Structural Damage Characteristics Research Articles

Interference effect of frequency selective surface on lightning attachment

Airborne electromagnetic functional devices represented by frequency selective surface (FSS) are receiving increasing attention due to the ever-growing complication of electromagnetic environment in air space. Previous investigations have highlighted the capability of FSS to induce the distorted electric field encompassing an airborne radome. This phenomenon interferes with lightning attachment behavior and compromises the effectiveness of anti-lightning devices. A current challenge is how to reveal the physical mechanism behind this interference. In this paper, a lightning model is established for a honeycomb sandwich composite-FSS structure and a single FSS array, respectively, to investigate the interference effect of FSS on lightning attachment. Arc behavior is verified by structural damage characteristics in relevant experiments. An equivalent circuit representing the process of an FSS array suffering a lightning strike is proposed to reveal the interference mechanism of FSS. The results indicate that the electrical connectivity of FSS has a significant impact on lightning attachment behavior. Patch FSS can induce partial discharge and exacerbate interface damage to a radome while aperture FSS eases energy accumulation, although the latter is prone to induce lightning leaders without integration with composites. The obtained results provide potential guidance for the structural and anti-lightning design of an airborne radome.

A novel semi-convex function for simultaneous identification of moving vehicle loads and bridge damage

For the simultaneous identification (SI) problem on the moving vehicle loads and bridge damage, the existing methods fail to appropriately consider the sparse characteristics of structural damage and ignore the prior information of vehicle loads, which make them suffering from challenges such as prolonged computation cost, poor noise robustness, and limited identification accuracy. To address this issue, a novel semi-convex function is proposed to construct a theoretical framework for the SI problem using the bridge dynamic responses subjected to moving vehicles in this study. Firstly, the bridge damage-induced virtual forces are conceptualized as a new form of moving residual forces characterized by block sparsity properties, and the damage location is then determined by the frequency characteristics with the largest fundamental frequency amplitude of moving residual forces. Secondly, a semi-convex function model encompassing moving forces and moving residual forces is defined. Combined with sparse regularization strategy, an improved alternating direction method of multipliers algorithm is proposed and applied to simultaneously solve for both moving vehicle loads and damage degrees. To assess the effectiveness and feasibility of the proposed method, extensive numerical validations are conducted in various bridge damage scenarios. Additionally, a series of truss bridge experiments are performed in laboratory under multiple damage and vehicle axle-weight conditions. The results show that compared with the existing outstanding methods, the proposed semi-convex function method can significantly reduce the identification cost, enhance robustness to noise, and demonstrate notable improvements in accuracy for the SI problem, which provides an innovative and more efficient solution to the SI problem in bridge engineering.

Study on the mesoscopic mechanical behavior and damage constitutive model of micro-steel fiber reinforced recycled aggregate concrete

This study employs in-situ 4D CT experimental techniques to investigate the mesostructured changes and mechanical behavior of micro steel fiber-reinforced recycled aggregate concrete (MSF-RAC) under uniaxial compression and cyclic loading conditions. The research aims to address the scientific problem of limited understanding of how micro steel fibers affect the mesoscopic mechanical behavior and structural damage characteristics of recycled aggregate concrete. High-resolution CT scanning technology was utilized for real-time observation of crack initiation and propagation, revealing the micro-mechanisms by which micro steel fibers enhance RAC. The study found that incorporating micro-steel fibers significantly improves the density of the interfacial transition zone (ITZ), inhibits crack development, and enhances the mechanical properties of the concrete. Based on these observations, an improved stiffness degradation damage constitutive model was proposed, which comprehensively considers the distribution orientation of micro steel fibers and ITZ characteristics. The model effectively predicts the stress-strain relationship of MSF-RAC under various conditions, demonstrating high accuracy and practicality. These findings provide important theoretical support and experimental evidence for the optimal design of RAC, showcasing significant engineering application value by promoting the sustainable use of recycled materials in construction.

Dynamic response and blast resistance of I‐shaped steel‐concrete composite beam under explosive loading

AbstractTo investigate the dynamic mechanical response and damage mechanisms of I‐shaped steel‐concrete composite beams under explosive loads, experimental research and numerical simulations were conducted on steel‐concrete composite structures. The accuracy of the numerical analysis model was validated by comparing the damage characteristics of the structures obtained from explosive tests on the steel‐concrete composite components. Based on this, numerical simulations were performed on steel‐concrete composite beams using the explicit dynamic analysis software ANSYS/LS‐DYNA, and a study on their damage mechanisms was conducted. This study resulted in the acquisition of dynamic mechanical response patterns, including time‐dependent stress, strain, displacement, acceleration, and so on. Different structural damage characteristics under various explosive conditions were summarized, and key parameters affecting the blast resistance of the structure were analyzed. The research findings indicated that, in contrast to the failure characteristics of I‐shaped reinforced concrete (RC) beams, the failure characteristics of I‐shaped steel‐concrete composite beams mainly include punching and shearing failure of the steel‐RC slab and local buckling of the steel beam. Under the same explosive conditions, steel‐concrete composite structures exhibit superior blast resistance, with certain changes in structural parameters significantly improving blast resistance. The research results can provide theoretical support and a scientific basis for the proactive design of blast protection in steel‐concrete beams.

Anti-explosion Performance of a New Type of Polyurea-Coated Corrugated Steel Plate Reinforced Concrete Slab

Improving the explosion resistance of the building wall has been a hot topic in the current protection engineering research, in this process, corrugated steel and polyisocyanate oxazolidine (POZD) were widely used, but there are few studies on the anti-explosion performance of the composite structure of the two. In this paper, the effects of POZD and corrugated steel on the explosion resistance of POZD-coated corrugated steel plate reinforced concrete slab (PSRC) under contact explosion were studied by test and numerical simulation. The finite element (FE) model of the PSRC slab was established by using Arbitrary Lagrangian–Eulerian (ALE) method. The principle of POZD coating reinforced structure was revealed by analyzing the attenuation process of stress wave propagation in the structure. Subsequently, a series of numerical calculations were conducted to investigate the effect of POZD thickness and corrugated steel angle on the performance of the PSRC slab under explosive load. The relationship between structural damage characteristics and the POZD coating was established, the empirical formula of the normalized maximum mid-span displacement considering POZD thickness and TNT mass was obtained. The effect of corrugated steel with different angles on its anti-explosion performance was analyzed, the empirical formula of the maximum deflection considering corrugated steel angle and TNT mass was obtained. Studies have shown that the peak stress of the stress wave generated by the explosion is only 2.79% of the incident wave after the POZD coating is coated on the back of the structure, the anti-explosion performance of the structure is greatly improved. Increasing the thickness of POZD can significantly increase the anti-explosion performance of PSRC slab, the maximum deflection of PSRC slab decreases exponentially with increasing POZD thickness. The explosion resistance of PSRC slab was enhanced with increasing corrugated steel angles. The corrugated steel angles is 50 , the improvement effect of PSRC is the best.

Study on damage characteristics of sandwich plate under the combined action of explosion shock wave and randomly distributed fragments

The load resulting from the explosion of a missile warhead comprises high-intensity shock waves and a random distribution of fragment loads characterized by diverse shapes, sizes, and distributions. Complex coupling between shock waves and fragments are necessary to comprehensively evaluate the blast-resistance performance of U-typed sandwich panels. A numerical model based on the finite-element software was established to investigate the dynamic response of U-typed sandwich-panel structures under the combined action of shock waves and randomly distributed fragment groups. The effectiveness of the numerical model was validated by comparing results with experimental values. A random fragment field-generation model that conforms to the characteristics of a power-law distribution is constructed through the implementation of the Voronoi segmentation algorithm and a Python-based computational module. Building on this framework, this study explored the complex coupling process between shock waves and randomly distributed fragments. Furthermore, an in-depth analysis was performed to examine the structural damage characteristics with various fragment distributions and fragment densities. Diverse perforation patterns were observed in the upper plate of the U-typed sandwich panel for different fragment densities. Furthermore, the perforation area of the upper plate initially increased, followed by a decrease with increasing fragment density.

Structural damage characteristics and mechanism of granite residual soil

Structural damage characteristics and mechanism of granite residual soil

Study on the effectiveness of impact factor in underwater explosion model test

The dimensionless quantity is the invariant under the unit conversion, and the only choice to characterize the laws of physics. Aiming at the similarity law of underwater explosion model test, the deficiency of traditional impact factor and the similarity condition of single value of model test are analyzed by using dimensional analysis method and combining with domestic and foreign research. In view of the shortcomings of traditional impact factors, a new impact factor is derived from the perspective of single-value similarity based on the impact dynamic response characteristics of underwater explosion structures. Taking the midship cabin structure of a certain frigate as the prototype, the scale model tests are designed based on the traditional and new impact factors respectively. The effectiveness of the impact factors is evaluated from the aspects of structural damage characteristics, dimensionless deformation deflection, dimensionless velocity and dimensionless acceleration at the center of the structure. To account for the impact of structural characteristics, scale ratio, and proportional distance on the impact factor's effectiveness, various grillage, cabin, and hull girder model tests are conducted using ships of different tonnages as prototypes. The results of the model test, guided by the new impact factor, align well with the prototype test data. In contrast to the traditional impact factor, the model test exhibits greater precision for predicting structural responses, with a broad spectrum of potential applications.

Micro-damage characteristics of cold recycled mixture under freeze–thaw cycles based on discrete-element modeling

Cold recycled mixture with bitumen emulsion (CRME) is an energy-saving and environmentally friendly material. However, the micro-scale damage characteristics under the coupling of water temperature are still unknown and need to be investigated. In this paper, based on the X-ray CT section, the two-dimensional discrete element method (DEM) was used to precise reconstruct the CRME under different freeze–thaw (F-T) cycles. Simultaneously, the fracture behavior, strength, and structural damage characteristics of CRME under F-T cycles were studied by DEM and digital image correlation technology. The results show that F-T cycle significantly damage the formation of strength force chain in CRME. After undergoing 20F-T cycles, the specimen exhibited tensile failure without any obvious crack penetration. The cracks required of the specimen after the F-T cycles to reach the peak load were less than the non-F-T. The stress–strain concentrations were reinforced, making the specimen more susceptible to unloading during the later stages of testing after F-T cycles. The repeated F-T cycles damaged the overall microstructure of the mixture, resulting in less noticeable tensile effects during the splitting test. Utilizing a precise DEM modeling method proved to be practical and effective in investigating the micro-damage characteristics of cold recycled mixture.

Simultaneous identification of impact force and structural local damage under pre-segmentation of structural elements

Identifying dynamic force and structural damage is often mathematically treated as an optimization problem. The number of optimization variables is closely related to the complexity and calculation amount of the identified problem. To reduce the number of optimization variables during the solution process and emphasize the localized characteristics of structural damage, a novel output-only method is proposed to address the problem of simultaneous identification under a pre-assumption of structural damage locations. The main idea is to decompose the identified problem into a series of subtasks. For each task, only part of a structure rather than the whole will be updated to reduce the discrepancy between the calculated responses and the measured ones. To realize this idea, the structure is simulated via a finite element (FE) model, and then the structural elements are divided into several groups. Each group is used to generate one identified task, in which the identified problem is formulated as a constrained optimization problem. Stiffness reduction coefficients of the elements, which are contained in the corresponding element group, are regarded as the optimization variables, while the impact force reconstructed via sparse regularization is mathematically formulated as a constraint for the optimization problem. The gradient descent method combined with a greedy strategy is introduced for solving the optimization problem of each task. The identified results obtained from all the tasks are regarded as candidates for a final one. To comprehensively consider the residual errors of structural responses and the sparsity of identified results, the Bayesian information criterion (BIC) is introduced for determining the final identified result. Numerical simulations and experimental studies are carried out. The illustrated results demonstrate that the proposed method is capable of simultaneously identifying the impact force and structural local damage, even though it still has shortcomings such as relatively poor robustness of identified damage and great subjectivity of group division for structural elements. Some relative issues are discussed as well.

Comparative Study of Using Displacement Influence Lines and Their Derivatives for Structural Damage Identification

Structural damage identification has recently become one of the most important topics for engineering structures due to its benefits in enhancing safety, reducing life-cycle cost, and providing guidance for system construction and maintenance. This research studies the accuracy of using displacement influence lines (DIL) and their derivatives (first and second derivative) for detecting structural damage characteristics (location and severity). The study includes analytical and numerical studies to investigate the sensitivity of displacement influence lines and their derivatives (first and second derivative) as a main parameter for damage identification. The results illustrate that the method can locate and quantify damage in both simply supported and continuous beams without the need for an optimization algorithm. Although, for simply supported beam, the optimal location of the displacement measurement point is at the middle of span. While, for continuous beam, one displacement sensor at the middle of each span enables locating the damages reliably. The advantages and disadvantages of using this index are also discussed.

Comparative study of using rotation influence lines and their derivatives for structural damage detection

Structural damage detection has recently become one of the most important topics for engineering structures due to its benefits in enhancing safety, reducing life-cycle cost and providing guidance for system construction and maintenance. This research studies the accuracy of using rotation influence lines (RIL) and their derivatives (first and second derivatives) for detecting structural damage characteristics (location and severity). The study includes an analytical investigation of damage detection of multiple damages in simply supported beam. Then, numerical studies have been conducted to investigate the effectiveness of the proposed method for damage identification of simply supported beam (determinate structure), continuous beam (indeterminate structure) with different damage characteristics. Furthermore, the most effective inclinometer locations and number of inclinometers for structural damage detection on simply supported and continuous beams are reported. Furthermore, noise intensity effects from the limited inclinometer precision, inclinometer faults and transmission errors are discussed in this paper.

Numerical study on structural damage characteristics under long pulse width of underwater nuclear explosions

ABSTRACT In this paper, the loading characteristics of underwater nuclear explosions with low peak and long pulse widths are simulated using the difference in peak pressure and pulse width caused by different charge shapes. The flow field loading characteristics under four charge shapes are analyzed, and the plate failure response under contact and equal impact factors are discussed. The results show that the load characteristics of spherical and cylindrical charge are high peak pressure and narrow pulse width; The load characteristic of truncated cones charge is low peak pressure and long pulse width, which can reflect the long pulse width load characteristics of underwater nuclear explosions. In addition, it was found that the damage patterns of structures with different load characteristics under the same loading conditions differed significantly. This paper has important guiding significance for the study of underwater nuclear explosions and their damage to structures.

Pore characteristics and micro-structure change of undisturbed loess induced by acid corrosion

With the rapid development of coal chemical base and urbanization construction in China's Loess Plateau, the phenomenon of acid corrosion induced loess geological disasters tends to occur frequently in this region. Loess is characterized by high water sensitivity, dense vertical joint surface, and rich in carbonate minerals, which providing a good precondition for acid solution corrosion. Due to the occurrence of chemical erosion, the changes of loess structure and strength become more complex, and there is a significant difference from the conventional water infiltration-induced loess disasters. In order to clearly grasp the internal mineral and structural damage characteristics of loess under acid dissolution conditions, this work studies the pore characteristics and micro-structure change of undisturbed loess under acid corrosion conditions with different pH values (7, 5 and 3) and dissolution times (5,10 and 15 days). It is found that the content of carbonate minerals in the undisturbed loess,and the combined structure characteristics are the two main factors affecting its acid corrosion effect. Specific findings include as: (1) With the decrease of pH, the dissolution of carbonate minerals such as calcite and dolomite intensifies (the element content of the precipitate: Ca96.58%, Mg1.26%), and the selective dissolution of silicate minerals (albite and chlorite) are obvious, which provides expansion space for pores. As a result, the change of the pore structure of undisturbed loess by acid leaching is as follows: Expansion of initial joints→Connectivity and enlargement of internal pores→The increase of new shallow pores. Meanwhile, under the action of acid dissolution, the cohesive substances were rearranged due to the dissolution, disintegration and rotation of the skeleton particles during the collapse, resulting in an increasing in the content of fine particles in the soil. (2) With the increase of corrosion time, the roundness increased from 7.19 to 25.98 which proves that the contact between the acid solution and mineral particles is more complete, and the effect of corrosion and particle aggregation is more significant. This results in a reciprocating unidirectional development of the pore structure. Flocculated particles with clay properties appear alternately in the soil structure. (3)The occurrence of acid-sensitive geological disasters in loess is mainly divided into three stages: The filling of the structural surface is eroded by acid→The horizontal and vertical erosion is intensify→The soil is broken down into particles that are washed away. This study has a certain reference for understanding the damage mechanism and early warning of loess eroded by acid solution in China's Loess Plateau.

Peridynamics simulation of structural damage characteristics in rock sheds under rockfall impact

Rock shed structure is widely constructed above a tunnel portal to protect the tunnel from rockfall hazards. The damage mechanism of rock sheds under rockfall impact is crucial, but is yet still unclear. In this study, a dynamic peridynamic model with a relatively simple yet effective failure criterion, which considers the strain rate effect for reinforced concrete shed structures under rockfall impact and is convenient for engineering applications, is developed. After assessing the proposed method by comparing with two experimental tests, varieties of simulation cases are simulated to thoroughly investigate the influence of different factors, including the shape, mass and drop height of the falling rock, on the damage behavior of rock sheds without backfills under rockfall impact. The safety of the tunnel and the damage position for strengthening are evaluated by the proposed method. The structural damage degree of the tunnel increases with the increase of drop height and rockfall mass, but the resulting growth rate differs. The penetration ability of a round falling rock is superior to a squared or an octagon falling rock. A non-circular falling rock could induce a larger damage zone. Under the angular falling rock impact, the structure is more likely to be penetrated with a sharp impact angle. The modes of local crush and flexural failure occur firstly, and then the tunnel is sheared by the falling rock until overall collapse happens. Shear failure is more obvious when the drop height is higher or under the non-circular falling rock impact. The work suggests that all exiting analysis techniques for simplifying the impact force as a static load are not sufficient to understand the resistance of rock sheds under rockfall.

Structural damage characteristics of MoSe2 nanosheets irradiated by oxygen ions

Molybdenum diselenide (MoSe2) is one of the most valuable Two-dimensional transition metal dichalcogenides (TMDs) materials due to their unique and exotic physical properties. Its properties can be easily altered in an irradiation environment and therefore affect the properties of MoSe2 based devices. In this work, we discussed the effect of oxygen ion irradiation on the structures and optical band gap (Eg) of the MoSe2 continuous nanosheets on sapphire substrates by using complementary characterization techniques. The results show that more lattice disorder and lattice damage induced by high fluences oxygen ion irradiation led to the structural degradation and produced tensile stress in the nanosheets. Average optical absorption rate decreased and Eg decreased from 1.495 eV to 1.46 eV. The results will be helpful for understanding the damage study of the MoSe2 continuous nanosheets with oxygen ion irradiation.

Structural Damage Characteristics of a Layer-to-Layer 3-D Angle-Interlock Woven Composite Subjected to Drop-Weight Impact

Abstract The most attractive structural feature of the three-dimensional (3D) angle-interlock woven structure is that the straight weft yarns are bundled by the undulated warp yarns, which induces the overall good structural stability and a stable fabric structure. Thus the 3-D angle-interlock woven composite (3DAWC) prepared by the vacuum-assisted resin transfer molding (VARTM) curing process has excellent mechanical properties by using the fabric and epoxy resin as the reinforcement and matrix, respectively. The low-velocity impact damage properties of the composites under different drop-weight energies (70, 80, and 100 J) were tested experimentally. The load–displacement curves, energy–time curves, and the ultimate failure modes were obtained to analyze the performance of resistance to low-velocity impact, as well as the impact energy absorption effect and failure mechanism, especially the structural damage characteristics of the 3DAWC subjected to the low-velocity impact of drop weight. By analyzing the obtained experimental results, it is found that the fabric reinforcement is the primary energy absorption component and the impact energy mainly propagates along the longitudinal direction of the yarns, especially the weft yarn system, which is arranged in a straight way. In addition, as the impact energy increases, the energy absorbed and dissipated by the composite increases simultaneously. This phenomenon is manifested in the severity of deformation and damage of the material, i.e., the amount of deformation and size of the damaged area.

Characterization of Near-Fault Effects on Potential Cumulative Damage of Reinforced Concrete Bridge Piers

The objective of this study is to characterize the potential damage of near-fault ground motions on reinforced concrete bridge piers, providing information for engineering practice. To achieve this objective, 200 real near-fault pulse-type records and a bridge pier were selected. The same number of real far-fault ground motions was also selected for comparison. Inelastic time history and damage analyses were performed for the pier subjected to the selected near-fault and far-fault ground motions. The obtained results showed that more than 91% near-fault motions caused the pier to collapse while the pier survived under almost all far-fault motions. The responses of the pier under near-fault motions were characterized by one or few large hysteretic cycles. The damage indices of the pier subjected to near-fault ground motions increased rapidly when the pier underwent pulses of near-fault motions, and the pier damage was mainly caused by pulses. Collapse of the pier subjected to near-fault motions occurred at the pulse time. The duration to collapse, which was defined as the duration from light damage to collapse, of the pier under near-fault motions was extremely short (approximately 2.3–2.5 s). These special and negative structural damage characteristics of near-fault ground motions should be considered in designing and mitigating seismic hazards for structures located in near-fault regions.

Structural damage location and evaluation model inspired by memory and causal reasoning of the human brain

Structural health monitoring system should handle massive sensor information correctly and complete the damage location and evaluation. This study proposes a structural damage location and evaluation model inspired by the memory and causal reasoning of the human brain. Mass-monitoring data filtering is conducted in the short-term memory area. The long-term memory area stores useful information that contains the characteristics of structural damage and has two functions. First, the support degree index is deduced to locate the damage source of the basement. Second, the historical acoustic emission data and sparse autoencoder classifier are utilized to identify moisture content and then evaluate the damage level of the basement. Experiments show the functions of the model, such as monitoring data reduction, locating the damage source, and evaluating the level of damage, without prior knowledge of mechanics.

Dynamic assessment of the seismic isolation influence for various aircraft impact loads on the CPR1000 containment

Abstract An aircraft impact (AI) on a nuclear power plant (NPP) is considered to be a beyond-design-basis event that draws considerable attention in the nuclear field. As some NPPs have already adopted the seismic isolation technology, and there are relevant standards to guide the application of this technology in future NPPs, a new challenge is that nuclear power engineers have to determine a reasonable method for performing AI analysis of base-isolated NPPs. Hence, dynamic influences of the seismic isolation on the vibration and structural damage characteristics of the base-isolated CPR1000 containment are studied under various aircraft loads. Unlike the seismic case, the impact energy of AI is directly impacting on the superstructure. Under the coupled influence of the seismic isolation and the various AI load, the flexible isolation layer weakens the constraint function of the foundation on the superstructure, the results show that the seismic isolation bearings will produce a large horizontal deformation if the AI load is large enough, the acceleration response at the base-mat will also be significantly affected by the different horizontal stiffness of the isolation bearing. These concerns require consideration during the design of the seismic isolation system.