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Birch plywood in timber connections : Investigation on the rope effect and full-scale trusses
No full textEarlier studies have demonstrated that birch plywood is a viable substitute for steel plates in timber connections, thanks to its excellent mechanical properties, workability, and sustainability. The mechanical properties of birch plywood have been thoroughly investigated concerning key parameters, such as face grain angle and moisture content. Furthermore, its potential use as gusset plates in timber connections has been studied. However, these investigations were mostly limited to uniaxial tension and rather small-scale compared to real applications. Therefore, additional research is needed to further understand the mechanical behaviour of birch plywood, thus ensuring a safe design of such connections. This thesis aims to gain new knowledge on connections with birch plywood plates. The results of this study will then be used to improve the design of such connections, both in terms of safety and structural efficiency. The influence of the connector type (i.e. smooth dowel or fully threaded screw) was investigated concerning the shear capacity of connections using birch plywood with varying thickness. The results showed that, when utilizing screws, the analytical estimations according to EN1995-1 Eurocode 5 (EC5) significantly underestimate the shear capacity. This is mainly due to EC5’s conservative estimation of the so-called “rope effect” contribution to the connection’s shear capacity. Moreover, when the number of shear planes was increased from two to four, the discrepancy between EC5’s estimation and experimental results substantially increased regardless of the type of fastener. This substantial discrepancy was associated with the failure mode in the inner shear planes. Furthermore, both glued and mechanical connections were investigated by performing tests on full-scale glulam trusses joined through birch plywood gusset plates. Failure was designed to occur in the plywood plates subjected to a complex stress state. In this investigation, the thickness of these plywood plates was varied between 9, 12 and 21 mm, testing only one specimen for each configuration. The experimental results showed that glued trusses possessed higher load-carrying capacity and almost twice the stiffness of those with mechanical fasteners. Failure occurred in the plywood plates for all trusses with mechanical fasteners and the glued truss with thinner plywood plates (9 mm). However, the trusses with thicker plates (i.e. 12 and 21 mm) showed glue line failure between the plywood plate and the glulam beam. The analytical estimations for specimens that failed in the plywood plate generally showed good agreement with the experimental capacity, although they exhibited a slight overestimation. This was expected and was attributed to the size effect, as the input strength values of plywood adopted in the analytical estimations were obtained from small-scale tests. Furthermore, based on the size of the glued area compared to previous studies, bonding strength values were estimated and used in the analytical calculations of the bonding capacity for glued connections. However, these strength values should be further investigated to calibrate the analytical model and obtain more realistic estimations. In addition, two-dimensional numerical models demonstrated good agreement in predicting the global stiffness of the tested trusses. For future work, it is suggested to investigate the size effect on the mechanical properties of birch plywood and bonding strength, respectively, to further calibrate and validate the analytical models. Furthermore, more advanced numerical simulations of the truss specimens are suggested.Tidigare studier har visat att björkplywood är ett effektivt alternativ till stålplåtar i träförband, främst tack vare dess goda mekaniska egenskaper, bearbetbarhet och hållbarhet. Dessa egenskaper har studerats ingående med avseende på viktiga parametrar såsom fiberriktning och fuktkvot. Dess användning som laskar i träkonstruktioner har även undersökts. Dock har tidigare studier främst varit begränsade till enaxliga dragprov och mindre provkroppar, vilket innebär att ytterligare forskning krävs för att förstå björkplywoodens mekaniska beteende i mer realistiska och komplexa tillämpningar. Syftet med denna avhandling är därför att bidra med ny kunskap om förband med laskar av björkplywood. Resultaten syftar till att förbättra dimensioneringen av sådana förband, med avseende på både säkerhet och strukturell effektivitet. Typen av fästdon (släta dymlingar eller skruvar) har undersökts i relation till skjuvhållfastheten i förband med varierande plywoodtjocklek. Resultaten visade att EN1995-1 Eurokod 5 (EC5) underskattar skjuvhållfastheten vid användning av skruvar, vilket främst beror på en konservativ uppskattning av den icke-linjära ökningen av motståndet vid glidning som bidrar positivt till förbandets bärförmåga. Vidare ökade avvikelsen mellan de analytiska beräkningarna och de experimentella resultaten avsevärt när antalet skjuvplan ökades från två till fyra, oberoende av typ av fästdon. Denna betydande avvikelse förknippades med brottmoden i de inre skjuvplanen. Vidare har både limmade och mekaniska förband undersökts genom fullskaleförsök på limträfackverk sammanfogade med skivor av björkplywood. Brott var avsett att initieras i plywooden, vilka utsattes för komplexa spänningstillstånd. Plywoodskivornas tjocklek varierades mellan 9, 12 och 21 mm, och en provkropp testades för varje konfiguration. De experimentella resultaten visade att de limmade fackverken uppvisade högre bärförmåga och nästan dubbelt så hög styvhet som de med mekaniska förband. Vid samtliga fackverk med mekaniska förband, samt det limmade fackverket med de tunnaste plywoodskivorna (9 mm), uppstod brott i plywooden. För de limmade fackverken med tjockare plywood (12 och 21 mm) inträffade dock brott i limfogen mellan plywooden och limträelementet. De analytiska beräkningarna för de prov där brotten uppstod i plywooden överensstämde generellt väl med de experimentella resultaten, även om en viss överskattning noterades. Detta var förväntat och tillskrivs skalningseffekter, då materialegenskaperna som använts i beräkningarna härrör från småskaliga tester. Baserat på jämförelser med tidigare studier uppskattades även limhållfasthetsvärden för att inkluderas i de analytiska beräkningarna av bärförmågan i limmade förband. Dessa värden bör dock undersökas vidare för att kalibrera och förbättra de analytiska modellerna. Därtill visade tvådimensionella numeriska modeller god överensstämmelse med den globala styvheten uppmätt i försöken. För framtida arbete föreslås en fördjupad undersökning av skalningseffekter på björkplywoodens mekaniska egenskaper samt limhållfasthet, i syfte att vidare kalibrera och validera de analytiska modellerna. Även mer avancerade numeriska simuleringar föreslås.QC 20250429</p
Birch plywood in timber connections : Investigation on the rope effect and full-scale trusses
No full textEarlier studies have demonstrated that birch plywood is a viable substitute for steel plates in timber connections, thanks to its excellent mechanical properties, workability, and sustainability. The mechanical properties of birch plywood have been thoroughly investigated concerning key parameters, such as face grain angle and moisture content. Furthermore, its potential use as gusset plates in timber connections has been studied. However, these investigations were mostly limited to uniaxial tension and rather small-scale compared to real applications. Therefore, additional research is needed to further understand the mechanical behaviour of birch plywood, thus ensuring a safe design of such connections. This thesis aims to gain new knowledge on connections with birch plywood plates. The results of this study will then be used to improve the design of such connections, both in terms of safety and structural efficiency. The influence of the connector type (i.e. smooth dowel or fully threaded screw) was investigated concerning the shear capacity of connections using birch plywood with varying thickness. The results showed that, when utilizing screws, the analytical estimations according to EN1995-1 Eurocode 5 (EC5) significantly underestimate the shear capacity. This is mainly due to EC5’s conservative estimation of the so-called “rope effect” contribution to the connection’s shear capacity. Moreover, when the number of shear planes was increased from two to four, the discrepancy between EC5’s estimation and experimental results substantially increased regardless of the type of fastener. This substantial discrepancy was associated with the failure mode in the inner shear planes. Furthermore, both glued and mechanical connections were investigated by performing tests on full-scale glulam trusses joined through birch plywood gusset plates. Failure was designed to occur in the plywood plates subjected to a complex stress state. In this investigation, the thickness of these plywood plates was varied between 9, 12 and 21 mm, testing only one specimen for each configuration. The experimental results showed that glued trusses possessed higher load-carrying capacity and almost twice the stiffness of those with mechanical fasteners. Failure occurred in the plywood plates for all trusses with mechanical fasteners and the glued truss with thinner plywood plates (9 mm). However, the trusses with thicker plates (i.e. 12 and 21 mm) showed glue line failure between the plywood plate and the glulam beam. The analytical estimations for specimens that failed in the plywood plate generally showed good agreement with the experimental capacity, although they exhibited a slight overestimation. This was expected and was attributed to the size effect, as the input strength values of plywood adopted in the analytical estimations were obtained from small-scale tests. Furthermore, based on the size of the glued area compared to previous studies, bonding strength values were estimated and used in the analytical calculations of the bonding capacity for glued connections. However, these strength values should be further investigated to calibrate the analytical model and obtain more realistic estimations. In addition, two-dimensional numerical models demonstrated good agreement in predicting the global stiffness of the tested trusses. For future work, it is suggested to investigate the size effect on the mechanical properties of birch plywood and bonding strength, respectively, to further calibrate and validate the analytical models. Furthermore, more advanced numerical simulations of the truss specimens are suggested.Tidigare studier har visat att björkplywood är ett effektivt alternativ till stålplåtar i träförband, främst tack vare dess goda mekaniska egenskaper, bearbetbarhet och hållbarhet. Dessa egenskaper har studerats ingående med avseende på viktiga parametrar såsom fiberriktning och fuktkvot. Dess användning som laskar i träkonstruktioner har även undersökts. Dock har tidigare studier främst varit begränsade till enaxliga dragprov och mindre provkroppar, vilket innebär att ytterligare forskning krävs för att förstå björkplywoodens mekaniska beteende i mer realistiska och komplexa tillämpningar. Syftet med denna avhandling är därför att bidra med ny kunskap om förband med laskar av björkplywood. Resultaten syftar till att förbättra dimensioneringen av sådana förband, med avseende på både säkerhet och strukturell effektivitet. Typen av fästdon (släta dymlingar eller skruvar) har undersökts i relation till skjuvhållfastheten i förband med varierande plywoodtjocklek. Resultaten visade att EN1995-1 Eurokod 5 (EC5) underskattar skjuvhållfastheten vid användning av skruvar, vilket främst beror på en konservativ uppskattning av den icke-linjära ökningen av motståndet vid glidning som bidrar positivt till förbandets bärförmåga. Vidare ökade avvikelsen mellan de analytiska beräkningarna och de experimentella resultaten avsevärt när antalet skjuvplan ökades från två till fyra, oberoende av typ av fästdon. Denna betydande avvikelse förknippades med brottmoden i de inre skjuvplanen. Vidare har både limmade och mekaniska förband undersökts genom fullskaleförsök på limträfackverk sammanfogade med skivor av björkplywood. Brott var avsett att initieras i plywooden, vilka utsattes för komplexa spänningstillstånd. Plywoodskivornas tjocklek varierades mellan 9, 12 och 21 mm, och en provkropp testades för varje konfiguration. De experimentella resultaten visade att de limmade fackverken uppvisade högre bärförmåga och nästan dubbelt så hög styvhet som de med mekaniska förband. Vid samtliga fackverk med mekaniska förband, samt det limmade fackverket med de tunnaste plywoodskivorna (9 mm), uppstod brott i plywooden. För de limmade fackverken med tjockare plywood (12 och 21 mm) inträffade dock brott i limfogen mellan plywooden och limträelementet. De analytiska beräkningarna för de prov där brotten uppstod i plywooden överensstämde generellt väl med de experimentella resultaten, även om en viss överskattning noterades. Detta var förväntat och tillskrivs skalningseffekter, då materialegenskaperna som använts i beräkningarna härrör från småskaliga tester. Baserat på jämförelser med tidigare studier uppskattades även limhållfasthetsvärden för att inkluderas i de analytiska beräkningarna av bärförmågan i limmade förband. Dessa värden bör dock undersökas vidare för att kalibrera och förbättra de analytiska modellerna. Därtill visade tvådimensionella numeriska modeller god överensstämmelse med den globala styvheten uppmätt i försöken. För framtida arbete föreslås en fördjupad undersökning av skalningseffekter på björkplywoodens mekaniska egenskaper samt limhållfasthet, i syfte att vidare kalibrera och validera de analytiska modellerna. Även mer avancerade numeriska simuleringar föreslås.QC 20250429</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Load-bearing wood connections using birch plywood : An experimental study of birch plywood gusset plates behaviour with mechanical connectors
No full textA growing sustainability concern is pushing the construction industry to seekalternative materials with lower environmental impact. In the last decade useof wood as load-bearing construction has become a common trend, however,connections of timber elements are still performed by the use of steel plates.An alternative to this could be using hardwood plywood instead of steelgusset plates. Connections with plywood are expected to reach a similarcapacity and reduce the environmental impact of wooden construction evenfurther. Hence research on plywood as a load-bearing construction materialis required in order to be able to design and use such connections in reality.Since birch plywood has high strength, it was chosen to study its’ loadbearingcapacity in dowelled connections with wood elements. The aim wasto analyse birch plywood failure modes and load capacity dependence on thevariation of plywood face grain angle and mechanical fasteners positioning inthe connection. The study was conducted with a total of 36 specimens of 4 different nailpatterns and 3 plywood load-to-face grain angle directions: 0°, 22.5° and 45°.These specimens were pre-designed to have failure modes either in block shearor net tension in the plywood board. They were later tested in the laboratory byapplying a tension load. Testing results showed that despite the prediction ofblock shear in some of the specimens, plywood plates always had net tensionfailure mode. Also, especially for 0° of face grain angle, plywood specimenswith wider dowels placement in connection resulted in significantly higherload capacity than narrow ones. This showed that the spreading angle of theload plays an important role in the strength of the connection. Additionally,it was observed, that 45° grain-to-load angle specimens, which had the lowestpredicted load capacity, resulted in similar values as 22.5° specimens. Thisimplies that there is no significant effect on connection strength due to plywoodgrain angle variation when it is not parallel to the applied load
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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