Ultrasonic pulse velocity technique is one of the most popular non-destructive techniques used in the assessment of concrete properties. However, it is very difficult to accurately evaluate the ...concrete compressive strength with this method since the ultrasonic pulse velocity values are affected by a number of factors, which do not necessarily influence the concrete compressive strength in the same way or to the same extent. This paper deals with the analysis of such factors on the velocity–strength relationship. The relationship between ultrasonic pulse velocity, static and dynamic Young’s modulus and shear modulus was also analyzed. The influence of aggregate, initial concrete temperature, type of cement, environmental temperature, and w/c ratio was determined by our own experiments. Based on the experimental results, a numerical model was established within the Matlab programming environment. The multi-layer feed-forward neural network was used for this purpose. The paper demonstrates that artificial neural networks can be successfully used in modelling the velocity–strength relationship. This model enables us to easily and reliably estimate the compressive strength of concrete by using only the ultrasonic pulse velocity value and some mix parameters of concrete.
The capability of a process is its ability to produce products that meet predefined requirements in industry and it is measured by capability indices. If data are not normally distributed, other ...techniques for capability estimation should be taken into consideration. One of frequently used methods are transformations to normal data distribution like Abbasi-Niaki, Box-Cox and Johnson transformation. In this paper, we propose modified power transformation method for non-normal process capability estimation. Proposed method is compared to Box-Cox, Johnson and Abbasi-Niaki transformation method using simulation studies under several theoretical non-normal distributions. Proposed modified transformation method finds optimal power to reduce data skewness in case of negatively and positively skewed data. In case the optimal power is not found, power to achieve minimal skewness is estimated. In case of negatively skewed data, algorithm transforms data to positively skewed. After applying each transformation, capability indices were estimated and then compared with theoretical indices by calculating relative bias. Proposed transformation method showed better performance than other methods in reducing skewness of negatively and positively skewed data. Study showed that performance of the proposed power transformation method was either better or comparable in estimating capability indices.
The paper presents the analytical model of a linear two-layer composite beam with partially debonded interlayer contact. The interlayer contact may be also locally fully debonded. The two-dimensional ...model is materially and geometrically linear, and the governing equations are based on Reissner beam theory. In the partially debonded interlayer contact, only axial slips are allowed. The finger joints are modelled as linear springs. The analytical solution is presented. The kinematic and equilibrium variables are evaluated along the simply supported beam. A parametric study was carried out to analyse the effect of the strength of finger joints and interlayer contact. In addition, different lengths and positions of the fully debonded area of the interlayer contact were analysed, and their effects on selected kinematic and equilibrium variables were observed and commented on. It was shown that the presence of the fully debonded interlayer contact and finger joints significantly affects the behaviour of the beam as well as the stiffness properties of the interlayer contact and finger joints.
Global Navigation Satellite System (GNSS) technology is widely used for geodetic monitoring purposes. However, in cases where a higher risk of receiver damage is expected, geodetic GNSS receivers may ...be considered too expensive to be used. As an alternative, low-cost GNSS receivers that are cheap, light, and prove to be of adequate quality over short baselines, are considered. The main goal of this research is to evaluate the positional precision of a multi-frequency low-cost instrument, namely, ZED-F9P with u-blox ANN-MB-00 antenna, and to investigate its potential for displacement detection. We determined the positional precision within static survey, and the displacement detection within dynamic survey. In both cases, two baselines were set, with the same rover point equipped with a low-cost GNSS instrument. The base point of the first baseline was observed with a geodetic GNSS instrument, whereas the second baseline was observed with a low-cost GNSS instrument. The results from static survey for both baselines showed comparable results for horizontal components; the precision was on a level of 2 mm or better. For the height component, the results show a better performance of low-cost instruments. This may be a consequence of unknown antenna calibration parameters for low-cost GNSS antenna, while statistically significant coordinates of rover points were obtained from both baselines. The difference was again more significant in the height component. For the displacement detection, a device was used that imposes controlled movements with sub-millimeter accuracy. Results, obtained on a basis of 30-min sessions, show that low-cost GNSS instruments can detect displacements from 10 mm upwards with a high level of reliability. On the other hand, low-cost instruments performed slightly worse as far as accuracy is concerned.
Monitoring displacements of the object can be performed using geodetic methods by selecting reference points on the surrounding terrain and points on the object that discretely describe the object’s ...behavior. The measurements are repeated in several epochs. By analyzing the geodetic network we can determine the status of a single point, i.e., whether the point has moved or not. The article discusses the testing of congruence, the testing of transformation of a single triangle, and the calculation of other deformation parameters in 2D networks resulting from the changes of points coordinates between two epochs. This is essentially the content of the Munich deformation method presented by W.M. Welsch, which includes the X- and L-method. The article also proposes some corrections to the original Munich approach. Finally, the applicability of the method is shown on a well-known practical example.
The aim of the present paper is to assess the non-destructive indicating properties of Slovenian beech (Fagus sylvatica) logs and correlate them with the mechanical properties of the final product, ...which is boards. Beech logs were visually graded according to the standard procedure and vibrational frequencies were measured. Logs were further on sawn into boards which were also non-destructively tested in wet and dry conditions. Finally, the boards were experimentally tested in tension. Special focus was directed towards visual parameters of the beech logs and their influence on the overall quality of the output material. The longitudinal natural frequencies of the logs were studied as potential indicating properties. The results showed that a majority of the visual log grading parameters do not result in good quality timber in terms of strength and stiffness properties, and only few are decisive for the final classification. The coefficient of determination of the static MOE vs. dynamic MOE of logs was r2=0.13, whereas vs. the MOE of wet boards was r2=0.49. Using a few visual characteristics in combination with dynamic measurements of logs and of wet boards could help to increase the yield of high quality beech wood.
In this paper, the applicability of the ultrasonic wave transmission method to estimate the initial setting time of an arbitrary cement paste is discussed. Ultrasonic pulse velocity measurements were ...fully automated and measured continuously. The Vicat Needle Test was used in order to determine the initial setting time of cement pastes. Different cement pastes were prepared in order to check the influence of the water/cement ratio, type of cement, curing temperature, cement fineness, and some clinker compositions, on the relationship between the initial setting time and ultrasonic pulse velocity. It was found that the initial setting time of an arbitrary cement paste can be estimated very accurately by the time the first inflection point appears on the ultrasonic pulse velocity curve. Moreover, it can be estimated quite accurately by the time the ultrasonic pulse velocity reaches a fixed value, close to the value of the ultrasonic pulse velocity in water.
This study presents a procedure for modeling the heat transfer process in a concrete dam, taking into account the time-varying boundary conditions on the upstream and downstream sides of the dam ...(i.e., the water level of the reservoir, spillover, insolation, and shading) which affect the temperature conditions of the dam. The large concrete arch-gravity Moste Dam (in North West Slovenia) was analyzed, where an automated system for the measurement of concrete and water temperatures, and for the monitoring of meteorological effects, was installed. Thermal analyses (1D and 2D) for non-linear and non-stationary heat conduction through solids were performed using a finite element method (FEM) based program, TeEx, which was complemented by two specially developed programs for determining the effects of convection and insolation, considering also the effect of shading. A 15-day period was analyzed, as well as a period of one year. It was found that the results of the performed analyses fitted in well with the experimentally determined concrete temperature measurements. The results showed that at the insolated side of the dam, the temperature gradient was largest in a very narrow area along the concrete surface, but the temperature did not stabilize shallower than at a depth of about 6 m. As part of the thermal analyses, uncertainty analyses of the results of the calculations were also performed.
Alternatively to empirical prediction methods, methods based on influential functions and on mechanical model, artificial neural networks (ANNs) can be used for the surface subsidence prediction. In ...our case, the multi-layer feed-forward neural network was used. The training and testing of neural network is based on the available data. Input variables represent extraction parameters and coordinates of the points of interest, while the output variable represents surface subsidence data. After the neural network has been successfully trained, its performance is tested on a separate testing set. Finally, the surface subsidence trough above the projected excavation is predicted by the trained neural network. The applicability of ANN for the prediction of surface subsidence was verified in different subsidence models and proved on actual excavated levels and in levelled data on surface profile points in the Velenje Coal Mine.
This paper presents the formulation of strain-based finite elements for modelling composite beams with finger joints considering slip between the layers. The finite elements are derived according to ...Reissner beam theory based on the modified principle of virtual work where the displacements and rotations are eliminated from the problem and the axial deformation, shear deformation and curvature of the layers remain only functions to be approximated within the finite element. Lagrange polynomials are used as shape functions to approximate the deformations and various interpolation methods are applied to numerical examples, with the Lobatto integration scheme giving slightly better results than Equidistant. The experimentally measured mechanical properties needed as input data for the numerical model are given for the four glued laminated beech beams. The numerical model is thoroughly verified and validated. The results show that the presented finite element formulation is an efficient tool for practical and accurate calculations.
•New finite elements for composite beams with slip and finger joints are proposed.•Numerical model is validated and verified with experimental results.•The finite elements exhibit no slip and shear locking.
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