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21 pages, 5977 KiB

Open AccessFeature PaperArticle

A Crack Characterization Method for Reinforced Concrete Beams Using an Acoustic Emission Technique

by Md Arafat Habib, Cheol Hong Kim and Jong-Myon Kim

Appl. Sci. 2020, 10(21), 7918; https://doi.org/10.3390/app10217918 - 8 Nov 2020

Cited by 16 | Viewed by 3149

This study aims at characterizing crack types for reinforced concrete beams through the use of acoustic emission burst (AEB) features. The study includes developing a solid crack assessment indicator (CAI) accompanied by a crack detection method using the k-nearest neighbor (k-NN) algorithm that [...] Read more.

This study aims at characterizing crack types for reinforced concrete beams through the use of acoustic emission burst (AEB) features. The study includes developing a solid crack assessment indicator (CAI) accompanied by a crack detection method using the k-nearest neighbor (k-NN) algorithm that can successfully distinguish among the normal condition, micro-cracks, and macro-cracks (fractures) of concrete beam test specimens. Reinforced concrete (RC) beams undergo a three-point bending test, from which acoustic emission (AE) signals are recorded for further processing. From the recorded AE signals, crucial AEB features like the rise time, decay time, peak amplitude, AE energy, AE counts, etc. are extracted. The Boruta-Mahalanobis system (BMS) is utilized to fuse these features to provide us with a comprehensive and reliable CAI. The noise from the CAI is removed using the cumulative sum (CUMSUM) algorithm, and the final CAI plot is used to classify the three different conditions: normal, micro-cracks, and fractures using k-NN. The proposed method not only for the first time uses the entire time history to create a reliable CAI, but it can meticulously distinguish between micro-cracks and fractures, which previous works failed to deal with in a precise manner. Results obtained from the experiments display that the CAI built upon AEB features and BMS can detect cracks occurring in early stages, along with the gradually increasing damage in the beams. It also soundly outperforms the existing method by achieving an accuracy (classification) of 99.61%, which is 17.61% higher than the previously conducted research. Full article

(This article belongs to the Special Issue Health Structure Monitoring for Concrete Materials, Volume II)

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25 pages, 3624 KiB

Open AccessArticle

Development of Advanced Computer Aid Model for Shear Strength of Concrete Slender Beam Prediction

by Ahmad Sharafati, Masoud Haghbin, Mohammed Suleman Aldlemy, Mohamed H. Mussa, Ahmed W. Al Zand, Mumtaz Ali, Suraj Kumar Bhagat, Nadhir Al-Ansari and Zaher Mundher Yaseen

Appl. Sci. 2020, 10(11), 3811; https://doi.org/10.3390/app10113811 - 30 May 2020

Cited by 20 | Viewed by 3377

Abstract

High-strength concrete (HSC) is highly applicable to the construction of heavy structures. However, shear strength (Ss) determination of HSC is a crucial concern for structure designers and decision makers. The current research proposes the novel models based on the combination of [...] Read more.

High-strength concrete (HSC) is highly applicable to the construction of heavy structures. However, shear strength (Ss) determination of HSC is a crucial concern for structure designers and decision makers. The current research proposes the novel models based on the combination of adaptive neuro-fuzzy inference system (ANFIS) with several meta-heuristic optimization algorithms, including ant colony optimizer (ACO), differential evolution (DE), genetic algorithm (GA), and particle swarm optimization (PSO), to predict the Ss of HSC slender beam. The proposed models were constructed using several input combinations incorporating several related dimensional parameters such as effective depth of beam (d), shear span (a), maximum size of aggregate (a_g), compressive strength of concrete (f_c), and percentage of tension reinforcement (ρ). To assess the impact of the non-homogeneity of the dataset on the prediction result accuracy, two possible modeling scenarios, (i) non-processed (initial) dataset (NP) and (ii) pre-processed dataset (PP), are inspected by several performance indices. The modeling results demonstrated that ANFIS-PSO hybrid model attained the best prediction accuracy over the other models and for the pre-processed input parameters. Several uncertainty analyses were examined (i.e., model, variables, and data), and results indicated predicting the HSC shear strength was more sensitive to the model structure uncertainty than the input parameters. Full article

(This article belongs to the Special Issue Health Structure Monitoring for Concrete Materials, Volume II)

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19 pages, 4966 KiB

Open AccessArticle

Parametric Investigation of the Effects of Localization and Slenderness on the Stress–Strain Response and Confinement Efficiency in FRP-Wrapped Concrete Cylinders

by Mazen Tabbara and Gebran Karam

Appl. Sci. 2020, 10(10), 3432; https://doi.org/10.3390/app10103432 - 15 May 2020

Cited by 8 | Viewed by 2232

Abstract

In order to improve the efficiency of fiber reinforced plastics (FRP) confinement as a method to repair and strengthen concrete structures, a parametric analysis was carried out to investigate the effects of cylinder slenderness and the stiffness of the confinement on the localization [...] Read more.

In order to improve the efficiency of fiber reinforced plastics (FRP) confinement as a method to repair and strengthen concrete structures, a parametric analysis was carried out to investigate the effects of cylinder slenderness and the stiffness of the confinement on the localization pattern, the stress–strain response and the effectiveness of the confinement. FRP-wrapped concrete cylinders under axial compression were modeled in a high-resolution finite element model. Concrete was modeled as a Mohr–Coulomb material. The bi-linear stress–strain structural responses concur with published experimental data. Localization along discrete shear planes results in a failure mechanism that causes non-uniform hoop stresses in the FRP wrap due to the movement of solid wedges in the mechanism. A characteristic length for localization was identified and found in agreement with published experimental observations. The confinement efficiency shows a clear dependence on the confinement level and a weak dependence on slenderness above the characteristic length. A simple mechanistic model is proposed for the second branch of the bi-linear stress–strain response curve. The results of this study can be used to estimate the confinement efficiency factor and refine the design recommendations of Equation 12.1 of ACI 440.2R17. Full article

(This article belongs to the Special Issue Health Structure Monitoring for Concrete Materials, Volume II)

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15 pages, 6826 KiB

Open AccessArticle

Numerical Modelling of Thermal Insulation of Reinforced Concrete Ceilings with Complex Cross-Sections

by Łukasz Drobiec, Rafał Wyczółkowski and Artur Kisiołek

Appl. Sci. 2020, 10(8), 2642; https://doi.org/10.3390/app10082642 - 11 Apr 2020

Cited by 11 | Viewed by 2903

Abstract

The article describes the results of numerical analyses and traditional calculations of the heat transfer coefficient in ceilings with a complex cross-section, and with materials of varying density built-in inside the cross-section. Prefabricated prestressed reinforced concrete, composite reinforced, and ribbed reinforced concrete ceilings [...] Read more.

The article describes the results of numerical analyses and traditional calculations of the heat transfer coefficient in ceilings with a complex cross-section, and with materials of varying density built-in inside the cross-section. Prefabricated prestressed reinforced concrete, composite reinforced, and ribbed reinforced concrete ceilings were analyzed. Traditional calculations were carried out in accordance with the EN ISO 6946:2017 standard, while the numerical analyses were carried out in a program based on the finite element method (FEM). It has been shown that calculations can be a good alternative to nondestructive testing (NDT) and laboratory tests, whose use in the case of ceilings with different geometries is limited. The differences between the calculations carried out in accordance with EN ISO 6946:2017, and the results of numerical analyses are 12%–39%. The way the air voids are taken into account has an impact on the calculation results. In the traditional method, an equivalent thermal conductivity coefficient was used, while in the numerical analysis, the coefficient was selected from the program’s material database. Since traditional calculations require simplifications, numerical methods should be considered to give more accurate results. Full article

(This article belongs to the Special Issue Health Structure Monitoring for Concrete Materials, Volume II)

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18 pages, 11920 KiB

Open AccessArticle

Region-Based CNN Method with Deformable Modules for Visually Classifying Concrete Cracks

by Lu Deng, Hong-Hu Chu, Peng Shi, Wei Wang and Xuan Kong

Appl. Sci. 2020, 10(7), 2528; https://doi.org/10.3390/app10072528 - 7 Apr 2020

Cited by 46 | Viewed by 6220

Abstract

Cracks are often the most intuitive indicators for assessing the condition of in-service structures. Intelligent detection methods based on regular convolutional neural networks (CNNs) have been widely applied to the field of crack detection in recently years; however, these methods exhibit unsatisfying performance [...] Read more.

Cracks are often the most intuitive indicators for assessing the condition of in-service structures. Intelligent detection methods based on regular convolutional neural networks (CNNs) have been widely applied to the field of crack detection in recently years; however, these methods exhibit unsatisfying performance on the detection of out-of-plane cracks. To overcome this drawback, a new type of region-based CNN (R-CNN) crack detector with deformable modules is proposed in the present study. The core idea of the method is to replace the traditional regular convolution and pooling operation with a deformable convolution operation and a deformable pooling operation. The idea is implemented on three different regular detectors, namely the Faster R-CNN, region-based fully convolutional networks (R-FCN), and feature pyramid network (FPN)-based Faster R-CNN. To examine the advantages of the proposed method, the results obtained from the proposed detector and corresponding regular detectors are compared. The results show that the addition of deformable modules improves the mean average precisions (mAPs) achieved by the Faster R-CNN, R-FCN, and FPN-based Faster R-CNN for crack detection. More importantly, adding deformable modules enables these detectors to detect the out-of-plane cracks that are difficult for regular detectors to detect. Full article

(This article belongs to the Special Issue Health Structure Monitoring for Concrete Materials, Volume II)

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12 pages, 3396 KiB

Open AccessArticle

Experimental Study of Gypsum-Concrete Dense-Column Composite Boards with External Thermal Insulation Systems

by Shaochun Ma, Peng Bao and Nan Jiang

Appl. Sci. 2020, 10(6), 1976; https://doi.org/10.3390/app10061976 - 13 Mar 2020

Cited by 9 | Viewed by 3395

Abstract

In this paper, a new kind of gypsum-concrete dense-column thermal insulation composite board was developed, with seismic tests conducted on three specimens under quasi-static loading conditions. The fracture feature, hysteresis behavior, material strain, load-bearing and deforming capacity, and energy-dissipating capacity of the composite [...] Read more.

In this paper, a new kind of gypsum-concrete dense-column thermal insulation composite board was developed, with seismic tests conducted on three specimens under quasi-static loading conditions. The fracture feature, hysteresis behavior, material strain, load-bearing and deforming capacity, and energy-dissipating capacity of the composite board were analyzed. The results indicated that this composite board has a favorable energy-dissipating capacity, i.e., relatively high seismic performance. By comparing with the experimental results of composite boards without thermal insulation systems, the influence regularity of thermal insulation system on the deformation behavior of composite board was investigated. The comparison result indicated that with a thermal insulation system, the bearing capacity and ductility of composite board are obviously increased, implying that the thermal insulation system is beneficial for the seismic performance of composite boards. Full article

(This article belongs to the Special Issue Health Structure Monitoring for Concrete Materials, Volume II)

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16 pages, 3331 KiB

Open AccessArticle

Basic Chemical Tests of Concrete during the Assessment of Structure Suitability—Discussion on Selected Industrial Structures

by Jacek Hulimka and Marta Kałuża

Appl. Sci. 2020, 10(1), 358; https://doi.org/10.3390/app10010358 - 3 Jan 2020

Cited by 13 | Viewed by 6330

Abstract

Making a decision to perform an overhaul of a damaged reinforced concrete structure should be preceded by an analysis of the real durability of that structure after the repair in connection with the anticipated service life. One of the basic problems is the [...] Read more.

Making a decision to perform an overhaul of a damaged reinforced concrete structure should be preceded by an analysis of the real durability of that structure after the repair in connection with the anticipated service life. One of the basic problems is the avoidance of further corrosion of concrete and steel after the repair, which depends on the degree of concrete contamination with harmful chemical factors. It is particularly important to determine the content of chloride and sulfate ions which cause corrosion. Concrete pH is equally significant because it conditions effective passivation of the reinforcement. The paper presents the basic issues related to the main chemical threats, including the main sources of their origin as well as their limit values. It emphasizes the importance of conducting the chemical tests of concrete, which should be treated as one of the methods of determining structure suitability for an overhaul, especially in the context of subsequent durability. This seems obvious to an experienced specialist, but in practice, such studies are often ignored. Those considerations are backed up with selected examples of reinforced concrete industrial structures exposed to aggressive chemicals during their operation. The text shows the correlation between their technical condition and chemical test results as well as the influence of those results on making decisions concerning effective overhauls. Full article

(This article belongs to the Special Issue Health Structure Monitoring for Concrete Materials, Volume II)

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18 pages, 7069 KiB

Open AccessArticle

Sustainable FRP-Confined Symmetric Concrete Structures: An Application Experimental and Numerical Validation Process for Reference Data

by Ali Raza, Syyed Adnan Raheel Shah, Ahsan Rehman Khan, Muhammad Asif Aslam, Tanveer Ahmed Khan, Kinza Arshad, Sabahat Hussan, Asad Sultan, Gullnaz Shahzadi and Muhammad Waseem

Appl. Sci. 2020, 10(1), 333; https://doi.org/10.3390/app10010333 - 2 Jan 2020

Cited by 45 | Viewed by 3806

Abstract

The use of fiber-reinforced polymer (FRP) jackets as external confinement is becoming popular, especially in seismic areas, because of its ability to enhance the strength and ductility of reinforced concrete to perform as a sustainable symmetric structural member. Therefore, various researchers have worked [...] Read more.

The use of fiber-reinforced polymer (FRP) jackets as external confinement is becoming popular, especially in seismic areas, because of its ability to enhance the strength and ductility of reinforced concrete to perform as a sustainable symmetric structural member. Therefore, various researchers have worked out for the prediction of strength and strain models of FRP-confined concrete. This study presents the improved strain models for the FRP confined cylindrical concrete members. Different previously proposed models of axial strain of FRP-confined concrete were evaluated based on a large database of 678 specimens from previous experiments and an improved model was proposed using the general regression analysis technique. Furthermore, the proposed model was validated using the previous experimental work of FRP-wrapped concrete cylinders and their finite elements analysis (FEA) using the ABAQUS software. The accuracy of the proposed strain model was quite satisfactory in comparison with the previous experimental and FEA results of the present study. Moreover, the proposed empirical strain model was used for the parametric study to investigate the effect of different geometric and material parameters such as the compressive strength of unconfined concrete, diameter of the cylinder, elastic modulus and thickness of the FRP layers, on the axial strain of FRP-wrapped cylinders. A close agreement among the proposed strain models and experimental outputs was observed. This study will help in understanding the behavior of sustainable FRP-confined symmetric concrete members. Full article

(This article belongs to the Special Issue Health Structure Monitoring for Concrete Materials, Volume II)

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