http://repositorio.lnec.pt:8080/jspui/handle/123456789/1007756 Sat, 04 Apr 2026 21:22:46 GMT 2026-04-04T21:22:46Z 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 http://repositorio.lnec.pt:8080/jspui/handle/123456789/1017102 Global and local geometrical imperfections of pultruded GFRP profiles based on a modal approach Lazzari, J.; Lages Martins, L.; Ribeiro, A.; Pinheiro, A.; Correia, J.; Silvestre, N. Elsevier Ltd. ABSTRACT - The ultimate capacity of pultruded glass fibre reinforced polymer (pGFRP) profiles depends significantly on geometrical imperfections (GIs), given their sensitivity to buckling phenomena arising from both thin walls and low elastic moduli. However, GIs are not yet comprehensively addressed in design guidance. This paper proposes a new approach to characterize the initial GIs of pGFRP profiles based on a modal approach. Given the lack of comprehensive knowledge in this area, this study presents a highly accurate and robust methodology to measure GIs and dimensional deviations (DDs) in pGFRP profiles using a 3D contact coordinate measurement machine (CMM). The modal approach encompasses the measurement of dimensional parameters and a point cloud transformation that enables the assessment of GIs associated with pure buckling modes of pGFRP profiles. This procedure allows the quantification of three types of global GIs associated to (i) minor-axis (weak axis), (ii) major-axis (strong axis) bending, and (iii) twist. Additionally, the procedure also includes the assessment of local GIs, considering the wall (plate-like) imperfections. The separation of GIs into these four types (shape and amplitude) is of major relevance as its paves the way to the development of analytical design formulas for the strength prediction of pGFRP members. The approach described in this paper also serves two important purposes: (i) the statistical analysis of DDs and GIs of pGFRP members, and (ii) the identification of distinct shapes and amplitudes of GIs that form the basis for reliable design considerations of pGFRP members. Fri, 05 Jan 2024 00:00:00 GMT http://repositorio.lnec.pt:8080/jspui/handle/123456789/1017102 2024-01-05T00:00:00Z