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1 Design of Hollow Block Slabs Dr. Hamed Hadhoud Cairo University

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2 Dr. Hamed Hadhoud Cairo University Cracked zone Solid Slab Hollow Block Slab Hollow block slabs are usually used if the thickness of solid slabs exceeds 15 cm Suitable for residential and office buildings Not suitable for factories because of vibration effect

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3 Dr. Hamed Hadhoud Cairo University Blocks Dimensions 40 cm 20 cm 15 cm 20 cm 25 cm Usually for 2-way Usually for 1-way

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4 Dr. Hamed Hadhoud Cairo University Typical Section e b t ts Minimum dimensions specified by Egyptian Code ts 5 cm ts e/10 b t/3 b 10 cm ≥ ≥ ≥ ≥ For blocks 20 x 40 x 15 or 20 x 40 x 20 ts= 5 cm, b=10 cm For blocks 20 x 40 x 25 ts= 7 cm, b=12 cm

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5 Dr. Hamed Hadhoud Cairo University Blocks and Ribs Arrangement

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6 Dr. Hamed Hadhoud Cairo University One-Way Hollow Block Slab Blocks Arrangement 40 cm 20 cm rib Solid part Ribs are arranged in the short direction Minimum solid part = 10 cm

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7 Dr. Hamed Hadhoud Cairo University One-Way Hollow Block Slab Cross Ribs Cross Ribs To improve load distribution under partial loading LL 300 kg/m 2 L 2 5 m no cross ribs L 2 > 5 m one cross rib LL > 300 kg/m 2 L 2 < 4 m no cross ribs 4 L 2 7 m one cross ribs L2 > 7 m three cross ribs ≤ ≤ ≤ ≤

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8 Dr. Hamed Hadhoud Cairo University One-Way Hollow Block Slab Arrangements Let n= number of ribs m= number of blocks in one row b4b4 b3b3 C2C2 C2C2 C1C1 C1C1 b2b2 b1b1 L c1 L c2 C1C1

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9 Dr. Hamed Hadhoud Cairo University One-Way Hollow Block Slab Arrangements b4b4 b3b3 C2C2 C2C2 C1C1 C1C1 b2b2 b1b1 L c1 L c2 C2C2 If no cross ribs

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10 Dr. Hamed Hadhoud Cairo University One-Way Hollow Block Slab Arrangements b4b4 b3b3 C2C2 C2C2 C1C1 C1C1 b2b2 b1b1 L c1 L c2 C2C2 If there are cross ribs

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11 Dr. Hamed Hadhoud Cairo University Loads Dimensions of blocks Dead Load kg/m 2 One WayTwo Way 15 x 20 x 40303336 20 x 20 x 40330380 25 x 20 x 40410478 This includes weight of blocks + ribs +5 cm top slab g s = dead load + flooring p s = live load w su = 1.5(g s +p s ) t/m 2 w u /rib= w su x spacing t/m Spacing = 0.5 m

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12 Dr. Hamed Hadhoud Cairo University Straining Actions Equal span + equal load (or 20% difference)

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13 Dr. Hamed Hadhoud Cairo University design 1 3 2 Sec. 1 & 3 d= t-2.5 cm Designed as T-sec RFT one straight and one bent Sec. 2 Knowing As (bent bars) and (ratio of straight/bent bars = 0.4) Moment of resistance (M ur ) M ur Minimum Solid Part td B= 50 cm b= 10 cm td

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14 Dr. Hamed Hadhoud Cairo University Details 10 20 10 26x20+10=530 15x10+16x40=790 25 10 25x20+10=510 15x10+16x40=790 25 10 7x20=140 1 16/rib 1 18/rib 1 16/rib 25 5 40 10 2 16/rib 5 6/m 4 6/m 5 8/m 10 2 16/rib 2 12/rib 5 8/m Main ribs Cross rib As) x-rib = As) main rib As’) x-rib = 0.5 As) main rib Scale 1:50 Scale 1:10

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15 Dr. Hamed Hadhoud Cairo University Two-Way Hollow Block Slab Arrangements b4b4 b3b3 C2C2 C2C2 C1C1 C1C1 b2b2 b1b1 L c1 L c2 Let n= number of ribs in direction (1) C1C1 C2C2 Similarly in direction (2)

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16 Dr. Hamed Hadhoud Cairo University Loads g s = dead load + flooring p s = live load w su = 1.5(g s +p s ) t/m 2 w u /rib) short direction = w su x x spacing t/m w u /rib) short direction = w su x x spacing t/m Spacing = 0.5 m WW WW Marcus Table Grashoff Table r1….. 2 0.396….. 0.849 0.396….. 0.053 r1….. 2 0.5….. 0.941 0.5….. 0.059

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17 Dr. Hamed Hadhoud Cairo University design Same as 1-way but; d= t-2.5 cm for short direction d= t-3.5 cm for long direction

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18 Dr. Hamed Hadhoud Cairo University Details 10 20 10 15x10+16x40=790 20 10 12x10+13x40=640 15x10+16x40=790 1 16/rib 25 5 40 10 2 16/rib 4 6/m 5 8/m Ribs Scale 1:50 Scale 1:10 12x10+13x40=640 1 12/rib 1 16/rib

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19 Dr. Hamed Hadhoud Cairo University Shear Design in Hidden Beams flooring 5 cm Use at least 4-branches stirrups, where distance between branches >= 25 cm

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