Effects of T-tabs and large deflections in DCB specimen tests

A simple strength of materials analysis was developed for a double-cantilever beam (DCB) specimen to account for geometric nonlinearity effects due to large deflections and T-tabs. A new DCB data analysis procedure was developed to include the effects of these nonlinearities. The results of the analysis were evaluated by DCB tests performed for materials having a wide range of toughnesses. The materials used in the present study were T300/5208, IM7/8551-7, and AS4/PEEK. Based on the present analysis, for a typical deflection/crack length ratio of 0.3 (for AS4/PEEK), T-tabs and large deflections cause a 15 percent and 3 percent error, respectively, in the computer Mode 1 strain energy release rate. Design guidelines for DCB specimen thickness and T-tab height were also developed in order to keep errors due to these nonlinearities within 2 percent. Based on the test results, for both hinged and tabbed specimens, the effects of large deflection on the Mode 1 fracture toughness (G sub Ic) were almost negligible (less than 1 percent) in the case of T300/5208 and IM7/8551-7; however, AS4/PEEK showed a 2 to 3 percent effect. The effects of T-tabs G sub Ic were more significant for all the materials with T300/5208 showing a 5 percent error, IM7/8551-7 a 15 percent error, and, AS4/PEEK a 20 percent error

Experimental and analytical investigation on CFRP strengthened glulam laminated timber beams: Full-scale experiments

© 2018 Elsevier Ltd Timber is one of the most appealing and aesthetic construction materials with excellent characteristics compared with other construction materials such as steel, concrete and clay bricks. It is one of the oldest sustainable construction materials and still continues to be a popular choice in modern infrastructure. In recent years, fibre reinforced polymers (FRP) has emerged to improve mechanical properties even further. In this study, results of experimental tests on strengthened glulam beams have been used to investigate potential parameters affecting flexural strength and ultimate load carrying capacity of glulam beams strengthened with externally bonded FRP sheets. Eight full-scale timber beams with and without FRP reinforcement were tested where the bonded length, width, and thickness of the FRP was varied for FRP strengthened beams. The test results pointed out that reduction of stress concentrations can enhance the mechanical performance of the strengthened beams. The ultimate load carrying capacity and flexural strength of reinforced beams improved significantly when bond length and bond width increased. Results of experiments showed that further increase in bond thickness predominantly improves stiffness and ductility of the strengthened timber beams which has a significant enhancement in ultimate deflection and serviceability limit state. An analytical model has been established to determine the ultimate flexural capacity of strengthened timber beam. Satisfactory correlation is achieved between measured and predicted flexural capacity, signifying the capability of the new models

Modelling the bond slip behaviour of FRP externally bonded to timber

Recent studies and applications have demonstrated that Fibre Reinforced Polymer (FRP) has become a mainstream technology for the strengthening and/ or rehabilitation of ageing and deteriorated structures. However, one of the main problems which limit the full utilisation of the FRP material strength is the premature failure due to debonding. This research study presents 1) a review of available FRP-to-timber and FRP-to-concrete bonded interface models, and 2) investigates factors affecting bond strength. A stepwise regression method has then been employed to evaluate the influence of potential factors on the bond strength. The proposed stepwise regression model is based on 195 experimental results of FRP-to-timber bonded interfaces. Results of this stepwise regression analysis are then assessed with results of pull-out tests and satisfactory comparisons are achieved between measured failure loads (R2=0.59) and the predicted loads (R2=0.71, P<0.0001)

Introduction to cross laminated timber and development of design procedures for Australia and New Zealand

Cross-laminated timber (CLT) is an engineered wood product which is gaining popularity in Europe and North America as a sustainable alternative to concrete and steel construction in commercial and multi-residential buildings. CLT is a panel type product made up of 3 or more layers of timber boards each layer running in orthogonal directions and can be used as wall or floor panels. Investment in sustainable softwood plantations over the past few decades has meant that there is now an abundant supply of renewable timber resources ready to be utilized, to produce light weight buildings with low carbon footprints, smaller foundations and transport requirements and increased speed and ease of construction. There is an increasing interest within the construction industry in Australia to start producing CLT panels. Research at the University of Technology Sydney has shown that CLT panels manufactured within Australia from Australian grown timber can compete with international products. CLT floor panels have been found to have significant strength to weight benefits, the potential to be used as two-way spans, higher than predicted char ratios and can comply with Building Code of Australia (BCA) requirements for acoustic design. This paper presents an overview of research and work completed to date, and a discussion of issues that have been identified and addressed to establish design procedures for CLT to meet Australian building standards and code requirements

Timber type effect on bond strength of frp externally bonded timber

© WCTE 2018 Committee. The performance of FRP composite bonded externally to timber is complex and limited attempts have been made to-date to investigate the bond behaviour of the FRP to timber interface. Furthermore, analytical solutions to determine the interface behaviour of FRP to timber have not been fully investigated and are not covered in current standards. This study investigates the influence of timber type and timber mechanical properties on the bond strength of FRP-to-timber joints. Two different types of timber (LVL and hardwood) have been used and results of experimental tests showed that with the increase of timber tensile strength and modulus of elasticity, the interfacial bond strength increases; however, the failure mode can be brittle. Specimens made from LVL exhibited more ductile behaviour failing gradually; while joints made from hardwood failed suddenly in a brittle manner. It was also observed that the local slip between FRP and timber was higher for joints fabricated from LVL compared to hardwood. Therefore, to achieve a satisfactory bonded joint, the effectiveness of timber mechanical properties is required to be accurately considered

Bond strength model for externally bonded FRP-to-timber interface

© 2018 Elsevier Ltd Despite the large number of studies on externally bonded elements using FRP composites, there is a significant knowledge gap to gain a comprehensive understanding of potential parameters such as bond width, bond length, material properties and geometries that influence bond strength. Behaviour of FRP bonded to concrete has been well investigated and there are a number of experimental and theoretical studies in this area; however, limited attempts have been made to investigate the bond behaviour of the FRP to timber interface. This paper reports an investigation on the behaviour of FRP externally bonded to timber. A novel theoretical model has been developed through stepwise regression analysis of 136 single shear FRP-to-timber joints. This has led to establishing a new predictive model for determination of the bond strength for FRP-to-timber joints. Results of this stepwise regression analysis are then assessed with results of experimental tests, and satisfactory comparisons have been achieved between ultimate applied loads and the predicted loads. Finally, a significant improvement in prediction of bond behaviour has been achieved when results of the proposed analytical model compared with the existing models from the literature, signifying the capability of the new models

Ultimate performance of timber connection with normal screws

This paper presents the results of experimental push-out tests on two different types of timber composite connections using only normal screws as the shear connecter. The push out tests were conducted based on Eurocode 5 recommendations and the load-slip responses obtained from lab tests are used to determine the stiffness of the connections at serviceability, ultimate and near collapse levels, and the performance of the connections are assessed at ultimate load. Moreover, an analytical model is derived for each type of connection based on the experimental results and using a non linear regression, which can be implemented into non-linear FE analysis of timber beams with normal screws. © 2013 Taylor & Francis Group

A comparative study of using static and ultrasonic material testing methods to determine the anisotropic material properties of wood

© 2015 Elsevier Ltd. This paper presents a comparative study using static and ultrasonic testing for the determination of the full set of orthotropic material properties of wood. In the literature, material properties are typically only available in the longitudinal direction, and most international standards do not provide details on the testing of the other two secondary directions (radial and tangential). This work provides a comprehensive study and discussions on the determination of all twelve orthotropic material properties of two hardwood species using static testing and an alternative testing approach based on ultrasonic waves. Recommendations are given on the execution of the tests and the interpretation and calibration of the results

REVIEW: Life-cycle, total-industry genetic improvement of feed efficiency in beef cattle: Blueprint for the Beef Improvement Federation

On a life-cycle basis, beef animals are able to consume large amounts of low-cost, low-quality forages relative to higher-cost concentrates compared with pigs and chickens. However, of the 3, beef is still more expensive to produce on a cost–per–edible pound basis. Accordingly, there is need for genetic programs and management changes that will improve efficiency, sustainability, and profitability of beef production. Options include improving reproductive rate, reducing feed used for maintenance, or both, while not reducing output. A goal for improving efficiency of feed utilization is to reduce the amount or proportion of feed used for maintenance. Such reduction is a target for genetic improvement, but such a goal does not include defining a single measure of efficiency. A single efficiency measure would likely lead to single-trait selection and not account for any potentially antagonistic effects on other production characteristics. Because we are not able to explain all variation in individual-animal intake from only knowledge of BW maintained and level of production, measuring feed intake is necessary. Therefore, our recommendation is that national cattle evaluation systems analyze feed intake as an economically relevant trait with incorporation of appropriate indicator traits for an EPD for feed intake requirements that could then be used in a multiple-trait setting such as in a selection index. With improvements in technology for measurement of feed intake, individual measures of feed intake should continually be collected to facilitate development of genetic predictors that enhance accuracy of prediction of progeny differences in national cattle evaluations

Control of CNS midline transcription by asymmetric E-box-like elements: Similarity to xenobiotic responsive regulation

Central nervous system midline cells constitute a discrete group of Drosophila embryonic cells with numerous functional and developmental roles. Corresponding to their separate identity, the midline cells display patterns of gene expression distinct from the lateral central nervous system. A conserved 5 base pair sequence (ACGTG) was identified in central nervous system midline transcriptional enhancers of three genes. Germ-line transformation experiments indicate that this motif forms the core of an element required for central nervous system midline transcription. The central nervous system midline element is related to the mammalian xenobiotic response element, which regulates transcription of genes that metabolize aromatic hydrocarbons. These data suggest a model whereby related basic-helix-loop-helix-PAS proteins interact with asymmetric E-box-like target sequences to control these disparate processes