TOUT" 



A special feature of the Tower is the system of 

 bracing employed to provide for tin- wind .sire>se>. 

 The bracing starts at the 39th tier 



OP an< ^ exlent ^ s to tne f 001 f tne co '" 

 umns. and is roini>osed of heavy 



diagonal X h races connected to gus- 

 sets on the columns at the floor levels and is de- 

 signed to withstand a horixontal wind pressure of 

 30 pounds per square foot of surface of the entire 

 vertical surface at the building. The uplift due to 

 the wind stresses is provided for by anchoring six 

 columns of the elevator shaft and four others, or ten 

 in all, of the tower columns by means of heavy pin- 

 connected anchorage bars which extend down about 

 44 feet into the concrete piers and are built in con- 

 crete. The l>ar> arc connected with the foot of the 

 columns by SJ-inch and 4J-inch diameter rods which 

 connect with the anchorage bars by means of a heavy 

 cast steel saddle illustrated on page 23. These 

 columns have a maximum calculated static load of 

 950,000 pounds and a maximum uplift of 540,000 

 pounds each, due to wind pressure, which is pro- 

 vided for by a cross sectional area of 169 square 

 inches of metal in the basement, the section, of course, 

 decreasing to the top. 



This wind bracing is further illustrated and de- 

 scribed as follows, as taken from The Engineering 

 Record of May 18, 1907: 



"The stresses developed by an assumed wind 

 pressure of 30 pounds per square foot on the entire 

 vertical surface of the Tower are resisted by a system 

 of 25 panels of X-bracing between pairs of columns ; 

 four of these panels terminate at the 14th floor. Six- 

 teen panels in corners of Tower are continued to the 

 32d, and the remainder are carried to the 36th floor, 

 just below the dome which surmounts the Tower. 



uoi/nxc; WIND HRACIM; OK TOWKK 



A\VAITIN<; DKIililCK U)AI) 



The arrangement of the Tower bracing is special in 

 order to provide clearance for the doors and windows, 

 which are located between or adjacent to the diagonals. 

 To this end one pair of X-braces forms a panel of 

 comparatively short height vertically at every alter- 

 nate floor line. 



"The spaces between these panels are filled with 

 X-braces forming long vertical panels and providing 

 wide spaces between the diagonals at the upper and 

 lower ends, thus leaving space for a door or window 

 between them, above and below the floor line, which 

 is intersected near the center of the panel. Alternate 

 stories thus have their doors and windows located 

 first in the upper and then in the lower space between 

 the diagonals. In the panels arranged for window 

 openings the horizontal struts at the ends of the 

 X-braces are located approximately symmetrical on 

 both sides of the floor line; in the door panels, the 

 horizontal struts are both depressed just below the 

 floor line so as to leave an unobstructed clearance for 

 the doorway reaching down to the floor level. No 

 knee-braces are used in the bracing system, all 

 diagonal members being full length and provided at 

 their extremities with special horizontal struts, thus 

 forming with the columns complete vertical trusses 

 extending for the full height of the columns. 



"In the 32d, or highest regular story, the horixon- 

 tal struts of the wind-brace system at windows and 

 doors are made with pairs of 10-in. 15-11). channels, 

 back to back, and the X-braces arc made with single 

 4 x 3-in. x 8^-lb. angles for the long panels, and with 

 3 x 3^-in. x 6.6-lb. angles for the short panels. In 

 the 30th story the long diagonals change to 7-in. 

 12^-lb. channels and in the 2Sth story to 8-in. 13J-lb. 

 channels, in the 24th story to 10-in. 20-lb. channels, 

 in the 20th story to 10-in. 25-lb. channels, and in the 



