Failure Of Bars Research Articles

Experimental investigations on the blast response of reinforced NSC, FRC and UHPC I-shape girders under contact explosions

To investigate the blast response and evaluate the structural resilience of reinforced I-shape girders, seven reinforced normal strength concrete (NSC), fiber reinforced concrete (FRC), and ultra-high performance concrete (UHPC) specimens are subjected to multiple contact explosions in this study. With the test results, the concrete damage regions and plastic deformation of steel bars are used to recognize the damage mechanism of the test specimens. The experimental results show that the damage modes of I-shape girders are mainly dominated by vertical punctures and transverse shear failures. Due to fragile characteristics, nearly 35 % of the punching crater in concrete webs, the entire shear failure of top plates, and severe plastic deformation of steel bars are discovered in NSC specimens. Polyethylene fibers improve ductility, allowing for smaller steel bar deflection and a reduction in punching depth to 21.6 % in FPC specimens. However, due to the oversized impact energies and the insufficient material strength, the transverse shear failure cannot be significantly mitigated. By contrast, not only significantly reduced punching depth but also greatly mitigated transverse shear failures are observed in UHPC specimens. Under 50 g∼200 g contact explosions, the punching depth ratios are reduced to 3.3 %, 16.6 %, and 25.8 %, merely. Apart from that, after explosions, the transverse shear failure and plastic deformation of steel bars can be effectively reduced. Due to the remarkably decreased damage regions, the UHPC specimens exhibit better structural resilience after blast loadings.

Bond behaviour of staggered/non-staggered lap-spliced GFRP bars in concrete

This paper reports on the results of an experimental and analytical investigation into the bond behaviour of glass fibre-reinforced polymer (GFRP) splices in concrete. Eleven full-scale beam specimens in which GFRP bars were spliced within the constant-moment zone are examined. The study incorporates several key test variables, encompassing the ratio of bars lapped (33%, 50%, and 100%), surface characteristics (including sand-coated, ribbed, and wrapped bars), bar diameter (12 mm and 16 mm), and splice length (ranging from 30 to 40 times the bar diameter). The findings reveal a reduction in bond strength ranging from 12 to 24% for staggered bars when compared to their non-staggered counterparts. Furthermore, an increase in bar diameter is shown to decrease bond strength by 16%, whilst surface treatment also influences both bond strength and the pattern of cracking in the splice region. Increasing the splice length from 30 to 40 times the bar diameter enhances bar failure stress by 26%, but it also reduces the average bond strength by 9%. A new predictive equation for the design bond strength of fibre-reinforced polymer (FRP) bars is developed by utilizing a data base of 151 test results. The predicted bond strengths demonstrate greater consistency with experimental outcomes in comparison to previous models.

Response Surface Optimization of Car Support Jack Bar on Design Parameter via Finite Element Analysis

The optimized design parameter of the car support jack bar is crucial in ensuring the safety of maintenance activity. Improper design of the bar and pinhole could induce the jack bar's failure when enduring the high loading of the car. This paper presents the response surface optimization on the design parameter of the car jack bar using finite element analysis. Three factors: outer diameter (A), pinhole diameter (B), and bar thickness (C), and two responses which are Von Mises stress (Y1) and displacement (Y2) of the jack bar, were considered in the optimization study. The design of the numerical experiment was constructed using the central composite design (CCD). The results revealed that outer and pinhole diameters are the two most significant factors in the responses. The changes in outer and pinhole diameters crucially affected the Von Mises stress and displacement of the jack bar. The optimized factors suggested in the optimization software are 49.79 mm outer diameter, 21.70 mm pinhole diameter, and 5.85 mm bar thickness. The application of optimized factors yielded the minimum responses that are 45.23 MPa Von Mises stress and 0.022 mm of displacement for the car jack bar. The optimization findings are expected to be useful for the engineer in designing the high-reliability car jack bar.

Progressive collapse behaviour of earthquake-damaged interior precast concrete joints with headed bars and plastic hinge relocation

This study investigated progressive collapse behaviour of earthquake-damaged interior precast concrete (PC) joints with headed bars. The main objective was to quantify the impact of slight and moderate earthquake damage on their residual collapse resistance. The research began with a numerical investigation to understand the interaction between a 2D frame’s global response to seismic loading and its local response during a threat-independent progressive collapse event. Additionally, a separate set of numerical studies examined interior PC joints under cyclic loading to determine maximum drift ratio demands, yielding 2.5% for slightly and 3.5% for moderately damaged joints. Subsequently, an experimental programme under quasi-static loading conditions was conducted on five interior PC joints under cyclic loading, followed by progressive collapse resistance tests. Test results indicated that damaged joints exhibited flexural and catenary action during progressive collapse, but compressive arch action could not be mobilised due to residual cracks from the initial cyclic loading phase. Comparing damaged joints to fully intact ones from a companion study revealed deterioration in stiffness and deformation capacity during a subsequent progressive collapse, with degree of severity proportional to the extent of damage sustained in the cyclic loading phase. Relative to the intact joints without being subjected to cyclic loading, moderately damaged specimens exhibited a degradation of 63% in stiffness and 38% in deformation capacity, compared to slightly damaged specimens, which showed reductions of 38% in stiffness and 28% in deformation capacity. In contrast, strain hardening of steel bars in both slightly and moderately damaged specimens led to slightly greater collapse resistance than the intact joints. Additionally, failure mode shifted from ductile fracture to premature pull-through failure of headed bars in moderately damaged specimens. In this regard, in post-earthquake progressive collapse assessment, it is recommended to use maximum crack width thresholds of 0.2 to 1.0 mm for slight damage and 1.0 to 2.0 mm for moderate damage.

Erosion mechanism of point bar retreat under the protection of a flexible mattress

Channel retreat can be responsible for the significant loss of banks, farmland, and wetlands, leading to drastic changes in fluvial sediment and local river regimes. Although current studies focus on the erosion process of natural river channels, the mechanism by which revetments, such as the flexible mattress, influence bank evolution is still unclear. Hence, by conducting a generalized model experiment, this study investigates the point bar failure process under the mattress protection, i.e., the episodic event when the soil reaches the static equilibrium state. Specifically, a scour hole develops at the junction between the soft and hard materials, causing mattress suspension on the bank toe’s side wall and resulting in a reduction coefficient for transverse scouring rate ranging from 0.08 to 0.15. Based on the theories of soil mechanics and river dynamics, the critical conditions for point bar instability were deduced, and a mechanical model describing its erosion process under the mattress protection was established. Furthermore, our model calculated the bank morphology and total erosion volume at different periods in the flume experiment, demonstrating a good agreement with the measured data. Additionally, variations in stability coefficient and forces exerted on soil (including shear strength, gravity, and fluid pressure) of the typical sections during point bar retreat were analyzed. Sensitivity analysis of the bank toe stability emphasized the controlling effect of soil mechanical properties and the negative feedback of mattress weight. The results reveal the interaction mechanism between the mattress protection and point bar failure, theoretically guiding the bank erosion strengthening and river management planning.

Experimental and finite element analysis on mechanical performance of prefabricated assembly inverted arch to lining joints of large section highway tunnel under direct shear loding

To investigate the mechanical properties of the prefabricated inverted arch to cast-in-place lining joints, 21 "Z"-shaped shear specimens for direct shear testing were designed and manufactured, with the interface planted steel bars ratio, interface size, and interface treatment method as variable parameters. The whole failure process of the joint under a direct shear stress state was observed and recorded during the test, the shear-slip curve of the specimen was obtained, failure mechanism and variation law of the joint's direct shear mechanical characteristics were carefully examined. The results reveal that the specimen's shear performance improves following the interface chiselling treatment. The specimens fail in three ways: simple concrete failure, simple planted steel bars failure, and assimilative failure of the concrete and the planted steel bars. The ultimate shear capacity, ductile failure capacity, resistance to damage evolution, and energy dissipation capacity of the specimens rise as the planted steel bars ratio increases. When the planted steel bars ratio increases from 0.7% to 1.1%, the improvement is the most significant, reaching 66.3%. When the planted steel bars ratio is the same, the shear bearing capacity improves as the interface size grows. The finite element model of the “Z”-shaped shear specimen of the prefabricated inverted arch and the cast-in-place lining joint is established, and the parameter extension analysis is performed. Based on the test results and the Extended Shear-Friction Theory, a high-accuracy calculation model of shear capacity of precast inverted arch and lining joint is presented.

Structure characterization and failure mechanisms of high chromium cast iron grate bar

Grate bars represent the main failure components within sintering machine trolleys. The quality of grate bars significantly impacts the production efficiency of the sintering process, and understanding the failure mechanisms of grate bars guides research in grate material development. In this study, we analyze the failure mechanisms of grate bars by comparing the structure of the grate matrix before and after failure and by examining the structural morphology of the failed zones. Our findings reveal that the austenite phase of the grate bars transforms into granular pearlite. The carbide type changes from M7C3 to M7C3 and eventually to M23C6 after extended service. P and S accumulate at the grain boundaries, resulting in the formation of the brittle phase Mx(S,P)y. Additionally, Cr diffuses to the surface, forming an oxide layer at high temperatures. The structural transformation from austenite to pearlite and the diffusion of Cr in the matrix phase increase electrode potential differences, which promote electrochemical corrosion between the matrix phase and the carbide at the grain boundary and within the inner grain. Cl being present in the service environment played an important role in the failure of grate bars by promoting high-temperature oxidation and being involved in crevice corrosion. Grate bar failure primarily results from high-temperature oxidation, electrochemical corrosion, brittle fractures, and compound actions. Finally, we propose recommendations to enhance the performance of grate bars through alloying treatments.

Effects of surface characteristics and alkalinity on the deterioration of BFRP bars and BFRP-SSC interface in seawater environment

This study investigated the surface characteristics and concrete alkalinity on the deterioration of basalt fiber reinforced polymer (BFRP) bars and the interface between BFRP bars and seawater sea-sand concrete (SSC) in a seawater environment. The degradation of BFRP bars with three surface characteristics (sand coating, helically-wound, and helically-wrapped) embedded in two alkalinities of SSCs and BFRP-SSC interface were studied by shear, tensile, and pull-out tests, respectively. Additionally, the microstructure of the BFRP and BFRP-SSC interface was characterized by Fourier transforms infrared spectroscopy (FTIR), X-ray computed tomography (X-CT), and scanning electron microscope (SEM). The experimental results showed that sand-coated BFRP bars exhibit the best durability performance among the three types of BFRP bars due to forming a protective layer of sand and the helically-wound BFRP bars degrade from the groove (rich fiber and less resin protection zone). The degradation of BFRP bars in low alkalinity (LA) SSC is significantly mitigated owing to the reduced alkalinity. Furthermore, the hindering effect of the sand layer also enhances the bond durability between bars and SSCs compared with the other two types of BFRP bars. The bond strength between BFRP bars and LA-SSC is slightly reduced after 180 days of seawater immersion, while that in ordinary (O) SSC decreases significantly. The pull-out failure of sand-coated BFRP bars in LA-SSC is wearing out of the sand layer and surface resin after environmental conditions, while that of helically-wound BFRP bars in LA-SSC are peeling off ribs. The research outcomes can serve as solid base for employing BFRP bars in the marine environment.

Detection of Broken Bars in Induction Motors Using Histogram Analysis of Current Signals

The lifetime of induction motors can be significantly extended by installing diagnostic systems for monitoring their operating conditions. In particular, detecting broken bar failures in motors is important for avoiding the risk of short circuits or other accidents with serious consequences. In the literature, many approaches have been proposed for motor fault detection; however, additional generalized methods based on local and statistical analysis could provide a low-complexity and feasible solution in this field of research. The proposed work presents a methodology for detecting one or two broken rotor bars using the sums and differences histograms (SDH) and machine learning classifiers in this context. From the SDH computed in one phase of the motor’s current, nine texture features are calculated for different displacements. Then, all features are used to train two classifiers and to find the best displacements for faults and health identification in the induction motors. A final experimental evaluation considering the best displacements shows an accuracy of 98.16% for the homogeneity feature and a few signal samples used in a decision tree classifier. Additionally, a polynomial regression curve validates the use of 50 samples to obtain an accuracy of 88.15%, whereas the highest performance is achieved for 250 samples.

A CNN-Based Methodology for Identifying Mechanical Faults in Induction Motors Using Thermography

Infrared thermography (IRT) has become an interesting alternative for performing condition assessments of different types of induction motor (IM)-based equipment when it operates under harsh conditions. The reported results from state-of-the-art articles that have analyzed thermal images do not consider (1): the presence of more than one fault, and (2) the inevitable noise-corruption the images suffer. Bearing in mind these reasons, this paper presents a convolutional neural network (CNN)-based methodology that is specifically designed to deal with noise-corrupted images for detecting the failures that have the highest incidence rate: bearing and broken bar failures; moreover, rotor misalignment failure is also considered, as it can cause a further increase in electricity consumption. The presented results show that the proposal is effective in detecting healthy and failure states, as well as identifying the failure nature, as a 95% accuracy is achieved. These results allow considering the proposal as an interesting alternative for using IRT images obtained in hostile environments.

Unconfined bond stress and slip characteristics of steel bars embedded in masonry cement mortars

Reinforcing bars are often embedded into cement mortar layers (bed joints and surface bonded) of masonry structures to enhance their structural performance to various effects. However, there is limited research available on the bond characteristics of steel bars embedded in the masonry mortars. This study was focused on assessing the bond stress and slip characteristics of steel bars anchored within masonry cement mortars. Steel bar embedded masonry cement mortar assemblages were constructed to test them under uniaxial pull-out loading to understand their bond stress and slip characteristics. A double-lap anchorage arrangement was used for these pull-out tests. In total, 72 samples were prepared, incorporating two types of masonry mortars, three steel bar diameters (6 mm, 10 mm and 12 mm) and four anchorage lengths (2.5d, 5d, 7.5d and 10d, where d is the diameter of the bar) to examine their influence on the bonding characteristics. Two types of failure modes were observed (1) pure pull-out failure of steel bars from the mortar and (2) tensile splitting of mortar, depending on the employed mortar types and steel diameters. The bond stress between the steel bars and cement mortars varied between 1.4 MPa and 7.9 MPa for the tested samples. The analytical formulations to predict the bond strength of anchored steel bars within the masonry cement mortars were verified for pull-out and mortar splitting failures to characterise the bond slip characteristics of steel bars anchored in cement mortars.

Experimental Study and Discrete Analysis of Compressive Properties of Glass Fiber-Reinforced Polymer (GFRP) Bars.

Glass fiber-reinforced polymer (GFRP) has superior characteristics over traditional steel, such as lightweight, high strength, corrosion resistance and high durability. GFRP bars can be a useful alternative to steel bars in structures, specifically those in highly corrosive environments, as well as structures subjected to high compressive pressure such as bridge foundations. Digital image correlation (DIC) technology is used to analyze the strain evolution of GFRP bars under compression. It can be seen from using DIC technology that the surface strain of GFRP reinforcement is uniformly distributed and increases approximately linearly, and brittle splitting failure of GFRP bars happens due to locally occurring high strain at the failure stage. Moreover, there are limited studies on the use of distribution functions to describe the compressive strength and elastic modulus of GFRP. In this paper, Weibull distribution and gamma distribution are used to fit the compressive strength and compressive elastic modulus of GFRP bars. The average compressive strength is 667.05 MPa and follows Weibull distribution. Moreover, the average compressive elastic modulus is 47.51 GPa and follows gamma distribution. In order to verify that GFRP bars still have certain strength under compressive conditions, this paper provides a parameter reference for their large-scale application.

Behavior of a novel corrugated grouted sleeve splice for prefabricated construction under uniaxial tensile loading

A corrugated grouted sleeve (CGS) made of a seamless tube, which is easy to produce at low cost, is presented. To investigate the connection behavior of CGS splices, a total of 33 specimens are manufactured and tested under monotonic loads. The effects of the corrugation number, groove depth, and steel bar diameter on the connection performance of the CGS are examined. The test results show that the proposed CGS is deemed an effective and reliable steel bar connector for precast structure buildings due to the groove in the corrugation, which plays a key role as a wedge to prevent bond failure of the steel bar splice and enhance the confinement action of the sleeve; one corrugation formed by the roll extrusion method at the end of the seamless tube is sufficient to provide a wedge action to ensure steel bar failure first; the depth of the groove is suggested to be more than 2 mm to ensure that the bond strength is sufficient before steel bar fracture. Finally, an analytical model is proposed to predict the tensile resistance of the CGS considering the influence of confinement caused by the corrugations, and the predictions are in good agreement with the experimental data.

Qualitative SEM analysis of fracture surfaces for dental ceramics and polymers broken by flexural strength testing and crown compression.

To perform qualitative analysis using scanning electron microscopy (SEM) of fracture surfaces for ceramic and polymeric dental materials broken via standardized flexural and crunch-the-crown (CTC) tests. Zirconia, glass-ceramic, and polymeric (Trilor; TRI, Juvora; JUV, Pekkton; PEK) materials were loaded using crowns for CTC tests, discs (zirconia and glass-ceramics) for piston-on-3 ball tests, bars (polymer) for 3-point bend tests, and bars (zirconia, glass-ceramics) for 4-point bend tests. SEM was used to characterize the fracture surfaces and identify fracture surface features (e.g., origin, mist, hackle, and the direction of crack propagation [DCP]). Electron dispersive spectroscopy was used to identify the local chemistry. Fracture surface features were found to be less visually apparent for glass-ceramics than zirconia. For zirconia bars, fractures originated roughly midway between the corner and center for processing defects related to sintering. Fractures originated at the bottom corners of glass-ceramic bars (void or surface flaw) and PEK bars (surface flaw). TRI bar failures exposed glassy fibers. Fracture features were generally less discernable for discs compared to bars for zirconia and glass-ceramics. Ceramic crowns fractured into 2 to 3 pieces, with fractures originating at the occlusal surface and clear evidence for the DCP. Failures of TRI and JUV specimens (bars and crowns) were less catastrophic than for the ceramics, with exposed fibers (TRI) and surface cracks (JUV). PEK crown and bar fractures presented dimple (ductile) features formed due to microvoid coalescence followed by brittle crack propagation. The critical flaws responsible for failure initiation were a function of material composition and test configuration. Fractographic analysis can reveal problems associated with the manufacturing of materials, their handling, grinding and finishing/polishing procedures, the structural design and choice of material, and the quality of the final laboratory-delivered restoration.

Contribution of longitudinal GFRP bars in concrete filled FRP tubular (CFFT) cylinders under monotonic or cyclic axial compression

Most of the current design guidelines/codes ignore the compressive contribution of glass fiber reinforced polymer (GFRP) bars in compression members, due to: (1) the compressive strength of GFRP bars is significantly lower than their tensile strength due to fiber micro-buckling or shear failure of GFRP bars under compression; (2) the peak axial load of an unconfined concrete column is achieved at a relatively low axial strain at which the GFRP bars develop small axial stresses due to their low elastic modulus. However, existing studies have demonstrated that, if adequate transverse bars are provided, the contribution of longitudinal FRP bars to the total load resistance of the column is significant partially due to the enhanced axial strain at peak axial load because of the confinement provided by the transverse bars. In concrete filled FRP tubular (CFFT) columns, which is an emerging and attractive form of columns for new construction, the ultimate axial strain of concrete is significantly enhanced by FRP confinement and thus the contribution of internal longitudinal GFRP bars is also expected to be enhanced. However, the compressive behavior of GFRP bars in CFFT columns has never been investigated. This paper therefore presents the results of an experimental program on CFFT cylinders with internal longitudinal GFRP bars. The test results demonstrated that FRP bars contribute significantly to the total load resistance of CFFT cylinders. The FRP bars in CFFT cylinders experienced crushing failure with load resistance close to that derived based on the compression tests on bare FRP bars. A simple analysis method for the axial load at FRP bar crushing for CFFT cylinders was finally proposed.

Common Diagnosis Approach to Three-Class Induction Motor Faults Using Stator Current Feature and Support Vector Machine

Induction motors are becoming crucial components in numerous industries. The daily usage of induction motors creates the demand for proper maintenance and slight fault detection to avoid serious damage to the induction motor and the shutdown of industries. Among the various kinds of faults in induction motors, bearing failures, broken rotor bar failures, and short-circuit insulation failures are the most common. Thus, detection and classification of slight these faults are attracting great attention. There are conventional methods for detecting such faults, such as the vibration method for bearing failure, the self-organizing map in the case of broken rotor bar failure, and motor current signature analysis for short-circuit insulation failure. From an industrial point of view, diagnosis methods that can classify all these major faults are required. However, reports on the detection and classification of slight these faults using common diagnosis methods are scarce. In this paper, all three kinds of notable faults in an induction motor were artificially induced, and diagnoses using motor stator current spectral features and the rotation speed of the motor were performed. The diagnosis was accomplished using an auto-tunable and arbitrary featured support vector machine algorithm. Although the faults were minor, a high accuracy rate was obtained. The capability to classify the faults and the high diagnosis accuracy prove the robustness and high sensitivity of the method, enabling its practical applications in industries.

A combined HT and ANN based early broken bar fault diagnosis approach for IFOC fed induction motor drive

In recent years, fault diagnosis in the Induction Motor Drive (IMD) has been a popular and important field in the motor-drive research area. The development of control circuits for induction motors has prompted the attention of both researchers and industrialists. This paper proposes a broken bar fault diagnosis using Hilbert Transform (HT) and Artificial Neural Networks (ANN), with the drive regulated through the Indirect Field Orientation Control (IFOC). The HT obtains the spectrum of stator current, which is utilized to identify the Broken Rotor Bar (BRB) failure. The magnitude and side-band frequency of the drive are extracted using the Fast Fourier Transform (FFT), and these parameters are fed into the ANN inputs. The fault severity is computed by the ratio of mean side-band frequency amplitude to the main frequency amplitude for finding the impact of failure in the drive. ANN is used to diagnose failure with high accuracy. The tested and training results are used to attain the minimum Mean Square Errors (MSEs). The IFOC is involved in this proposed system to ensure high performance under the variable speed drives. The proposed scheme is validated in both MATLAB/Simulink and experimental platforms.

Side-Face Blowout Failure of Headed Bars in High-Strength Concrete

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Numerical Solutions for Chloride Diffusion Fluctuation in RC Elements from Corrosion Probability Assessments

Mechanical diffusion of chloride ions in reinforced concrete (RC) structures varies in time and space, and depends on uncertain factors such as material properties, temperature, humidity, and aging. In this paper, different scenarios considering the time of corrosion initiation and the influence of the chloride diffusion coefficient for different loadings (i.e., constant, sinusoidal, Gaussian, and random) were proposed. Stochastic analyses were carried out to estimate the probability of failure of steel bars, and to evaluate the influences of the internal and external factors. Advanced numerical solutions were developed to account for these influences under non-constant diffusion coefficient and non-steady-state condition. Results show that the chloride content can assume low values by using the oscillations of the generic function (e.g., sinusoidal and general) instead of constant function. The influence of the temperature appears relevant. The 3D analyses, considering the random variability, show that chloride content can be higher than ~1.50 compared to chloride content using traditional approaches. Stochastic approaches plus advanced solutions allow, in a more complete way, the sustainability decision-making process during the design phase, maintenance, inspections, and repair.

Seismic behavior of RC columns strengthened with near-surface-mounted aluminum alloy bars and CFRP wraps

This paper proposed a near-surface-mounted (NSM) strengthening technique by using aluminum alloy (AA) bars and carbon fiber-reinforced polymer (CFRP) wraps to improve the seismic behavior of square reinforced concrete (RC) columns. Eight strengthened concrete columns with square cross sections of 250 mm × 250 mm and 1600 mm shear span were tested under axial compression and reversal cyclic loading to investigate the effects of NSM reinforcement ratios (0.36–1.29%), layers of CFRP wraps (0 and 3), and axial compression ratios (0.1 and 0.4) on the seismic behavior. The failure mode, hysteretic response, load-bearing capacity, ductility, stiffness degradation, and energy dissipation capacity of those column specimens were analyzed. Results indicated that the lateral load-bearing capacity, stiffness, and cumulative energy dissipation capacity increased with the increase of the NSM reinforcement ratio. The CFRP wraps in the NSM technique can provide hoop confinement to avoid the buckling failure of NSM AA bars, and improve the seismic behavior by mitigating spalling of concrete. When increasing the axial compression ratio from 0.1 to 0.4, the lateral load-bearing capacity and cumulative energy dissipation capacity increased significantly, while the stiffness degradation became obvious. In addition, three-dimensional (3D) finite element (FE) models were developed and verified by comparisons in the deformation and lateral loads at characteristic points, as well as the strain distribution along NSM AA bars. The verified FE models can be used to analyze the damage of concrete and the stress distribution at the interface between epoxy and concrete.