Slabs with spans not exceeding 3.0 m Beams in which the sum of the column stiffnesses exceed 8 times the sum of the beam stiffnesses at each end of the span EXAMPLE For the floor system shown below, design the slab and beams. fc' = 30 MPa and fy =400 MPa. The slab is loaded with a working LL =12 kPa and a finishing DL = 1.5 kPa. Max. For (ϵt = 0.005, kn = 6.75 MPa, =0.02), (ϵt = 0.004, kn = 7.5 ρmax. MPa, =0.0228). ρmax. SOLUTION DESIGN OF SLAB The slab is a one-way, since (L/S = 8.25/3.65 = 2.26 > 2.0). From Table (9.5.a) in the ACI Code, the min. thickness for continuous one-way slab (S/28). ≥ Min. t S/28 =3.65/28 = 130 mm. Use t =150 mm. ≥ Slab weight = 0.15×1×1×24 = 3.6 kPa Total DL =3.6+1.5=5.1 kPa Total factored load wu = 1.2×5.1+1.6×12=25.32 kPa Min. thickness of the beam According to Table (9.5.a) of the ACI Code h ≥ L/21=8.25/21=393 mm, Use h = 550 mm, and b = 300 mm. Therefore the clear span of the slab =3.65 -0.3=3.35 m m = 400/(0.85×30) = 15.69 d = 150-20-12/2=124 mm b.d2 = 1(0.124)2 = 0.015376 Max. kn = 6.75 MPa, = 0.02 ρmax. Design of Slab Span Exterior Interior Moment -ve +ve -ve -ve +ve -ve M.Coeff. 1/24 1/14 1/10 1/11 1/16 1/11
Slabs with spans not exceeding 3.0 m Beams in which the sum of the column stiffnesses exceed 8 times the sum of the beam stiffnesses at each end of the span EXAMPLE For the floor system shown below, design the slab and beams. fc' = 30 MPa and fy =400 MPa. The slab is loaded with a working LL =12 kPa and a finishing DL = 1.5 kPa. Max. For (ϵt = 0.005, kn = 6.75 MPa, ρmax. =0.02), (ϵt = 0.004, kn = 7.5 MPa, ρmax. =0.0228). SOLUTION DESIGN OF SLAB The slab is a one-way, since (L/S = 8.25/3.65 = 2.26 > 2.0). From Table (9.5.a) in the ACI Code, the min. thickness for continuous one-way slab ≥ (S/28). Min. t ≥ S/28 =3.65/28 = 130 mm. Use t =150 mm. Slab weight = 0.15×1×1×24 = 3.6 kPa Total DL =3.6+1.5=5.1 kPa Total factored load wu = 1.2×5.1+1.6×12=25.32 kPa Min. thickness of the beam According to Table (9.5.a) of the ACI Code h ≥ L/21=8.25/21=393 mm, Use h = 550 mm, and b = 300 mm. Therefore the clear span of the slab =3.65 -0.3=3.35 m m = 400/(0.85×30) = 15.69 d = 150-20-12/2=124 mm b.d2 = 1(0.124)2 = 0.015376 Max. kn = 6.75 MPa, ρmax. = 0.02 Design of Slab Span Exterior Interior Moment -ve +ve -ve -ve +ve -ve M.Coeff. 1/24 1/14 1/10 1/11 1/16 1/11
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