Engineering Wonders of the World
Volume I

STEEL-FRAME BUILDINGS. 13 taken, a skyscraper terrible conflagration will come through a without suffering in- Fig. 28.—CITY HALL, SAN FRANCISCO, AFTER EARTHQUAKE. Note that the steel skeleton did not support the wall which was wrecked. (From Proc. Amer. Soc. C.E., vol. xxxiii., No. 3, Plate XXII.) juries that cannot be repaired speedily. In. that disaster, we may note, the protective casings had been damaged previously by an earthquake, yet a special committee ap- pointed to inquire into the effects of the double disaster reported that “ steel frames were the least injured of any part of the structures. Where properly protected there was no injury. Where the protection was faulty, or where there was none, the destruction was com- plete.” Fears have been expressed that the framework of steel- skeleton buildings may be undergoing continuous and serious, though slow, deteriora- tion from the corrosion of the metal. There is evidence, however, to prove that these fears are quite groundless where reasonable precautions have . , . , , Corrosion been taken to prevent the . Dangers. penetration of rain and mois- ture. We might quote many examples of the excellent condition of encased steelwork after standing many years. If the metal be em- bedded in good Portland cement concrete, it is protected against the effects of moisture so effectively that its condition would be the same many hundreds of years hence ; in fact, the steel would be practically as permanent as the concrete itself. One of the most interesting features of a steel-frame building is the provision made to enable the structure to withstand the pressure of high winds. During squalls that sweep over Manhattan r . bracing. Island the wind attains a veloc- ity of 70 miles an hour, which means a pres- sure of about 30 lbs. on every square foot of a surface which it strikes at right angles. A little simple arithmetic will show that the total wind thrust on a structure having a vertical area of several thousand square feet Figs. 47-5G.—METHODS OF PROTECTING GIRDERS AND ROOF MEMBERS AGAINST FIRE BY CONCRETE AND TERRA-COTTA BLOCKS.