STEEL STRUCTURES.


At a recent meeting of the Engineers' Club of Philadelphia, Mr. James
Christie presented a paper upon "The Adaptation of Steel to Structural
Work." The price of steel has now fallen so low, as compared with iron,
that its increased use will be actively stimulated as the building
industries revive. The grades and properties of the steels are so
distinct and various that opinions differ much as to the adaptability of
each grade for a special purpose. Hitherto, engineers have favored open
hearth steel on account of uniformity, but recent results obtained from
Bessemer steel tend to place either make on equality. The seeming
tendency is to specify what the physical properties shall be, and not how
the steel shall be made.

For boiler and ship plates, the mildest and most ductile steel is
favored. For ships' frames and beams, a harder steel, up to 75,000 pounds
tenacity, is frequently used. For tension members of bridges, steel of
65,000 to 75,000 pounds tenacity is usually specified; and for
compression members, 80,000 to 90,000 pounds. In the Forth Bridge,
compression steel is limited to 75,000 to 82,000 pounds. Such a marked
advantage occurs from the use of high tension steel in compression
members, and the danger of sudden failure of a properly made strut is so
little, that future practice will favor the use of hard steel in
compression, unless the material should prove untrustworthy. In columns,
even as long as forty diameters, steel of 90,000 pounds tenacity will
exceed the mildest steel 35 per cent., or iron 50 per cent., in
compressive resistance.