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Unformatted text preview: Lecture 18 – Design Lecture 18 – Design July 18, 2003 CVEN 444 Lecture Goals Lecture Goals Slab design example Total beam design OneWay Slab Example OneWay Slab Example The cross section of a continuous oneway solid slab in a building is shown. The slabs are supported by beams that span 24 ft. Between simple supports. The dead load on the slabs is that due to selfweight plus 60 psf; The live load is 120 psf. Design the continuous slab and draw a detailed section. Given: f c = 3 ksi, f y = 40 ksi. OneWay Slab Example OneWay Slab Example Determine the thickness of the slab. 12 ft. Minimum thickness of interior bay: 12 in. 12 ft 1 ft. 5.14 in. 28 28 L h = = = OneWay Slab Example OneWay Slab Example Use h= 6 in. Dead weight b coverage 2 0.5 in. 6 in. 0.75 in. 5.0 in. 2 d d h = = = ( 29 sl 3 2 2 1 ft 6 in. 150 lb/ft 60 lb/ft 12 in. 135 lb/ft DL h DL γ = + = + = OneWay Slab Example OneWay Slab Example Determine the load on the floor For slab design ρ is seldom > 0.01. Use c/d = 0.2 ( 29 ( 29 2 2 2 2 1.2 1.6 1.2 135 lb/ft 1.6 120 lb/ft 354 lb/ft 0.354 k/ft U DL LL = + = + = ( 29 ( 29 ( 29 ( 29 ( 29 1 u c 1 0.85 1 2 0.85 0.2 0.85 3 ksi 0.85 0.2 1 0.397 ksi 2 k R f k β β = = = OneWay Slab Example OneWay Slab Example Find the coefficient of the moment diagram The maximum moment is ( 29 2 2 2 u n u 0.354 k/ft 11 ft. 10 10 4.28 kft/ft w l M = = = OneWay Slab Example OneWay Slab Example Find the design d for a onefoot strip If b =12in. then d = 3.46in., which for c/d = 0.2, so d = 5in., the slab is OK. u 2 u 3 12 in. 4.28 kft/ft ft 0.9 R 0.397 ksi 143.9 in /ft M bd φ = = = OneWay Slab Example OneWay Slab Example Find the coefficient of the shear The maximum shear is ( 29 2 u u v 0.354 k/ft 11 ft. 1.15 2 2 2.24 k/ft w l V C = = = OneWay Slab Example OneWay Slab Example Check the shear capacity of the slab ( 29 ( 29 ( 29 ( 29 u c w 0.75 2 0.75 2 3000 12 in. 5 in. 4930 lb. 4.93 k > 2.24 k V f b d φ = = = = Use h = 6in., d = 5in. and w u = 0.354 k/ft OneWay Slab Example OneWay Slab Example Minimum about of steel is (use ACI 7.12 ) ( 29 ( 29 ( 29 s min 2 0.0020 0.002 12 in. 6 in. 0.144 in A bh = = = Moment capacity of the slab (12in. beam) u s y 2 a M A f d φ = ( 29 0.925 0.925 5 in. 4.625 in. 2 a d d 2245 = = Assume OneWay Slab Example OneWay Slab Example Compute the moments Moment capacity of the beam A B C D E l n 11 ft. 11 ft. 11 ft. 11 ft. 11 ft. M coef 1/24 1/14 1/10 1/11 1/16 M u 1.78 kft 3.06 kft 4.28 kft 3.89 kft 2.68 kft A min 0.144 in 2 0.144 in 2 0.144 in 2 0.144 in 2 0.144 in 2 A s 0.128 in 2 0.221 in 2 0.309 in 2 0.280 in 2 0.193 in 2 OneWay Slab Example OneWay Slab Example Compute the moments ( 29 ( 29 ( 29 ( 29 2 u u u s y y 2 0.354 k/ft 11 ft 1.78 kft 24 0.925 2 12 in....
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