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Design of Hollow Block Slabs Dr. Hamed Hadhoud

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

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Design of Hollow Block Slabs Dr. Hamed Hadhoud

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

  2. 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

  3. 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

  4. Cairo University Dr. Hamed Hadhoud Typical Section ts t e b 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

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

  6. 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

  7. Cairo University Dr. Hamed Hadhoud One-Way Hollow Block Slab Cross Ribs Cross Ribs To improve load distribution under partial loading ≤ LL 300 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 ≤ ≤

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

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

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

  11. Cairo University Dr. Hamed Hadhoud Loads 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

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

  13. 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

  14. Cairo University Dr. Hamed Hadhoud 10 Details 15x10+16x40=790 4f6/m 5f6/m 10 10 26x20+10=530 1F16/rib 1F18/rib 5 25 20 2F16/rib 5f8/m 10 40 25 15x10+16x40=790 Main ribs 10 10 25x20+10=510 1F16/rib 1F16/rib 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 1:50 Scale 1:10

  15. 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

  16. Cairo University Dr. Hamed Hadhoud Loads gs= dead load + flooring ps= live load wsu= 1.5(gs+ps) t/m2 wu/rib) short direction= wsux ax spacing t/m wu/rib) short direction= wsux bx spacing t/m Spacing = 0.5 m Wa Wb Marcus Table Grashoff Table

  17. 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

  18. 1F16/rib 1F12/rib Cairo University Dr. Hamed Hadhoud Details 10 15x10+16x40=790 4f6/m 4f6/m 10 10 12x10+13x40=640 1F16/rib 5 1F16/rib 25 2F16/rib 20 5f8/m 10 40 20 Ribs 15x10+16x40=790 10 10 12x10+13x40=640 1F16/rib 1F16/rib 10 Scale 1:50 Scale 1:10

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

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