The first edition of the Specification on Steel Structures for Buildings, which was issued in December, 1924, was succeeded by a second and revised edition in January, 1930. Since the issuing of this second edition the use of higher strength steel has been progressing and in 1935 the Association issued four structural steel specifications covering Medium Steel, Mild Steel, Silicon Steel and Rivet Steel. These specifications covered materials which would allow the use of higher unit stresses in the design of steel structures and it has, therefore, become necessary to issue a revised edition of this Specification. Advantage has been taken of the opportunity to make other revisions which have been considered desirable. The Specification is now issued under a new division entitled Steel Construction.
In this new edition the use of medium steel is regarded as normal and reference is only made to mild steel because of the fact that large stocks may still exist and some new material will continue to be rolled. The column formula has again been revised -and much discussion centered around the question of adopting the more complicated type of formula such as the Perry or the Secant instead of the simple straight line expression. The final decision to maintain the straight line but to include the Perry formula in the Appendix is a recognition of two facts, firstly, the preference for simple expressions for ordinary use in the drafting and designing offices, and secondly, the realization that some engineers are leaning toward the more complex expressions feeling that they include a more scientific treatment of the various elements likely to affect the buckling strength of columns. Other simplifications have been introduced in order to conform to the majority opinion and some recognition has been given to the generally accepted superiority of plate girder construction.
A11 reference to silicon steel Has been eliminated due, basically, to the feeling that there is very little prospect of this material entering into the ordinary run of building construction but, secondly, to the wide diversity of opinion regarding the behaviour of this metal under compression, particularly in slender columns. Further simplification in the recommended Wind load has been introduced largely 1n view of research work undertaken by special committees.
Rather more time than usual has been consumed in the preparation of this revised edition but the Committee feels that there have been good and sufficient reasons for this apparent slowness, and hopes that the final result will prove acceptable to the profession at large.
As mentioned in the Prefaces of the previous editions, the Committee wishes to stress the importance of having a competent Professional Engineer who will be responsible for the computations involved in any structural design. This is particularly essential owing to the great advances which have been made in the construction of important buildings during recent years.
Special attention is drawn to the summary of changes in this third edition which appears at the end of the Specification proper, and it is hoped that this will prove useful 1n making a comparison between this and previous editions.
This revised Specification was formally approved by Letter Ballot by the Committee on. Steel Structures for Buildings in May, 19.40, by the Sectional Committee on Steel Construction in June, 1940, and by the Main Committee with authority to publish it as a C.E.S.A. standard in July, 1940.