introduction and general info about hollow block & brief design rules with solved example

1. Hollow Block Slab
Done by : Ahmad Baalbaky

2. Outline:
 Introduction
 Benefits of rib and block slab
 Pictures from site
 Comparison between different codes
 Types of hollow block slab
 Steps of design
 Solved example

3. Introduction:
 Hollow block and Ribbed slabs are formed by placing
blocks on the slab and concrete ribs.
 In case of hollow block slab voided blocks are placed to
reduce the total weight of the slab .
 In case of ribbed slab the blocks are not permanent but the
wooden frame is not continuous so its hard to be applied
and expensive.
 The blocks are considered as non-structural element as
they do not contribute to strength of the slab.
 Blocks may be made concrete with lightweight aggregate
or other material as polystyrene ( foam ).
 hollow block slab can be one way or two way slabs .
Ribbed slab
Hollow block slab
Hourdi block different sizes

4. Benefits of Hollow block slab:
 Improved sound and heat insulation further enhance this system.
 The electrical slab boxes, which are the same size as the concrete slab blocks, allow for down-
lighters anywhere in the slab and the electrical conduits to be positioned correctly. Electrical and
plumbing services can easily be accommodated
 Plastered smooth ceilings with no grooves give a quality finish to your slab
 Easy installation guaranteed! No cranes or formwork needed.
 Reduced cost for labor, installation and very quick to install
 A hollow block system is 30% lighter than a solid cast system on the supporting walls and foundation
Block material Block height in cm
H= 25cm H=20cm H=15cm
Concrete hollow
block
240N 190N 140N
Cement hollow
block
320N 250N 190N

5. The shape of the hourdi blocks before formwork

6. Pictures from site
Hourdi block The last block placed on its side Spaces for ribs appear
Column steel bars continue to
the next floor
Preparing beams to be placed Formwork

7. Comparison between different codes
ACI 318 ECP 203
BS 8110 Euro code 2

8.  Limitations of Hollow block slabs :
• Net distance between ribs "e" shall not exceed 700 mm.
• Web width "b" shall not be less than 100 mm or one the third of
• depth "t", whichever is greater.
• Compression slab thickness "ts" shall not be less than 50 mm or one Tenth
1/10 of distance "e", whichever is greater.
 Limitations of Ribbed slabs:
• Distance between ribs axes can be increased up to 1.5 m .
• Thickness of upper slab is determined by a value not less than e/12 or 50
mm whichever greater.
• The minimum value of rib width (b) isn't less than 1/4 slab thickness (t) or
100 mm whichever greater, with taking into account requirements of
concrete cover, distance between bars and fire requirements
Egyptian code (ECP 203)

9. British code (BS 8110)
 Limitations of Hollow block slabs :
• Clear distance between ribs (e) not more than 500
mm , jointed in cement : sand mortar ts is 25
mm.
• Clear distance between ribs (e) not more than 500
mm not jointed in cement : sand mortar ts is 30
mm.
• All other slabs with permanent blocks ts is 40 or
one-tenth 1/10 of clear distance between ribs,
whichever is great
 Limitations of Ribbed slabs:
• Clear distance between ribs not more than 1.5 m
ts is 50 mm or one-tenth of clear distance between
ribs, whichever is greater
b ≤ t/4
e
b
t

10. Euro code (En2)
 Limitations of Ribbed slabs:
• The rib spacing does not exceed 1500 mm.
• The depth of the rib below the flange does not
exceed 4 times its width.
• The depth of the flange is at least 1/10 of the
clear distance between ribs or 50 mm,
whichever is the greater.
• Transverse ribs are provided at a clear spacing
not exceeding 10 times the overall depth of the
slab.
 Limitations of Hollow block slabs :
• One limitation will change from ribbed slab The minimum
flange thickness of 50 mm may be reduced to 40 mm.

11.  Limitations of Hollow block slabs & Ribbed slab:
American Concrete Institute (ACI)
• When permanent filling material having a
unit compressive strength at least equal to fc′
in the joists are used ts shall be not less than
1/12 the clear distance between ribs, nor less
than 40 mm.
• Otherwise ts is not to be less than 1/12 the
clear distance between ribs, nor less than 5.0
cm
• Ribs are not to be less than 10 cm in width,
and a depth of not more than 3.5 times the
minimum web width.
• Clear spacing between ribs is not to exceed
75.0 cm

12. Dimensions of hollow block slab

13. Types of hollow block slab
Loaddirection
Load direction

15. Steps of design:

21. Solved example:

27. Thank you for listening