Underwater cracks in concrete structures are often difficult to detect due to their complexity of the service environment. With numerical and experimental analysis of concrete beams immersed in water, an active monitoring system, based on a cement-based piezoelectric intelligent module array (CPIMA), was developed to locate and quantify the underwater cracks. Time reversal (TR) of the stress wave field is accomplished to focus on the crack area through the concrete beam specimen by the system. First, a piezoelectric actuator is applied to emit the initial propagating wave, which can be reflected, attenuated, and diffracted by the crack, transmitted through water filled in the crack, as well as diffracted by the coarse aggregates. To extract the damage waveforms associated with the crack and analyze the robust time-reversal invariance under the high-order multiple scattering effect, a pair of homogeneous and heterogeneous forward finite element (FE) models is established. Then, the damage waveforms are time-reversed and re-propagated in the inverse numerical model, where an optimal refocusing is achieved on the crack that behaves as an acoustic source. Finally, the damage area is obtained in the form of the stacked energy distribution of each time step. The focus results are represented by cloud images and compared with root-mean-square deviation (RMSD) values. Numerical simulation and experiments show that this method can identify and quantify underwater cracks effectively. As a porous solid colloid, concrete usually suffers from micro cracks resulting from pore water, pore air, and chemical admixtures in the early stages of construction. For underwater concrete structures, such as dams, pipelines, and bridge piers, these micro cracks may propagate to macro cracks under cyclic environmental loads, creep, and shrinkage ,2. To evIn recent years, the ultrasonic pulse-based structural health monitoring (SHM) method has been widely used to detect the depth of underwater concrete cracks owing to the strong penetration ability and simplicity of operation ,8. HowevWith the advantage of low cost, low power consumption, fast response, and wide frequency response range, cement-based piezoelectric modules have arisen wide concern in SHM ,16. CompResearchers have conducted a lot of studies on the electrical and mechanical properties of the piezoelectric module and the propagation characteristics of stress waves in concrete, laying a foundation for the use of the wave-based method for the piezoelectric module in concrete. Song et al.  first deTo image underwater cracks, the time-reversal method (TRM) was herein introduced . TRM is In this paper, a TRM-based imaging technique is developed to detect underwater concrete cracks with the help of a piezoelectric-based monitoring system. The application of TRM is improved by using the damage-related waves and the crack information is better used. The feasibility and robustness of the proposed method is studied by the forward and inverse heterogeneous FE simulation, respectively. In the experiment, a group of concrete specimens with artificial cracks were immersed in water and tested by the CPIMA-based active monitoring system. Finally, the imaging results are discussed and compared with the energy-based RMSD results.Piezoelectric intelligent modules are the basic monitoring components in this method. Since the piezoelectric patches are composed of a thin brittle material, they are encapsulated in cement as intelligent modules to enhance the durability and the compatibility with concrete . In thisBecause of the direct and inverse piezoelectric effect, the piezoelectric intelligent modules can be used as sensors, which can record real-time stress waves as voltage signals, and can also function as actuators to stimulate modulated signals. For the self-made piezoelectric intelligent module, the stimulated signal would propagate in the form of both P-waves and S-waves through solid materials. The P-wave can travel across a long distance along the polarization direction. Since the good orientation of the P-wave can help to form more effective propagating paths between CPIMA, the P-wave is herein simulated. If there is a crack in this propagation path, the traveling wave will be blocked, reflected, and diffracted. According to Huygens’ principle, all these influences behave as secondary wave fronts, which originate from the crack, see Concrete is a typical heterogeneous material since it is composed of aggregates, mortar, and cement matrix. When waves are propagating through such heterogeneous mediums, noises are generated due to refraction, diffraction, and multiple scattering. The random spatial distributed physical composition of concrete also leads to the inhomogeneities of sound speed, which can distort and redirect the traveling wave. Previous studies have shown how an optimal focusing is achieved through inhomogeneous media, using the time-reversal invariance of wave equations. The TR focusing process acts as a spatial-temporal matching filter . Its selmaxd = 5 mm (diameter-to-wavelength ratio of 0.19 < 0.5), low scattering herein is expected. The numerical simulation also shows the feasibility of robust focusing through inhomogeneous media when the propagating wavefield generated by the crack is dominant over the noise.The aggregate of concrete can be approximately equivalent to a scatterer, which results in information loss of the signals whose wavelengths are smaller than the classical diffraction limit (diameter-to-wavelength ratio of 0.5). Given the P-wave speed of 4000 m/s, when the governing frequency is set as 150 kHz, the calculated wavelength is 26.7 mm. Considering a maximum concrete aggregate size T and n receivers 1, R2, ..., RnR are embedded in the test specimen, with a crack divided into m point-like areas 1, D2, ..., DmD. The propagation wave is emitted by a transducer T, then the damage-related wave is extracted by differentiating the wave field of the damaged beam from the healthy one, which originates from the crack. The inverse simulation is a re-emission process. The damage-related signal is time reversed and imported into the numerical model to re-emit from receivers 1, R2, ..., RnR. As a result, the damage-related signals are focused on each point-like area iD at different time steps. Then, the whole crack area is obtained by accumulating the focus results by time.The principle of TRM in a concrete beam basically contains two parts: forward simulation and inverse simulation. The forward simulation aims to extract the damage-related signal to be focused, which is used as the input signal in the following reversal simulation. As shown in ix(t) is generated from damage point iD, then the received signal at jR in the time domain is:H  is the transfer function from the damage point iD to the receiver jR.The input signal P in the control domain is:If the signal is reversed and re-emitted in the time domain, the received signal at any point P = iD, according to the symmetry of the transfer function that H  = H , a constructive temporal coherence is obtained as follows:For the wave source where ω is the angular frequency. Py (ω), Diy (ω), and ix (ω) are the Fourier transforms of the signals Py (t), Diy (t), and ix (t), respectively.Equations (2) and (3) can be expressed in the frequency domain:iD  emit the damage signals and the receiver array jR  re-emit the input signals. The output signal at a given damage area kD  can be expressed as:Let the whole crack kD, their reversed waves can only converge in the original source kD among all the complex paths, while a poor spatial coherence is obtained in the other area due to the interference. This phenomenon can also be explained by the time-reversal invariance of the wave equations.From the above formula, we can find that for all the damage signals diverging from source Wavelet packet analysis is an effective tool in signal processing, which can decompose a time-domain signal into different frequency components and evaluate the sensitivity of different frequency bands to damage. In this paper, the wavelet packet is introduced to calculate the energy of the signal, and the damage index is obtained to analyze the energy attenuation of cracks of different depths, and then to be compared with the imaging results.S is decomposed into 2n signal sets as {X1, X2,…, X2n}, where each signal can be presented asj is the frequency range , m is the number of samples contained in the signal, and n is the level of wavelet packet decomposition, where n = 3 is herein assumed.The sensor signal The energy of each signal is calculated as:hE and of the damage beam dE can be expressed as:The energy of the received signal of the healthy beam The energy-based damage index can be presented in the form of the root-mean-square deviation (RMSD) as:D is the vector of electric displacement, EC is the elastic stiffness matrix, E is the electric field intensity vector, e is the piezoelectric stress factor matrix, and For linear elastic materials, the mechanical and electrical behavior is governed by the following piezoelectric constitutive equations in the matrix form:When the piezoelectric patch is exposed to the coupled stress-electric field, the equilibrium equation of the piezoelectric material is derived using the virtual displacement principle. In FEM, displacements and electric potentials are interpolated by nodal quantities, then the equilibrium equation is derived in the following matrix form:D11 of 424, D22 of 424, and D33 (in polar direction) of 450. The mechanical property is presented by the stiffness matrix as follows:Due to the high sensitivity and low cost, the PZT-5A patch is selected as the core transducer of a CPIM, the dielectric property of which is defined by the permittivity values The tie constraint surface contact is used to define the contact between the concrete and the piezoelectric patch. More information of the piezoelectric patch model is presented in .Step 1—estimate the particle size distribution. The random sampling principle of the Monte Carlo method is applied to obtain the particle size distribution in the simulation, following the grading curve with a maximum grain size of 5 mm.Step 2—determine the geometry of each aggregate. First, a circular particle size is generated with the size from step 1. Then, it is cut into a polygon, whose side length and inner angle are controlled by the irregularity parameter.Step 3—release the aggregates into the beam. Before placing the aggregates, the beam should be meshed into structured grids. The grid size is considered to be 1mm to achieve a good balance of image resolution and computing cost. The aggregates are then randomly mapped to the grid in the order from large ones to small ones. It is also necessary to check the potential problems, such as aggregate overlap, boundary intersection, and gaps between cement faces. If the above problems occur, the aggregates should be re-dropped.To describe the heterogeneity of concrete components , a random aggregate model is established by the secondary development of ABAQUS software based on Python. The random aggregate structure consists of two parts: the randomly distributed concrete aggregates and mortar filling the remaining area. The model is generated by the following steps:An obtained random aggregates model is presented in t, which should be small enough to satisfy the Neumann criterion. The quadrangle unit is herein used and the element size has a great influence on the calculation accuracy and computing cost. Based on the simulation theory, the number of finite elements n per wavelength should not be less than 10 [The dynamic explicit algorithm adopts the time difference scheme of the dynamic equation. It is effective to solve non-linear dynamic problems, such as wave propagation modeling in an inhomogeneous medium, due to the fact that it does not need to iterate or to solve the tangent stiffness directly. The stability of the explicit model depends on the time increment Δ than 10 . SupposiA forward numerical model is established to simulate the fields and analyze the influence of the crack. The dimension of the concrete beam model is 0.5 × 0.15 × 0.15 m. An artificial crack is set at mid-span, locating from the top surface and extending to the central axis of the beam. A piezoelectric actuator is embedded on the left side of the beam along the central axis, which stimulates sine signal. Then, the horizontal displacement field is obtained under three states: (a) healthy, (b) damaged, and (c) the difference of the healthy and damaged beam, see For the healthy state shown in It can be seen from The inversion model simulates the focusing process of the backward wave field. Crack 1 was introduced as an example to the random aggregates FE model, whose location is shown in x is calculated as [u  is the displacement at location x at time step T − t. T is the total focusing time period. Ω is the detection domain. To display the energy field, the energy density of the P-wave at the position lated as :(15)E(x)n piezoelectric modules, n tests are conducted for the detection of each crack. Each piezoelectric module is chosen as an actuator in turn from the first to the last, while the rest function as sensors. Hence, the average of n groups of energy density is used as the image condition The different image conditions  have a great influence on the imaging results. In a previous study, there are two typical energy calculation methods based on the maximum energy value and the accumulated the energy by time ,36. The A total of three concrete specimens were studied, with the strength of the cement of 32.5 MPa and a mixture ratio of water, cement, fine sand, and stones of 0.44:1:1.42:3.17. The diameter of coarse aggregates was 3 mm~5 mm, and the size of the specimens was 500 mm × 150 mm × 150 mm. Four piezoelectric modules (PZT1~4) were fixed in each concrete beam before pouring. All piezoelectric modules were located on the neutral surface of the specimen see , with a After the curing period of 28 days, each concrete specimen was first tested in the healthy state to get reference signals by recording the received signals, which were propagated from the piezoelectric actuator and captured by the remaining three piezoelectric sensors. Note that the actuator was chosen in turn from PZT1 to PZT4, hence there were four groups of reference signals for each specimen. Then, each of the three specimens was cut into an artificial crack of crack 1, crack 2, and crack 3, respectively. The crack setup is shown in The Agilent 33522A arbitrary waveform signal generator was employed to send signal to the piezoelectric actuators. A digital filter was applied to filter the low-frequency AC noise. Signals were recorded by an Agilent DSO7034B oscilloscope with a bandwidth of 350 MHz and a sampling frequency of 3 MHz. The experimental setup is shown in A 5-cycle 150 kHz Hanning-windowed tone burst, with a maximum amplitude of 10 V, was applied as the excitation signal. In order to reduce the influence of the reflected waves from the external boundary, the first arrival wave of the response signal was studied. The experimental data used were filtered by wavelet analyzer to extract signals of the dominant frequency of 150 kHz. The normalized excitation and response signal are shown in The experiment consists of three steps: (1) Forward process: Each of the three healthy beams were first placed underwater and tested to get reference signals. The depth of the water was about 0.15 m to precisely immerse the beam and avoid the effect of water pressure. After the test, the beam was carried out of the water to prevent water seepage in the concrete. Then, each beam was cut by a sewing machine into crack 1, crack 2, and crack 3, respectively. The cracked beams were immersed in water and tested again to get the damaged signals; thus, damage-related signals were extracted. The entire test process was finished within one week to avoid the effect of temperature change; (2) Inversion process: The first arrival wave of the time damage-related signals was reversed in the time domain and was imported as input signals in the inverse model. The obtained displacement and energy field were recorded; (3) imaging process: The energy value of each node was superimposed and converted to a true-color colorful cloud image after normalization to visualize the crack, see In order to verify the effectiveness of the proposed method and its robustness to noise, the above process was simulated by FE models as a comparison, and the imaging results are shown in The imaging results include colors from dark blue to red consistent with the average energy density In the FE simulation group, note that the width of the identified damage area is wider near the crack opening with higher energy density, while the opposite phenomenon can be observed near the crack tip. This rule is more obvious for cracks with a shorter depth. For crack 2, crack 1, and crack 3, the width of the identified damage areas on the upper edge is 30, 25, and 18 mm, respectively. This is because for surface cracks with a shorter depth, a higher proportion of the crack-initiated waves is reflected by the surface of the concrete beam during propagation, making the surface a strong wave source comparable to the wave strength emitted from the crack. For crack 3, the identification of a deep surface crack is not seriously influenced by the reflected waves from the upper concrete surface; therefore, the energy density is equally distributed and the identified width is always about 18 mm along the vertical direction. However, an artifact appears about 20 mm below the crack tip. There are two possible reasons to explain this: The strong scattering of an exceptionally large concrete aggregate, or the information loss. From the random aggregates model see , no concFor the experimental imaging results, all three cracks are successfully detected, and the imaging results of crack 1 and crack 2 have good consistency with the actual ones. Crack 3 can also be identified from the image; however, the energy density of is unevenly distributed in the damage area due to the environmental effect, such as electromagnetic interference.The energy attenuation-based detection method and RMSD damage index are very established in concrete crack detection. For underwater conditions, all the RMSD values are above 0.2, indicating the sensitivity to the existence of concrete cracks. Further, for crack 2 and crack 3 in the same position, the RMSD value is changed consistently with the increase of the crack depth. This shows that the energy-based RMSD damage index is an effective and reliable approach to the underwater concrete crack detection and can be a reference to TRM. However, the TRM imaging result is able to provide much more information about the crack than RMSD.In FE simulation, the fineness of the mesh influences the resolution of the model, not only for shaping the aggregates and cementing surface but also for simulating the propagating wave fronts. However, since the higher element density will consume additional computing resources and the self-focusing character of TRM does not depend on the wave paths, extra fine mesh is unnecessary when Neumann criterion is satisfied. The element size of 1 mm is conformance to the resolution requirements of the presented frequency  and the scale of the applied specimen .Based on the wave-based detection theory, the dominant frequency is one of the determining factors of detection resolution. For the frequency of 150 kHz, the wavelength  is one order larger than the actual crack width . As a result, the width of the identified crack area is usually lager than the actual one. In theory, higher frequency means higher resolution but will lead to more serious attenuation  and scattering in concrete. Concrete can be regarded as a low-pass filter, and for frequencies over 400 kHz, which is believed in  to be thTo analyze the influence of frequency on the accuracy of the proposed method, crack 1, crack 2, and crack 3 were identified by FE simulation with the dominating frequencies of 100 and 200 kHz. The imaging results are shown in In this study, a CPIMA monitoring system and TRM-based imaging technique were applied to detect and image underwater cracks of concrete structures. To overcome the challenge of water filled in the crack and to improve the application of TRM, the concept of damage-related waves was proposed. A heterogeneous FE numerical model, including the piezoelectric constitutive model and the wave propagation model characterized by displacement, was established. This model was used to simulate both the forward process and inverse process of TR focusing. The forward process depicts the wave propagation through healthy and damaged underwater concrete beams, showing the effectiveness of the proposed damage-related wave based TRM focus in underwater conditions and its robustness to heterogeneous material (concrete).The inverse process simulates the backpropagating wave field, then the focusing results of different cracks were obtained. Three underwater concrete cracks, with different locations and depths, were imaged by the proposed TRM-based detection method by both FE simulation and experiment. The FE simulation results show the feasibility of the proposed method in heterogeneous media to detect underwater cracks. The reflection of the concrete surface near the crack opening has some influence on the shape of the identified areas but has little influence on the accuracy of the identification of crack opening. The influence of the dominant frequency on the resolution is complex, and for the presented different frequencies, the accuracy of the imaging results is similar. The experimental imaging results show that the underwater surface cracks in concrete beams are imaged by limited piezoelectric modules with an acceptable error, indicating the application potential in underwater crack detection of concrete structures. Various effects  on the performance of piezoelectric modules and received signals need to be further studied before being adapted to in situ monitoring for underwater concrete structures.


Ab initio calculations in the framework of the density functional theory, aimed at studying the phonon states, are performed for SLs with both equal and unequal layer thicknesses. The frequencies of the vibrational modes are calculated, and atomic displacement patterns are obtained. Raman spectra are calculated and compared with the experimental ones. The results of the ab initio calculations are in good agreement with the experimental Raman spectra and the results of the group-theoretical analysis. As a result of comprehensive studies, the correlations between the parameters of acoustic and optical phonons and the structure of SLs are obtained. This opens up new possibilities for the analysis of the structural characteristics of short-period GaN/AlN SLs using Raman spectroscopy. The results obtained can be used to optimize the growth technologies aimed to form structurally perfect short-period GaN/AlN SLs.We report the results of experimental and theoretical studies of phonon modes in GaN/AlN superlattices (SLs) with a period of several atomic layers, grown by submonolayer digital plasma-assisted molecular-beam epitaxy, which have a great potential for use in quantum and stress engineering. Using detailed group-theoretical analysis, the genesis of the SL vibrational modes from the modes of bulk AlN and GaN crystals is established.  In modern semiconductor devices, short-period superlattices (SLs) are widely used in the active and buffer regions of various heterostructures and have a great potential in quantum and stress engineering. The SLs based on the  N bulk crystals can be employed in both the ultraviolet (UV) and infrared (IR) optoelectronics. In the first case, the ability of GaN/AlN SLs with a period of several atomic layers to possess a precisely adjusted effective band gap from 3.4 to 6.1 eV can be used in light-emitting and adsorption layers instead of traditional ternary AlGaN alloys ,6,7. GaNFrom a fundamental point of view, short-period SLs can be considered as a metamaterial that simultaneously possesses both a number of properties inherent in conventional solid solutions  and several completely new properties that are not comprehensively studied at the moment. The effective use of such periodic structures requires a detailed study of their fundamental physical properties, as well as the development of new methods of quantitative diagnostics in order to improve the technology of their growth.ab initio calculations of lattice dynamics, and Raman measurements of the phonon modes in short-period hexagonal GaN/AlN SLs. The results of such an integrated approach can be useful for obtaining new information on the microscopic nature of phonon SL modes and establishing correlations between the structure of the SL and the observed features in the Raman spectra, which can be used to optimize the parameters of the growth process in order to form structurally perfect short-period GaN/AlN SLs.Raman spectroscopy is a recognized tool for the non-destructive study of the phonon spectrum of SLs. Group-theoretical analysis and model methods for studying the phonon spectra form the basis for quantitative analysis of the experimental information. A joint analysis of the theoretical and experimental results makes it possible to establish the microscopic nature of the vibrational states associated with the lines in the Raman spectra, which is the basis for the development of a quantitative technique for assessing important parameters of the studied SLs. The existence of localized and delocalized modes in GaN/AlN SLs at the frequencies different from the frequencies of any mode inherent in the layers composing the SL was theoretically predicted within the framework of the dielectric continuum model ,16. It w2-plasma source HD-25 , as described in detail in , A4 → Г1 [A1(LO)]. In turn, the Г4 [B1] state also transforms into the Г1 [A1(LO)] mode. Thus, among the Г1 [A1(LO)] modes in the SL, there are strong modes originated from the bulk Г1–A1 (A1(LO)-branch) and relatively weak modes originated from the bulk Г4–A4 (B1 -silent branch).These branches also stick together at the A-point of the BZ, i.e., they form a pair of complex-conjugated irreps Atate see . In SLs,m/(AlN)n SLs in the A1(LO) frequency range to the case of odd n. The following rules can be suggested:−1 interval has relatively low intensity (less than the intensity of the first line) and does not overlap with the A1(LO)-GaN line, then in the studied SL, the number n is even and is twice the number of lines observed in this spectrum.If the line with the lowest frequency in the 740–900 cmA1(LO)-GaN line (which manifests itself as a doublet splitting of this line), then in the SL under study, the number n is odd and equal to 2k + 1, where k is the number of lines observed in this spectrum.If this last line has a high intensity (comparable to that of the first line) and is close in frequency to the Thus, we can extend the scheme for interpreting the A1(TO) frequency on the concentration parameter A1(LO) Raman peaks in the LO(AlN) spectral region. The latter method was first proposed in this work.The results presented in this Section can be summarized as follows. The established close-to-linear dependence of the The experimental Raman spectra for the 4/4, 6/6, and 8/8 SLs are shown in m/GaNn SLs (m + n ≤ 16) SLs grown by the submonolayer digital PA MBE method were studied. A comprehensive group-theoretical analysis made it possible to establish the genesis of the SL phonon modes from the modes of bulk AlN and GaN crystals. A symmetry relationship was established between the vibrations of the bulk GaN (AlN) crystal and the SL’s at the high-symmetry points of the Brillouin zone. Based on the genesis of the phonon modes, the conclusions on the frequencies and intensities of the corresponding bands in the Raman spectra of the SL have been made. Ab initio calculations in the framework of the density functional theory, aimed to study the phonon states, were performed for SLs with both equal and unequal layer thicknesses. As a result, the phonon mode frequencies were calculated, and the atomic displacement patterns were established. The number and symmetry of the vibrational modes in the calculated spectrum are in good agreement with the results of the group-theoretical analysis. The Raman tensor was calculated within density functional perturbation theory for the series of SLs, and simulated Raman spectra were compared with experimental ones. The results of the ab initio calculations are found to be in good agreement with the experimental Raman spectra.The dynamical properties of short-period AlNE(TO) modes are localized in the constituent SL layers. The doublet structure of the E(TO) lines localized in the GaN and AlN SL layers genetically related to the E2(high)- and E1- branches of the bulk crystal was first revealed and explained. The results can be used to obtain information about the strain in each layer forming the SL. In turn, it was confirmed that the A1(TO) mode has a delocalized nature. It was established that the ωA1(TO) frequency value can be used to estimate such an important SL composition parameter as A1(LO)-branch folded from the A-point at the BZ boundary have a higher intensity than the accompanying satellite lines originating from the silent B1-branch also folded from the A-point. The calculations revealed a strong dependence on the layer thickness of the number and intensities of the modes localized in AlN layers forming the SL. An approach was proposed for estimating the number of AlN monolayers forming SL, both for equal and unequal thicknesses of constituent GaN and AlN layers of the SLs.The doublet structure in the low-frequency range of the Raman spectra is explained by the presence of two types of folded LA phonons, which differ in the position of the nodal planes. For one type of modes, the nodal planes coincide with the interfaces, whereas for other modes, they are located approximately in the middle of the SL layers. The dependences of the positions and intensities of the folded LA and TA bands in the Raman spectra on the period of the SL are determined. It was found that the frequencies of the folded acoustic bands depend not only on the total period of the SL, but also on the ratio of layer thicknesses, which opens up new possibilities for the diagnostics of the SL structure. It has been established that the As a result of comprehensive studies, the correlations between the parameters of acoustic phonons and localized and delocalized optical phonons and the structure of SLs were obtained. This opens up new possibilities for analyzing the structural characteristics of short-period GaN/AlN SLs using Raman spectroscopy. The results obtained can be used to optimize the parameters of the growth process in order to form structurally perfect short-period GaN/AlN SLs with different ratios of the thicknesses of the layers forming the SL, as well as digital AlGaN alloys grown on the basis of related nanostructures.


There is paucity of information on antibiotics utilization amongst farmers, factors associated with administration of antibiotics and farmers’ knowledge of the effects of antibiotics on the soil ecosystem in Ghana.A cross sectional quantitative survey across three coastal regions of Ghana was undertaken amongst poultry and livestock farmers. Six hundred respondents were selected from five districts each across the three regions. Pretested and structured questionnaire were used to collect data through face to face interview. Data were summarized using descriptive statistics and regression analysis. Factors associated with antibiotic administration were determined using binary multiple logistic regression at p ≤ 0.05.Out of the 600 farmers, 95% administered antibiotics and 84% bought antibiotics over-the-counter without prescription. Approximately 9% of antibiotic administration was carried out by veterinary officers, and the remaining, 91% based on farmer’s experience. Approximately 93% had access to antibiotics without any difficulty. Withdrawal period was always observed by only 16% of farmers. Majority (74%) of farmers never had education on antibiotics and none of the farmers screened manure for the antibiotic residuals. Years of farming, income status, level of education of farmers, type of animal kept, access to extension services, registration with farmers’ association, employing veterinary services, location of farm, system of production, education on antibiotics and access to antibiotics positively and significantly predicted the administration of antibiotics by farmers. Majority of farmers had inadequate knowledge of the effects of antibiotics on soil ecosystem with mean score ranging between 2.87±0.60 and 2.98 ± 0.7 on a scale of 5.0.The study exposed the poor practices regarding antibiotic use and also inadequate knowledge on its effect on the soil ecosystem amongst farmers in Ghana. This calls for development of strategies to increase awareness on antibiotics because its misuse can negatively impact human, animals, environment and impact food security. Antibiotic use is widespread not only in the general population but also in the agricultural industry for crop and animal production. Substantial evidence exists on successful use of wide range of these antibiotics in farm animals for metaphylaxis, prophylaxis and growth promotion , 2, 3. TIn the pig, dairy and poultry industries, antibiotics are used extensively, as component of their feeding and routine management practices globally, either to prevent diseases or stimulate growth , 8. The Over the years, growing concerns from the public and the scientific community have been consistent in relation to the emergence and/or development of microbial resistance from exposure to clinical and veterinary antibiotics. These are legitimate concerns because of the potential negative impact antibiotics could have on humans, soil health and subsequently food security. A number of disease conditions have been reported in humans , 15, livIn soil, antibiotics could negatively impact soil health through its interaction with the microbial community. It has been reported that antibiotics affect the overall population of soil microorganisms , 18, enzIn order to regulate antibiotic use, conserve its efficacy and reduce or prevent the development of microbial selection in the environment and prevent disruption of soil biodiversity, the World Health Organization (WHO) has suggested its use must be under supervision of licensed veterinary officer and related health experts . In addiFarmers are major stakeholders in antibiotic utilization, yet there is paucity of information regarding the extent to which they utilize antibiotics and their characteristics that influence the administration of antibiotics in Ghana. Few studies conducted have not ascertained farmers’ knowledge on what happens to soil ecosystem when antibiotics are applied to soil , 25. ThiA cross sectional method was adopted for the study between September, 2018 and April, 2019 in three Coastal regions of Ghana; Volta, Central and Greater Accra. Farmers in those regions are greatly involved in the raising of poultry, pigs and diary yet there is limited information on their antibiotics utilization. The three regions have 25 (Volta), 20  and 26 (Greater Accra) districts and have farmers who are greatly involved in poultry and livestock production . The directors opined that poultry and livestock are a major part of Ghanaian traditional meals serving the protein needs in most household diets hence their production is increasing each day. The manure is used as fertilizers for crop production [The study employed multistage sampling technique. Five districts from each region  were ranFarmers who met the criteria were listed to participate in the study. A total of 702 farmers were listed but only 600, representing 85%, agreed to enroll on the study. The 15% who could not participate was due to time unavailability, accessibility to farms and small farm sizes. Quantitative survey of 600 farmers who agreed to participate in the study were undertaken.An initial meeting was scheduled with the farmers who met the eligibility criteria. A total of six data collectors and two supervisors were trained to assist in data collection. The training provided the data collection assistants information on: aim of the study, reasons for confidentiality of respondent’s information, rights of respondents and data collection procedure.Data collection was done using a pretested and structured questionnaire. The questionnaire had three sections based on the objectives of the study. The sections included; farmers’ socio demographic features and other farm characteristics, practices regarding antibiotics utilization and knowledge of farmers on the effects of antibiotics on the soil ecosystem. Variables about farmers and farm characteristics captured were: sex, age, years of farming, level of education, income, type of animal kept, location of farm, system of production. The second section solicited information on whether farmers had ever administered antibiotics. Farmers who responded in the affirmative were interrogated on where they bought the antibiotics, who administered the antibiotics, whether dosage administered was recommended or it was based on farmers’ experience and reasons of given antibiotics to their animals. Other farmer’s characteristics interrogated were: access to extension services, access to veterinary services, access to antibiotics, education on antibiotics, observation of withdrawal periods and screening of manure for antibiotics presence and quantity. The last section solicited information on the knowledge of farmers regarding the effect of antibiotics on soil ecosystem. The section had seven items and responses were on a five point Likert scale in a continuum from “not sure” to “strongly agree’ coded as 1 = strongly disagree, 2 = disagree, 3 = not sure, 4 = agree and 5 = strongly agree. The items were; ‘substantial quantity of antibiotic given to animals end up in manure’, ‘antibiotics compete with other soil cations/anions for exchange site’, ‘antibiotics cause the death/inhibit growth of microbial groups involved in ecosystem functions’, ‘antibiotics influence nutrients transformation; decrease nitrification in N cycle’, ‘antibiotics cause decrease in bacteria/fungi ratio in soil’, ‘antibiotic resistance genes (ARGs) in soil increase the likelihood of human pathogens acquiring resistance’, and ‘antibiotics decrease soil respiration’.Prior to data collection, the questionnaire was piloted on 15 farmers, which prompted some minor modification to suit the research objectives. Data were collected by explaining the questionnaire to the respondents in English. However, the dominant native language ‘Twi’ and ‘Ewe” were used where farmers had no formal education or could not read and write.Descriptive statistics including mean and standard deviation as well as inferential statistics was employed to summarize the data. Chi square association between set of explanatory variables (farm and farmer’s characteristics) and the dependent variable (antibiotic administration) was established at 95% confidence interval. Additionally, Cramer’s V was used to determine the magnitude of association between variables. Variables that had a significant positive relationship analyzed using Chi square, were considered in a binary multiple logistic regression to establish the relative crude and adjusted odd ratios at 95% confidence interval. Multicollinearity among independent variables was checked using variance inflation factor (VIF) and goodness of fit by Hosmer and Lemeshow respectively. Mean score rating for knowledge of farmers was done with the following interpretation; 1.0–1.9 = ‘very poor knowledge’, 2.0–2.9 = ‘poor knowledge’, 3.0–3.9 = ‘good knowledge’, > 3.9 = ‘very good knowledge’. The mean rating was translated from the mean analysis of the five point Likert scale used to determine the extent of farmers’ knowledge on antibiotic effects on soil ecosystem.The study was reviewed and approved by Authors, and an internal Research Board of the School of Agriculture, University of Cape Coast. The aim of the study was explained to the participants in their mother tongue. ‘Twi’ was used for participants from Central and Greater Accra regions and ‘Ewe’ for those from Volta region for easy understanding since appreciable number of the farmers could not read, write and comprehend the English language. Informed permission was obtained from the respondents before questionnaires were administered and they were told that their identification was not required. Furthermore, they were told they could opt out from the study at any time. The consent was verbal due to the fact that their responses do not have any personal, economic and or political ramifications. Moreover, no risk was identified to be associated with the responses that could endanger the lives of the participants. The confidentiality of solicited information from the participants was ensured and access to answered questionnaire was permitted after agreement was reached by the researchers.A total of 600 respondents enrolled on the study. Only 8.5% of antibiotic administration was carried out by veterinary officers whilst, 65.3% was done by farm workers, and 23.2% by farm managers. Regarding dosage of antibiotics, 79.0% indicated they administered based on experience, 12.9% administered veterinary prescribed dosage, and 8.1% administered based on the advice from colleague farmers. Majority (90.7%) claimed they administered antibiotics as a routine practice at the farm. Of the 210 farmers who said they employed the services of veterinarian, few (11.9%) did it once in every month, 21.4% accessed between one and six months and 66.7% employed veterinary once in 6 months or more. The results of the study also showed that withdrawal period following antibiotic administration was always observed by 16.4%, and 27.6%, sometimes do it and the remaining 56.0% never observed the period. Our study found that none of the farmers screened manure for the presence of antibiotics.Farmers profile, their farm characteristics and other factors that predicted the administration of antibiotics are shown in Our study showed that farmers with more than 10 years of farming experience were more likely  than 10 years and less, to administer antibiotics. Then again farmers in high income bracket were highly likely  to administer antibiotics compared with farmers in the low income bracket. Level of education was shown to be a significant predictor of antibiotic administration with literate farmers highly likely  than illiterates in administering antibiotics. Type of animal kept was found to be significantly and positively related with antibiotic administration.Farmers in the poultry industry were more likely  than other livestock farmers in administering antibiotics.The study also revealed that farmers’ who have access to extension services have higher likelihood  than their counterparts in administering antibiotics. The results also show that registered farmers had higher odds  and therefore likely to give antibiotics to the animals. Our study showed that farmers who had access to veterinary services have higher odds  and likely to administer antibiotics compared with farmers who do not have access.Farm location was a significant predictor where urban farms were highly likely  than rural farmers in administering antibiotics. Farmers practicing controlled production systems were more likely  to administer antibiotic than farmers in uncontrolled production system.Farmers who had education on antibiotic effects are 260% times  likely than those who had no education on antibiotics effect, to administer antibiotics. Farmers who had easy access to antibiotics were highly likely  to administer antibiotics when compared with those who had it with difficulty.Farmers knowledge regarding effects of antibiotics on different properties and processes of soil were inadequate with mean score ranging from 2.87 ± 0.60 and 2.98 ± 0.7 on a scale of 5.0 , an indiSimilarly, mean of 2.91 ± 0.55 was obtained for ‘substantial quantity of antibiotic given to animals end up in manure’.Moreso, mean score of (2.91±0.56), indicating inadequate knowledge was recorded for ‘antibiotics compete with other soil cations/anions for exchange site’. Similarly, mean score (2.94 ± 0.40), indicating inadequate knowledge, was obtained for the statement ‘ARGs in soil increase the likelihood of human pathogens acquiring resistance’.Farmers’ knowledge on whether ‘antibiotics cause the death/inhibit growth of microbial groups involved in ecosystem functions’ scored a mean of 2.96 ± 0.38. Antibiotics cause decrease in bacteria/fungi ratio in soil and farmer’s mean knowledge score was 2.98 ± 0.41.Similarly, when farmers were asked to affirm if antibiotics influence nutrients transformation; decrease nitrification in N cycle, few responded in the affirmative with mean of 2.98 ± 0.7.Successful use of antibiotics in the agriculture sector for disease prevention, treatment and growth promotion have been reported , 2. RegaPractices of farmers on antibiotics utilization, showed that the purchase of antibiotics over-the-counter and without prescription was prevalent amongst farmers in the study area. This was consistent with assertions that antibiotics can easily be bought without prescription in some developing countries . Even ifOur study also revealed that, none of the farmers ever screened their manure for antibiotic residue. A number of studies have reported substantial quantities of antibiotic in manure , 10 posiA number of factors were also found to influence the administration of antibiotics which included farmers’ characteristics and related variables. It was evident that as years of farming increased, farmer’s experiences with new technologies also increased . This isIt is imperative that the provision of education to farmers would help their analysis of information and enhance their knowledge from reading labels and other sources of information. It would ensure administration of appropriate antibiotics for a specific disease condition, ensure precision in dosage and observation of withdrawal period. From our study, appreciable number of farmers could not read and write and therefore may be handicapped in processing and analyzing information on antibiotics. This consequently, results in inappropriate handling and administration of the antibiotics . FarmersSalmonella species and Escherichia. coli [Furthermore, other variables such as the extent of susceptibility of the type of animal to infection had association with antibiotic administration. It has been reported that poultry are associated with higher infections from ia. coli  and thisia. coli .Similarly, veterinary officers have key roles in the poultry and livestock sector and this include but not limited to educating and training of farmers on best practices including diagnosing disease conditions of the animals, prescribing and administration of drugs. The exposure of farmers to these veterinarians enhances farmers’ knowledge and acceptance to give antibiotics to their animals. Empirically, the location of the farm has a bearing on antibiotic administration such that rural farmers may be less privileged in terms of unavailability of appropriate antibiotics, veterinarians, high cost. Moreover, most rural farmers might not have the financial strength to travel to urban centers to purchase the antibiotics. The counterparts in the urban setting are advantaged in accessing information on antibiotics, easy access to antibiotics, technical support and availability of veterinarians.Characteristically, most of our farmers did not belong to farmers’ groups. Belonging to farmers’ association helps to access interventions which include education on products needed to facilitate farm operations and enhance productivity. The association also promotes internal learning where farmers learn from each other . In otheWhere animals are kept in a controlled system, farmers gave antibiotics more than farmers in uncontrolled (free range) production system did. These could be as a result of the routine practice of antibiotic administration usually through feed or water given to the animals, usually in the intensive system. Unlike the intensive system, animals raised under free range system has disadvantage of not been fed regularly with antibiotic laden feed or water, so could be susceptible to disease pathogens acquired as they move from one location to the other.Education of farmers regarding antibiotics could be pivotal in influencing farmers’ decision to administer antibiotics. Less education means, farmers are bereft of information on antibiotics, hence there is likelihood of compromised practices. Education on antibiotics could come in the form of seminars, workshops and farm visits to increase the understanding of farmers on antibiotics, expose farmers to handling, administering and observation of withdrawal period. Our study corroborates other assertions that access to antibiotics was easy  in most 2+ and Ca2+, increase ARGs in soil [A major source of plant nutrient is manure, but have been found to contain substantial amounts of antibiotic residues , 41, 42. in soil , 13. TheIt is important to note that our research did have limitations. This study sampled respondents from five districts each from the regions with assumption that; the selected districts were amongst leading poultry and livestock producers. This might have resulted in leaving out possible districts with high level of production. Although this couldn’t compromise our findings due to the census method used. Moreover, to be able to get the true reflection of the phenomena under investigation, the study used census method to ensure data is captured from all farmers who raised birds and livestock. Generalizing the findings of our study to reflect the state of antibiotic utilization and knowledge of farmers regarding antibiotics effects on soil in Ghana, is valid. However, regions in Northern Ghana where farmers are mostly into diary production and reduced poultry could report contrasting findings compared with our findings. This calls for research study in Northern Ghana. Irrespective of the limitations, our study, the first of its kind in Ghana was able reveal the knowledge of farmers regarding antibiotic effects on soil ecosystem, is an important finding to aid in policy directions for antibiotic deployment in the animal production sector and use of manure for soil fertility management.In conclusion, our study revealed high and indiscriminate utilization of antibiotics amongst animal producers in Ghana. It also exposed the poor practices regarding antibiotic use and the inadequate knowledge regarding its effect on soil ecosystem amongst farmers in Ghana. This calls for development of strategies to increase awareness on antibiotics amongst farmers because its misuse can negatively impact human, animals, environment and food security. We also suggest a collaboration between Ghana Health Service, Food and Drugs Authority and Ministry of Food and Agriculture to draft and implement regulations to guide the use of antibiotics at the farm gate.S1 File(PDF)Click here for additional data file.


This article investigates the possibility of applying weldable optic fiber sensors to the corrugated rebar in reinforced concrete structures to detect cracks and measure the deformation of the steel. Arrays have initially been designed comprised of two weldable optic fiber sensors, and one temperature sensor to compensate its effect in measuring deformations. A series of tests were performed on the structures to evaluate functioning of the sensors, and the results obtained from the deformation measures shown by the sensors have been stored using specific software. Two reinforced concrete beams simply resting on the support have been designed to perform the tests, and they have been monitored in the zones with maximum flexion moment. Different loading steps have been applied to the beams at the center of the span, using a loading cylinder, and the measurement of the load applied has been determined using a loading cell. The analysis of the deformation measurements of the corrugated rebar obtained by the optic fiber sensors has allowed us to determine the moment at which the concrete has cracked due to the effect of the loads applied and the deformation it has suffered by the effect of the different loading steps applied to the beams. This means that this method of measuring deformations in the corrugated rebar by weldable optic fiber sensors provides very precise results. Future lines of research will concentrate on determining an expression that indicates the real cracking moment of the concrete. It is fundamental to know the steel deformation in order to correctly calculate concrete structures. Although it deforms slightly before the concrete has not yet cracked, as shall be seen below, it acquires its greatest deformation when the concrete cracks, as it is not able to absorb traction. This article examines the appearance of the first cracks in reinforced concrete, embedding optic fiber sensors welded to the corrugated rebar steel, and it evaluates their deformation, comparing them with the values obtained from traditional material resistance calculation.Although there is a lot of literature regarding crack detection in structural elements of reinforced concrete, the novelty of this article lies in the use of optic fiber sensors based on Bragg gratings (FBGs) welded to the corrugated steel rebars, which allows, on the one hand, determination of the precise moment when the crack appears, as the deformation of the steel shows a highly significant leap at the moment when it takes place, due to the concrete ceasing to collaborate in traction and the steel beginning to do so and, on the other hand, the deformation the steel suffers during the successive loading steps.Diverse procedures have been used since methods have existed to detect cracks in reinforced concrete elements: infrared thermography ,2,3, acoFiber optic sensors based on Bragg gratings (FBGs) have been chosen for this study as they are more durable than conventional electric gages. They also provide long term signal stability and system stability, even under very unfavorable conditions, such as the vibration caused by roads. The cable length has no impact on the precision of the measurement. Multiplexing use allows different sensors to be placed on the same fiber optic cable, a much lighter cable than the conventional one of electric extensometric gages. The optic sensors are immune to electromagnetic and radiofrequency (EMI/RFI) interference, and resist hostile environments in the presence of water, salt, extreme temperatures, pressure (up to 400 bar), potentially explosive atmospheres and high voltage zones. Definitively, fiber optic sensors based on Bragg grating offer greater economic advantages, performance and precision than traditional electric gages .FBG have been used both to detect cracks on the surface as well as by embedding them in the concrete. They have also been used to measure temperature and strain , biaxialIn this study, we investigate the use of optic fiber sensors welded to the corrugated rebar to detect the moment at which the first crack takes place and the deformation the steel suffers from that moment onward during the whole process of loading the structural element. There are different devices on the market to measure deformations. The sensors chosen, within the group of Bragg grating (FBG) sensors, are weldable sensors, as these are to be integrated with the structural steel of the reinforced concrete structural elements to be tested.The fiber optic sensors are highly temperature sensitive, so in order to compensate these effects, a temperature sensor will be included within the array. An array is a chain of sensors linked by a fiber optic cable; custom made for the structural element that is to be tested. The array to be installed on our beams shall contain two weldable deformation sensors and a temperature sensor. Each one of the deformation sensors shall be welded to the two bars that reinforce the beam under flexion and are to be stressed. As the temperature sensor only measures this, it will not be welded to the steel bars and will be located near to the deformation sensors.Two beams of reinforced concrete are to be tested, with sections of 200 × 300 mm and 300 × 500 mm, and a length of 3000 mm. These sections have been chosen so they are sensitive to the loads to be applied.The fiber optic deformation sensors used are weldable . These aThe sensor chain was custom manufactured for each beam. Each chain has a temperature sensor  to compeThe first structural element we are going to test is a reinforced concrete beam with a section of 200 × 300 mm. Its reinforcement is of four rebars with a diameter of 12 mm, with stirrups with a diameter of 8 mm every 200 mm. The steel quality is B500S. The beam length between resting points is 3000 mm. The reinforcement scheme and placement of the fiber optic sensors is illustrated in The choice of this beam with this section and reinforcement is due to the loads that are to be applied to it, so it is deformed significantly, and one may measure the deformations the steel suffers, as well as observe the cracks in the structural element, something that will be decisive in the section study.The sensors are placed in the center of the beam, which is where the different loading steps are to be applied and where, as it is a beam that is simply resting on the support, there will be the maximum deformations in the structural element.The temperature sensor has been placed attached to one of the corrugated steel bars, near the center zone, so it may compensate the effects the temperature has on the deformation sensors.The second structural element we are going to test is a reinforced concrete beam with a section of 300 × 500 mm. It is reinforced by two rebars with a diameter of 25 mm on the lower face and 2 rebars with a diameter of 12 mm on the upper face. The frames are rebar with a diameter of 8 mm, every 20 mm. As with the 200 × 300 mm beam, the length between support points is 3000 mm. In this case, the sensors have only been placed on the lower bars, with a diameter of 25 mm, as the maximum deformation will take place on these and in the center of the span. As with the 200 × 300 mm beam, the temperature sensor has been placed near to the deformation sensors.In order to perform the experiment, the beams will be placed under different loading steps. The successive loads will be applied by a hydraulic press that will press on an RTN type loading cell of 10 Tn, with a ring torsion for the 200 × 300 mm beam. The device specifications are as follows: Nominal load: 10 t; Precision class: 0.05; Body measured: stainless steel; Protection class: IP68 to EN 60529; Cable type: shielded round cable, four wires in the case of the 200 × 300 mm beam, and for the 300 × 500 mm beam under RTN 100 Tn maximum ring torsion loading, Nominal load: 100 t; Precision class: 0.05; Body measured: stainless steel; Protection class: IP68 to EN 60529; Cable type: round shielded cable, four wires-Extensometric gages on a circuit of 1⁄4, 1⁄2 with full bridge, variable bridge power (DC or bearing frequency of 1200 Hz), internal terminal resistance on 1/4 bridge (120 or 350 ohm); - Voltage (± 10 V);-Pt100, resistance-Potentiometer-Sampling speed: max. 20 kS/s-Automatic transducer identification: TEDS-European Union Declaration of Conformity No. 263/2017-07.Both loading cells are HBM brand  with European Union Declaration of Conformity No. 238/2017-07 connected to an HBM QuantumX MX1615 data acquisition system with 16 channels, compatible with the following transducer technologies in all the channels:In the process of successively loading the beam, the sag acquired by the structural elements will be measured by a linear potentiometer displacement transducer of 20 mm, 0.1% precision, compatible with MX1615B amplifier. The displacement transducer will also be connected to the QuantumX MX1615 data acquisition system.The QuantumX MX1615 data acquisition system is connected to a computer in which software is installed to collect all the information, both from the loading cells as well as the displacement transducer. The software is Catman Easy, by the commercial brand HBM.Data acquisition from the elements to measure applied force and deformation have been connected to the aforementioned QuantumX data acquisition system. Both the deformation as well as temperature sensors are connected to another device called interrogator. An optic interrogator is an optoelectrical instrument able to read fiber sensors with Bragg grating (FBG) in static and dynamic monitoring applications.The same interrogator may obtain readings from an ample network of sensors of various types  connected through different fiber lines. All the data may be acquired simultaneously and with different sampling frequencies.During the data acquisition, the interrogator measures the bandwidth associated with the light reflected by the optic sensors and converts it to technical units.The interrogator model we are going to use is the FS22 (HBM), a device designed to interrogate Bragg grating based sensors. Its technology is continuous laser scan. This includes a reference to scannable bandwidth that provides continuous calibration and guarantees the long-term precision of the system. These interrogators are executed in an operating system in real time to acquire high quality data from a large number of sensors provided by the combination of broadband tuning range and simultaneous and parallel acquisition.The interrogator is connected to the computer, which uses specific Catman Easy software, providing us the data on the deformations suffered by the beams in real time. The data acquisition system installed is shown in The deformations we are going to measure are those of the steel, as that is the material the optic fiber is measuring. The cracking moment is a fundamental datum, as we know the moment at which the concrete ceases to absorb traction, in order for the steel to begin to work.Between the crack lips, the steel takes on the full traction strain on its own, but between the cracks, there is the anchorage of the reinforcement in the concrete and part of the traction force on the steel is transferred to it. If the traction on the concrete equals its resistance to traction, a new crack is formed”.We must take into account, quoting Calavera  that “BeThis means that there is, between cracks, part of the concrete that absorbs deformations. At the exact point where there is a crack, the concrete does not collaborate and the whole deformation is absorbed by the steel. That fact is fundamental to understand how the structural element works .In the process of loading the structural elements, a visual inspection of the cracks that appear is carried out, to subsequently compare them with the theoretical calculations .ct): 5.4 MPa; Resistance to compression of the concrete (fck): 54.6 MPa; Concrete elasticity module (E): 33.400 MPa; and for the 300 × 500 mm beam: Resistance to flexion-traction of the concrete (fct): 8.9 MPa; Resistance to compression of the concrete (fck): 58.8 MPa; Elasticity module of the concrete (E): 33.053 MPa.Laboratory test were carried out on the two beams studied, obtaining the following figures: For the 200 × 300 mm beam, the laboratory data is: Resistance to flexion-traction of concrete (fct) to calculate the cracking moment. The cracking moments are calculated by applying the Equation (1), obtaining the following results:We used the values obtained in the laboratory for resistance of flexion-traction of the concrete  given above.We obtain the real resistance to traction of the concrete, that shall be 2.13 MPa. With that data, we input the value in the characteristics of our concrete in the FAGUS program. The program provides a value of the steel deformation in the crack, and another in the uncracked concrete. The section studied is between two cracks, so that figure must be averaged. In Considering these results, We observe that the theoretical deformation value interpolated grows over a soft curve. This is due to the sensor being approximately in the center between cracks, which makes the concrete between cracks contribute to less deformation of the steel than if the sensor were to be very near to a crack or in the actual crack. That is precisely what happens in the following beam studied, where we observe that the interpolation curve suffers a major leap at the moment of the cracks taking place.In order to be able to determine the precise moment when the crack takes place and how this grows by application of the successive loads, we shall transform In It is evident that concrete is a material regarding which we cannot do more than approach its behavior by experience, although with embedded sensors we are able to know the moment at which the material cracks, and with that result, know its behavior much better. One may see that, while the beam has not cracked, the steel is gradually deformed, on the contrary to what traditional structure calculation theory says as, in this, the traction is absorbed by the concrete, a fact that is proven not to be the case in these graphs. Once the cracks start, when we go from 8.07 to 9.05 kN applied load, the deformation of the steel is much more significant, as the concrete contributes to a lesser extent to absorb the traction. The greater or lesser contribution by the concrete depends on the position of the sensor between the cracks.The section of the beam that will be analyzed below is shown in Loading begins in the center of the beam span, at an interval ranging from 5.20 kN to 275 kN. After applying these loads, and using Catman software, we obtain the deformation that takes place in the corrugated steel bars according to the loads applied .Once more, the beam has cracked before reaching the calculated cracking moment. The cracking process of the beam was observed, as with the 200 × 300 mm beam, obtaining perceptible cracking on visual inspection with a load of 58 kN. In fis = 111.25 mkN.The steel deformation shall first be analyzed using the data obtained in the laboratory, compared with that provided by the optic fiber. To do so, a concrete has been created with the characteristics described above, with fct = 8.9 MPa, and MThe steel deformation is obtained using the program FAGUS. We shall show the result provided by FAGUS for a moment of 127.88 mkN, the rest of the results having been obtained in the same way .The same method shall be applied as for the 200 × 300 mm beam, considering the steel deformation for resistance to traction of the concrete obtained by the laboratory tests, and subsequently that obtained with the optic fiber .For a load of 54 kN, the moment corresponds to 40.5 mkN, and applying Equation (1) we obtain a resistance to traction of the concrete of 3.24 MPa, compared with the 8.9 MPa obtained in the laboratory. In this case, the crack has opened at a point very near to the optic fiber, so the concrete can barely contribute to avoid deformation of the steel .We see what happens when the resistance to traction of the concrete with which we perform the calculations using the FAGUS program corresponds to the 3.24 MPa. We observe that by inputting the behavior real values of the concrete, the beam deformation curve corresponds to the data provided by the optic fiber sensors. In this case, as the optic fiber is very near to a crack, there is a sharp leap at the moment it takes place. As we shall see in the slope figures, these are much steeper than in the previous case, in which the optic fiber was approximately in the center between the cracks, which caused these slopes to be less steep. The slope values of these curves are recorded in In The moment at which the crack in the beam takes place is evident, as the deformation of the steel grows evidently. The load at which the crack takes place is 54 kN, compared with the 58 kN observed during the visual inspection.As happened with the 200 × 300 mm beam, the theoretical deformation of the beam reinforcement is far from appearing like its real behavior. In this case, the crack has opened up at a point very near to the optic fiber, so the concrete shall not collaborate when its traction tension is reached.In this case, we must observe what happens at the loading point of 54 kN, where the slope of the curve is much steeper, something that did not happen in the graph of beam 200 × 300 mm. This is due to the crack having opened very near to the location of the optic fiber, so that, in analysis of the section, the concrete barely collaborates in traction of the beam, and practically all the traction is borne by the steel.It is noted that the optic fiber shows us the precise moment at which the beam cracks, that the cracks open much earlier than what the laboratory tests say, and that taking the data provided by the optic fiber, we may determine the behavior of the structural element in a much more precise way.It is evident that when calculating a structural element, we do not know what will happen to it, when the piece will really crack. Considering an expression that draws that value closer to reality shall be a matter to be studied in future lines of investigation.Two beams with a rectangular section in which fiber optic sensors were embedded have been tested to analyze the real deformation of the steel when they are submitted to different loading stages. Appearance of the first cracks has been observed in both cases. These appear much earlier than the calculation predicts. The appearance of the first cracks is a fundamental matter to understand the real behavior of the structures. Fiber optic sensors were used to observe how a sudden change in deformation of the steel takes place. Moreover, with the advantage of the measurements being in real time, a fact that provides greater value to evaluation of the structural health of the elements tested. It is evident that this sudden change leads to it being deformed to greater extent as a consequence of the concrete cracking.Thus, considering the results obtained, we may know the precise moment at which the beam cracks through embedded fiber optic sensors. On studying the deformations, it has been noted that even when test pieces extracted at the moment of concrete pouring were tested, and they were tested on the day when the tests were to be carried out, these values do not match the behavior of the concrete under traction. In both cases, the beam cracked much before the laboratory tests indicated.Thus, placement of sensors welded on corrugated steel bars within reinforced concrete structural elements, at their maximum effort points, is a precise, reliable method to determine the moment at which the first cracks take place, as it has been possible to prove according to the results obtained.After ascertaining the real cracking moment of the concrete, we precisely obtained its resistance to traction and, thus, the real deformation of the corrugated steel during application of the loads.As stated in the introduction, the existing studies on concrete cracking use diverse methods to detect cracks. As is known, concrete is a material that resists compression well, but that is not the case with traction efforts. The reinforcement of the structural elements is placed, among other reasons, to bear the traction the concrete is not able to bear. The method proposed herein provides, as a novelty, detection of cracks that is observed thanks to the optic fiber sensors welded to the corrugated steel bars, at the precise moment when the steel begins to deform significantly. This causes a leap in its deformation, which is detected for the relevant load applied. Moreover, once the steel begins to deform, it is possible to know the deformation it will suffer during the whole period of application of the different loading steps to which the structural element is submitted. It has been proven that the deformation of the steel measured with optic fiber sensors corresponds to the theoretical values of the traditional materials resistance calculation, as long as the real cracking moment of the concrete is taken as the starting point.We may conclude, considering these graphs obtained from the experiment carried out, on the one hand that laboratory tests to determine flexion-traction resistance of concrete provide very conservative results, that have nothing to do with what really happens in the structural element. And on the other, that deformation of the steel, obtained with these tests, are quite far from its real behavior. This method of evaluating the structural health of a simple element of reinforced concrete may be transferred to more complex structural elements of buildings in construction to know the behavior of the structure when the formwork removal takes place and their actual weight begins to bear down on the structures, and subsequently the application of deadweight and overburdens in use, when the building is put into operation.A monitored building may provide us information on what overburdens it is able to bear, a highly important factor when one wishes to change the use of a building and the overburdens it is to be subject to are higher than those initially designed. In this case, and according to the data obtained, one might even be able to avoid possible structural reinforcement, as we would know what the building may really bear, with the financial savings that would involve.


Denosumab is a potent antiresorptive agent that substantially increases bone mineral density and reduces fracture rates at all skeletal sites for as long as it is administered. However, its favorable skeletal effects reverse quickly upon its discontinuation, because of a vast increase of osteoclast number and activity, which leads to a subsequent profound increase of bone turnover above pre-treatment values, a phenomenon commonly described as “rebound phenomenon”. More importantly, most patients experience rapid, profound bone loss due to this burst of bone resorption that may lead in a minority of these patients to occurrence of fractures, especially multiple vertebral fractures. Therefore, subsequent antiresorptive treatment is mandatory, although the optimal regimen is yet to be clarified. In the present review, we outline what is currently known regarding the negative effects of denosumab discontinuation on different aspects of bone status, the factors that may affect them, and strategies to prevent them. Osteoporosis is a chronic disease, requiring long-term management. Although osteoanabolic agents, such as parathyroid hormone (PTH) analogs and romosozumab, achieve impressive increases of bone mineral density (BMD), they can be administered only for a relatively short period of 1–2 years. Therefore, antiresorptive agents still remain the cornerstone of osteoporosis treatment . AdditioIn this review, we summarize the most recent evidence regarding the negative effects of Dmab discontinuation on different aspects of bone status, the factors that may affect them, and strategies to prevent them.We searched for articles published in PubMed and Cochrane Library from inception up to November 2020, to identify published original articles concerning Dmab discontinuation. In particular, we searched for articles that directly or indirectly investigated the consequences of Dmab discontinuation on bone health. The term “denosumab discontinuation” was matched with the following terms: C-terminal telopeptide of type I collagen (CTX), N-terminal propeptide of type I procollagen (P1NP), bone turnover markers (BTM), BMD, fracture, osteoblast and osteoclast, osteoporosis, rebound phenomenon, bisphosphonate, alendronate, risedronate, ibandronate, zoledronate.We searched for articles published in English and to minimize differences, studies were included if they met the following criteria: (1) those that were cohort studies, case-control studies, or cross-sectional studies, case reports or case series; (2) the exposure of interest was Dmab use/discontinuation, the outcomes were BMD loss, BTM changes, fractures, and osteoporosis. Exclusion criteria included non-primary research, review articles, lack of a primary outcome related to the relationship between Dmab discontinuation and bone health, or non-English language publications. Two investigators (G.T. and A.M.N.) independently searched papers, screened titles and abstracts of the retrieved articles, reviewed the full-texts, and selected articles for their inclusion.Under normal conditions of bone remodeling, old and damaged bone is removed by osteoclasts and replaced by newly formed bone matrix laid by osteoblasts in a fine-tuned mechanism . The whoDmab binds RANKL, thus preventing its binding to RANK on the surface of cells of the osteoclastic lineage. Consequently, Dmab suppresses osteoclast recruitment, maturation, function, and survival, and significantly decreases bone resorption and subsequent bone loss ,18 Figub. As a bAs a monoclonal antibody, Dmab circulates in the bloodstream, binds to secreted RANKL in the extracellular fluid and is cleared from the circulation through the reticuloendothelial system, with a half-life of approximately 26 days. In contrast with bisphosphonates (BPs), Dmab is not incorporated in the bone matrix, and its discontinuation induces significant and abrupt changes in bone remodeling. During the robust inhibition of RANKL, immature preosteoclasts that are unable to resorb bone accumulate in the bone tissue leading to a mass increase in osteoclastogenesis and RANKL release after stopping Dmab (rebound phenomenon) ,21 Figuc. HistomSummary: The discontinuation of Dmab leads to significant and abrupt changes in bone remodeling. Enhanced osteoclastogenesis and osteoblastogenesis is evident at tissue level leading to seriously compromised bone structure.Dmab discontinuation leads to a rapid, profound increase in the concentrations of BTM, frequently to above pre-treatment baseline levels ,23. EvenIn postmenopausal women participating in phase 2 and phase 3 trials, investigators described a fluctuating trend for serum CTX that began rising within a mean of 3 months after Dmab discontinuation (9 months following the last injection), with a peak after a mean of 6 months, and returned to pre-treatment concentrations after a mean of 24 months. A similar pattern was found for P1NP, suggesting that remodeling remained coupled during the discontinuation phase ,28.The pathophysiology of the “rebound effect” on BTM has not yet been fully elucidated. Dysregulation of the Wnt inhibitors SOST and DKK-1 and/or an abrupt increase in expression of RANKL following the loss of effect of Dmab, and/or an increased pool of dormant osteoclast precursors during the treatment period have been proposed ,21. In aWeak evidence supports the notion that pre-treatment with BPs might have a protective role after the cessation of denosumab ,31. In aThe behavior of BTM following Dmab discontinuation probably has a role in the evaluation of the effectiveness of the follow-up antiresorptive treatment.Summary: The discontinuation of Dmab leads to a rapid increase of BTM concentrations, frequently above pre-treatment baseline levels. The pathophysiology of the “rebound effect” on BTMs still remains uncertain. Previous treatment with BPs may have a protective role.Discontinuation of Dmab is typically associated with a decline in BMD at all skeletal sites. In postmenopausal women treated with Dmab for 24 months and subsequently followed for another 24 months off-treatment, BMD loss at all skeletal sites was evident 6 months after the last injection. The greatest BMD loss in the lumbar spine (LS) was noted at a mean of 18 months off-treatment while both total hip (TH) and 1/3 radius BMD continued to decline up to a mean of 30 months after the last injection .Reports from single centers who monitored their patients following the completion of the pivotal denosumab trials (FREEDOM and its Extension) concluded that the rate and amount of bone loss might be predicted by the total duration of Dmab use: patients treated for a longer period had more pronounced BMD loss at all skeletal sites ,33. The The magnitude of BMD loss after Dmab discontinuation seems to be linked with the phenomenon of multiple vertebral fractures. Indeed, in a post hoc analysis of 1001 participants from the FREEDOM and FREEDOM Extension trials, the patients who sustained multiple vertebral fractures (VFs) following Dmab discontinuation had significantly greater annual BMD loss than those without VFs .To date, it is still uncertain if pre-treatment with BPs preserves BMD gain after Dmab discontinuation. Some evidence suggests that in postmenopausal women, prior BP therapy might not affect the decline of BMD following Dmab discontinuation . In contUp to now, no consistent data are available regarding BMD changes after discontinuation in clinical conditions other than postmenopausal osteoporosis.Summary: The discontinuation of Dmab is most commonly associated with a significant decline in BMD at all skeletal sites which tends to return to pretreatment values after 1–2 years off-treatment. The rate and amount of bone loss might be predicted by the duration of denosumab use. The magnitude of BMD loss after Dmab discontinuation seems to be linked to the occurrence of vertebral fractures. It is still uncertain if pre-treatment with BPs prevents BMD loss after Dmab discontinuation.Discontinuation of Dmab is associated with a 3- to 5-fold higher risk for vertebral, major osteoporotic, and hip fractures ,39. Thisp = 0.049), corresponding to a 3.4% and 2.2% risk of multiple vertebral fractures, respectively [A post hoc analysis of FREEDOM and FREEDOM Extension did not identify an increased risk of VFs compared to placebo. Namely, among 1001 women who discontinued denosumab after 7 or 10 years of treatment, the annualized risk for VFs rose to 7.1%, similar to the risk in untreated participants. However, among the participants who had sustained at least one VF, the percentage of multiple ones was larger among those who discontinued denosumab (60.7%) than placebo . The latest evidence shows that even a 4-month delay in the injection significantly increases VF risk . The incTaken together, it seems that fractures most commonly occur at the thoraco-lumbar junction, at the same location as the common osteoporotic VFs. This finding implies that despite the higher number and severity of fractures after Dmab discontinuation compared to the commonly seen in insufficiency fractures, the etiopathogenesis may not differ between the two conditions ,51. AlthIt is not clear whether Dmab discontinuation increases the risk for non-VFs. The detrimental effect of stopping Dmab seems to affect mainly the trabecular bone, probably due to its fast remodeling rate compared to that of cortical bone .Summary: The discontinuation of Dmab is associated with an increased risk of multiple, clinical VFs that may occur a few months after the Dmab effect depletion. The risk of non-VFs has not been clearly estimated yet.All of the above reported findings are strongly affected by several study limitations such as a weak study design, small sample size, and enrolments focused mainly on women, and in particular elderly patients (mean age >65 years); furthermore, most of the studies did not rule out other comorbidities that might influence bone health. Other confounding factors might be represented by the relatively short off-treatment observation period and other concomitant medication during the off-treatment period ,22,40. FAccording to currently existing evidence, prevalent VF(s) before or during the treatment period are the strongest predictor of new VFs upon discontinuation ,34. ThisOther factors associated with increased risk of RAVFs, that were identified at the post-hoc analysis of FREEDOM and its Extension follow-up study, include longer duration of the off-treatment period, greater gain in hip BMD with Dmab treatment, and greater loss of hip BMD after discontinuation .The duration of Dmab treatment has been proposed as a factor predisposing to VFs, probably because the higher the number of Dmab doses administered is, the more prominent is the rebound effect . Longer Vertebroplasty has also been identified as another factor setting patients who discontinue Dmab at risk for VFs, especially at the adjacent vertebrae ,44,52. IAlthough younger age has been reported to be a risk factor for bone loss after discontinuation , RAVFs iWeak evidence suggests that concomitant AI administration in breast cancer patients may aggravate the withdrawal effect of Dmab on the skeleton, even in normal BMD values, predisposing to VFs ,26. Of nAlthough previous BP treatment lessens the rebound of BTM, it is uncertain whether it prevents RAVFs. Alendronate failed to avert spontaneous clinical VFs in two high-risk postmenopausal women previously exposed to BPs who discontinued Dmab .Summary: Patients with prevalent VFs, greater gain in hip BMD while on Dmab treatment, greater loss of hip BMD after discontinuation, and longer duration of Dmab treatment and of the off-treatment period, are more prone to RAVFs following Dmab discontinuation.The timing of Dmab discontinuation is a crucial clinical question in the chronic management of an osteoporotic patient. Some experts, based on a post-hoc analysis, suggest that the incidence of non-VFs under Dmab treatment is inversely related with total hip T-score, and the fracture rate decrease reaches a plateau at a T-score range between −2.0 and −1.5, independently of age and prevalent fractures; nevertheless, this is not the case for the vertebral fracture risk which seems to exhibit the same inverse relationship with total hip BMD values but without a restrictive T-score threshold . TherefoIn case Dmab discontinuation is decided, it is the rebound phenomenon in bone remodeling that needs to be quickly counteracted in order to avoid bone loss and to minimize the risk of subsequent multiple VFs , althougThe administration of a subsequent antiresorptive agent following Dmab discontinuation is currently a recommended practice, irrespective of the attained BMD at the time of the transition between treatments. Currently published randomized clinical trials (RCTs) and prospective studies investigating the effectiveness of various antiresorptive agents following Dmab discontinuation are summarized in Oral BPs have also been tested regarding their efficacy to prevent bone loss following Dmab discontinuation in studies of different duration and designs. In a study designed to test the adherence, preference, and satisfaction (DAPS study) of patients receiving either Dmab or alendronate, 115 out of the total 250 postmenopausal women with BMD T-scores between −4 and −2 were randomized to receive one year Dmab followed by one year oral alendronate ,71. AparThe two currently published RCTs with zoledronate suggest that the duration of previous Dmab treatment probably has a significant impact on the efficacy of the subsequent antiresorptive treatment to maintain bone gains. Specifically, among postmenopausal women previously treated with Dmab for an approximate period of 2.5 years, a single i.v. administration of zoledronate 6 months after the last Dmab injection preserved the BMD gains for three years in around 80% of the participants ,46. HoweThe timing of the subsequent antiresorptive treatment initiation has also been a subject of controversy. It has been speculated that suppressed bone remodeling from the last Dmab injection may reduce the ability of a BP to sufficiently bind to bone surfaces, since the active resorptive sites are limited, thus reducing its efficacy . AlthougGiven all the available information and recent recommendations, a rational approach would be the initiation of either oral BPs or zoledronate following Dmab discontinuation. As oral BPs might not adequately consolidate the BMD gains, the measurement of BTM is suggested after 3 months in order to monitor the efficacy and adherence through a level below the mean of healthy premenopausal women  . BTM meaSummary: Subsequent antiresorptive treatment following Dmab discontinuation is currently a recommended practice to consolidate BMD gains and to avoid the rebound-induced fractures. An at least one-year treatment with either a potent oral BP or i.v. zoledronate is recommended to follow 6 months after the last Dmab injection.Dmab is a very effective antiresorptive agent and a useful tool in the long-term management of osteoporosis. However, its favorable skeletal effects can reverse quickly following its cessation  due to aPreventing bone loss upon Dmab discontinuation is an issue of concern.There are currently limited data and evidence regarding the optimal management of patients discontinuing Dmab. However, this is a matter of ongoing clinical research and new data are continuously emerging.BTM should be measured at 3 months after initiation of an oral BP to monitor adherence and efficacy; the maintenance of BTM below the mean of healthy premenopausal women could be considered as an adequate response . In caseBMD testing should be performed at Dmab discontinuation and at 12 months of subsequent antiresorptive treatment ,83. A BMSpine X-rays and/or vertebral fracture assessment (VFA) should accompany each DXA measurement to identify new VFs.According to current evidence, zoledronate infusion or oral alendronate could be preferred as subsequent treatment in patients discontinuing Dmab. No robust data are available for the use of teriparatide.The duration of subsequent BP treatment is proposed to last 1–2 years, although this has not been proven in prospective studies.The duration of subsequent BP treatment to prevent bone loss may be affected by the duration of Dmab treatment. Physicians should have this in mind when they plan their treatment strategy.