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Critique of Southwell plots with proposals for alternative methods

Paper examines those situations in which the Southwell plot works poorly and proposes alternative techniques for finding Pc

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Abstract

The theory of the Southwell plot is outlined and its history traced. Examples are given in which the technique fails to give a straight line; these are classified into low-load and higher-load nonlinearities. It is shown that the former may be due to inherent zero errors in the deflection measurement and that this can cause serious errors in the apparent critical loadP c. A new approach involving “pivot points” is introduced and used to formulate plots which may help to linearize the data; an application to one of Karman's classical column tests is given.

For plates, use is made of a general post-critical equation of which Donnell's result for a simply supported square plate is a special case. A new graphical technique is proposed for findingP c for plates with small imperfections, and applied to example data from published test results. A more general numerical technique is also proposed and applied to results from a test during which the experimental boundary conditions were changing.

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Authors and Affiliations

  1. Applied Mechanics Group, Hatfield Polytechnic, England

    H. H. Spencer (Senior Lecturer)

  2. University College, London, England

    A. C. Walker (Reader)

Authors
  1. H. H. Spencer
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  2. A. C. Walker
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Spencer, H.H., Walker, A.C. Critique of Southwell plots with proposals for alternative methods. Experimental Mechanics 15, 303–310 (1975). https://doi.org/10.1007/BF02318661

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  • DOI: https://doi.org/10.1007/BF02318661

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