Damage Assessment Of Concrete Structures Research Articles

Damage assessment of concrete structures subjected to internal explosion under air-backed and water-backed conditions

There has been an increasing concern about the dynamic response and damage assessment of offshore structures under blast loads due to accidents and terrorist attacks. These concrete structures will face severe threats of internal explosions from powerful bombs. After the internal detonation of a bomb, the blast wave in the concrete structure will gradually propagate to two types of fluid-structure interfaces: the air-concrete interface or the water-concrete interface. The purpose of this paper is to investigate the nonlinear response and damage assessment of the concrete structures to internal explosion considering air-backed and water-backed conditions. Two types of blast tests are conducted to obtain the damage mechanisms and degrees of the concrete targets under internal explosion conditions. A fully coupled numerical approach is used to model the internal explosion and the fluid-structure interaction, and it is validated through comparing the test and the numerical results. The shock-wave and damage propagation of the concrete targets under air-backed and water-backed conditions are compared. The damage ranges of the concrete targets with various explosive weights, buried depths, and fluid-structure interfaces are presented. Its results are used to propose a damage assessment method for the concrete structures to internal explosion under air-backed and water-backed conditions.

Semantic Segmentation and 3D Reconstruction of Concrete Cracks

Damage assessment of concrete structures is necessary to prevent disasters and ensure the safety of infrastructure such as buildings, sidewalks, dams, and bridges. Cracks are among the most prominent damage types in such structures. In this paper, a solution is proposed for identifying and modeling cracks in concrete structures using a stereo camera. First, crack pixels are identified using deep learning-based semantic segmentation networks trained on a custom dataset. Various techniques for improving the accuracy of these networks are implemented and evaluated. Second, modifications are applied to the stereo camera’s calibration model to ensure accurate estimation of the systematic errors and the orientations of the cameras. Finally, two 3D reconstruction methods are proposed, one of which is based on detecting the dominant structural plane surrounding the crack, while the second method focuses on stereo inference. The experiments performed on close-range images of complex and challenging scenes show that structural cracks can be identified with a precision of 96% and recall of 85%. In addition, an accurate 3D replica of cracks can be produced with an accuracy higher than 1 mm, from which the cracks’ size and other geometric features can be deduced.

Development of a novel approach to detect damage in concrete structures with millimeter wave radar assessment system.

Nonintrusive damage assessment of concrete structures is evolving using newer technological interventions. Researchers are using different assessment techniques having their intrinsic limitations. A few are partially destructive, whereas others only provide qualitative information about the damages. Therefore, there is a need for a method using high-resolution imaging techniques for the assessment of exact damages and their depth along with intensity. Millimeter wave may be one of the good options for damage assessment. It is an efficient technique used in imaging applications due to its high resolution and effective penetration. Therefore, a novel millimeter wave assessment method is used in this study as a nondestructive post-fire damage test of concrete based civil engineering structures. An active millimeter wave radar system of 55-65GHz has been used to measure the complex relative permittivity of concrete cube specimens for evaluation of damages caused by fire. In this study, fire damaged and control concrete cube specimens of 150mm size were used for the measurement. The results were compared with the existing technique of ultrasonic pulse velocity, and it was found to be in good agreement.

Fractal analysis of nonlinear ultrasonic waves in phase-space domain as a quantitative method for damage assessment of concrete structures

The present paper applies fractal dimension as a mathematical tool to extract a quantitative geometric feature from nonlinear ultrasonic waves in phase-space domain. The feature is then used for damage assessment of concrete material under different service loads after experiencing extreme compressive loads. For this purpose, concrete samples are loaded in two different scenarios: the first loading part is set to initiate micro cracks and generate macro cracks, while the second loading procedure is set to simulate service loads and change the cracks' boundary conditions. Due to nonlinear ultrasonic waves’ sensitivity to cracks in early stages, nonlinear ultrasound test is performed. In contrast to traditional approaches which analyze nonlinear ultrasound waves in frequency domain, in this paper, nonlinear ultrasonic waves in phase-space domain are studied. Phase-space domain is a powerful mathematical tool that allows researchers to analyze data quantitatively and qualitatively using different signal processing techniques like fractal dimension. For the first time, fractal analysis of nonlinear ultrasound waves in phase-space domain is performed to measure the nonlinearity of the waves due to interactions with loaded-induced cracks in concrete materials. In general, fractal analysis makes it possible to assign dimension for sets that do not have integer dimension. To calculate fractal dimension, the box-counting method, as a pragmatic method, is used. A two-dimensional (2D) and three-dimensional (3D) box-counting method for calculating the fractal dimension of nonlinear ultrasonic waves in phase-space domain are utilized. It is shown that fractal dimension is a powerful signal processing tool for analyzing nonlinear ultrasonic signals in phase-space domain and extracting quantitative damage-sensitive features in presence of service load. In contrast, results of frequency domain analysis show a lack of noticeable trend, especially for large service loads. This observation indicates that features extracted in frequency domain may not be reliably used as damage-sensitive features for evaluating the level of cracking in concrete material under service load.

Damage assessment of concrete using a non-contact nonlinear wave modulation technique

This paper presents the development of a nonlinear vibro-acoustic modulation technique based on non-contact piezoelectric sensors to detect the crack progression of concrete subjected to both mechanical and thermal load. Two types of crack are investigated in the work including the isolated single crack induced by the three point bending test and distributed mapping cracks caused by heating treatment. Experimental results show that the damage index defined in the air-coupled wave modulation method – ultrasonic nonlinear parameter presents a positive correlation with the growth of single crack in bending test and the accumulation of mapping crack in thermal test. The sensitivity of developed method is validated through a comparison between the ultrasonic nonlinear parameter and two traditional linear parameters namely the phase velocity of Rayleigh wave and resonance frequency of vibrations. X-ray Computed Tomography (CT) technique and three-dimensional (3D) image reconstruction method are used to visualize microstructure of thermal damage. The CT images show that proposed nonlinear parameter is reliable and well correlated with the microstructural defects of concrete specimen. The repeatability of the air-coupled method is better than the contact method because the coefficient of variation of non-contact measurements is averagely about 43.2% of the contact measurements. Due to the advantage of removable characteristic of non-contact ultrasonic measurements, the developed air-coupled nonlinear wave modulation method could be promising for fast damage assessment of concrete structures in engineering practice.

Impact of grain sizes on the quantitative concrete analysis using laser-induced breakdown spectroscopy

In civil engineering concrete is the most used building material for making infrastructures like bridges and parking decks worldwide. It is as a porous and multiphase material made of aggregates with a defined grain size distribution, cement and water as well as different additives and admixtures depending on the application. Different grain sizes are important to ensure the needed density and compressive strength. The resulting porous cement matrix contains a mixture of flour grains (aggregates with a grain size below 125 μm) and cement particles (particle size ≈ 50μm). Harmful species like chlorides may penetrate together with water through the capillary pore space and may trigger different damage processes. The damage assessment of concrete structures in Germany is estimated due to the quantification of harmful elements regarding to the cement content only. In the evaluation of concrete using LIBS a two-dimensional scanning is necessary to consider the heterogeneity caused by the aggregates. Therefore, a LIBS system operating with a low energy NdCr:YAG laser, a pulse energy of 3 mJ, a wavelength of 1064 nm, a pulse width of 1.5 ns and a repetition rate of 100 Hz has been used. Different Czerny-Turner spectrometers with CCD detectors in the UV and NIR range have been used for the detection. Large aggregates (macro-heterogeneity) can be excluded from the evaluation, whereas small aggregates in the range of the laser spot size (flour grains) cannot be spatially resolved. In this work the micro heterogeneity caused by flour grains and their impact on the quantification with LIBS will be discussed. To analyze the effect of changing grain sizes and ratios, the ablation behavior has been determined and compared. Samples with defined grain sizes were made and analyzed using LIBS. The grain size distributions were analyzed with laser diffraction (LDA).

Damage assessment of concrete structures through dynamic testing methods. Part 2: Bridge tests

The present paper is split into two parts: in the first part the different dynamic damage indicators are defined and applied to beam and slab structures under laboratory conditions, whereas the present second part deals with experiments carried out on two real post-tensioned bridges. The damage indicators defined in part one are based on swept sine excitation and reveal the drop of the eigenfrequencies, the changes in damping, the varying dependency range of the first eigenfrequency on excitation force amplitude and the occurrence of higher harmonics, which changed the Total Harmonic Distorsion (THD) and a special transfer-function called TF or FRF small. In the first part it was proved that the amount of nonlinearities varies with damage and that harmonic excitation is favorable for good test conditions. In the laboratory this can easily be done using an electric or hydraulic shaker, but on real bridges this kind of excitation becomes more complicated due to the higher forces and the necessity to provide counter bearing for any shaker system. That is why two machines were designed and used to excite big structures harmonically, e.g. real bridges in this part. The different indicators are applied to assess the state of two post-tensioned bridges, which had been in good order and condition before artificial damage in multiple steps was caused. It turns out that the decrease in the eigenfrequencies is the most important damage indicator, provided temperature and mass dependant effects can be eliminated. All other indicators may be used as supplements to give correct tendencies, but no strict limits.

Damage assessment of concrete structures through dynamic testing methods. Part 1 – Laboratory tests

The present paper is split into two parts: Part 1 is about laboratory tests whereas the second part deals with experiments on real bridges. This article aims at summarizing several experimental dynamic testing methods with different damage indicators to evaluate the state of prestressed as well as of passively reinforced concrete structures. First the differences between prestressed and passively reinforced concrete are repeated for static behavior, before the transition to dynamics is made. As it will be proved in the following that the amount of nonlinearities increases with damage, harmonic excitation is favorable to realize good testing conditions. It is applied to visualize variations in linear as well as in non-linear structural characteristics, which are subsequently used as damage indicators, e.g. the drop of the eigenfrequencies, the changes in damping and modeshapes, the occurrence of higher harmonics and a varying dependency of the eigenfrequency on excitation force amplitude. These different indicators will be used on passively reinforced beam elements and industrially produced prestressed slabs in the first part and on two real post-tensioned bridges in the second part. All these structures were in good order and condition before artificial damage was applied in multiple steps and the sensitivity of each damage indicator was analyzed.

Acoustic emission diagnosis system and wireless monitoring for damage assessment of concrete structures

Concrete is the most widely used materials for building civil structures. First, this study aims to identify the differences of AE event patterns caused by both actual crack development and the other sources. Secondly, it was focused to develop acoustic emission diagnosis system for assessing the deterioration of concrete structures like a bridge. Thirdly, a feasible study was done for the application of wireless acoustic emission sensor module to concrete structures. In this work, the algorithm for determining the damage status of concrete structures was developed and some criteria for decision making were also suggested. For the future application of wireless monitoring, a compact wireless acoustic emission sensor module was developed and applied to the concrete beam for performance test. Finally, based on the self-developed diagnosis algorithm, new AE system for practical AE diagnosis was demonstrated for assessing the conditions of damage and distress in concrete structures.

Smart Concrete, Sensors and Self-Sensing Concrete Structures

Smart concrete technology provides a new alternative way for health monitoring of reinforced concrete structures. In this paper, the piezoresistivity of two kinds of smart concrete filled with carbon black or carbon fiber was studied, and two types of embedded sensors were fabricated using the smart concrete with favorable piezoresistivity. The sensing performance, the measuring methods and the response to environmental temperature and humidity of embedded sensors were investigated. A compensation circuit was incorporated to reduce the effect of temperature and humidity on the output of embedded sensors. The sensors were embedded in concrete beams and columns to monitor the structural compressive strain under field conditions. Experimental results indicate that the embedded sensors fabricated using smart concrete filled with carbon black or carbon fiber feature favorable sensing performance (gauge factors are 55.28 and 138 respectively). The self-sensing concrete components embedded with these sensors can realize the monitoring of their local compressive strain. It therefore can be concluded that the prepared smart concrete and the developed embedded sensors have great potential to be used for health monitoring and damage assessment of concrete structures.

Nondestructive Assessment of Reinforced Concrete Structures Based on Fractal Damage Characteristic Factors

Nondestructive damage assessment of civil engineering structures has become a focus of increasing interest for recent decades. Its core is to extract effective damage characteristic information capable of reflecting structural damage status. In this study, fractal theory is adopted to extract the fractal damage characteristic factors of a reinforced concrete structure by characterizing its surface-crack distributions. The concentrated and even load spaces are generalized as applicable spaces for employing fractal-to-structural damage assessment. As demonstrated in the damage assessment of reinforced concrete beams under four-point bending and aged crossbeams of an operation bridge in a sluice, the surface-crack distributions of reinforced concrete structures exhibit monofractal character in the concentrated load space, and multifractal character in the even load space. The physical damage interpretations of the extracted monofractal and multifractal damage characteristic factors in the respective load spaces are then established by analyzing the correlations between the monofractal dimension and the natural frequency, and between the multifractal singular spectrum and the average carbonized depth and residual material intensity, respectively. The closely linear fitting relationships between the fractal quantities and traditional damage characteristic factors indicate that the fractal (i.e., monofractal and multifractal) quantities can serve as viable and novel damage characteristic factors in the online damage assessment of concrete structures. It is significant that the proposed fractal damage characteristic factors overcome some disadvantages of traditional damage characteristic factors in practical applications, and they extend the technique of fractal into the meaningful damage assessment of reinforced concrete materials.

The damage assessment of concrete structures by time-frequency distributions

This paper discusses the use of ultrasonic methodology when studying the damage caused to cubeshaped concrete specimens by uniaxial compressive loading. It uses the time-frequency distribution of the cross-ambiguity function (CAF). An algorithm capable of computing the coefficients of the Zak transform needed to discretize the crossambiguity function is also given, together with the definition of a coefficient that permits the study of different damage mechanisms and their evolution. These provide a means of effectively measuring the extent of the resulting damage. The results of the experiment show that this methology is extremely sensitive in detecting and monitoring damge processes in concrete.

Symbolic propagation and sensitivity analysis in Gaussian Bayesian networks with application to damage assessment

In this paper we show how Bayesian network models can be used to perform a sensitivity analysis using symbolic, as opposed to numeric, computations. An example of damage assessment of concrete structures of buildings is used for illustrative purposes. Initially, normal or Gaussian Bayesian network models are described together with an algorithm for numerical propagation of uncertainty in an incremental form. Next, the algorithm is implemented symbolically, in Mathematica code, and applied to answer some queries related to the damage assessment of concrete structures of buildings. Finally, the conditional means and variances of the nodes given the evidence are shown to be rational functions of the parameters, thus, discovering its parametric structure, which can be efficiently used in sensitivity analysis.