|Abdelrahman, Ahmed Hussain Ali
|Advanced analysis and design of steel structures with single angle members
|Chan, Siu-lai (CEE)
Building, Iron and steel -- Design and construction
Hong Kong Polytechnic University -- Dissertations
|Department of Civil and Environmental Engineering
|xxii, 208,  pages : color illustrations
|Light-weight steel structures are extensively used around the world for many purposes. Latticed tower structures such as communication tower masts and transmission line towers are examples of structures, which single angles are a part. Robotic welding machines (RWM) and building information modelling (BIM) eliminate the constraints of fabricating thin-walled sections like single angles. Such members, however, usually experience complex behaviors in the member-global and section-local levels. Single angles are often asymmetric sections; their shear center does not coincide with the centroid, and they are thin-walled open sections, thereby making the section local and/or distortional buckling prevail. Besides, angle members are often eccentrically connected; hence, they are susceptible to bi-axial bending. As a result of the above, analysis and design of angle structures are decidedly one of the most problematic space frames to analyze. Designers still employ the full-scale field test for investigations of latticed-like structures due to uncertainties associated with the analysis of this kind of structures. The current analysis methods and stability checking equations for single angle members encountered several difficulties. The linear interaction equations for evaluation of asymmetric single angles subjected to axial force and bi-axial bending are conservative and inaccurate. Moreover, most design specifications adopt the assumption that the flexural buckling will govern the ultimate strength of single angles. Besides, the flexural buckling about the principal minor axis is assumed as the dominant failure mode in the existing conventional line elements for direct analysis of angle structures. On the other side, full-scale tests on transmission towers revealed large discrepancies between the numerical simulation and experimental results because the significant joint slip effects have not well considered in the former. The existing joint slip models are oversimplified that many key parameters had not been taken into account. Therefore, this research intends to provide robust and efficient analysis and design scenarios for angle members in line with the member-based design methods and direct analysis method (DAM).
In this thesis, a finite-element (FE) modelling protocol is developed to simulate single angle members employing the shell-based FE method. The member imperfections, including the initial geometric imperfections and residual stresses are explicitly modelled. The FE results are thoroughly validated and verified using the analytical and experimental results in the literature. Based on extensive FE results, a new hand-calculating design method considering the section plasticity and member stability is proposed; the member global buckling such as flexural and flexural-torsional buckling are well-considered. For DAM, an effective stress-strain relationship for single angle members is presented. The member imperfections, including the global and local imperfections, are implicitly incorporated in the proposed curve. The relationship is so simple that it can be adopted to implement the direct analysis of angle structures utilizing any conventional line elements. Furthermore, an advanced joint slip model accounting for the number of bolts, bolt load, friction at contact face, angle sizes and plate thickness, steel and bolt grades, and hole tolerance are developed for further incorporation in the second-order direct analysis of transmission towers. A batch of examples is used to illustrate the accuracy and efficiency of the proposed design and analysis methods. This work is essential for the practical design of steel structures with angle sections. Investigating the complex behavior of general thin-walled members are decidedly important; thus, simulations of such members with arbitrary-shaped cross-sections for static and dynamic loads are provided in the final part of the thesis utilizing an integrated FE modelling protocol. This work is motivated by the higher accuracy of the shell FE-based modelling to capture the local and global complex behaviors of asymmetric thin-walled members.
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