published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

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Thesis (Ph. D.)--University of Hong Kong, 1998. / Includes bibliographical references (leaves 162-175).

The objective of the work reported in this thesis is to study the behaviour of stiffened compression flanges of steel box girder bridges. Various collapse modes and many different parameters that effect the behaviour of the stiffened panels which make up the flanges have been considered. In order to achieve this, a series of three parametric studies have been carried out using a finite element package (LUSAS), which allows for both material and geometric non-linearities. The aim of the work was, in the main, to provide a datum for assessing design recommendations being prepared for the ECCS (European Convention for Constructional Steelwork), and to help in their development. The recommendations were developed as part of this research programme. The first parametric study looked at a range of isolated stiffened panels subjected to uniform uniaxial compression, representing the compression flange of a box girder subjected to pure moment. This validated the basic requirements within the recommendations for the strength of longitudinally stiffened flange panels. The second study was aimed at examining the effect of the shear flexibility of the flange of a girder loaded by vertical shear. In order to study the influence of this flexibility which results in a lag in stresses across the box width relative to the edges (shear lag), finite element results were generated for panels loaded along their longitudinal edges by in-plane uniform shear stress. A new model has been established from these results to predict the effect of shear lag. The model consists of two equations. The first is concerned with the prediction of the elastic shear lag effective breadth ratio while the second is concerned with the effect of shear lag at collapse. The latter is substantially different because of the ability for plastic redistribution of direct stress to occur across the flange prior to collapse. Finally, a third study looked at the forces on, and the behaviour of the cross-frames in orthogonally stiffened flanges. The results of the study showed that the flange applied a more complex lateral load distribution to these stiffeners than currently considered in design practice with, for some parameters, substantially higher load levels than required in the strength requirement of the British code for the design of bridges. A modification is proposed to the rules to provide transverse stiffeners which satisfy both stiffness and strength considerations.

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Thesis (M.S.)--Worcester Polytechnic Institute. / UMI no. 30-31030. Keywords: chip breaking; prediction; turning; grooved inserts. Includes bibliographical references (p. 113-121).

Structural elements in buildings and civil engineering infrastructure can often be vulnerable to various kinds of impact actions during their service life. These actions could result from various sources e.g. collision of vehicles, ships and vessels or falling masses in industrial buildings. Since, for various reasons, such accidental actions have not always been considered in the existing engineering design of buildings and civil engineering structures such as bridges etc., investigation of effective structural strengthening techniques is justified. As fibre reinforced polymer (FRP) composites have commonly been employed efficiently to strengthen steel members against static and fatigue loads, examining the FRP strengthening technique to enhance structural steelwork in impact situations is the main focus of this study. The research aims to experimentally investigate the dynamic behavioural response of axially loaded steel columns and steel beams strengthened with various carbon fibre reinforced polymer (CFRP) configurations. To achieve this goal, a series of experimental tests was implemented including testing a number of CFRP strengthened and unstrengthened steel beams and columns under static and impact loads. The experimental results show that CFRP can improve the global and local behaviour of steel members subjected to impact loads. This improvement varied depending on the CFRP configuration, the amount of CFRP and the pre-existing axial load value in the member. In order to examine all the parameters that can affect the dynamic behaviour of CFRP strengthened steel members in addition to those not included in the experimental programme, a comprehensive numerical simulation of the experimental work was carried out using a validated finite element model. Afterwards, an extensive parametric study was conducted to provide a comprehensive understanding of the behaviour of CFRP strengthened steel members subjected to impact load. The simulation results illustrate that the effectiveness of CFRP increases with high impact energies. The parametric study results have also revealed that the configurations and distributions of CFRP have a major influence on the effectiveness of the reinforcement. A detailed numerical assessment has also been performed to find the CFRP effectiveness when applied to full-scale steel columns. It has been found that strengthening with CFRP in practical quantities and configurations could prevent steel columns from failure under transverse impact loading. The strengthening effectiveness was found to be dependent on boundary conditions, impact velocity, impact mass, impact location, preloading level, impact direction, CFRP configuration, and the length and thickness of the CFRP. Based on the results obtained from the full-scale simulation, it has been found that the CFRP strengthening technique can be used efficiently and effectively at the scale of elements common in everyday building and infrastructure. This study also provides a useful database for different kinds of strengthening configurations, impact velocities and masses, boundary conditions, etc.

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Thesis (Ph.D.)--University of Wollongong, 2008. / Typescript. Includes bibliographical references: leaf 166-180.