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Sir,-The problem of column design has been discussed with great thoroughness by Baker in the reports of the Steel Structures Research Committee, by the American Society Civil Engineers Committee1 on Steel Column Research, and by others. It would have been useful if Mr. Warren had indicated thextent to which his paper presents ideas not considered in the above studies. The chief value in the Euler formula as applied to practical columns is as an upper limit for the strength of very slender columns. Mr. Warren proposes to apply results for the effective length of struts derived from the equation for slender “ideal” struts to “practical” struts of intermediate slenderness ratio. The only justification for this is apparently contained in a table of nine examples (page 462). There is, however, no difficulty in picking an empirical formula to fit any group of results for axially loaded struts, and the fact that this can be done does not indicate that the method can properly be applied to eccentrically loaded members. Salmon has expressed the opinion that such a method can only be considered a very rough approximation; Baker and Holder have stated that it is not only inaccurate but is potentially dangerous.
IN a previous paper read last year before the South African Society of Civil Engineers; the reasons for strengthening of concrete structures were given and some such work was described. This present paper is not so pretentious as to give a complete description of every consideration necessary for the strengthening of all kinds of structures, but it wishes to be only a description of some such jobs carried out in South Africa, with a few personal comments by the author.