Undamaged Structure Research Articles

Passive defect localization on a vibrating plate using Matched-Field Processing

Passive defect localization on a vibrating plate using Matched-Field Processing (MFP). The aim of this study is to investigate the use of MFP for passive localization of a local change in parameter of a vibrating shell in the modal regime. Matched-Field Processing is a beamforming method that uses the correlation between the recorded data and a controllable digital model of wave propagation (replica) to locate a source. Vibration measurements were conducted on an aluminum plate using a laser vibrometer. The plate was tested both with and without damage (added mass) while being excited by a shaker. Replicas were created by performing modal analysis on measurements taken from the undamaged structure. Matched-Field Processing is applied directly to the measured data to locate the active source (shaker) and to the residues (field difference between undamaged and damaged states) to locate a local variation of the parameter (defect). The method's feasibility is also being explored for passive measurements in modal analysis and residue computation.

Progressive collapse of regular RC structure considering flexibility of slabs under gravity and wind loads

Abstract Progressive collapses are disastrous phenomena which occur in the structure due to manmade incidents or natural disasters. There are not any significant studies considering the flexibility of slabs in the structures, as an alternative to treating them as rigid diaphragms. The present study deals with the progressive collapse of a regular reinforced concrete structure considering flexibility of slabs, comparing the same when the slabs are considered as rigid diaphragms. 20 storey(G+19) building is modeled using ETABS software and nonlinear static analysis is performed under the action of gravity and wind loads. At the outset, the analysis is done for undamaged structure to find the behavior of structure and then the damaged models have been analyzed by removing one of the critical column in different locations at first storey, based on general services administration (GSA) guidelines[16]. Various response parameters such as base force capacity, storey stiffness and storey displacements have been compared for undamaged and damaged structures considering and not considering the flexibility of slabs. From the comparison of the results, it was noticed that the chance of progressive collapse is high when the corner column is damaged and also resistance to wind load is considerably higher when stiffness of slabs is considered for the analysis in both undamaged structure and the four cases of damaged structure (ii), which is about three times higher.

Predictive Probability of Localization Curves (P-POL) for Structures with Changing Environmental Conditions

One of the fundamental challenges in structural health monitoring (SHM) is the lack of data from the damaged state, which is required to verify the automated damage detection algorithms. In this paper, a recently developed approach is presented that allows one to assess the detectability of damages before they occur. The approach is based on so-called probability of detection curves that can be evaluated based on data and a model from the undamaged structure, in a “predictive” way. The method is based on four fundamental assumptions: the damage-sensitive features can be approximated through a normal distribution, the variance in the measurement remains constant for different damage scenarios, an analytical model of the examined structure is available for the sensitivity computation, and the relationship between measurements and structural changes can be linearized for small structural changes. In previous publications, this approach has already been applied to natural frequency and mode shape monitoring as well as ultrasonic testing. In this paper, it is applied to strain and inclination measurements from numerical case studies for the first time, demonstrating the universality of the method. Moreover, it is analyzed how changes in the environmental and operational variables (EOVs) affect the predicted POD. The results demonstrate that the predicted POD are valid even in the presence of environmental changes, but they depend on the user-defined hyperparameters of the algorithms that remove the environmental effects from the measurements. Therefore, the hyperparameter selection is critically discussed and an optimal monitoring strategy is outlined.

Using the DIC Technique in Damage Detection for a Cantilevered Composite Beam

The subject of the article is the use of the Digital Image Correlation (DIC) technique in tests of damage detection in a composite cantilevered beam. Laboratory tests of the beam were conducted using the Q-400 system from Dantec Dynamics GmbH. The research aimed to study the behaviour of the structure under external forces and to analyse the influence of cross-section damage on the displacement field of the beam. The analysed quantities were also the changes in strain fields of the structure. For the laboratory model, the finite element models were prepared, and satisfactory compliance in terms of displacement fields between numerical and laboratory models for undamaged structure was obtained. The research has shown, that it is possible to indicate the approximate location of damage based on the information about changes in the displacement field.

Identification of damages in a concrete beam: a modal analysis based method

Structural Health monitoring (SHM) strategies can play a pivotal role in the perspective of enhancing structures and infrastructures life cycle and maintenance operations. A plethora of sensors and technologies can be employed in this field; in a seismic context, vibrational tests are particularly relevant, being able to give an insight on the dynamic characteristics of the structure itself. In particular, modal parameters can be considered in order to detect damages. A comparison between a certain test time and 0 test time (i.e., undamaged structure) is commonly performed; to this aim numerical models result particularly useful to provide baseline data (often unavailable in pre-existing structures), but they need to be validated before use. Non-contact techniques, like scanning laser Doppler vibrometry, can be exploited to do this. In this paper a numerical model of a scaled concrete beam is realized and validated through LDV data, then it is used to design load tests for progressive damages generation. Modal analysis is conducted after different load trials to evaluate changes of modal parameters in relation to the damage occurred; also, damage-related indices are proposed. The results confirmed the suitability of LDV for dynamic analyses of cement-based structures and this can be particularly useful when big structures (e.g., bridges) have to be monitored in-field. The numerical model was validated with acceptable absolute errors in terms of natural frequencies (between 26 Hz and 131 Hz) and high Modal Assurance Criterion (MAC) values (0.85-0.93). Moreover, the proposed methodology allows to detect damages also in a concise way through synthetic indices (with changes >50% in damaged vs undamaged conditions) and early warnings could be generated according to their values, hence supporting decision-making procedures in the building management scenario.

Repair of Cracks in Concrete with the Microbial-Induced Calcite Precipitation (MICP) Method

Abstract In this study, the microbiologically-induced calcium carbonate precipitation (MICP) method was employed to examine its potential for repairing cracks in concrete. In addition, specific gravity and porosity values were measured to examine the effect of calcite formations on concrete surfaces and microstructures. Bacteria-supplemented concrete repaired cracks up to 0.4 mm wide by filling them with CaCO3. Furthermore, this study not only examined the healing of the width but also the length of cracks. However, as the width of the treated cracks decreased, their length increased. This indicated that the MICP treatment is more effective in a limited crack range. Specific gravity values increased, and porosity values decreased in concrete supplemented with calcifying bacteria. SEM analyses showed that calcite is a bacterial product that forms a very tight bond with a cement gel and that calcite fills visible cracks and voids and creates more of a void-free and undamaged concrete structure.

Damage Identification in Cement-Based Structures: A Method Based on Modal Curvatures and Continuous Wavelet Transform.

Modal analysis is an effective tool in the context of Structural Health Monitoring (SHM) since the dynamic characteristics of cement-based structures reflect the structural health status of the material itself. The authors consider increasing level load tests on concrete beams and propose a methodology for damage identification relying on the computation of modal curvatures combined with continuous wavelet transform (CWT) to highlight damage-related changes. Unlike most literature studies, in the present work, no numerical models of the undamaged structure were exploited. Moreover, the authors defined synthetic damage indices depicting the status of a structure. The results show that the I mode shape is the most sensitive to damages; indeed, considering this mode, damages cause a decrease of natural vibration frequency (up to approximately -67%), an increase of loss factor (up to approximately fivefold), and changes in the mode shapes morphology (a cuspid appears). The proposed damage indices are promising, even if the level of damage is not clearly distinguishable, probably because tests were performed after the load removal. Further investigations are needed to scale the methodology to in-field applications.

State-dependent aftershock resilience analysis of reinforced concrete structures considering the effect of corrosion

Numerous aging structures are currently confronted with a seismic crisis due to successive earthquakes. Previous mainshock damage and material deterioration significantly impact the capacity of structures to resist future aftershocks. Conducting resilience analyses, taking into account the current damage state, is crucial to assess the safety of these buildings. In this paper, an analytical methodology is presented for deriving state-dependent resilience curves while considering the coupling effect of corrosion and aftershock. This methodology reforms the structural functionality and introduces a state-dependent resilience function conditional on the mainshock damage state. The aftershock damage data is grouped by the structural response under mainshocks. Then, the state-dependent aftershock fragility and seismic resilience are generated based on the grouped dataset. To demonstrate the proposed methodology, a case study is conducted on a seismic-designed reinforced concrete frame building with varying degrees of corrosion damage. Results show that the proposed methodology effectively evaluates the resilience levels of buildings, considering various mainshock damage states. The mainshock damage significantly influences the aftershock resilience results. A severe mainshock damage can cause a 34 % reduction in seismic resilience compared to an undamaged structure. Furthermore, the reduction in structural resilience caused by the combination of corrosion and aftershock exceeds the sum of the reductions caused by the individual effects of each factor. The findings of this study also emphasize the importance of considering the scenarios involving corrosion and aftershocks when assessing the resilience of structures throughout their service life.

A modified mode shape data-based method for beams structural damage detection

Damage detection methods based on changing modal parameters have received considerable attention in engineering applications due to the satisfactory results and the low associated cost compared with other techniques. The Mode Shape Data Based Indicator (MSDBI) is a damage indicator available in the literature, being used to identify damage in beam structures from the mode shape, mode shape slope and mode shape curvature, in the undamaged and damaged configurations of the element under study. However, in some situations, the configuration of the displacement mode shape of the ith mode, of the undamaged structure compared to the damaged one, presents mirroring. The damage identification algorithm could be a better indicator when these situations occur. Them, this paper presents a proposal to modify this method, called MSDBIM. The proposed modified method (MSDBIM) and the traditional method (MSDBI) were applied in two numerical examples that were elaborated in commercial software of finite elements, namely a simply supported concrete beam and a fixed-end steel beam in different single and multiple damage scenarios with sensitivity studies. A new discretization for the fixed-end beam was performed to assess whether there is a direct influence on the damage identification method. The results show that the proposed method (MSDBIM) performs better than the traditional method (MSDBI).

Localizability of damage with statistical tests and sensitivity-based parameter clusters

Damage localization based on ambient vibration data in combination with finite element models can be challenging, in particular due to the large number of parameters in the model and noisy measurement data. Changes in different structural parameters can cause similar changes in data-driven features, and vice versa, it can be challenging to identify which parameter caused the deviation in the data. The problem is ill-conditioned and slight variations in the features, due to inherent statistical uncertainty, can lead to significant errors in the result interpretation. A possible solution is sensitivity-based statistical tests in combination with a parameter clustering approach that considers the uncertainties of data-driven features. In this context, this paper introduces the concept of damage localizability, and provides a framework to evaluate it based on the minimum detectable parameter changes, possible false alarms in unchanged parameters, as well as the achievable damage localization resolution. Since clustering approaches depend on user-defined hyperparameters, such as the number of clusters, the second objective of this paper is to optimize the performance of the damage localization, by adjusting the hyperparameters for clustering. A particular strength of the approach is that the analysis can be conducted based on data and a numerical model from the undamaged structure alone, making it a suitable approach to assess and to optimize the diagnosis performance before damage occurs. For proof of concept, a laboratory case study on a simply-supported steel beam is presented, where the localizability of mass changes is analyzed and optimized.

Predictive probability of detection curves based on data from undamaged structures

This paper develops a model-assisted approach for determining predictive probability of detection curves. The approach is “model-assisted,” as the damage-sensitive features are evaluated in combination with a numerical model of the examined structure. It is “predictive” in the sense that probability of detection (POD) curves can be constructed based on measurement records from the undamaged structure, avoiding any destructive tests. The approach can be applied to a wide range of damage-sensitive features in structural health monitoring and non-destructive testing, provided the statistical distribution of the features can be approximated by a normal distribution. In particular, it is suitable for global vibration-based features, such as modal parameters, and evaluates changes in local structural components, for example, changes in material properties, cross-sectional values, prestressing forces, and support conditions. The approach explicitly considers the statistical uncertainties of the features due to measurement noise, unknown excitation, or other noise sources. Moreover, through confidence intervals, it considers model-based uncertainties due to uncertain structural parameters and a possible mismatch between the modeled and the real structure. Experimental studies based on a laboratory beam structure demonstrate that the approach can predict the POD before damage occurs. Ultimately, several ways to utilize predictive POD curves are discussed, for example, for the evaluation of the most suitable measurement equipment, for quality control, for feature selection, or sensor placement optimization.

Selective leaching of V, W and recycling of TiO2 carrier from waste V2O5-WO3/TiO2 catalysts by mixed alkali liquor

Recovery of selective catalytic reduction (SCR) denitrification catalysts is important to reduce costs and environmental pollution. To recover and reuse the metal resources in the waste V2O5 - WO3/TiO2 catalyst, a mixed alkaline leaching system of NH3·H2O and sodium compounds was used. The method keeps the carrier composition and structure unchanged while achieving the separation of V and W. The effects of three additives, NaOH, Na2CO3 and NaCl, were investigated after determining the optimum leaching concentration of NH3·H2O at 6.0 mol‧L−1. The results showed the most superior leaching efficiency of V and W in NH3·H2O - NaOH solution. Next, the effects of additive concentrations and process parameters on the leaching of V and W were systematically investigated. Under optimum leaching conditions, 77.47%V and 47.7%W were leached without destroying the carrier. Moreover, this method showed similar separation of valuable metals from different components of waste catalysts, demonstrating its versatility. Meanwhile, the TiO2 carriers with undamaged structure can be directly prepared as new denitrification catalysts. Finally, the comprehensive utilization of 92.84%W, 91.94%V and 92.17%Ti resources in the waste denitrification catalyst is realized. Overall, the method may be an environmentally friendly solution for resource recovery of waste SCR catalysts.

Analize učinaka oštećenja na rešetkasto postolje izvanobalne platforme

In this paper, an offshore platform subjected to dynamic loading for different damage cases was modelled via fluid-structure interaction (FSI) analysis. Different damage models were considered in the case where one leg was broken, and the Young’s modulus of the damaged member was reduced with four different severity ratios. In addition to the five damaged structures, the undamaged structure was modelled according to two different leg spacing conditions. Thus, the damaged models were compared among themselves as well as with undamaged models. In this study, models were investigated using a numerical FSI technique. The numerical technique was verified using semi-analytical modelling. At this stage, the equation of motion of one of the structural models was solved using a semi-analytical method based on a multi-degree-of-freedom system. In addition, the numerical environment model was verified using a semi-analytical solution of the free-surface motion equation and the wave velocity-wave force curve. An Abaqus finite-element analysis program was used to model the structures and their surroundings. While the structures were modelled using the Lagrangian technique, the fluid surroundings were modelled using the Eulerian technique. Both the conditions of leg spacing and different severity ratios were modelled, and the most negative damage type was revealed.

Interlayer Nano-Dots Induced High-Rate Supercapacitors.

The fast OH- transfer between hydroxide layers is the key to enhancing the charge storage efficiency of layered double hydroxides (LDH)-based supercapacitors (SCs). Constructing interlayer reactive sites in LDH is much expected but still a huge challenge. In this work, CdS nano-dots (NDs) are introduced to interlayers of ultra-thin NiFe-LDH (denoted CdSinter. -NiFe-LDH), promoting the interlayer ions flow for higher redox activity. The excellent performance is not only due to the enlarged layer spacing (from 0.70 to 0.81nm) but also stems from anchored interlayer reactive units and the undamaged original layered structure of LDH, which contribute to the improvement of OH- diffusion coefficient (1.6×10-8 cm2 s-1 ) and electrochemical active area (601mFcm-2 ) better than that of CdS NDs on the surface of NiFe-LDH (2.1×10-9 cm2 s-1 and 350mFcm-2 ). The champion CdSinter. -NiFe-LDH electrode displays high capacitance of 3330.0Fg-1 at 1Ag-1 and excellent retention capacitance of 90.9% at 10Ag-1 , which is better than the NiFe-LDH with CdS NDs on the surface (1966.6Fg-1 ). Moreover, the assembled asymmetric SCs (ASC)device demonstrate an outstanding energy density/power density (121.56Whkg-1 /754.5Wkg-1 ).

Advanced Video-Based Processing for Low-Cost Damage Assessment of Buildings under Seismic Loading in Shaking Table Tests.

This paper explores the potential of a low-cost, advanced video-based technique for the assessment of structural damage to buildings caused by seismic loading. A low-cost, high-speed video camera was utilized for the motion magnification processing of footage of a two-story reinforced-concrete frame building subjected to shaking table tests. The damage after seismic loading was estimated by analyzing the dynamic behavior (i.e., modal parameters) and the structural deformations of the building in magnified videos. The results using the motion magnification procedure were compared for validation of the method of the damage assessment obtained through analyses of conventional accelerometric sensors and high-precision optical markers tracked using a passive 3D motion capture system. In addition, 3D laser scanning to obtain an accurate survey of the building geometry before and after the seismic tests was carried out. In particular, accelerometric recordings were also processed and analyzed using several stationary and nonstationary signal processing techniques with the aim of analyzing the linear behavior of the undamaged structure and the nonlinear structural behavior during damaging shaking table tests. The proposed procedure based on the analysis of magnified videos provided an accurate estimate of the main modal frequency and the damage location through the analysis of the modal shapes, which were confirmed using advanced analyses of the accelerometric data. Consequently, the main novelty of the study was the highlighting of a simple procedure with high potential for the extraction and analysis of modal parameters, with a special focus on the analysis of the modal shape's curvature, which provides accurate information on the location of the damage in a structure, while using a noncontact and low-cost method.

Failure Initiation Analysis of a PRSEUS BWB Wing Subjected to Structural Damage

In this study, a finite element approach was used to analyze the PRSEUS-based undamaged wing structure of a civil aircraft with a blended-wing-body configuration. The displacement, stress, and strain distribution of the PRSEUS wing structure were studied under an aerodynamic load with three different values of the factor of safety. This was used as a reference to study the response of the same wing configuration, first with a single stringer, where failure was initiated at the fourth loading value, while the second loading condition was sufficient to initiate failure in the triple-stringer damage wing. In addition, damage to rib components was investigated, and it was shown that damage to a single rib and double rib did not impose significant risks to the structural integrity of the wing structure, and the results have shown that the values of displacement, stress, and strain do not differ much from those of the undamaged wing, even as the length of the rib damage is increased.

Reinforced Hydrophobic Molecular Layer Promoting Waterproof Lithium for High-Performance Lithium-Metal Batteries

The employment of lithium (Li) metal is crucial to sustainable Li metal batteries (LMBs) with realistically high energy density. The management and usage of Li in reality, however, remain high challenge due to the desirable of obtaining an undamaged Li structure arising from the indispensable in extenuating strongly environmental dependence of Li during stored procedure and minimizing the Li depletion and pulverization on long-term cycles. Herein, we impair the molecular hydrogen bonding cooperation between lithium and water molecules on the surface of Li to demonstrate an achievement of environmental independent and durable Li via integrating a reinforced molecular hydrophobic interface on the surface of Li. As a result, the molecular hydrophobic interface modified Li metal can exhibit dendrite-free Li deposition and achieve stable operation for 200 cycles in Li-S full cell at a current of 1 C.

A Bayesian hypothesis testing-based statistical decision philosophy for structural damage detection

In this article, a new statistical decision philosophy is developed to tackle structural damage detection problems which are defined in the context of novelty detection. In line with this philosophy, structural damage detection is achieved by deriving the posterior probability of damage presence from the Bayesian testing of two competing hypotheses, with the null and alternative hypotheses representing the undamaged and damaged states of a structure of concern, respectively. To resolve the tricky problem of prior appropriateness in Bayesian hypothesis testing, a general prior specification criterion is devised based on the notion of risk management, including the risk of false positive indication (an undamaged structure is incorrectly identified as damaged) and the risk of false negative indication (a damaged structure is incorrectly identified as undamaged). To determine an optimal risk level, two principles, namely the principle of posterior probability difference minimization (PPDM) and the principle of posterior probability product maximization (PPPM), are defined. The PPDM principle is to minimize the difference between the ability of a novelty detector to avoid a false positive and its ability to avoid a false negative, and the PPPM principle is to maximize the product of the two capabilities. Both principles essentially act as a means of achieving an optimal trade-off between the false positive and false negative risks stipulated in pursuing damage detection. To demonstrate the effectiveness of the proposed statistical decision philosophy for structural damage detection, experimental data obtained from a 5-story steel frame model and a 38-story concrete building model have been investigated.

In Ukrainian

The undamaged structure and functionality of the skeleton are a prerequisite for ensuring the quality of human life. The introduction of the latest treatment methods and prosthetics in traumatic surgery, oncology, cranial surgery, and dentistry form a demand for biomaterials with functionalized properties. The growth of new bone tissue is a cell-regulated process based on creating a specific bone morphology, which combines the organic matrix and its inorganic content. The inorganic component of human bones and teeth is calcium deficiency hydroxyapatite (cdHA), with a molar ratio of Ca/P ranging from 1.5 to 1.67. The combination of cdHA and natural polymers in the material allows the incorporation of proteins and growth factors into the polymer matrix. It promotes biocompatibility and the growth of new bone tissue. This review considers the critical role of the porosity parameter of biomaterials (BM) in their use for bone regeneration. Porosity is an essential characteristic of BM and guarantees the interaction of the material with cells in bone formation, promoting vascularization and the process of biosorption of synthetic graft when it is replaced by newly formed native bone. At the same time, the degree of porosity should correlate with mechanical stability to maintain the structural integrity of BM in the process of hard tissue regeneration. Processes involving cells and proteins during BM implantation with both high (70–80 %) and low (≤ 45 %) degrees of porosity are considered. Data on existing methods of obtaining BM in porous scaffolds are given. The specified degree of porosity is provided by chemical (cross-linking) and physical (sublimation) methods. The effects of pores of different sizes and shapes on bone formation and vascularization are considered. It is shown that porosity is an influential factor influencing the mechanical properties of scaffolds, in particular, the stiffness of BM - a parameter that affects the proliferation of osteoblasts by regulating cell adhesion in the scaffold structure. The influence of the biopolymer component (Sodium Alginate - AN) on the porosity and swelling of hybrid apatite-biopolymer (HA/AN) composites, in which nanometric needle crystallites represent HA, is analyzed in detail.

A Methodology for a Coupled Structural - CFD Analysis of Compressor Rotor Blades Subjected to Ice Impact with Uncertain Impactor Parameters

Abstract A method for a coupled structural - Computational Fluid Dynamics (CFD) analysis of a compressor rotor blade subjected to an ice impact scenario is investigated to assess the impact related blade deformations from a structural and fluid-dynamics perspective. On the basis of a probabilistic approach, in total 50 impact scenarios are derived for this study. In a first step the numerical structural model based on Finite Elements (FE) is discussed, including several parameter variations like impact location, ice diameter, ice density and rotor speed. Different analysis steps are subsequently carried out using LSDYNA implicit / explicit on a high performance computing (HPC) cluster. Resulting blade deformations are evaluated in terms of local plastic deformation, cup size and modal parameters in comparison to the undamaged reference structure. The resultant post-impact blade geometry is extracted from the result data and passed to the CFD simulation setup in a fully automated manner. Based on this deformed structural mesh data, the fluid mesh is morphed via a radial basis function (RBF) approach and analysed with CFD. Finally, an uncertainty quantification study is performed to assess the variability of results with regard to the definition of the ice impactor.