Thesis (Ph. D.)--Lehigh University, 1999. / Includes vita. Includes bibliographical references (leaves 160-162).

No description available.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

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

This thesis proposes two forms of external confinement for concrete filled steel tubular (CFST) columns. The confinement efficiency is studied by examining the axial strength enhancement and ductility improvement of the CFST columns with external confinement. Due to the heavy demand of confining steel to restore the column ductility in seismic regions, it is more efficient to confine these columns by hollow steel tube to form CFST column. Compared with transverse reinforcing steel, steel tube provides a stronger and more uniform confining pressure to the concrete core, and reduces the steel congestion problem for better concrete placing quality. The CFST columns are therefore characterised by higher strength, ductility and large energy absorption before failure. However, a major shortcoming of CFST columns is the imperfect steelconcrete interface bonding occurred at the elastic stage as steel dilates more than concrete in compression. This adversely affects the confining effect and decreases the elastic modulus. To resolve the problem, it is proposed in this thesis to use external steel confinement in the forms of rings and ties to restrict the dilation of steel tube. For verification, a series of uni-axial compression test was performed on some CFST columns with external steel rings and ties. From the results, it was found that the external steel rings could improve both the axial strength and stiffness of the CFST columns significantly. However, the steel ties could not improve either the axial strength or elastic stiffness significantly. The confining efficiency was then investigated by comparing the strength of these confined-CFST columns with the reinforced concrete (RC) columns counterparts with the same concrete and steel volume. It is evident that the axial strength of CFST columns is much higher than the RC columns, which suggests that the application of CFST columns can utilise less construction materials and reduce the demolition waste. A theoretical model is also proposed for predicting the axial strength of ring-confined CFST columns. Comparison between the predicted results and the test results obtained by the author and other researchers shows that the proposed model gives good estimation for both unconfined and confined CFST columns. / published_or_final_version / Civil Engineering / Master / Master of Philosophy

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 269-283) Also available in print.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004. / Includes bibliographical references (leaves 149-154). Also available in electronic version. Access restricted to campus users.

In this study, the objective was to develop a method of predicting the energy-absorption capability of composite subfloor beam structures. Before it is possible to develop such an analysis capability, an in-depth understanding of the crushing process of composite materials must be achieved. Many variables affect the crushing process of composite structures, such as the constituent materials’ mechanical properties, specimen geometry, and crushing speed. A comprehensive experimental evaluation of tube specimens was conducted to develop insight into how composite structural elements crush and what are the controlling mechanisms In this study, the four characteristic crushing modes, transverse shearing, brittle fracturing, lamina bending, and local buckling were identified and the mechanisms that control the crushing process defined. An in-depth understanding was developed of how material properties, affect energy-absorption capability. For example, an increase in fiber and matrix stiffness and failure strain can, depending upon the configuration of the tube, increase energy-absorption capability. An analysis to predict the energy-absorption capability of composite tube specimens was developed and verified. Good agreement between experiment and prediction was obtained. Sine-wave and integrally stiffened composite beams were evaluated. Composite energy-absorbing beams crush in modes similar to tubular specimens that are made from the same material and have similar geometry. Energy-absorption trends of the composite beams are similar to energy-absorption trends from composite tube specimens. Composite beams are equal or superior energy absorbers to comparable geometry metallic beams. Finally, a simple and accurate method of predicting the energy-absorption capability of composite beams was developed. This analysis is based upon the energy-absorption capability of the beams’ constituent elements. / Ph. D.

published_or_final_version / abstract / Civil Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Civil Engineering / Doctoral / Doctor of Philosophy