Testing the Flyby Anomaly with the GNSS Constellation

We propose the concept of a space mission to probe the so called flyby anomaly, an unexpected velocity change experienced by some deep-space probes using earth gravity assists. The key feature of this proposal is the use of GNSS systems to obtain an increased accuracy in the tracking of the approaching spacecraft, mainly near the perigee. Two low-cost options are also discussed to further test this anomaly: an add-on to an existing spacecraft and a dedicated mission.Comment: 8 pages, 1 figure, 4 table

Da inspeção à avaliação de segurança na reabilitação de estruturas de madeira

A avaliação de estruturas existentes em madeira e consequente planeamento de intervenções requer conhecimentos específicos provindos de diferentes fontes e áreas técnicas, devendo estas serem complementares e aferidas por meio do uso de uma metodologia de inspeção e diagnóstico sistemática e rigorosa. Este trabalho apresenta, de forma resumida, as diferentes fases consideradas na avaliação estrutural de uma construção existente em madeira desde a fase inicial de diagnóstico e inspeção até à escolha de possíveis métodos para a avaliação de segurança, sendo estas fases fundamentais para a definição adequada do plano de intervenções a tomar posteriormente

Use of random sampling and Bayesian methods in the prediction of chestnut timber beams bending stiffness

The assessment of global bending stiffness of three old timber beams is predicted by use of random sampling and Bayesian Network approaches. The information for the prediction models derive from the visual grading and localized mechanical testing of 20 beams retrieved from the same building, which have been scope of analysis in previous studies. Although the results indicate moderate correlations between predicted and experimental results, significant percentage errors are also found. To minimize the percentage error between experimental and predicted values, coefficients corresponding to the scale effect relation between existing chestnut timber elements with round cross section and sawn beams of smaller dimensions with rectangular cross section were proposed.Fundação para a Ciência e a Tecnologia (FCT)Agência de Inovação (ADI

Prediction of global bending stiffness of timber beams by local sampling data and visual inspection

The results of visual inspection according to UNI 11119:2004 and bending tests made on 20 old chestnut (Castanea sativa Mill.) beams according to EN 408:2010 were statistically analyzed in order to provide a consistent and feasible procedure to predict their modulus of elasticity (MOE) in bending. Local data obtained from smaller size specimens was used for the prediction of the global mechanical properties of full structural size members and compared with the results of mechanical tests. The prediction models took into account the visual strength classes and the influence of defects on the determination of the MOE. Moreover, random sampling was considered in order to demonstrate the possibility of using smaller representative samples, thus avoiding excessive need of removal of on-site samples and allowing for a smaller number of mechanical tests. The models using random sampling predicted the behavior of full size scale elements accurately, with strong correlations to the experimental results (coefficient of determination r2 ranging from 0.70 to 0.79) and a percentage error lower than 20 %, thus allowing a reliable estimation of mechanical characteristics of existing timber members with a combination of visual inspection and local sampling.Fundação para a Ciência e a Tecnologia (FCT

Characterization of cross sections from old chestnut beams weakened by decay

This work aims to experimentally assess the material properties of old chestnut (Castanea sativa Mill.) cross sections weakened by decay. Specimens were taken from critical zones of twenty floor beams, mostly corresponding to their ending parts, in contact with granite masonry walls. These specimens were compared with clear wood specimens taken from non-decayed parts . The experimental campaign comprised of visual inspection, non-destructive testing (ultra-sound, impact penetration and drilling resistance tests) and uniaxial compression tests, parallel to the grain. Pin penetration test evidenced a depth of penetration 36% higher for decayed specimens compared to non-decayed specimens, proving the loss of capacity in the superficial decayed layer. The results of decayed specimens exhibited a decrease of approximately 30% in the compressive strength parallel to the grain. A reduction of approximately 5% was found for the dynamic and elastic moduli. The coefficients of variation for decayed specimens are significantly higher than for sound specimens. Different decay models are considered and compared aiming at analyzing decay evolution along time and determining the decrease of load bearing cross section. Finally, the results were used to calibrate a bi-parametrical decay model for above ground timber structures, considering a linear relation between time and decay depth.Fundação para a Ciência e a Tecnologia (FCT

Use of bending tests and visual inspection for multi-scale experimental evaluation of chestnut timber beams stiffness

The assessment of existing timber structures requires the determination of the mechanical properties of the individual timber members, which is often obtained by visual grading combined with information of small clear wood specimens. The purpose of this work is to present the results obtained in a multi-scale experimental evaluation of 20 old chestnut (Castanea sativa Mill.) beams, aimed at defining the correlations between bending modulus of elasticity (MOE) in different scales of timber members in combination with visual grading. The results of bending tests, according to EN 408:2010, were statistically analyzed to obtain correlations of bending MOE between and within different scales size. The results of visual inspection according to UNI 11119:2004 regarding the presence and distribution of defects were considered for variation analysis of MOE, evidencing a significant variance between samples of different visual strength grades. Strong correlations within the same phase (coefficient of determination r2 from 0.82 to 0.89) and moderate to high correlations for different phases (r2 from 0.68 to 0.71) were found for bending MOE. Cumulative distribution functions for global MOE remained similar throughout the experimental phases. Moreover, percentage of segments attributed to a specific visual grade is given for each member and compared between scales.The financial support of the Portuguese Science Foundation (Fundacao para a Ciencia e a Tecnologia, FCT), through PhD Grant SFRH/BD/62326/2009, is gratefully acknowledged. The authors acknowledge also the support of Augusto de Oliveira Ferreira e Companhia Lda. (offer of specimens) and of the Structural Lab from University of Minho (test facilities)

Glulam mechanical characterization

The glued laminated timber (glulam) mechanical properties may be evaluated through the determination of the key mechanical properties of the lamellae that compose that element. Simple bending and tension parallel to the grain tests were performed in order to assess the strength class of three glulam elements. Regarding the bending tests, 8 samples were taken from a glulam beam and assessed. Values for the resistant bending tension and both local and global modulus of elasticity were obtained. For the tension parallel to the grain tests, a total of 120 samples were assessed. The samples were divided regarding the structural element from where they were extracted as well to the type of failure mode found in the tests. The values of the lamellae properties were then used for determination of the properties of the glulam material. The data gathered from the tests was assessed statistically and concluded that the mechanical properties of the glulam elements did not fulfill the required parameters of the normative requirements.Fundação para a Ciência e a Tecnologia (FCT

Effectiveness and subjectivity of visual inspection as a method to assess bending stiffness and strength of chestnut elements

Besides the difficulty of assessing an existing timber structure on site, the efficiency and accuracy of visual inspection is often compromised by its subjective nature inherited by the level of expertise of the inspector. This often leads to conservative predictions of the mechanical properties, even with the use of specific visual grading norms. The main objectives of this work are to assess the effectiveness of visual inspection as to define different classes of strength and stiffness and to provide a statistical analysis on its subjectivity. For that aim, visual inspection using Italian standard UNI 11119:2004 and bending tests of 20 old chestnut beams (Castanea sativa Mill.) at different scales, were carried out. Comparisons and effectiveness of visual inspection is analyzed within and between different scales, and also regarding different level of expertise of inspectors. The results evidence similar percentages of segments classified with higher and lower visual grades and proved to be a good qualitative indicator of bending strength between sawn beams. For the most experienced inspectors, an overall 42% accuracy was found with a better differentiation between visual classes, whereas lower level inspectors scored approximately 5% less. Lower level inspectors evidenced higher concentration of values around a higher mean for each class denoting a more conservative approach. Regardless of the inspector level, knot size was the main limiting visual parameter with higher influence in small scales of the timber elements. When studying the characterization of a single knot, coefficients of variation of 15.7% and 21.8% were found for measuring the minimum and maximum diameter. Bayesian probability networks were considered as to individually assess the accuracy in stiffness prediction of different level of inspectors, and by combination of their information, evidencing that parallel combination for prior information may allow the increase in visual inspection accuracy.Fundação para a Ciência e a Tecnologia (FCT

A holistic methodology for probabilistic safety assessment of timber elements combining onsite and laboratory data

The assessment of existing timber structures comprises several fields of knowledge, each one providing its own piece of information aiming at an effective answer. Even if general guidelines are available, there is still a need for a holistic approach that is able to combine information from different sources and infer upon that information allowing also, in that process, for an updating scheme aiming at a more substantiated decision process. In that scope, this work proposes a methodology for a holistic assessment of timber elements. The methodology combines information gathered in different scales and follows a probabilistic framework that allows for the structural assessment of existing timber elements with possibility of inference and updating of the mechanical properties of the elements, through Bayesian methods. The described methodology is based in four main steps: (i) scale of information; (ii) local and global data; (iii) probability assignment; and (iv) long term structural analysis. After the description of the methodology, its limitations and possible future modifications are discussed.The financial support of the Portuguese Science Foundation (Fundacao de Ciencia e Tecnologia, FCT), through Ph.D. Grant SFRH/BD/62326/2009, is gratefully acknowledged

Experimental analysis of Maritime pine and Iroko single shear dowel-type connections

"Available online 21 March 2016"In this study, screwed connections were experimentally evaluated, checking the plausibility of Eurocode 5 for two selected wood species, Iroko (Milícia excelsa) and Maritime pine (Pinus pinaster). Single shear screwed connections, considering self-tapping screws, were tested and the experimental campaign aimed at evaluating various mechanisms of resistance suggested by Eurocode 5 for this typology of connection, including axial withdrawal capacity of the screw, pull through parameter for screws, and local embedment of wood. The experimental results evidenced that the analyzed connection system had similar results with either wood species. The results were consistent with the calculation through Eurocode 5.This work was supported by FCT (Portuguese Foundation for Science and Technology), within ISISE, project UID/ECI/04029/2013