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

2. 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

3. 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

4. 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

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

6. 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

7. 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 ≤ ≤

8. 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

9. 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

10. 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

11. 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

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

13. 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

14. 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

15. 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

16. gs= dead load + flooring ps= live load wsu= 1.5(gs+ps) t/m2
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

17. 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

18. 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

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