in which l = the unsupported length of the column in inches and r = its least radius of gyration in inches.

This is quite a sudden jump from the old standard formula,

The change indicates one of two things: Either that hitherto we have been over- stressing compression members 15 to 25 per cent, or that there is going to be wasted a vast quantity of metal in the future.

Moreover, in making such a sweeping change in the compression formula, the writers of the Canadian specifications were not consistent, because in Clause 47 they allow for the compression flanges of beams an intensity of

In the case of railway stringers l/b is generally in the neighborhood of 10; hence the intensity of working stress is about 14,000 lbs. As b is equal to about 4.5 r, for l/b = 10 we shall have l/r = 45. Substituting this in the Canadian column formula gives

In the case of one compression member of a bridge, it appears to be legitimate to stress the metal up to 14,000 lbs. per square inch, and in another up to only 11,400 lbs. per square inch, a difference of 23 per cent. And there is no valid reason for stressing differently a strut which forms a part of the top chord of a truss and a strut which forms a part of the top flange of a beam. "Consistency, thou art a jewel!"

If the correctness of the formula for compression flanges of beams be conceded—a formula which, for a dozen years or more, has been one of the clauses of the American Railway Engineering Association's standard bridge-specifications, and which the Engineering Institute of Canada has appropriated without change—and if it be granted that b is generally equal to about 4.5 r—why should not the equivalent formula,

p = 16,000 - 45 l/r

apply in general to struts with fixed ends? Be it noticed that this formula gives higher results than does my old formula,

p = 16,000 - 60 l/r.

The American Railway Engineering Association is getting ready to trim down materially its old intensities for steel struts, although not to the extent that the Engineering Institute of Canada has done.*

What aggravates the effect of this proposed decrease of compression intensities is that, simultaneously therewith, the American Railway Engineering Association is contemplating increasing its tensile intensity of working stress from 16,000 lbs. to 18,000 lbs.; and other specification writers are advising that it be made as high as 20,000 lbs.

* The 1920 A. R. E. A. bridge specifications permit the following intensities of working compressive stresses:

Struts..........15,000-50 l/r but not to exceed 12,500 lbs.

Flanges of girders.......14,000 - 200 l/b.

The previous strut formula of the A. R. E. A. was 16,000 - 70 l/r; hence the new formula gives lower results when l/r is less than 50 and higher results when it is greater.