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3. Westinghouse Research Laboratory, Pitts-burgh, U.S.A., private communication.
4. S. Timoshenko, ?Strength of Materials, Part I, Elementary Theory and Problems? (Van Nostrand, New York, 1930) p. 359.
5. G. R. Terwilliger, Ph.D. Thesis, University of Utah, (1968) A-15.