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Title: Buckling in continuous composite beams
Author: Fan, Chun Keung Roger
ISNI:       0000 0000 6593 880X
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1990
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Two aspects of the buckling behaviour of continuous composite beams of steel and concrete are considered. The first part relates to the study of moment redistribution in braced slender beams (Class 3 draft Eurocode 4) due to local buckling in the hogging moment regions. The second part describes the experimental work to investigate the ultimate load behaviour of unbraced compact beams (Classes 1 and 2 draft Eurocode 4) in the hogging moment regions. For a braced continuous slender composite beam, local buckling at an internal support allows a redistribution of bending moment from the hogging regions to the sagging regions, in addition to material nonlinearity. This effect was studied by a computer simulation on two-span beams. The program takes into account not only the effect of local buckling, but also material nonlinearity and residual stresses, on moment redistribution. The ultimate loads designed to the less conservative method for Class 3 beans in the draft Eurocode 4 were used as a datum in the parametric study. The simulation then gave an independent assessment of the appropriateness and safety of these loads at the ultimate limit state. It is shown that the design method is slightly conservative. Residual stresses have very little effect on the ultimate carrying capacity. Furthermore, in design to the draft Eurocode 4, unpropped construction is more restrictive than propped construction, and hence the results are also more conservative. Lateral buckling of continuous unbraced composite beams in the hogging moment regions can only occur in a distortional mode, and is most unlikely to happen in practical building or bridge structures using hot-rolled steel sections of span up to about 30m. Various design methods based on numerical studies now exist to predict the ultimate strength of continuous composite beams affected by distortional lateral buckling, but few experimental results are available to validate their theoretical assumptions and accuracy. Tests at realistic scale on two T-beams and two inverted U-frames at the Class 2-3 Interface, in accordance with the draft Eurocode 4, are reported. Their results are compared with predictions by five design methods, four of which are satisfactory for the beams tested except BS5400:Part 3. Due to premature fracture of reinforcing fabric in one of the U-frame tests, it is recommended not to include their contribution in moment resistance, when the composite cross-section is plastic and a design requires a large amount of rotation capacity in the hogging moment regions. Based on limited test results, a tentative method is proposed to provide a quick check, whether distortional lateral buckling needs to be considered or not, for continuous composite beams with Class 1 or 2 cross-sections.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA Engineering (General). Civil engineering (General)