# Design of Hollow Block Slabs

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

Suitable for residential and office buildings
Cairo University Dr. Hamed Hadhoud 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

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

Minimum dimensions specified by Egyptian Code
Cairo University Dr. Hamed Hadhoud Typical Section ts t b e Minimum dimensions specified by Egyptian Code ts 5 cm ts e/10 b t/3 b 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  ts= 7 cm, b=12 cm

Blocks and Ribs Arrangement
Cairo University Dr. Hamed Hadhoud Blocks and Ribs Arrangement

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

One-Way Hollow Block Slab
Cairo University Dr. Hamed Hadhoud One-Way Hollow Block Slab Cross Ribs Cross Ribs To improve load distribution under partial loading LL kg/m2 L2 5 m  no cross ribs L2 > 5 m  one cross rib LL > 300 kg/m2 L2< 4 m  no cross ribs 4 L2 7 m  one cross ribs L2 > 7 m  three cross ribs

One-Way Hollow Block Slab
Cairo University Dr. Hamed Hadhoud One-Way Hollow Block Slab Arrangements b4 C2 Lc2 C1 C1 b1 Lc1 b2 C2 b3 Let n= number of ribs m= number of blocks in one row C1

One-Way Hollow Block Slab
Cairo University Dr. Hamed Hadhoud One-Way Hollow Block Slab Arrangements b4 C2 Lc2 C1 C1 b1 Lc1 b2 C2 b3 If no cross ribs C2

One-Way Hollow Block Slab
Cairo University Dr. Hamed Hadhoud One-Way Hollow Block Slab Arrangements b4 C2 Lc2 C1 C1 b1 Lc1 b2 C2 b3 If there are cross ribs C2

This includes weight of blocks + ribs +5 cm top slab
Cairo University Dr. Hamed Hadhoud Loads Dimensions of blocks Dead Load kg/m2 One Way Two Way 15 x 20 x 40 303 336 20 x 20 x 40 330 380 25 x 20 x 40 410 478 This includes weight of blocks + ribs +5 cm top slab gs= dead load + flooring ps= live load wsu= 1.5(gs+ps) t/m2 wu/rib= wsu x spacing t/m Spacing = 0.5 m

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

RFT  one straight and one bent
Cairo University Dr. Hamed Hadhoud design 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 a (ratio of straight/bent bars = 0.4)  Moment of resistance (Mur) 2 1 3 B= 50 cm Mur t d b= 10 cm Mur t d Minimum Solid Part b=10 cm

As’)x-rib= 0.5 As)main rib 2F16/rib 25 10 25 1F16/rib Cross rib
Cairo University Dr. Hamed Hadhoud Details 10 15x10+16x40=790 4f6/m 5f6/m 10 10 26x20+10=530 1F18/rib 1F16/rib 5 25 20 2F16/rib 5f8/m 10 40 25 Main ribs 15x10+16x40=790 10 10 1F16/rib 1F16/rib 25x20+10=510 As)x-rib= As)main rib 2F12/rib 5f8/m As’)x-rib= 0.5 As)main rib 2F16/rib 25 10 25 1F16/rib Cross rib 7x20=140 10 10 Scale 1:10 Scale 1:50

Two-Way Hollow Block Slab
Cairo University Dr. Hamed Hadhoud Two-Way Hollow Block Slab Arrangements b4 C2 C1 C1 Lc2 b1 Lc1 b2 C2 b3 Let n= number of ribs in direction (1) C1 Similarly in direction (2) C2

Cairo University Dr. Hamed Hadhoud Loads gs= dead load + flooring ps= live load wsu= 1.5(gs+ps) t/m2 wu/rib) short direction= wsu x a x spacing t/m wu/rib) short direction= wsu x b x spacing t/m Spacing = 0.5 m Wa Wb Marcus Table Grashoff Table r 1 ….. 2 a 0.396 0.849 b 0.053 r 1 ….. 2 a 0.5 0.941 b 0.059

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

Details 10 4f6/m 15x10+16x40=790 4f6/m 10 10 12x10+13x40=640 5
Cairo University Dr. Hamed Hadhoud Details 10 4f6/m 15x10+16x40=790 4f6/m 10 10 12x10+13x40=640 5 1F16/rib 1F16/rib 25 2F16/rib 5f8/m 20 10 40 20 Ribs 15x10+16x40=790 10 10 1F16/rib 1F16/rib 12x10+13x40=640 1F12/rib 1F16/rib 10 Scale 1:10 Scale 1:50