The daily morning journal and courier., 1907-04-25

strength of his steel frame. The nature of the occupations of the tenants has first to be taken into consideration, for If the occupants are to use heavy ma chinery in their work 1t means so much more strength necessary for the struc- ture.
 Another thing the weighers have to lfigure on is elevators The elevators that hang from cables require a neavy overhead structure to sustain them and meet the strain of the heavily loaded cars, and this is a factor in the weigh CTS work. As he is figuring for cost, he must make special allowance for this, because half-ton steel beam or one of the big wheels on which the ele- vator cable runs, or, in fact, anything of weight, is a much more expensive proposition on the thirtieth floor than lit would be on the first floor. The growing use of elevators of the plunger type for the talest buildings, however, has sinplified this problem, ais these elevators are not pulled up on overhead cables, but are operated from below by a great steel column or plunger as long as the elevators maximum rise. When the elevator descends this column sinks into steel cylinder deep in the rock foundations of the earth. The fact that { this elevator device saves much space in the building for the use of tenents is also a factor in the weighers calcu- lations.
 Thn i0h OF xuotey1niytc t1a hOHry r<P Va building, however, is to the expert .ap-1 parently very simple. He knows how much foot of wall weighs, and so f1g- ures the whole. But as the wall of a thirty story skyscraper is thirty-two inches thick at the bottom and twelve inches thick at the top, with gradually decreasing thicknesses between as one goes up, this task Is also one that calls for figuring. In weighing the steel frame the task is also comparatively simple-for the expert. He finds out how much steel will be required for the while, and then to get the total weight he simply nultiplies the weight of a known steel unit. IA similar process gives him his foundation weight and his weight of flooring.
 But every bolt and bar and beam and ! window sash has to be summed up in the reckoning, and then there Is the problem of live weight, including desks, chairs, books, safes, human beings and the other incidentals In an office. The law, however, provides that the engin- ger shall allow a fixed figure for every square foot of live weight, so that here again his task Is matter of multipli- cation. This, however must be figured on floor by floor, and in a thirty-two- story skyscraper with 100000 square feet of rentable area it is apparent that lconsiderable multiplication can be in- dulged in this matter alone.
 The wind pressure, however, is the most difficult thing to figure on, and the height of the slkyscraper, its shape and the area exposed to the wind are all factors in a matter of most delicate calculation.
 Even with this the weighers task Is not over. In figuring costs he must as- certain how deep below the surface of the ground where the building is to be erected New York's rocky backbone lies. Borings must be made to deter mine the character of the ground, for an SO,0OO ton skyscraper cannot rest on loose gravel. Fortunately, New York is built on solid granite, though in the downtown district this is often found as far as 100 feet below the surface. II the granite is too deep for foundations
 however, the engineer is certain to fint