Thesis (Ph.D.) in Forest Resources--University of Maine, 2002. / Includes vita. Bibliography: leaves 116-124.

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xxiii, 200 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 140-142).

Strengthening of aluminium and stainless steel structural tubular sections using adhesive bonded fibre-reinforced polymer (FRP) subjected to web crippling has been investigated. Aluminium and stainless steel tubular sections may experience web crippling failure due to local concentrated loads or reactions. The web crippling strength can be enhanced by strengthening the webs of the sections in localized regions. The current international specifications of aluminium and stainless steel structures do not provide web crippling design rules for strengthening of tubular sections. Therefore, there is a need to develop safe and reliable web crippling design rules for FRP strengthened aluminium and stainless steel structures. An extensive test program was performed on FRP strengthening of aluminium and cold-formed stainless steel tubular sections subjected to web crippling. The test specimens consisted of 6061-T6 heat-treated aluminium alloy, ferritic stainless steel type EN 1.4003 and lean duplex type EN 1.4162 square and rectangular hollow sections. A total of 254 web crippling tests was conducted in this study. The tests were performed on eighteen different sizes of tubular sections which covered a wide range of web slenderness (flat portion of web depth-to-thickness) ratio from 6.2 to 62.2. The web crippling tests were conducted under the four loading conditions according to the American Specification and Australian/New Zealand Standard for cold-formed steel structures, namely End-Two-Flange, Interior-Two-Flange, End-One-Flange and Interior-One-Flange loading conditions. The investigation was mainly focused on the effects of different adhesive, FRP, surface treatment, widths of FRP plate and web slenderness of tubular sections for strengthening against web crippling. Six different adhesives, six different FRPs, two different surface treatments, three different widths of FRP plate were considered. It was found that the web crippling capacity of aluminium tubular sections are significantly increased due to FRP strengthening, especially for those sections with large value of web slenderness. The web crippling strength can be increased up to nearly 3 times using the appropriate adhesive and FRP for aluminium tubular sections, whereas the web crippling strength can be increased up to 51% and 76% for ferritic and lean duplex stainless steel tubular sections, respectively. The finite element models for FRP strengthened aluminium and stainless steel tubular structural members subjected to web crippling were developed and calibrated against the experimental results. The debonding between FRP plate and aluminium or stainless steel tubes was carefully modelled using cohesive element. It is shown that the calibrated model closely predicted the web crippling strengths and failure modes of the tested specimens. An extensive parametric study included 212 web crippling specimens was carried out using the verified finite element models to examine the behaviour of strengthened aluminium and stainless steel tubular sections subjected to web crippling. Design equations are proposed to predict the web crippling strengths of FRP strengthened aluminium and stainless steel tubular sections based on the experimental and numerical results. The web crippling strengths obtained from the tests and numerical analysis were compared with the design strengths calculated using the proposed equations. The reliability of the proposed design rules was evaluated using reliability analysis. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

Existing reinforced concrete (RC) structural members such as beams, columns and joints can be strengthened and repaired with externally bonded high-strength and light-weight fibre-reinforced polymer (FRP) composites. The effectiveness of such strengthening can, however, be limited by premature debonding of the FRP at strains well below the strain capacity of the FRP. Such failures are also generally sudden and give rise to brittle member behavour. It is therefore important to prevent or even delay debonding failure in order for the FRP strengthening to be more effectively and efficiently used. Anchorage of the FRP strengthening is a logical solution and to date several different types of anchorage systems have been developed and tested. Anchors made from FRP, which are herein referred to as FRP anchors, are singled out for deeper inspection in this doctoral program of research. FRP anchors are an attractive form of anchorage as they are non-corrosive, relatively easily made by hand, and can be used in a variety of shaped RC elements ranging from beams to walls. There have been limited systematic studies though conducted on anchorage devices including FRP anchors. This knowledge gap forms the scope of the program of doctoral research reported herein. This dissertation is concerned with investigating the ability of FRP anchors to anchor externally bonded FRP in flexural strengthening applications. This is done by investigating the influence of FRP anchors on FRP-to-concrete bonded interfaces. Following a review of relevant literature, tests on FRP-to-concrete joints anchored with FRP anchors are reported as well as tests on FRP-strengthened RC slabs anchored with FRP anchors. The joint tests are used to investigate and understand the influence of key geometric and material properties such as, but not limited to, anchor type and position as well as plate length. The optimal arrangement of FRP anchors enabled significant increases in FRP plate strain utilisation to be achieved in the joints. Two modelling approaches based on regression analysis as well as partial interaction modelling are developed for the modelling of the joint tests. In the latter method of analysis, the complete debonding process is able to be simulated. The test and modelling results of the joint specimens are then used to design anchorage schemes for application to RC slabs strengthened in flexure with externally bonded FRP plates. The slab test results show the importance of strategic FRP anchor installation for enhancing the strength, ductility and deformability of FRP-strengthened RC slabs. Future research needs are finally presented in light of the outcomes of the experimental and analytical components of the research reported herein. / published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy

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The degree of cure and temperature are consistent variables used in models to describe the state of material behaviour development for a thermoset during cure. Therefore, the validity of a cure kinetics model is an underlying concern when combining several material models to describe a part forming process, as is the case for process modeling. The goals of this work are to identify sources of uncertainty in the decision-making process from cure measurement by differential scanning calorimeter (DSC) to cure kinetics modeling, and to recommend practices for reducing uncertainty. Variability of cure kinetics model predictions based on DSC measurements are investigated in this work by a study on the carbon-fiber-reinforced-plastic (CFRP) T800H/3900-2, an interlaboratory Round Robin comparison of cure studies on T800H/3900-2, and a literature review of cure models for Hexcel 8552. It is shown that variability between model predictions can be as large as 50% for some process conditions when uncertainty goes unchecked for decisions of instrument quality, material consistency, measurement quality, data reduction and modeling practices. The variability decreases to 10% when all of the above decisions are identical except for the data reduction and modeling practices. In this work, recommendations are offered for the following practices: baseline selection, balancing heats of reaction, comparing data over an extensive temperature range (300 K), choosing appropriate models to describe a wide range of behaviour, testing model reliability, and visualization techniques for cure cycle selection. Specific insight is offered to the data reduction and analysis of thermoplastic-toughened systems which undergo phase separation during cure, as is the case for T800H/3900-2. The evidence of phase separation is a history-dependent Tg-α relationship. In the absence of a concise outline of best practices for cure measurement by DSC and modeling of complex materials, a list of guidelines based on the literature and the studies herein is proposed.

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