Oblique Crack Research Articles

Residual load-carrying performance of CFRP strengthened RC beam after drop hammer impact

Carbon fiber reinforced polymer (CFRP) external bonding is a common approach to strengthen the bearing capacity of the reinforced concrete (RC) members. In this study, two types of RC beams, i.e., CFRP strengthened beam and conventional RC beam, were tested under drop hammer impact and subsequent quasi-static loading. The strengthening effect of the CFRP on the dynamic responses, failure modes and residual load-carrying performance of the RC beams were fully investigated. Then, a high-resolution explicit numerical simulation was conducted to further investigate the residual load-carrying mechanism of the CFRP strengthened beam. The experimental results demonstrate that even though the CFRP sheet peels off from the soffit of the investigated beam instantaneously upon impact, which provides a little contribution to the impact damage elimination in the mid-span of the beam, the oblique cracks within the flexure-shear zone were reduced moderately. Further, the bonded CFRP sheet can effectively reduce the maximum and residual displacement of the beam and improve the recovery performance of deformation. In addition, the residual resistance, residual stiffness and post-impact energy absorption capacity of the beams with CFRP are shown to be higher than those of the unstrengthened ones. The experimental and numerical results both show that the effective anchoring approach has an important effect on the residual loading performance enhancement. Larger impact energy and more significant impact dynamic effect tend to degrade the bearing performance of the beam more.

Experimental and Theoretical Investigation of the Mechanical Behavior of RC Beams Strengthened with Anchored Carbon–Glass-Fiber-Reinforced Polymer Plates

This paper focuses on the shear behavior of reinforced concrete (RC) beams strengthened with carbon–glass-fiber-reinforced polymer (C-GFRP) plates under different anchoring schemes. The study consisted of four reinforced specimens: specimen CS-1 with no reinforcement and three groups of reinforced specimens SR-1, SR-2 and SR-3. The studies used a four-point bending test to evaluate the reinforcement effect of mechanically anchoring C-GFRP plates. The results of the analysis of load–deflection, strain and bearing capacity indicated that a better reinforcement effect was observed with fiber-reinforced polymer. The test results suggested that the occurrence time of critical oblique cracks was delayed and the development speed of critical oblique cracks was limited by mechanically anchoring the C-GFRP plates. C-GFRP plates significantly increased the stiffness of the reinforced specimen and reflected the superiority of mechanical anchoring. The ultimate shear capacity of the mechanically anchored C-GFRP plates has been significantly improved. With a reasonable increase in the amount of C-GFRP plate, the shear resistance of the test beam became stronger. Compared with the CS-1 specimen without reinforcement, the yield load values of the reinforced specimens SR-1, SR-2 and SR-3 increased by 5.56%, 18.80% and 26.50%, respectively. The ultimate load of reinforced specimens SR-1, SR- 2 and SR-3 increased by 11.64%, 17.47% and 31.51%, respectively. The researchers deduced their theoretical calculation method from the bearing capacity of RC beams strengthened by anchoring with carbon–glass-fiber-reinforced polymer plates. The test findings were in good accord with the theoretical calculation model of bearing capacity suggested in this research.

AUTOMATIC ROAD CRACK RECOGNITION BASED ON DEEP LEARNING NETWORKS FROM UAV IMAGERY

Abstract. Roads are one of the essential transportation infrastructures that get damaged over time and affect economic development and social activities. Therefore, accurate and rapid recognition of road damage such as cracks is necessary to prevent further damage and repair it in time. The traditional methods for recognizing cracks are using survey vehicles equipped with various sensors, visual inspection of the road surface, and recognition algorithms in image processing. However, performing recognition operations using these methods is associated with high costs and low accuracy and speed. In recent years, the use of deep learning networks in object recognition and visual applications has increased, and these networks have become a suitable alternative to traditional methods. In this paper, the YOLOv4 deep learning network is used to recognize four types of cracks transverse, longitudinal, alligator, and oblique cracks utilizing a set of 2000 RGB visible images. The proposed network with multiple convolutional layers extracts accurate semantic feature maps from input images and classifies road cracks into four classes. This network performs the recognition process with an error of 1% in the training phase and 77% F1-Score, 80% precision, 80% mean average precision (mAP), 77% recall, and 81% intersection over union (IoU) in the testing phase. These results demonstrate the acceptable accuracy and appropriate performance of the model in road crack recognition.

Experimental study on forced response characteristics and anti-dislocation performance of articulated tunnel structure under dislocation action of normal fault

The stick–slip dislocation of normal faults will produce large permanent displacement. The tunnel lining structure crossing active normal faults is easily affected by fault dislocation. It is necessary to study the mechanical behavior of tunnel lining structure under fault dislocation. Therefore, taking the subway tunnel of Urumqi Rail Transit Line 1 crossing the Jiujiawan fault project as an example, based on the optimal mix ratio determined by the indoor similar material ratio test, the self-designed large-scale active fault dislocation simulation loading system is used to carry out the stick–slip dislocation model test of normal fault with 60° dip angle. The mechanical behavior difference between the conventional tunnel structure and the flexible articulated tunnel structure is compared and analyzed, and the cracking range, damage characteristics and failure mode of the tunnel lining structure are defined. The results show that: (1) The failure modes of the conventional tunnel structure and the flexible articulated tunnel structure are basically the same, including the large eccentric failure of the inverted arch and the wall foot, and the compression shear failure at the fault plane, which are longitudinal cracks and oblique cracks respectively. In addition, there are longitudinal cracks in the inner side of the invert and the lateral side of the wall foot, but few circumferential cracks. (2) Because the flexible articulated structure increases the overall longitudinal flexibility of the tunnel, the flexible joints between segments can share part of the fault dislocation displacement, so the deformation range, failure degree and number of cracks of the articulated tunnel structure are significantly reduced compared with the conventional tunnel structure, and the anti-dislocation performance is better. (3) Considering the influence of fault dislocation on tunnel structure, the loose area and empty area should be investigated and repaired in the rapid repair and reinforcement of post-disaster tunnel. At the same time, the case study ideas and test methods in this paper can provide some reference value and guidance for other similar tunnel engineering studies in the future.

A deeper generative adversarial network for grooved cement concrete pavement crack detection

Periodic grooved cement concrete pavement crack detection is of great importance for pavement condition monitoring and maintenance. The current state-of-the-art (SOTA) detection solutions highly depend on datasets. However, due to the limited access to crack images, more efficient methods are urgently needed to advance the detection of cracking on grooved cement concrete pavement. This study proposes an improved deeper Wasserstein generative adversarial network with gradient penalty (WGAN-GP) to generate datasets of pavement images with a size of 512 × 512 pixels 2. Poisson bleeding is adopted to create the synthesized grooved cement concrete pavement crack images based on the generated crack images and groove images. The robustness of the proposed improved deeper WGAN-GP model is validated by Faster R-CNN, YOLOv3, and YOLOv4 models trained on original crack images and generated crack images for region-level detection. U-Net and W-segnet are used to achieve pixel-level crack detection to evaluate the effectiveness of proposed model. Results show that the improved deeper WGAN-GP could generate more realistic transverse, longitudinal and oblique crack images. In addition, the Poisson bleeding algorithm contributes to synthesizing grooved cement concrete pavement crack images. Moreover, it is observed that YOLOv3 trained by the augmented dataset could achieve a mean average precision (MAP) of 81.98%, 6% MAP higher than the non-augmented dataset. U-Net and W-segnet benefit from augmented dataset with a better pixel-level segmentation result. Based on the results, it can be concluded that the improved deeper WAGN-GP image generation method can provide a straightforward way to fill the data shortage gap of grooved cement concrete pavement cracks, thus increasing the problem-solving capability of the SOTA crack detection models.

Crack resistance of bent concrete structures with fiberglass reinforcement

This article presents experimental data on the appearance and development of normal and oblique cracks in relation to the longitudinal axis of the element under the influence of transverse loads on bending concrete beams equipped with shishaplastic Composite fittings made of ordinary heavy concrete.

Design and Experiment Research of Oblique Crack Detection System for Rail Tread Based on ACFM Technique

Design and Experiment Research of Oblique Crack Detection System for Rail Tread Based on ACFM Technique

Numerical simulation and experimental research on cracking mechanism of twin-roll strip casting

Abstract Based on the three-dimensional field of molten pool and twin-roll strip casting experiments, this work verified the cracking mechanism of the strip by establishing mathematical model and rolling experiments. The results showed that due to the instability of the thermophysical field of the molten pool and the inconsistency of kiss curve height, the newly solidified strip will undergo incompatible deformation through the rolling. The stress concentration will appear around the large reduction area and then form slip bands. When plastic strain exceeds the limit of the metal, the oblique cracks will appear in the slip bands periodically or completely penetrate the strip. In addition, tensile cracks could also be produced by incompatible deformation. Therefore, keeping the uniformity and stability of the thermal physical field in molten pool is the key factor to restrain cracks.

The Influence of Cross-Section Shape on Failure of Rock Surrounding the Main Tunnel in a Water-Sealed Cavern

The influence of cross-section shape on rock stability was investigated by designing a similar model test and numerical simulation using particle flow code (PFC). The test results showed that the left- and right-hand sides of the entrance are subjected to tension, mainly forming vertical cracks or oblique cracks with a large dip angle. The vicinity of the entrance is subjected to the shear effect and the overall failure of the model is brittle in the similar test. Mesoscopic fractures mainly appear as tensile fractures, and a small number of shear fractures are found in the vicinity of the entrance. A long narrow coalescent-fracture zone is separately formed at the left- and right-hand sides of the entrance when approaching peak load in PFC test. Stress concentration occurs at the end of the long axis of the elliptic cross-section. The stress is high at the arch foot and spandrel of a horseshoe-shaped cross-section and a coalescent fracture zone formed at the arch foot on the right-hand side caused the tunnel to fail. The ovoid-shaped and vertical-wall-arched cross-sections are under significant tension, owing to the force chains distributed along the tunnel wall, show a large included angle with the tunnel wall. From the perspective of bearing capacity, a circle is the best section. From the perspective of failure mode, the horseshoe-shaped section is more suitable for use in corresponding practical engineering.

Effect of Water Immersion on Compressive Properties of Coir Fiber Magnesium Phosphate Cement.

Magnesium phosphate cement (MPC) is a new type of inorganic cementitious rapid repair material, but it has poor toughness and is easy to crack. According to our previous research, these problems can be ameliorated by adding natural coir fiber (CF) into MPC. As coir fiber magnesium phosphate cement (CF-MPC) may be used in humid or rainy areas, its water resistance is an important property in consideration. However, at present, little research has focused on this aspect to provide a good theoretical and experimental basis for the practical application of CF-MPC. In this paper, static compression test and solubility test were used to study the mechanical properties and solubility of CF-MPC under water. At the same time, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to test the changes of hydration composition and microstructure of the test specimen, so as to understand the deterioration mechanism of CF-MPC in water. The results suggested that, when compared with CF-MPC cured in air, CF-MPC cured in water is more prone to encounter oblique cracks and through cracks in the compression process. Moreover, with the extension of curing time, the compressive strength and elastic modulus of CF-MPC cured in water will continue to decrease, the concentrations of PH, K+, and Mg2+ in the curing solution will change significantly, resulting in the gradual decrease in the mass ratio of MgO and MgKPO4·6H2O in CF-MPC matrix, cracks and pores, and looseness in the microstructure.

Influence of impact velocity on dynamic performance of reinforced concrete beams strengthened with CFRP

In order to study the impact resistance and dynamic damage rule of reinforced concrete (RC) beams strengthened with carbon fiber reinforced plastics (CFRP) under different impact velocities, four CFRP strengthened RC beams were tested by using a drop-hammer impact device. The analysis results of the failure pattern, crack propagation rule, dynamic time history response and energy dissipation of the strengthened beams show that with increase of the impact velocity, the width of the main bending crack in the mid-span of CFRP strengthened beam increases first and then decreases, and the width of the main oblique crack in the mid-span increases continuously. It can also be identified that overall crack distribution converges to the mid-span area. Furthermore, the peak impact force and the mid-span peak displacement are linearly dependent to the impact velocity. The energy dissipation capacity of strengthened beams increases nonlinearly with the increase of impact velocity. The greater the impact velocity is, the less the increase rate of the energy dissipation capacity of the strengthened beam is. In addition, four stages can be divided in the test based on development of mid-span displacement, which are linear growing, nonlinear growing, rebounding and stable stages, respectively. The study can provide reference for optimal design of RC beams strengthened with CFRP.

Comparative Analysis of Curved Beam with different Types of Holes in Middle Section by use of Ansys Software

Reinforced concrete beam with transverse web opening is a facility that allows the services such as telephone lines air conditioning and ventilating ducts, to pass through the structure. Because of the change in the beam section the corners of the opening are subjected to large concentration of stress, possibly producing oblique cracks in the beam. The region nearby the openings are measured as the weaker part of the beam. Therefore, a decline in bearing capability and also a change in the load transport mechanism is experienced. This thesis investigates the analytical study on the influence of various opening shapes with constant area on shear behavior of RC beams without extra shear reinforcement around the opening. In this thesis nonlinear analysis using ANSYS 18.1 is used to analyze the beam. The RC beam with opening is a method that permits the services to move towards the construction. Due to rapid changes in the beams crosssection, the edges of the opening stimulate crosswise cracks and can be subjected to high stress concentrations. The reliability and constancy of the beam will then be considered compromised, and the regions nearby the opening is the weakest element of the beam. Therefore, a decline in the bearing capability and also a change in the load transport mechanism is experienced. If safety actions are not in use, preventable accidents are likely to ensue.

Study on Dynamic Impact Response and Optimal Constitutive Model of Al-Mg-Si Aluminum Alloy.

Al-Mg-Si series aluminum alloy is a heat-treatment-strengthened alloy. Research on the impact resistance of Al-Mg-Si series aluminum alloy is of great significance to expand its application in engineering. Taking 6082-T6 aluminum alloy as the concrete research object, using the split Hopkinson pressure bar (SHPB) device, the dynamic mechanical response of the material under different temperatures and average strain rates was studied, and the service performance of the material under extreme conditions was determined. The absolute temperature rise was introduced to optimize the existing constitutive model. The results show that when the environment temperature is 298.15~473.15 K under high-speed impact, the internal thermal softening effect of the material is dominant in the competition with the work hardening, resulting in a decrease in the flow stress of the material. Through the analysis of the real stress-strain curve, it was found that the elastic modulus of the material was negatively correlated with the strain rate, negatively correlated with the temperature, and showed an obvious temperature-softening effect. Yield strength was negatively correlated with temperature and positively correlated with strain rate, which showed an obvious strain rate hardening effect. Based on SEM microscopic analysis, it was found that under given conditions, adiabatic shear bands appeared in some samples, and their internal structures demonstrated obvious change. It was judged that when high-speed impact occurs, cracks are induced at the shear bands, and the cracks will continue to develop along the adiabatic shear bands, resulting in many oblique cracks which will gradually become larger and eventually lead to material failure. Finally, based on the model, the strain rate and temperature softening terms were improved, and a rise in adiabatic temperature rise was introduced. The improved model can better describe the strain rate effect of the material and accurately describe its flow stress. It provides a theoretical basis for the engineering application of materials.

Road damage detection using UAV images based on multi-level attention mechanism

Pavement damage detection is essential for subsequent road maintenance decisions. However, recent detection networks have low accuracy and fail to detect most diseases on the road, which means that testing is very inefficient. Therefore, this study uses the unmanned aerial vehicle (UAV) road damage database and describes a multi-level attention mechanism called Multi-level Attention Block (MLAB) to strengthen the utilization of essential features by the You Only Look Once version 3 (YOLO v3). Adding MLAB between the backbone and feature fusion parts effectively increases the mAP value of the proposed network to 68.75%, while the accuracy of the original network is only 61.09%. The network is able to detect longitudinal cracks, transverse cracks, repairs, and potholes with high accuracy, and significantly improves the accuracy of alligator cracks and oblique cracks. The findings of this study will accelerate the application of non-destructive automatic road damage detection.

Effects of coarse aggregate morphology on concrete mechanical properties

The morphology of coarse aggregate can significantly affect the mechanical performance of concrete. In this study, the correlation between the compressive properties of concrete and the coarse aggregate morphology was systematically explored. Three kinds of aggregates with significant morphology differences were selected: Spherical Aggregates, Flaky Aggregates, and Elongated Aggregates. Three-dimensional morphological information was obtained by 3D Structured-Light Scanner, and quantitative statistical analyses were conducted to assess the distribution of morphological characteristics for these three-types aggregates. It is found that the three-type aggregates with the same mesh size can be properly discriminated through the axis length, flatness, elongation, the product of flatness and elongation, and sphericality. The simplex-centroid design was used to build the correlation between aggregate morphology and the compressive strengths of concrete with different water-cement ratios. The concrete with 100% spherical aggregates owns the highest compressive strength, which is higher than that of concrete mixed with other two aggregates by 9.4%–36.2% and 5.2%–28.8% at the curing of 3-day and 28-day, respectively. When the ratio of spherical aggregates reaches above 50%, the strength loss caused by the elongated aggregates and flaky aggregates content is not obvious. Further, the failure mechanism of concrete with 100% spherical aggregates, 100% flaky aggregates, and 100% elongated aggregates under cyclic loadings were investigated by X-ray computed tomography scanning. It is found that the cracks inside spherical aggregates concrete mainly initiate from the edges and the core section remains almost intact before the destruction by a major oblique crack. Meanwhile, the high residual strain after cyclic loadings can originate from the generated vertical cracks under compression. The research findings in this study can serve as a solid base for the designing of concrete structures.

Study on the Mechanical Response Mechanism and Damage Behavior of a Tunnel Lining Structure under Reverse Fault Dislocation

In this paper, the mechanical response mechanism and damage behavior of a railway tunnel lining structure under reverse fault dislocation were studied. The damage behavior of railway tunnel linings under reverse fault dislocation was validated by undertaking laboratory tests and three-dimensional numerical simulations, where Coulomb’s friction was used in the tangential direction of the interface. The failure damage, which increasingly accumulates with displacements, mainly concentrates in fault fracture neighborhoods 0.5 D to 1.5 D (D is the tunnel diameter) within the footwall. The maximum surrounding rock pressure and the maximum longitudinal strain develop in the tunnel near the hanging wall area. The damage begins as longitudinal cracking of the inverted arch. With the increase in dislocations, those cracks develop upward to the arch foot and the waist. Consequently, those oblique cracks separate lining segments, leading to abutment dislocation. The research results provide technical guidance and theoretical support for on-site construction and follow-up research, and they have important application value.

ANALISA KUAT GESER BALOK BETON BERTULANG BERLAPIS BETON NORMAL-BETON STYROFOAM

This study aims to analyze the shear strength of layered reinforced concrete beams as a composite. Concrete beams consist of normal concrete f'c 25 MPa on the compression side and lightweight concrete of 2.55 MPa, 1.32 MPa and 0.31 MPa on the tensile side as a consequence of the use of styrofoam as much as 30%, 40% and 50% of the concrete volume. This layered concrete beam is intended to reduce the weight of the structure. The tested beam is designed without shear reinforcement with dimensions of .150 cm long, 15 cm wide and 32 cm high, given 3Æ12 flexural reinforcement. The beam test used two concentrated loads with an effective shear-span ratio (a/d) 1.43 to ensure shear failure. The shear strength of layered concrete beams depends on the quality of each layer of concrete where the higher the quality of the cross-sectional concrete, the higher the shear strength. The prediction of shear strength based on the regulation is in line with the shear strength in the first oblique crack condition.

Bearing Capacity of Reinforced Concrete Beams with Initial Cracks Reinforced with Polymer Composite Materials.

The use of polymer-composite materials for strengthening the reinforcing of concrete structures represents a current scientific trend. The article is devoted to experimental studies of the strength of inclined sections of bent concrete elements, reinforced with transverse polymer reinforcement with initial inclined cracks, with different shear spans and transverse reinforcement options. The characteristics of reinforced concrete specimens with initial inclined cracks and the test results of 22 experimental beams, each of which was tested twice, are given. A significant influence of all eight variable factors was established: three spans of the section, equal to 1.5 ; 2 and 2.5 ; two types of compound clamps and their layout; and opening width of oblique cracks from 0.6 to 0.9 mm. It is shown that the strengthening of the beams supporting sections with external polymer reinforcement using three-sided U-shaped and vertical double-sided stirrups significantly changes their stress-strain state (SSS) and the form of destruction. SSS transforms from the classical destruction of the compressed zone above the end of the inclined crack to the destruction of the beam zone of average height at α = 2.0 and brittle crushing of concrete in the tension zone. Unfavorable combinations of force and geometric factors are revealed. Recommendations are proposed that can be used for structures operated in all weather conditions.

Depth and Angle Evaluation of Oblique Surface Cracks Using a Support Vector Machine Based on Seven Parameters

To intelligently and quickly verify the depths and angles of oblique surface cracks using the laser ultrasound technique, a crack geometry information evaluation method using a support vector machine (SVM) is proposed. The relationships between several parameters—which are based on transmitted waves and reflected waves containing crack geometry information in the time domain, frequency domain and time–frequency domain, and crack size—are presented in detail. To decide which feature parameters are involved in the SVM model, two selection standards are proposed according to the correlations between feature parameters and crack size and between the feature parameters themselves. Finally, a seven-feature-parameter SVM model which has an excellent ability to classify oblique crack depths and angles is built. The results of simulations using the finite element method (FEM) and experimental data show that seven parameters based on the SVM model are available for the oblique surface crack depth and angle evaluation and can be used to nondestructively detect natural cracks.

Transient heat transfer analysis of an orthotropic composite plate with oblique cracks using dual-phase-lagging model

Cracks have a significant effect on heat transfer in composites, yet the influence of oblique cracks on the temperature response of composites has not been fully investigated under strong transient thermal shock, in which the heat propagation velocity cannot be assumed to be infinite. In this work, the dual-phase-lagging heat transfer model is employed to capture the transient temperature response. By imposing different boundary conditions on the crack surface, an extended boundary correction algorithm has been derived to avoid the problem of non-convergence when dealing with large and small angle cracks. The effects of crack orientation angle and interaction between cracks on dual-phase-lagging heat conduction in orthotropic materials are analyzed at the macroscale. For the two-dimensional representative volume element (RVE) of fiber reinforced composite material, the influence of the multi-crack distribution on dual-phase-lagging heat conduction at the mesoscale is further discussed in detail.