Damage assessment in reinforced concrete beams using eigenfrequencies and mode shape derivatives

The paper investigates the influence of dynamic characteristics of building structures on the mechanisms of progressive collapse development. It is shown that natural frequencies, mode shapes, and damping levels significantly affect the propagation pattern of collapse following the initial failure of one or more load-bearing elements. Based on the obtained results, vulnerability assessment criteria are formulated that take into account the dynamic properties of structures. Purpose of the article. The purpose of this study is to establish the relationship between the dynamic characteristics of a structural system and the mechanisms of progressive collapse development. Special attention is given to the effect of natural frequencies, vibration modes, and damping level on the likelihood of structural excitation leading to instability or further collapse. Based on a numerical analysis of a steel-framed building, a direct relationship is demonstrated between local damage and the redistribution of stiffness in the structural system. The analysis of changes in dynamic characteristics makes it possible to identify potentially vulnerable zones with reduced resistance to progressive collapse. To assess collapse vulnerability, it is advisable to determine the first 3–5 natural frequencies and corresponding mode shapes, as well as damping properties. A significant reduction in stiffness leads to the localization of vibrations, increased amplitudes, and potential energy accumulation. If the system is unable to dissipate vibrations due to insufficient damping, cascading failure may occur. Critical warning signs include a frequency decrease of more than 30 %, an increase in deformation amplitude by over 50 %, the emergence of localized vibration modes, and a reduction in damping. Clarifications are proposed to the conditions of the energy-based approach for evaluating the propagation of progressive collapse, taking into account dynamic characteristics and the localization of deformations within vibration modes (i. e., structural vulnerability). The criteria for determining the dynamic coefficient are refined to consider the frequency spectrum and damping. Design tasks are formulated based on dynamic analysis to enhance resistance to progressive collapse. Conclusions. The use of dynamic coefficients (impact factors) recommended by building codes is justified but insufficient without considering the individual properties of the specific structure. The analysis of structural vibration modes can reveal potential weak spots where deformations and stresses are expected to be the highest. This is crucial for predicting the mechanisms of progressive collapse propagation. The results of this research can be applied in assessing the vulnerability of existing buildings and in designing new structures resistant to progressive collapse in accordance with modern safety requirements.

A novel damage index for damage detection and localization of plate-type structures using twist derivatives of laser-measured mode shapes

Many buildings during their operational period incur damage of different origin: man-made, natural, operational, etc. Dynamic tests are performed for detailed assessment of the technical condition of buildings and structures in accordance with the regulatory documents for general analysis of the building damage state. In a large number of papers, the results of comparison of full-scale tests and numerical analysis using finite element method are presented. When analyzing the results, it can be concluded that the dynamic method is reliable, but has several limitations. The advantage of the dynamic method of building damage assessment is the possibility to adjust finite element models in software systems taking into account results obtained from in-situ tests, which allows to obtain more accurate results for the assessment of bearing capacity under seismic loading. To examine the effect of damage to buildings on their seismic resistance, an experiment with corrosiondamaged reinforced concrete columns was performed. The result of the first stage of the experiment is the assessment of the change in dynamic characteristics (eigenfrequency, vibration decrement, vibration damping coefficient, etc.) of reinforced concrete column specimens subjected to corrosion damage.

In this paper, modal characteristics of self-compacting concrete (SCC) beams were studied through experiment. 3 self-compacting concrete beams were gradually damaged and then subjected to vibration test in free-free boundary conditions after each load step. From analysis, eigenfrequencies could indicate the existence of damage but it could not represent the damage locations. Modal Assurance Criterion (MAC) is lesser reliable to indicate crack damage compare to eigenfrequencies. Next to these, capacity for damage detection and localization of Coordinate Modal Assurance Criterion (COMAC) and the flexibility matrix method are also examined and compared. This paper introduces in detail the dynamic properties and damage localization methods in SCC, which provide basal databases of damage diagnosis for SCC structures and promote the popularization of SCC in civil infrastructures.

Failure behavior of a rock-coal-rock combined body with a weak coal interlayer

The present work reports results from an extensive set of measurements which has been performed in order to formulate standard method to remove temperature changes from impedance measurements. The other issue addressed here is the investigation of influence of boundary condition and temperature changes on electromechanical impedance measurement for structural member. Due to electromechanical coupling, changes in dynamic characteristics can be seen in electrical impedance of piezoelectric transducer. Two different systems have been used during this measurement process. System based on FBG sensors has been used for temperature changes measurement while PZT transducers mounted on the structure with impedance analyser were used for electrical parameters measurement. During research electrical impedance and resistance of piezoelectric transducer were measured in order to analyze changes in amplitude of peaks and the frequency shift of peaks due to temperature variations and different configurations of the beam.

Global Positioning System (GPS) technology with 10–20‐Hz sampling rates allows scientifically justified dynamic measurements of relative displacements of long‐period structures. The displacement response of a simulated tall building in real time and permanent deployment of GPS units at the roof of a building are described. To the authors’ best knowledge, this is the first permanent deployment of GPS units (in the world) for continuous dynamic monitoring of a tall building. Data recorded from the building during a windy day is analyzed to determine the structural characteristics. When recorded during extreme motions caused by earthquakes and strong winds, such measurements can be used to compute average drift ratios and changes in dynamic characteristics, and therefore can be used by engineers and building owners or managers to assess the structural integrity and performance by establishing pre‐established thresholds. Such information can be used to secure public safety and/or take steps to improve the performance of the building.

Analysis of wave propagation within buildings in response to earthquakes enables the tracking of changes in dynamic characteristics using impulse response functions. The velocity of traveling shear waves and the intrinsic attenuation of buildings can be retrieved, providing valuable input for system identification. The Factor Building at the University of California, Los Angeles campus (henceforth referred to as the UCLA Factor Building), an instrumented 15-story steel moment frame structure, is selected for dynamic response characterization. Shear wave travel time and attenuation are computed from wave propagation using seismic interferometry applied to recorded motions, with deconvolved waves used to compute these parameters. In this study, the natural logarithm of the envelopes of waveforms deconvolved with the basement signal provided the measure of attenuation. Additionally, the waveforms deconvolved with the basement motion, indicating the building’s fundamental mode. The frequency and time decay further constrained the shear velocity and attenuation. Shear velocity was determined using arrival times measured from deconvolved waves, resulting in an average velocity of 147.1 m/s. The observed quality factor was 10.8, with a corresponding damping ratio of 5%. The shear wave velocity and damping ratio estimates derived from deconvolved waves showed consistency with those obtained from basement deconvolved waveforms. This consistency validates wave deconvolution as an effective method for isolating building response from excitation and ground coupling. By incorporating the resonant frequencies and damping ratios derived from previous analyses into a refined element model, this study underscores the potential of wave deconvolution for extracting building dynamic characteristics, thereby enhancing our understanding of their responses to earthquakes.

The dynamical model of multiple honeycomb plates connected by hinges, including the thermal–structural coupling effect, is investigated in this paper. Under the assumption of small deformations and strains, the classical plate theory is used to establish the dynamical model of the honeycomb plate. The Chebyshev polynomial is adopted to describe the deformation of the plate and the linear torsional spring to represent the elastic hinge. Using the Rayleigh–Ritz method, the characteristic equation of the honeycomb sandwich structure is derived, from which the natural frequencies are obtained. Considering the thermal effect of the plate, the thermal–structural coupling dynamical equation is obtained. The thermal conduction in the thickness direction is calculated by the finite difference method. The present model is validated by comparing with the result generated by an equivalent orthotropic plate model established by the finite element (FE) software MSC Patran. The response analysis reveals the important effect of the metal skin and the hinge stiffness on the dynamic characteristics of the honeycomb sandwich structure. Numerical simulations reveal thermal–structural coupling features for the multi-honeycomb-plate structure from the perspective of the change in dynamic characteristics and the distribution of the temperature gradient. The thermal–structural coupling calculation method adopted herein can be used to solve the thermal conduction of the plate. It serves as the theoretical method for analyzing the dynamical behavior of the solar panel subjected to the solar heat.

Ultrasonic guided wave (UGW) technology is an effective method for intelligent monitoring of crack damage in thin-walled plate structures. In this paper, a finite-element (FE) model of UGW propagation in Q345 steel plate with crack damage was established and verified. A visual localization method for crack damage in steel plate based on the time reversal–probability damage imaging (TR-PDI) method is proposed. On this basis, the time–frequency domain characteristics of UGW signal are extracted using continuous wavelet transform. Two deep learning (DL) models, the two-dimensional convolutional neural network (2D-CNN) and DenseNet, are used to quantify the crack length and depth by UGW signal. The robustness and generalization performance of the automatic quantification method of crack damage based on UGW-DL algorithm were verified using three databases. The results show that the TR-PDI method can realize visual localization of crack damage in steel plate. The accuracy of two DL models in quantifying crack length and depth exceeded 92.9% and 99%, respectively, and the DenseNet model outperformed the 2D-CNN model. The fusion database constructed using the experimental results and FE data can significantly improve the robustness and generalization ability of the UGW-DL algorithm in crack diagnosis.

The use of modal curvatures for damage localization in beam-type structures

The effectiveness and the sensitivity of a Wireless impedance/Admittance Monitoring System (WiAMS) for the prompt damage diagnosis of two single-storey single-span Reinforced Concrete (RC) frames under cyclic loading is experimentally investigated. The geometrical and the reinforcement characteristics of the RC structural members of the frames represent typical old RC frame structure without consideration of seismic design criteria. The columns of the frames are vulnerable to shear failure under lateral load due to their low height-to-depth ratio and insufficient transverse reinforcement. The proposed Structural Health Monitoring (SHM) system comprises of specially manufactured autonomous portable devices that acquire the in-situ voltage frequency responses of a network of twenty piezoelectric transducers mounted to the RC frames. Measurements of external and internal small-sized piezoelectric patches are utilized for damage localization and assessment at various and increased damage levels as the magnitude of the imposed lateral cycle deformations increases. A bare RC frame and a strengthened one using a pair of steel crossed tension-ties (X-bracing) have been tested in order to check the sensitivity of the developed WiAMS in different structural conditions since crack propagation, damage locations and failure mode of the examined frames vary. Indeed, the imposed loading caused brittle shear failure to the column of the bare frame and the formation of plastic hinges at the beam ends of the X-braced frame. Test results highlighted the ability of the proposed SHM to identify incipient damages due to concrete cracking and steel yielding since promising early indication of the forthcoming critical failures before any visible sign has been obtained.

Experimental Investigation on Dynamic Characteristics Changes of Fire Exposed Reinforced Concrete and Steel Members

Abnormal changes of dynamic topological characteristics in patients with major depressive disorder

Dynamic mechanical properties and constitutive model of shale with different bedding under triaxial impact test