Modal Frequencies Research Articles

Complex modal analysis of structural vibration and acoustic radiation of plates

Inhomogeneous damping distribution leads to the occurrence of complex modes of structures. Complex modes' vibration and acoustic radiation characteristics are different from real modes. This paper studies the complex modal characteristics of inhomogeneously damped plates for forced vibration. We used the state space method to obtain the complex eigenvalues and eigenvectors of the vibration system and calculated the relationship between modal coordinates and frequency under unit force. The results show that the absolute values of the modal coordinates of two conjugate complex eigenvectors are different, and the structure's vibration is dominated by the eigenvectors corresponding to eigenvalues with positive imaginary parts near natural frequencies. When investigating the structural sound radiation in the vibration mode space, each mode's acoustic radiation is not independent but coupled with each other. The influence of the coupling between complex modes on the calculation results of the acoustic radiation power of the plate is studied in this paper. The results show that the coupling effect between modes cannot be ignored when calculating the acoustic radiation power based on complex modes. Finally, the error of calculating acoustic power using the decoupling approximation instead of the complex mode method is analyzed.

Modal properties of fractal trees as recursive analytical solutions

This study analyzes the modal properties of two-dimensional fractal trees under the assumptions of linear-elastic vibrations and axially inextensible branches. The examined fractal trees are of a generalized sympodial architecture with possibly non-zero and non-uniform branching angles. The study first presents the construction of tree geometry via iterated functions and then formulates the trees’ dynamic matrices from a renormalization viewpoint. The study proposes a novel recursive analytical solution to capture the trees’ modal properties. The proposed solution perceives the modal analysis of the fractal trees as an equivalent static analysis of trees with a modified configuration. These “modified” trees are made from the original trees but with all branches connected to the ground via negative stiffness springs. The analysis shows that identifying the lateral trunk displacements of the modified trees (under a static unit force) is associated with the recursive construction of a new family of functions that are introduced in the study, called the auxiliary P-functions. The results reveal that the modal frequencies of the original fractal trees are given by the roots of all auxiliary P-functions. Crucially, these auxiliary P-functions allow the graphical construction of the trees’ mode shapes. Illustrative examples demonstrate how the proposed recursive analytical solutions can be used to determine the trees’ modal properties. Lastly, the study concludes that the repetition of branches, even without geometrical symmetry, is a necessary condition for the existence of a unique vibration mitigation mechanism in fractal trees, namely the self-similar modes.

Reducing false alarms in structural health monitoring systems by exploiting time information via Binomial Distribution Classifier

This paper proposes an approach for anomaly/damage detection via structural health monitoring (SHM) systems based on a Binomial Distribution Classifier (BDC). The approach consists of two monitoring levels, labeled as alert and alarm states, respectively, where a damage index (DI) is computed and tracked over time. The alert state is reached when the DI exceeds a given threshold. At this stage, the BDC algorithm starts counting the number of DI values above the threshold within an observation window and computing the related probability of occurrence by using the binomial probability distribution. If the probability falls below a desired limit, the alarm state is triggered. Conversely, the SHM system returns in the non-alert condition. The proposed approach is discussed and evaluated through case studies involving both simulated and experimental data. In the examples, the DI is computed using the Mahalanobis distance of the monitored modal frequencies. The results demonstrate the capability of the BDC to reduce false alarms while preserving the probability of detection.

Method for extracting the free vibration response of transmission tower

The analysis of the free vibration in transmission towers is aimed at better evaluating their health status. Due to the non-stationarity of the height of non-uniform wind-induced vibration, there is a sustained forced vibration response in the vibration signal of transmission towers. This will lead to a decrease in the stability of vibration characteristics, which brings great difficulty to transmission tower status identification. In order to solve this problem, this paper proposes a method for extracting the free vibration response of transmission towers. By using Void–Kalman filtering (VKF) and generalized demodulation transform (GDT) for modal frequency tracking and pseudo-peak elimination, the signal is maximally cleaned while retaining all modal information. In addition, this paper combines variational theory and time-frequency domain features to decompose all effective modal orders in the vibration response. This not only solves the errors that exist when GDT and VKF directly process the original signal, but also makes the extraction of frequency parameters of each modal orders more convenient. The effectiveness of this approach is demonstrated by extracting the free vibration response of a 110 kV cat-head type tower. And by comparing it with existing mainstream signal processing methods using the example of bolt loosening faults. The results show that the signal processed by this approach can more stably and accurately capture the fault characteristics, providing a new idea for the extraction of free vibration response in the field of transmission tower health monitoring.

Variability in measured resonance frequencies and loss factors of a bolted panel structure

Structural bolted joints are not perfectly contiguous or rigid. Instead, the joint stiffness, mass, and damping depend on many parameters including the joint thickness, number and size of bolts, the bolt preload, and the motion of the jointed region. Also, damping can vary with motion type (stick-slip for friction and impact for joint opening and closing) and amplitude. Finally, all joint dynamic parameters vary from installation to installation. We measured the variability of bolted joint stiffness and damping for four low-order modes of a bolted Aluminum panel structure - two flexural modes and two twisting/torsional modes. While a large portion of the bolted joint literature features a lap joint or an assembly of two beams, there are few studies dealing with flanged connections of plates. Two flanged rectangular panels were bolted together with two cap screws threaded into one of the flanges. Modal resonance frequencies and loss factors were tracked throughout a decaying vibration response induced by hammer impacts on the structure. Measurements were made for three bolt torques and two flange thicknesses, three impact force strengths, and three repeated assemblies (the panel was unbolted and bolted together again). Relative motion at the joint with respect to mode shape determines whether the joint primarily adds stiffness or mass, as well as the amount of added damping. Not surprisingly, reducing bolt preload reduces resonance frequencies. Only minor variability in resonance frequency and loss factor were observed for most conditions, except for cases with low bolt preload. In these cases mild nonlinearity is evident in the response, where resonance frequency decreases and loss factor increases with increasing vibration amplitude. Also, variability of resonance frequencies and loss factors between installations often exceeds that due to variability in preload and vibration amplitude.

Anti-vibration Design of the Civil Aircraft’s Horizontal Tail Trailing Edge Compartment

The horizontal tail trailing edge compartment is a vital component of civil aircraft, situated between the horizontal tail beam and elevator. Its primary function is to connect the elevator and meet the aerodynamic sealing requirements of the unflapped elevator, and to transfer the aerodynamic and inertial load of the elevator to the outboard wing box of the horizontal tail in concentrated form. Under aerodynamic or other excitation, the horizontal tail trailing edge compartment may experience vibration, increasing the risk of structural damage. This study aims to enhance the anti-vibration capability of the horizontal tail trailing edge compartment via parametric finite element analysis. This analysis examines various design elements of the horizontal tail end cabin and compares the first-order modal frequency to deduce the influence of factors on the stiffness. The results provide a reference for the anti-vibration design of the horizontal tail trailing edge compartment in civil aircraft.

An efficient automatic modal identification method based on free vibration response and enhanced Empirical Fourier Decomposition technique

This paper presents an efficient yet practical approach for the automatic modal identification of structures based on their free vibration response. The proposed approach relies on the Empirical Fourier Decomposition (EFD) technique. It implements a new procedure to recognize automatically the number of modal components to be extracted from noisy data in such a way to prevent both mode-mixing and mode-splitting effects. A suitable strategy is adopted to improve the segmentation of the frequency spectrum of the free vibration response, so as to identify accurately the bounds of the frequency spectrum partition corresponding to each modal component. The related modal damping ratios are estimated by means of a robust area-based approach in order to mitigate the noise-induced disturbances whereas a time-domain method based on the phase shift of the free vibration response peaks is employed to identify the mode shapes.The proposed approach is first validated through the analysis of synthetic signals that embed closely spaced components and a lowly excited vibration mode. Finally, the proposed approach is applied to two real bridges. The first case-study deals with the identification of modal frequencies and damping ratios of the cables of a stay-cabled bridge. The second case-study involves the modal identification of a steel railway bridge deck that exhibits two closely spaced vibration modes. The outcomes obtained using the proposed approach based on EFD technique are compared with the results obtained by means of the Variational Mode Decomposition (VMD) technique as well as with those computed through classical operational modal analysis techniques. The consistent estimates produced by means of the proposed approach demonstrate its accuracy and robustness.

Finite element analysis of a 108-year-old unreinforced brick masonry tower following the 2015 Nepal earthquakes

After a visual inspection following the 2015 Nepal earthquakes, a finite element analysis (FEA) was conducted on a 108-year-old unreinforced brick masonry tower. The focus of study was on the brick masonry clock tower standing at a height of 30.48 m on the Senate Hall (SH) building of Allahabad University in India. This tower, which spans five storeys and features a rectangular cross-sectional shape, exhibits substantial cracks and material degradation across its connections and binding points. The process involved creating geometric plans and a 3D finite-element model through visual inspection and implementing ANSYS Workbench. The study utilised the mechanical properties of the aged materials, sourced from various studies encompassing surveys of old monumental structures, codes, and historical records. The clock tower’s behaviour was assessed through static, modal, and site-specific simulated time history analyses. The static analysis results revealed a maximum deflection of 3.76 mm at the top and a maximum equivalent (von-Mises) stress of 1.81 MPa at the joint of the first-floor level. Modal frequencies for the first three modes were determined to understand the tower’s free vibration behaviour. The time history analyses presented the acceleration, velocity, and displacement response under a peak ground acceleration (PGA) of 1.29 m/s2 simulated for the site. The dynamic analysis highlighted stress responses in critical locations, exposing severe cracks and damages across various points.

Modal and Structural Identification of Historic Bell Tower in Čuntić, Croatia Using Ambient Vibration Testing

In this study, modal and structural identification of a historic masonry bell tower in Čuntići, Croatia, damaged during the recent Petrinja earthquake, was performed. The results of the ambient vibration tests (AVT) and operational modal analysis (OMA) were used to update the finite element numerical model of the bell tower. Three modes were experimentally determined: the first two were bending modes (f1 = 4.395 Hz and f2 = 4.639 Hz), and the third was a torsional mode (f3 = 10.303 Hz). The experimentally determined and the originally calculated (preliminary NM) modal shapes agreed well, but in terms of modal frequencies, the correlation was poor. After model updating, some structural parameters were identified, and a reliable finite element numerical model was established. The proposed method can provide a reliable evaluation of the structural parameters of historic masonry buildings.

Identification of reaction wheel assembly disturbances based on variable modal frequencies

Micro-vibrations of the reaction wheel assembly (RWA) can have a negative impact on spacecrafts’ attitude control, surveillance, and measurement. Evaluating the micro-vibration magnitude during the design stage is possible by establishing an accurate dynamic model of the RWA disturbance characteristics and identifying the relevant parameters. Doing so can provide references for spacecraft design and development, ultimately leading to more efficient and effective spacecraft operations. However, the conventional methods of modeling and identifying the RWA and of predicting the distribution and magnitude of the disturbing force/torque are limited, as it relies on stable and constant modal frequencies. In the development mission of a satellite, a specific scenario is found that the modal frequency of the RWA changes with speed. This study proposes a novel modeling and parameter identification method for the RWA disturbances based on variable modal frequencies and is advantageous in this scenario. The RWA’s dynamic model is considered a covariant system related to the rotational speed. Additionally, frequency-domain and time-domain models have been established for the RWA’s translational and swinging motions. Simultaneously, the identification method of the model parameters is developed, which involves identifying the harmonic factors, the variable modal frequencies, and the amplitude coefficients. Finally, the method is validated by numerical simulations and experiments. The results indicate that the proposed method offers excellent identification performance, surpassing conventional methods in model accuracy and identification performance. This achievement holds significant reference value in the micro-vibration suppression and optimization design of spacecraft.

Effects of model fidelity and uncertainty on a model-based attitude controller for satellites with flexible appendages

This paper investigates the effects of model fidelity and parameter uncertainty on the performance of a hybrid model-based feedback-feedforward control scheme for attitude tracking of a satellite with flexible appendages. The feedforward component is an inverse model-based term produced through a computational approach known as inverse simulation (InvSim), which works by iteratively solving a discretised reference trajectory. The hybrid controller’s feedback is proportional-derivative (PD) based, using body attitude and rate feedback to provide stability and robustness. Furthermore, to ensure that the flexible modes do not trigger instability, the PD control gains are tuned to give a closed-loop response that is significantly slower than the flexible modes. Additionally, excitation of the flexible modes is reduced by minimising jerk through polynomial rest-to-rest manoeuvres, following the shortest quaternion path using spherical–linear-interpolation (SLERP). The effects of the appendage flexing on attitude tracking are then compensated through the feedforward element of the hybrid controller, with performance being compared to a traditional PD tracking law. The effect of the model fidelity on the performance of the hybrid controller is investigated through the use of both rigid body and multiple-fidelity finite-element mathematical models. Additionally, the effect of uncertainties in the model parameters is investigated to determine the accuracy of the model required to obtain significant improvement in attitude tracking. It is found that in the absence of any model parameter uncertainty, the hybrid controller outperforms the PD tracking control law by at least one order of magnitude when the finite-element model is used. Increasing the number of finite elements was found to provide no significant improvement in performance, with one element being sufficient and favourable with its lower computational overhead. It was also found that to ensure good performance compared to the PD tracking controller, the uncertainty in the inertia tensor should be <1%. Similarly, uncertainty in the first flexible modal frequency should be <0.5 rad/s.

Vibrational behavior of a 3D printed biomimetic dual‐core composite sandwich beam: An experimental and numerical study

AbstractComposite sandwich structures have been used in various applications like aerospace, automotive, and maritime sectors. The process of identifying the core design and the selection of a prominent core is crucially important in sandwich structures. In this study, biomimetic core development and vibration responses of composite sandwich beams with a dual biomimetic honeycomb core are investigated. The composite face layers are fabricated by the hand lay‐up method, and the fused deposition modeling is used to 3D print the PLA honeycomb cores. Based on ASTM‐E1876 and the alternative dynamic approach, the face layer elastic properties and rigidity modulus of the cores are evaluated, respectively. The numerical simulation is used to predict the sandwich panels' natural frequencies and mode shapes and verified with experimental results. There was an excellent agreement between the calculated and experimental natural frequencies. Due to the presence of the core and enhanced rigidity modulus, the dual lamellar honeycomb core sandwich beam produces the highest natural frequencies among all‐composite sandwich beams, followed by the dual regular honeycomb, single lamellar honeycomb, and single regular honeycomb cores. The geometric parametric studies, including core thickness, length‐to‐breadth ratio, lamination schemes, support conditions, and transverse vibration responses were also analyzed for different sandwich patterns. As a result of this work, thick composite sandwich panels in aeronautical and marine structures can be replaced with dual biomimetic core structures. The study highlights the fact that the dual‐core sandwich beam provided greater modal frequency than the single‐core beam with the same weight proportions.Highlights Pistachio nut shell‐based biomimetic honeycomb core has been developed. Alternative dynamic approach is used to find sandwich‐core shear properties. Lamellar‐infused biomimetic model yields higher shear modulus and stiffness. Dual‐core beam having high flexural stiffness enhances the natural frequency. Various parametric studies were analyzed for different sandwich patterns.

An experimental and FEA approach to investigate effect of cracks on a rotor bearing system

The field of rotordynamics primarily focuses on the analysis and characterization of lateral and torsional vibrations of rotor bearing system. In this study, the lateral vibrations of a single disc rotor bearing system are studied. The effect of crack location, crack depth, and number of cracks has been studied for structural health monitoring of shafts. For the finite element approach, Ansys version 19.0 is used, and a modal analysis was conducted in order to determine the participation factor and bending modal frequencies. Also, a Campbell diagram for critical speeds and whirl direction is plotted. A single-disc rotor bearing system is treated as a simply supported case. Experimental performance has been carried out on a self-designed testbed, and results are obtained using a DEWEsoft FFT Analyzer. A plot of the frequency spectrum is plotted for all shaft cases. After comparing FEA and Experimental results, a maximum variation of 5 percent was found. The investigational results are corelated; hence, the above methodology for rotordynamic analysis may be suggested.

ICEEMDAN-based Combined Wind Power Forecasting

Background:: With the depletion of fossil energy and the increasingly serious environmental pollution, the task of developing renewable energy is imminent. As a green and pollutionfree renewable energy, the penetration of wind energy in the power grid continues to rise. Objective:: In order to reduce the volatility and randomness of wind power series and increase the accuracy of wind power prediction, a wind power combination model based on the ICEEMDAN (improved adaptive noise full set empirical mode decomposition) method is proposed. objective: In order to reduce the volatility and randomness of wind power series and increase the accuracy of wind power prediction, a wind power combination model based on ICEEMDAN (improved adaptive noise full set empirical mode decomposition) method is proposed Methodology:: First, the complex original wind power data have been decomposed into several relatively simple subsequences using the ICEEMDAN method. Aiming at the different lengths of coarse grain time series and data loss in traditional multi-scale entropy, a fine composite multiscale dispersion entropy is proposed to calculate the entropy value of each decomposition component, and divide the high- and low-frequency modal components to predict the modal components of different frequencies; secondly, differential moving autoregressive model (ARIMA) and shortterm memory neural network (LSTM) are used to establish the prediction models of high- and low-frequency components, respectively. Results:: Finally, the prediction results of each component have been superimposed and reconstructed to obtain the final prediction results. The effectiveness of the combined model is verified by the actual operation data of a European wind farm. result: The effectiveness of the combined model is verified by the actual operation data of a European wind farm. The results show that compared with the other four single and combined forecasting models, the combined model in this paper has higher forecasting accuracy. Conclusion:: As the effectiveness of the combined model is verified by the actual operation data of a European wind farm, the results have shown that compared to the other four single and combined forecasting models, the combined model in this paper has higher forecasting accuracy. Therefore, the model proposed in this article can be used for predicting wind power with significant fluctuations, which will help to provide support for optimized scheduling and energy storage configuration of wind farms, thereby reducing costs and increasing income for the power grid and wind farms. conclusion: ICEEMDAN decomposition algorithm can effectively reduce the influence of white noise on mode decomposition, and the prediction accuracy of wind power can be better improved by putting different frequency power components into different prediction models

Physical modelling of a harp from Central Africa.

Central Africa harps are string instruments, often anthropomorphic, serving an essential cultural role. Compared to pedal harps, their body is small in size with a soundboard mainly made of animal skin and a neck made of a wood beam. In this paper, a physical model is developed as a tool for assessing the specificities of these musical instruments, from a vibro-acoustic perspective. The modeling strategy is based on the modal Udwadia-Kalaba formalism which is a multibody substructuring technique. Input modal parameters of the body and the strings are experimentally identified and the main steps of the estimation procedures are detailed. The reliability of the physical model is investigated via the comparison between simulated and experimental data for several plucking configurations. Different hypotheses are assessed such as the string/neck coupling which proves to strongly influence the dynamic response of the body when there is a coincidence between string and neck modal frequencies. The inclusion of geometrical nonlinearities proves to be of major importance, even for a weak plucking, as it allows qualitative representation of double frequency terms in the simulations. Overall, physical simulations of the soundboard motion are in good agreement with measurements indicating characteristic features of the instrument are captured.

Lithography-free high sensitivity perfect absorption based on Graphene/α-MoO3/SiC and Tamm plasmonic structure

In this paper, we propose a tunable perfect-absorption lithography-free refractive index sensor structure, which couples the Tamm phonon polariton (TPhP) mode and Graphene/α-MoO3/SiC (GMS) mode. By aligning the modal frequencies of TPhP and GMS, the coupling of the two modes is realized with perfect absorption. We utilize the transfer matrix method (TMM), resonance equation and coupled mode theory (CMT) to theoretically analyze the absorption of different modes and apply the structure to refractive index sensor. By modulating the structure parameter, the sensitivity of the sensor can be as high as 6 μm/RIU. This work could contribute to several fields such as refractive index sensors, photodetectors, absorbers, and energy harvesting devices.

A Field Investigation of Stability Characteristics of Pressure Fluctuation and Vibration in Prototype Pump Turbine at Multiple Working Points

In practical operation, pump turbines typically operate far from their designed working points, which has a significant impact on the stability of the unit’s operation. In this paper, we conducted a field test to investigate the stability characteristics of prototype pump turbines at different working points. By adjusting the given power of the generator in a stepwise manner to control its working point, we obtained the statistical and spectral characteristics of pressure signals and acceleration signals. In turbine mode, the result shows that, at low, medium, and high power, the variation in pressure fluctuation characteristics is influenced by three different factors, while vibration generally reaches its maximum value at approximately 50 MW. In pump mode, variations in pressure were observed among different measurement points in the low-frequency range, and the characteristics of vibration acceleration were influenced by both the rotor–stator interaction (RSI) and the structural modal frequencies. We emphasized that the high-frequency bands have influences on the unit comparable in magnitude to those of the rotor–stator interaction, which has rarely been mentioned in previous studies. Through detailed testing and analysis of the unit’s actual operation, we can gain a better understanding of its behavior and performance in the turbine and pump modes, and these results hold significant importance for ensuring the stability and reliability of the unit.

Multi‐Mode Vibrational Triboelectric Nanogenerator for Broadband Energy Harvesting and Utilization in Smart Transmission Lines

AbstractThe advantages of the triboelectric nanogenerator (TENG) in environmental energy harvesting and utilization determine that they have great development potential in the digital application of power grids. This work focuses on the harvesting and utilization of vibration energy from transmission lines, specifically in the context of breeze vibrations and sub‐span oscillations. To this end, this work proposes a novel multi‐mode vibrational triboelectric nanogenerator (MV‐TENG) and three smart transmission line application strategies based on the MV‐TENG. The MV‐TENG design consists of an S‐beam to broaden the frequency response range by reducing high‐order modal frequencies, and a pair of allegro electrodes to efficiently harvest horizontal and vertical vibration energy. The MV‐TENG demonstrates the capability to harvest vibration energy within a range of 1–3.5 Hz horizontally and 4 Hz, 9–60 Hz vertically, covering the occurrence range of breeze vibrations and sub‐span oscillations of transmission line effectively. Three application strategies include self‐powered tower obstacle alerting, temperature and humidity online monitoring, and high‐temperature wireless warning of transmission lines based on MV‐TENG. In summary, this work presents a comprehensive implementation scheme for digitally integrating TENGs into smart transmission lines, thereby facilitating the engineering development of TENG technology in grid systems.

Seismic responses and failure mechanism of the superstructure-integrated underground structure considering the seismic aboveground-underground interaction

The superstructure-integrated underground structure (SIUS) is an innovative infrastructure in an urban city, in which the aboveground part and underground part are coupled together to be a large synthesis structure. During earthquakes, the SIUS is primarily influenced by the soil deformation and structural vibration, and the seismic aboveground-underground interaction (SAUI) would be considerable due to structural characteristics. This paper aims to investigate the seismic response and failure mechanism of the SIUS and reveal the influence mechanism of the SAUI with a quantitative method for the seismic aboveground-underground interaction coefficient (SAUIC). In this paper, a credible numerical model of the whole soil-SIUS system compiled with the viscous-spring artificial boundary is established. The modal analysis of the SIUS is carried out, and the distinctive structural characteristics are discussed. The seismic responses of the SIUS are thoroughly investigated, and the failure mechanism of vulnerable positions is further revealed. Based on the modal frequency response analysis and a novel correlation analysis, the SAUIC is quantitatively proposed to evaluate influence effects of the SAUI on seismic responses of the SIUS. The results show that the SAUI has great influence effects on seismic responses of the SIUS, even changes the seismic failure mode of the underground part to be flexural failure; the quantitative SAUIC demonstrates the SAUI increases with the increasing seismic intensity and increases from outside to inside of the SIUS, and the SAUI would be highly considerable on positions with irregularities in structural stiffness, especially on the aboveground-underground interface.

Modal strain monitoring of the old Nieuwebrugstraat Bridge: Local damage versus temperature effects

Vibration-Based Monitoring (VBM) from modal strains is a promising alternative to traditional VBM methods, which are primarily based on exclusively monitoring natural frequencies. The advantages of modal strains are that they offer a lower sensitivity to temperature and a higher sensitivity to small-scale damage, when compared to natural frequencies, rendering them ideal for detecting damage at an early stage. Furthermore, modal strains can be obtained in a dense grid with a relatively low cost, when fiber-optic sensors, such as fiber-Bragg gratings (FBG) are employed, which enables the monitoring of several critical locations and increases the possibility of early damage detection and localization. Modal strains can be obtained with high accuracy and precision thanks to a recently developed methodology that makes use of FBG sensors and of a high resolution acquisition system. The temperature sensitivity of modal strains has been investigated in the field but their damage sensitivity has previously only been investigated through laboratory experiments and numerical simulations. In this study, a 110-years-old steel railway bridge is monitored with 80 FBGs. Its modal strains and natural frequencies are automatically identified with the use of hierarchical clustering from ambient and operational dynamic strains. Before the scheduled replacement of the bridge, artificial damage is introduced by means of local cuts, simulating fatigue cracks, in order to investigate the damage detection and localization capabilities of modal strains on a full-size civil structure for the first time. The influence of temperature and operational factors is also investigated and compared with that of damage.