1,720,966 research outputs found
"Long term deformation of epoxy glued glulam portal frame knee joints" May 2009.
No full textThis project was initiated to resolve uncertainty regarding the long-term performance of epoxied rod connections in glue laminated timber (glulam), specifically the long term-deformations associated with beam-column moment joints. The excellent short-term performance of this type of connection is well known. However there is some scepticism in industry over the long-term performance. The behaviour of this connection when subjected to long term loading is thought to be primarily affected by creep in the timber and heterogeneity of the cross section. It has been hypothesised that the stress distribution at the beam-column interface may change over time leading to a localisation of stresses, rotations within the joint and ultimately, excessive deflections of the frame at serviceability limit states. Furthermore, crushing of the timber perpendicular to the grain may occur in the long-term as a result of the stress redistribution over time which could cause failure at ultimate limit state. In order to investigate the long term performance, two types of experimental testing were carried out in this project: (i) long term testing of several frames and lever specimens; and (ii) short term testing of several smaller glulam specimens.
Four frames with a “C” shaped layout (i.e. one column and two beams) were tested. Two of these frames used the “fully-epoxied” connection, where the steel rods were epoxied along the full length, whilst the other two frames used the “tensioned half epoxied” connection, where the steel rods were epoxied into one member and tensioned to the other. Two different geometries were tested (the column running past the end of the beam and the beam extending over the top of the column).
The lever specimens were designed to individually measure the different components of creep. These measured the creep of the timber itself (both parallel and perpendicular to the grain), the creep of a timber specimen with epoxied rods at both ends, and the creep of the glue alone.
Short-term bending, compression and pullout tests were carried out on glulam according to ISO recommendations to characterise the timber used in this project. The results of the compressive strength tests perpendicular to the grain gave compressive stresses that were approximately 50% of that specified in the New Zealand Timber Standard. This is of concern and needs attention given the importance of this property when designing any joints where structural performance depends on bearing perpendicular to grain.
Some important conclusions have been reached. The results from the Glulam Lever Specimens showed that creep perpendicular to the grain may be up to 8 times greater than that parallel to the grain. The remaining lever specimens showed that long term pullout deformations are likely to be negligible in dry conditions. The “fully epoxied” connection performed significantly better than the “tensioned half epoxied” connection. This is due to better transfer of forces in the “fully epoxied” connection and hence very little reliance on the compressive strength of timber perpendicular to the grain. Creep of timber was found to mainly affect the deflection of the frame specimens, as no significant stress redistribution was noticed in the long-term between timber and rods. It was also pointed out that a significant contribution to the total deflection is given by the flexibility semi-rigidity of the connection itself, which is usually designed as a rigid joint but should more realistically be considered as a semi-rigid connection. Design equations have been proposed and are shown to correlate well with the results obtained. Lastly, a method has been described to estimate the long-term stresses in the glulam and steel elements
"Moment joints in timber frames using glued-in steel rods: experimental investigation of long-term performance"
No full text"Long term deformation of epoxy glued glulam portal frame knee joints" May 2009.
No full textThis project was initiated to resolve uncertainty regarding the long-term performance of epoxied rod connections in glue laminated timber (glulam), specifically the long term-deformations associated with beam-column moment joints. The excellent short-term performance of this type of connection is well known. However there is some scepticism in industry over the long-term performance. The behaviour of this connection when subjected to long term loading is thought to be primarily affected by creep in the timber and heterogeneity of the cross section. It has been hypothesised that the stress distribution at the beam-column interface may change over time leading to a localisation of stresses, rotations within the joint and ultimately, excessive deflections of the frame at serviceability limit states. Furthermore, crushing of the timber perpendicular to the grain may occur in the long-term as a result of the stress redistribution over time which could cause failure at ultimate limit state. In order to investigate the long term performance, two types of experimental testing were carried out in this project: (i) long term testing of several frames and lever specimens; and (ii) short term testing of several smaller glulam specimens.
Four frames with a “C” shaped layout (i.e. one column and two beams) were tested. Two of these frames used the “fully-epoxied” connection, where the steel rods were epoxied along the full length, whilst the other two frames used the “tensioned half epoxied” connection, where the steel rods were epoxied into one member and tensioned to the other. Two different geometries were tested (the column running past the end of the beam and the beam extending over the top of the column).
The lever specimens were designed to individually measure the different components of creep. These measured the creep of the timber itself (both parallel and perpendicular to the grain), the creep of a timber specimen with epoxied rods at both ends, and the creep of the glue alone.
Short-term bending, compression and pullout tests were carried out on glulam according to ISO recommendations to characterise the timber used in this project. The results of the compressive strength tests perpendicular to the grain gave compressive stresses that were approximately 50% of that specified in the New Zealand Timber Standard. This is of concern and needs attention given the importance of this property when designing any joints where structural performance depends on bearing perpendicular to grain.
Some important conclusions have been reached. The results from the Glulam Lever Specimens showed that creep perpendicular to the grain may be up to 8 times greater than that parallel to the grain. The remaining lever specimens showed that long term pullout deformations are likely to be negligible in dry conditions. The “fully epoxied” connection performed significantly better than the “tensioned half epoxied” connection. This is due to better transfer of forces in the “fully epoxied” connection and hence very little reliance on the compressive strength of timber perpendicular to the grain. Creep of timber was found to mainly affect the deflection of the frame specimens, as no significant stress redistribution was noticed in the long-term between timber and rods. It was also pointed out that a significant contribution to the total deflection is given by the flexibility semi-rigidity of the connection itself, which is usually designed as a rigid joint but should more realistically be considered as a semi-rigid connection. Design equations have been proposed and are shown to correlate well with the results obtained. Lastly, a method has been described to estimate the long-term stresses in the glulam and steel elements
"Moment joints in timber frames using glued-in steel rods: experimental investigation of long-term performance"
No full text
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
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
- …
