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Fei, Clarence
Hollow structural section (HSS) , Polygonal hollow section (PHS) , Weak-axis bending , telescopic boom
This thesis consists of two sections: the first section evaluates the structural behaviour of hollow structural sections (HSS) including polygonal hollow sections (PHS) and rectangular hollow sections (RHS) under weak-axis four-point loading, and the second section focuses on the complementary structural evaluation of PHS and RHS beams via distributed fiber optic strain sensors (DFOS). The moment capacity of the RHS tested were determined to be higher than that of their companion PHS: 32% higher for an RHS305×203×6.4 versus a PHS305×203×6.4 and 40% higher for an RHS356×254×6.4 versus a PHS356×254×6.4. Local buckling on the compression flange/upper part of the web was observed to be the primary failure mode for all beams. Vertical crushing was observed to be more extensive on PHS beams than on RHS beams due to the flattening and folding of the diagonal corners of the PHS beams. The performance of DFOS was evaluated for thin-walled hollow steel sections under bending and it was determined that it can effectively to identify stress concentrations at loading points and to monitor the evolution of local buckling and other failure modes. The integration of strains from DFOS can be used to calculate beam deflections within the linear elastic response range of a thin-walled beam with the accuracy of these calculation results depending on the coverage of beam along its length. The calculated deflections were observed to be 15-20% lower than deflections measured from conventional linear potentiometers for RHS beams with the optical fibers covering 90% of the beam length; whereas the calculated deflections were seen to be 20-30% lower for PHS beams with a fiber coverage of 82-87% of the beam length.
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