http://repositorio.lnec.pt:8080/jspui/handle/123456789/1007756 Mon, 26 Oct 2026 10:13:31 GMT 2026-10-26T10:13:31Z http://repositorio.lnec.pt:8080/jspui/handle/123456789/1019634 A Metrologically Validated Cost-Effective Solution for Laboratory Measurement of Long-Term Deformations in Construction Materials Fathi, A.; Martins, L.; Pereira, J.; Vasconcelos, G.; Azenha, M. Sebastiano Candamano Abstract - Investigating the long-term performance of building materials, such as drying shrinkage,moisture expansion, creep, and others, usually requires long-lasting tests with a high number of specimens. Given the initial costs, required data acquisition systems, and the time allocated, conventional sensors like LVDTs become costly for such long-term experimental studies. This article proposes an innovative cost-effective solution combining optical microscopy imaging, 3D printed sliding rulers, and Python-based artificial vision to overcome these limitations. The 3D printed rulers establish a local physical reference frame, while the artificial vision system uses contour detection and point tracking of optical targets to quantify displacements. Unlike continuous monitoring systems, the proposed solution utilises a discontinuous point-tracking approach, allowing a single USB microscope to monitor an unlimited number of specimens while maintaining the possibility for moisture exchange between the material surface and the environment. The system was metrologically validated against a laser interferometer, achieving an expanded instrumental uncertainty of 0.0042 mm (4.2 μm), determined through strict calibration. These results demonstrate that the proposed solution delivers accuracy comparable to conventional sensors but with significantly higher scalability and lower cost, making it highly suitable for extensive long-term experimental programmes. Fri, 13 Feb 2026 00:00:00 GMT http://repositorio.lnec.pt:8080/jspui/handle/123456789/1019634 2026-02-13T00:00:00Z http://repositorio.lnec.pt:8080/jspui/handle/123456789/1018081 Influence of rainfall time series sample rate in the improvement of decision-making based on high intensity rainfall events Simões, C.; Ribeiro, A.; Almeida, M. C.; Covas, D.; Coelho, G.; Pinheiro, A. IMEKO Abstract - This study aims Lo assess whether data acquisition frequency can affect the understanding of high-intensity precipitation events. Time series from a weighing gauge and a weighhridge gauge installed at the sarne site were analysed, with rainfall intensity data acquisition frequencies of 10 seconds and 5 minutes, respectively. To check the consistency of the data ohtained by the two types of rainfall measuring instruments, a correlation analysis was carried out between the two time series. The results relating to acquisition frequency showed that, for an acquisition frequency of 5 minutes. there are significant losses of information (especially during heavy rainfall events) compared to acquisition frequencies of l0 seconds. The correlation analysis showed that the gauges are measuring correctly and that the data is accurate. Thu, 01 Aug 2024 00:00:00 GMT http://repositorio.lnec.pt:8080/jspui/handle/123456789/1018081 2024-08-01T00:00:00Z http://repositorio.lnec.pt:8080/jspui/handle/123456789/1018077 Validation of a Iaboratory method for the traceability of a rainfail weighing gauge Simões, C.; Ribeiro, A.; Almeida, M. C.; Covas, D.; Dias, L.; Coelho, G. ABSTRACT This study aims to develop a Iaberatory method for the traceability of a rainfali weighing gauge, including an evaluation of the measurement uncertainty. The adopted procedure is similar to the one used for the non-automatic weighing instruments. A static approach is followed to achieve the caiibration deviation of the precipitation scale. The method used te evaluate the measurement uncertainty is based on a nonlinear mathematical model. The Monte Cano method is used to calculate uncertainties and validate estimates following the convencional Guide te the Expression of Uncertainty in Measurement (GUM) approach. Measurement uncertainty contributions of input quantities te the mathematical model used to calculate rainfail also require specific calibration procedures. Results show the Fri, 01 Mar 2024 00:00:00 GMT http://repositorio.lnec.pt:8080/jspui/handle/123456789/1018077 2024-03-01T00:00:00Z http://repositorio.lnec.pt:8080/jspui/handle/123456789/1017504 Metrological quality of the excitation force in forced vibration test of concrete dams Lages Martins, L.; Gomes, J. P.; Ribeiro, A. IOP Publishing Abstract. This paper describes the study of the metrological quality of the excitation force in the context of force vibration test of concrete dams. For this purpose, a measurement uncertainty evaluation was performed, based on available probabilistic information about the input quantities – rotation frequency, mass, radial position, dimension, diameter and density of the generator’s rod – which support the determination of the excitation force in an eccentric masses vibration generator, used by LNEC in concrete dam’s field observation. The uncertainty propagation from the input quantities to the output quantity was performed by a Monte Carlo method, considering the mathematical model used for the determination of the excitation force. Two experimental cases were studied: (A) the use of five weights in the generator in the frequency range of 1 Hz up to 6 Hz; and (B) the use of a single weight in the generator in the frequency interval comprised between 5 Hz and 15 Hz. In the first case, the excitation force estimates and expanded measurement uncertainties (considering a 95 % confidence interval) varied between 3.55 kN ± 0.14 kN and 127.68 kN ± 0.91 kN, being rotation frequency the major contribution for the obtained dispersion of force values. In the second case, the excitation force estimates and expanded measurement uncertainties varied between 16.71 kN ± 0.25 kN and 150.4 kN ± 1.8 kN, being the generator’s rod diameter the main contribution for the output measurement uncertainty. The obtained knowledge is essential to assure confidence and rigorous knowledge about the applied excitation force, namely, in extreme situations near dynamical structural safety limits of the observed concrete dam and of the testing equipment. Mon, 01 Jan 2024 00:00:00 GMT http://repositorio.lnec.pt:8080/jspui/handle/123456789/1017504 2024-01-01T00:00:00Z