4. A 12-story building has a floor plan that is 120 ft square and has 12 stories
ID: 1712769 • Letter: 4
Question
4. A 12-story building has a floor plan that is 120 ft square and has 12 stories that are 15-ft high. The wind load on the windward (front) face gets larger at the higher elevation stories but is a constant value on the leeward (back) wall in the Figure. Sketch the diaphragm load diagrams for the tenth- and second-floor diaphragms. Assume that VLFRS is around the perimeter of the building and also down the centerline of the building (i.e., 60 ft in from the outside). Roof (180 29.1 psi 284 pst 27.6 psf 26.8 ps 25.9 psf 25.0 psf 23.9 pst 22.7 psf 21.3 psf 19.6 psf 17.5 ps 14.3 psf 12th Floor t65 n I Ith Floor 150 ft 10th Floor 135 t 9th Floor 120 ft 8th Floor 105 t 7th Floor 90 t 194 paf 6h Floor 75 ft 5th Floor 60 ft iso ft 4th Floor 45 t 3rd Floor 30 t 2nd Floor 15 ft Dashed lines represent diaphragm levels Load values transition al mid-height hetween diaphragms (typical assumption for design).Explanation / Answer
Floor to floor height=15 ft
Width of building=120 ft
Windward pressure in tenth floor diaphragm = 26.8 psf
Tributary area of diaphragm = 120*15=1800 ft2
Windward load on tenth floor diaphragm=26.8*1800=48240 lb
Leeward pressure in tenth floor diaphragm=19.4 psf
Leeward force on tenth floor diaphragm=19.4*1800=34920 lb
Total force in tenth floor=48240+34920=83160 lb=83.16 kips
Windward pressure in second floor diaphragm = 14.3 psf
Tributary area of diaphragm = 120*15=1800 ft2
Windward load on second floor diaphragm=14.3*1800=25740 lb
Leeward pressure in second floor diaphragm=19.4 psf
Leeward force on second floor diaphragm=19.4*1800=34920 lb
Total force in second floor=25740+34920=60660 lb=60.66 kips
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