated with a given probability of detection (POD) and probability of false alarm (PFA). The approach is demonstrated using natural frequencies computed from finite element models of the healthy and damaged structure, also accounting for temperature fluctuations and measurement noise. The approach first builds a baseline dataset of modal frequencies for a yearly thermal cycle on the healthy structure. Then, different damage conditions are simulated. For each sample of natural frequencies, a Damage Index (DI) is computed as the Mahalanobis distance between the considered sample and the baseline distribution. The alarm threshold is defined as the DI value for a given PFA. Based on the DIs obtained for the damaged structure, the POD is computed for the considered system threshold. This operation is repeated by increasing the damage entity. The MDD is thus defined as the level of damage associated with a desired value of POD. The proposed idea is tested on a steel truss bridge, where the MDD for each element is estimated by considering PFA=5% and POD=95%.
Impact force identification on a ferry dock bridge
Authors: Sibille L , Nord T S , Siedziako B , Fenerci A
Published: June 2024

There is a scarcity of literature on the monitoring of operational loads and structural health of coastal infrastructure assets. In this paper we show the very first estimates of the impact force acting on a ferry quay bridge during ferry berthing based on vibration measurements. The input and state of the structure are estimated by means of a joint input-state estimation algorithm in conjunction with a modally reduced-order finite element model. The estimated and measured accelerations are compared, and a strong agreement is found, even when only a limited number of sensors was used, paving the way for an efficient full-scale monitoring of the structure in the long term.
Assessment of dynamic loading with reverse engineering using vibration measurements
Authors: Xu T , Meijers W , Meijers SJH , Verlinde R
Published: June 2024

This paper presents the application of reverse engineering in assessing the dynamic loading on an industry steel structure. The studied steel structure is subjected to a frequently occurring plug load from the pipeline of a conveying system. This dynamic load leads to significant vibrations of the structure, and it is likely to govern the fatigue analysis. To assess the magnitude of the dynamic load, vibration measurements have been performed. Velocities in the transverse, longitudinal and vertical directions are measured at five points throughout the structure for a continuous period of seven days. A parametric finite element (FE) model of the structure is properly set up such that its eigenfrequencies match the dominant vibration frequencies found in the measurement data. Furthermore, a linear time history (LTH) analysis with impulse loading is carried out, to interpret and reproduce the measured vibrations. Two selected measurements transients, one representative excitation and one randomly selected excitation, are used to validate and fine-tune the FE model to match the vibration responses of the structure. The magnitude and duration of the impulse load is determined such that the response of the analysis model corresponds best to the measurement data in terms of the first and the second peak velocities, as well as the dominant frequencies. Lastly, a statistical analysis is performed to determine the distribution of vibration velocities over the entire measurement period. With the combination of vibration measurements, FEM analysis and statistical analysis, a good estimation of the occurred dynamic load and the amount of stress cycles in 50 years is made for the fatigue analysis of the steel structure.
Assessment of regression variabilities and biases: a demonstration in the context of structural health monitoring.
Authors: Roberts Callum , Avendaño-Valencia Luis David , Cava David Garcia
Published: June 2024

The challenge that is at the forefront of data-driven vibration-based structural health monitoring (VSHM) is the detrimental effect caused by environmental and operational variations (EOVs). Therefore, action must be taken in order to mitigate the effects of the EOVs without affecting the influence of damage. A number of regression-based approaches have been applied in VSHM, using measured environmental and operational parameters to model damage sensitive features (DSFs). In this work, a forward stepwise method is compared with Lasso regression for the purpose of regression model optimisation. The Akaike information criterion (AIC) and the variance of the covariance of the input variables are used to quantitatively assess the quality of the regression models. Additionally, the F-statistic is used to determine which DSFs should or should not be regressed. The results of the analysis showed that the reduced order forward stepwise regression had the lowest AIC and was the most appropriate model despite not having the most stable coefficient matrices. Ultimately, the choice of optimisation method has a significant impact on the quality of future predictions.
Monitoring fatigue crack growth using magnetic stray field measurements
Authors: Meijers P C , Malschaert D H , Veljkovic M
Published: June 2024

To monitor the growth of fatigue cracks in steel specimens, several methods exists. In this paper, the magnetic stray field, which is generated by the magnetisation of the specimen, was measured during loading to investigate how to utilise this data to reliably monitor fatigue crack initiation and growth. Data was collected in a series of fatigue tests on Compact Tension specimens with different force ratios. The evolution of the mean value of the dominant stray field component displayed a sensitivity to stress, plastic deformation and displacement of the specimen. By analysing the stress field induced by the loading, these three causes were distinguished from another. Crack initiation was marked by a large change of the mean magnetic stray field. Moreover, the amplitude of the magnetic stray field components showed a clear peak, at which moment 20% of the life time of the specimen is remaining, indicating that the magnetic stray field might provide a useful method to monitor the evolution of fatigue cracks.
Damage Detection in Beam Structures Based on Curvature Change Estimated from Incomplete Mode Shapes
Authors: Modesti Martina , Reynders Edwin , Lombaert Geert , Palermo Antonio , Gentilini Cristina
Published: June 2024

In this work, a procedure for damage localization and quantification in beam structures is presented. The proposed technique exploits the variations of the curvature between healthy and damaged structures, computed from the flexibility matrix. The flexibility matrix is approximated using the lowest structural frequencies and mode shapes, which can be easily derived on-site from vibration-based monitoring of the structure. Since in real-case scenarios structures can be instrumented only with a limited number of sensors, a procedure based on the expansion of the measured modal components is proposed. The presented technique is verified by testing two beam structures affected by different damages in terms of position and extension.
Uncertainty quantification of damage localization based on a probabilistic convolutional neural network
Authors: Lu HY , Mardanshahi A , Cantero-Chinchilla S , Gryllias K , Chronopoulos D
Published: June 2024

SHM is vital in quantitatively identifying engineered critical structural damage due to its potential economic and security interests. Convolutional Neural Network (CNN) is a popular method used for SHM on damage localization and classification. However, traditional CNN methods have limitations in predicting performance uncertainty and only provide point evaluations without indicating their accuracy. To address this issue, this paper introduces a PCNN framework, which combines a traditional CNN with a probabilistic layer to generate overall confidence intervals (CIs) for prediction results, as well as conditional probability distributions (CPDs) and likelihood for each prediction result. The PCNN method provides a manner to quantify the prediction uncertainty of neural networks and determine the confidence of each prediction. The paper also recommends using Leaky ReLU as the activation function, which retains negative value information. The effectiveness of the PCNN method is illustrated through case studies of carbon fiber-reinforced polymer beams with different layups. The results show that PCNN is effective in giving damage location prediction for CIs, CPDs and likelihood.
An Application of Domain Adaptation for Population-Based Structural Health Monitoring
Authors: Giglioni Valentina , Poole Jack , Venanzi Ilaria , Ubertini Filippo , Dervilis Nikolaos , Worden Keith
Published: June 2024

In the field of civil infrastructure, Structural Health Monitoring generally suffers from a scarcity of labelled damage-state data. To solve this issue, this work adopts a Transfer Learning approach for leveraging information from a source structure, characterised by a rich class of damage labels, to improve inferences on a target structure with limited knowledge. The goal is to train a machine learning algorithm on a bridge undergoing damage and to afterwards transfer the available labelled damage-state data across the members of the investigated population. Given possible differences exhibited by each structure, a domain adaptation technique in the field of statistic alignment, called Normal Condition Alignment (NCA), is applied to match different distributions in a shared feature space. The methodology is validated on a heterogeneous population composed of two numerical bridges of different geometry and materials, representing the Z24 and the S101 benchmark bridges. Finite Element Models are built to simulate healthy conditions and several damage cases. The natural frequencies describing such scenarios are considered as damage-sensitive features and thus employed to characterise the two domains and fed to a supervised learning-based classifier. The presented approach is deemed effective to provide mappings that allow the exchange of health-state information from source to target datasets, becoming a promising approach to be applied within a population of real bridges.
Random vibration response-based damage diagnosis for a population of composite aerostructures under varying operating conditions and uncertainty: experimental assessment
Authors: Spiliotopoulos P E , Fera F T , Saramantas I E , Ofir Y , Kressel I , Tur M , Konis P , Kriatsiotis I M , Sakellariou J S , Fassois S D , Giannopoulos F , Spandonidis C , Tzioridis Z
Published: June 2024

The problem of random vibration response-based damage diagnosis (detection & type characterization) for a population of 26 composite aerostructures under varying operating conditions and uncertainty is experimentally investigated. Four damage scenarios are considered in a small sample of the population: Two distinct sizes of a square-shaped delamination and two energy levels of an impact-induced damage. The analysis of the intact (healthy) population indicates rich dynamical information within the range of 0 – 2 kHz with the uncertainty factors, due to manufacturing and experimental setup discrepancies compounded with the temperature and excitation variability, to be strong enough to “mask” the effects of the considered damages, thus leading to a highly challenging damage diagnosis problem. Damage detection is tackled via two unsupervised and robust data-driven vibration-response-only methods: The first is based on the Multiple Model (MM) and the second on the Hyper-Sphere (HS) based frameworks, while damage type characterization is tackled via a hierarchical classification. All methods utilize the Multiple Input Single Output Transmittance Function (MISO-TF) in order to properly compensate for the effects of the varying excitation. The results based on hundreds of test cases indicate impressive detection performance even for the smallest level damage scenarios, with the two detection methods complementing each other, as well as very good damage type characterization, accuracy despite the limited number of damaged aerostructures.
An Exploratory Study on Data-Driven Vibration Based Damage Detection and Characterization for a Population of Composite Aerostructures
Authors: Saramantas I E , Konis P E , Kriatsiotis I M , Ofir Y , Kressel I , Spiliotopoulos P E , Fera F T , Sakellariou J S , Fassois S D , Giannopoulos F , Spandonidis C , Tur M , Tzioridis Z
Published: June 2024

This study investigates the effectiveness of four robust to uncertainty data-driven methods of machine learning type for random vibration response-only damage detection and characterization in a population of composite aerostructures under various uncertainty factors. The employed methods are based on the Multiple Model (MM) and the Hyper-Sphere (HS) frameworks using Multiple Input Single Output AutoRegressive with eXogenous excitation Transmittance Function (MISO TF-ARX) models that may account for excitation uncertainty. The methods capabilities are explored via numerous Monte Carlo simulations using digital, Abaqus based, models allowing for maximum flexibility in experimentation. Based on these, a population of 90 Carbon-Epoxy square hollow beams with lightweight composite aerostructures properties is employed taking into account manufacturing, temperature and excitation uncertainty. In addition, early-stage debonding and delamination damages are inserted to a portion of the population at two levels per damage and at two distinct locations for the methods evaluation. All considered damages affect slightly and similarly the structural dynamics overlapping with the effects caused by uncertainty in order to increase the diagnosis (detection & characterization) difficulty and explore the methods’ performance limits. The results indicate almost perfect detection in all considered damage scenarios except from the low level debonding, while damage characterization (type, location and level), which is performed via a hierarchical classification scheme, is very promising.
Application of fixed-lag Kalman smoother for nonlinear state estimation
Authors: Al-Hagri Ammar , Caglio Luigi , Stang Henrik , Katsanos Evangelos
Published: June 2024

During their lifetime, civil structures and infrastructures are subjected to environmental and human-induced hazards that may lead to structural damages or, in some cases, to full collapse. Such failures are associated with increased risk for life and limb, while also environmental and monetary losses may be triggered with adverse societal footprint. Consequently, it is highly relevant to screen reliably the condition of the structural systems and, if necessary, to intervene to safeguard the structural integrity and avoid undesirable failures. To this end, several structural health monitoring schemes are becoming a key element for various structures and infrastructure systems, enabling the continuous assessment of their state. The latter, in turn, can allow for detecting damages at an early age, avoiding extensive failures or even sudden collapse. In order to identify the failures due to excessive loading events, measured time-varying responses are frequently used as the basis for damage detection. However, in reality, practical restrictions exist in mounting sensors on all the locations of the structure that an engineer would prefer to know the structural response. For example, sensing data from the submerged part of an offshore platform is commonly not available, while the latter is also valid for various locations in bridges where the access is limited to apply and operate sensors. Therefore, the available measured data is mostly incomplete since only a limited number of sensors can be employed. Additionally, various noise sources usually pollute the sparsely measured responses, and the overall quality is compromised. As a remedy to this challenge, a new framework is proposed herein to aid in estimating reliably the nonlinear dynamic response of a structural system with the use of limited and noisy measurements. Especially, a Kalman smoothing technique called the fixed-lag algorithm is coupled with an augmented extended Kalman filter, and such an integrated scheme is anticipated to increase the state estimation accuracy. The current study adopts a simulation framework as the testbed for the proposed scheme. The use of the FE software OpenSees allows the numerical nonlinear modeling of the structural system subjected to time-varying loads. Compared with the ones calculated directly from nonlinear response history analysis, the estimated responses based on the proposed scheme are found to be associated with increased accuracy.
Vibration-based FE-model updating for strain history estimation of a 3MW offshore wind turbine tower
Authors: Amador Sandro D R , Rasmussen Søren , Brincker Rune , Rex Simon , Skog Mathias , Gjødvad Johan F
Published: June 2024

At present, the fatigue-life design of Offshore Wind Turbines (OWTs) is based on design assumptions accounting for significant uncertainties both on loading and fatigue-resistance of different vulnerable structural details. Monitoring of strain histories can potentially have a significant positive impact when estimating the remaining life of OWTs, as the uncertainties are reduced. However, strain-based monitoring approaches present the important drawbacks, that only instrumented locations can be assessed and that there tend to be accessibility issues associated with the installation process. In this paper, the initial results of a novel methodology developed to estimate strain time histories are presented. The underlying idea of such an approach is to combine an updated FE model with the vibration response histories acquired with only a few sensors to estimate the strain histories at any location of an OWT tower.
Spatiotemporal extrapolation for vibration to strain estimation using domain adaptation
Authors: Eshkevari Soheila Sadeghi , Eshkevari Soheil Sadeghi , Dabbaghchian Iman , Marasco Giulia , Pakzad Shamim N.
Published: June 2024

Structural health monitoring relies on direct measurements from the structure for a variety of necessary investigations including operational modal analysis, life-cycle assessment, damage detection, and model updating. Although, because of complications and inherent inaccuracies in this direct measurement, engineers have been seeking to facilitate the data collection using machine learning-based approaches for a more robust strategy. In this work, a novel transfer learning framework is proposed to enable spatiotemporal strain estimation from acceleration measurement of the bridge for unmeasured or faulty locations and times. This task is executed by extraction of time-dependant and location-dependant contents of collected vibration signals and reconstruction of strain signal merely by providing the desired time and location. The framework has been verified on a simulation case study and showed high accuracy signal reconstruction metrics.
Instrumentation and Strain Monitoring of BFRP Bars in Pedestrian Bridge Deck Link slab
Authors: ElSafty A , Okeil A , Fletcher J , Fowler T , Jones D , Nolan S
Published: June 2024

Eliminating bridge deck expansion joints is considered a feasible alternative for addressing problems associated with deck joints, which results in reduced maintenance and improved bridge-deck design life. Link slabs introduce partially continuity for bridge girders and improve the seismic performance, wind and storm wave loads resistance. It also leads to lower cost, improved riding quality, and improved structural integrity, and may lead to longer spans. The goal of this study is to monitor the performance of a link slab employed in a pedestrian bridge where Basalt Fiber Reinforced Polymer (BFRP) bars were used for its reinforcement. The pedestrian bridge was constructed from simple-span concrete girders that were made continuous by creating the continuity link slab between the girders’ ends. The paper will present the link slab instrumentation, monitoring, and instrumentation system employed in the project. Strain, temperature, and elongation data were collected for the purpose of investigating the performance of link slabs. Two groups of sensors were used in this project, namely surface-mounted and embedded sensors. Monitoring of the link slab occurred during and after concrete casting. Several types of sensors including vibrating wire sensors with integrated thermistors were used in this study. The sensors were installed strategically to detect and capture strains in the BFRP bars, strains in the concrete link slab, and movement of the gap between adjacent girders’ ends. A data acquisition system recorded strains and deformations at regular time intervals. Data was collected during service over two periods of approximately 3 months each. The collected data was in effect a result of temperature and shrinkage of the concrete and did not include any significant live load effect, i.e., the bridge was not load tested with vehicular loads. Sensor measurements were corrected for ambient temperature changes as per the manufacturer’s manual. Based on the monitoring data, it can be concluded that the strains experienced by the sensors in the link slab BFRP were small compared to the BFRP rupture strain. After approximately 90 days since the initial casting date, the average strain recorded in the mid-joint gauges did not significantly change indicating that minimal creep or shrinkage restraint was experienced by the link slab. The maximum daily strain change due to thermal effects was about 500 microstrain. The cyclical nature of thermal effects could contribute to concrete cracking over time in the link slab if tension stresses build up due to global shrinkage and creep restraint of the connected Florida Slab Beams (FSB) spans.
Advanced signal processing methodology of vibration response data toward Structural Health Monitoring purposes
Authors: Ferrari R , Zola M , Cornaggia A , Rizzi E
Published: June 2024

This paper outlines a comprehensive and consistent methodology for signal processing analysis of vibration response data, applicable for final structural monitoring and identification purposes. The methodology combines classical and advanced techniques, including, in its pre-processing phase, the adoption of a Time Domain Compression (TDC) technique and the application of an AutoRegressive Moving Average (ARMA) modeling approach. The TDC technique removes lower-quality subsamples from the full data set, resulting in a higher-quality modified signal that may display a weakly stationary character. The ARMA modeling approach enhances the understanding of the response signals by modeling unknown source inputs; as a peculiarity, the inherent polynomial function applied to a white noise source in the model is interpreted as a filtering term that transforms the source into a non-white noise configuration, enabling the effective deciphering of the structure transfer function features. The research is part of a more comprehensive case study concerning the structural evaluation of a historical reinforced concrete arched bridge over the Adda river in Lombardy, Italy. The focus of this paper is specifically on the application of the TDC and ARMA techniques to the signal response data collected from the bridge under operational conditions.
Bayesian operational modal analysis in time domain using Stan
Authors: Cara Javier
Published: June 2024

Modal identification consists of determining the natural frequencies, damping ratios and mode shapes of a build structure using measured dynamic data. The Bayesian approach is very appealing when the goal is not only to estimate the modal parameters but also their uncertainty, calculated from their joint probability distribution. This paper presents an example of Bayesian modal identification in time domain using the state space model and the software Stan.
Modal analysis for damage identification of partially continuous multi-span bridges
Authors: Tomassini E , García-Macías E , Reynders E , Ubertini F
Published: June 2024

Among the compendium of highway civil infrastructures built in the last decades, many repetitive or quasi-periodic configurations can be found, such as multi-span simply supported bridges. Structural Health Monitoring (SHM) strategies for this kind of structures should properly consider such structural periodicity. Literature studies already demonstrated that multi-span bridges are particularly challenging target structures for Operational Modal Analysis (OMA) since the modal properties typically appear as dense clusters of poles with closely spaced frequencies and mode shapes with similar wavelengths. Hence, this circumstance considerably hinders the identification of physical poles using standard stabilization diagrams. The imperfect independence between spans is typically due to the presence of a continuous deck over the simply supported girders, weak deck/asphalt connections and/or imperfect expansion joints. In this context, the coupling degree of spans manifests through global mode shapes and frequencies spanning between the limit cases of simply supported and continuous multi-span conditions. In this light, this work proposes a novel method to assist the clustering of modal poles extracted using OMA. The proposed method is based on the analytical modal solution to the free vibration problem of multi-span beams with weak rotational coupling between adjacent spans. The developed method is validated through the modal identification of a real-world in-operation multi-span reinforced-concrete girder bridge.
A new fully automated operational modal analysis algorithm intended for large civil structures
Authors: Dederichs A C , Øiseth O
Published: June 2024

A new fully automated operational modal analysis (AOMA) algorithm based on the time-domain covariance-driven stochastic subspace identification (cov-SSI) system identification method is proposed. The new algorithm is intended for large civil structures, such as long-span suspension bridge for which an application example is included. It is shown that the new algorithm is capable of consistently detecting all expected structural modes of the Hardanger bridge, without requiring any prior tuning or parameter selection. The dominating three-step approach to AOMA algorithms in published literature on this topic is highlighted and used as a basis for the new algorithm; it first removes spurious poles using a Gaussian mixture model by analysing their distance to their nearest neighbour. Secondly, hierarchical clustering is used to regroup similar poles, and finally, the groups representing physical modes are selected through a similarity analysis of the size of hierarchical clusters.
Characterization and dynamic behaviour of Masonry Newly Concept Vault realized by 3d Printer
Authors: Sabbà M F , Rizzo F , Giannoccaro N I , Mansour S , La Scala A , Foti D
Published: June 2024

Masonry vaults represent one of the most recurrent types of horizontal structural elements in architecture in European countries, even in areas characterized by a high level of seismic risk. Therefore, their structural evaluation remains of primary importance. This paper proposes to apply already consolidated structural analysis methodologies on a contemporary vaulted space; in particular, on a small-scaled vault model. The aim, therefore, is to investigate the behaviour of a newly concept vault generated starting from the “Flat vault of Abeille” patented in 1699 starting by a scaled model made by 3D printer. The identification of this “new type” of vault is essential to design it correctly and to optimize the geometry for structural purposes. So, the dynamic identification of 1:8 small-scale vault model in 3D printing was studied. All the vault blocks were made in Polylactic Acid (PLA), have an infill of 70% and are assembled with dry joints. The paper describes the process to acquire the environmental and forced vibrations and to analyse them with the Operational Modal Analysis (OMA), identifying the natural frequencies and the mode shapes. Subsequently the results were compared with those of numerical distinct element method (DEM).
Modal Identification of a Steel Platform Specimen with a Subspace Implementation of the Poly-reference Complex Frequency Method Formulated in Modal Model (pCF-MM)
Authors: Amador S D R , Brincker R
Published: June 2024

When performing modal identification of structural systems, the main goal is to accurately extract the modal properties from the measured vibration data. The system identification can be carried out either in time or frequency-domain depending on the primary data used in the identification process, i.e., a time-domain free decay or frequency-domain function. In this paper, a subspace implementation of the new poly-reference Complex Frequency formulated in Modal Model (pCF-MM) is introduced. The technique operates in the frequency domain and uses either the Frequency Response Function or the Half Spectrum as primary data. The idea behind the subspace implementation of the pCF-MM is to use different subspaces of the observability and frequency-domain controlability matrices, carry out eigen-system realizations to estimate the modal properties corresponding to each chosen subspace. In order to illustrate its robustness, the subspace-driven pCF-MM is applied to the vibration data of a steel platform specimen to estimate its first vibration modes.