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1
2
Under supervision of
Dr . Mohamed Nabil
This report has been prepared by :
 Mohamed Mohsen Mohamed Hussein
 Mohamed Na...
Outlines
■ Introduction.
■ Comparison between different codes.
■ Solved example by different codes.
■ One & two way slab s...
Introduction
 Hollow block and Ribbed slabs are formed by placing blocks on the slab
and concrete ribs.
 In case of holl...
Introduction
The advantages of Ribbed and Hollow block slabs are as follows:
■ They provide an economical, versatile light...
ACI 318 ECP 203
BS 8110 Euro code 2
Comparison between different codes
6
7
■ Net distance between ribs "e"
shall not exceed 700 mm.
■ Web width "b" shall not be less
than 100 mm or one the third ...
8
■ The minimum value of rib width (b) isn't less than 1/4 slab thickness
(t) or 100 mm whichever greater, with taking int...
9
Comparison between different codes
British code (BS 8110)
 Limitations of Hollow block slabs :
■ Clear distance between...
Euro code (En2)
■ The rib spacing does not exceed 1500 mm.
■ The depth of the rib below the flange does
not exceed 4 times...
11
American Concrete Institute (ACI)
■ When permanent filling material
having a unit compressive strength at
least equal t...
12
Simply sup. L/20 L/20
-----------
L/16
1 end cont. L/25 L/20.8 L/18.5
2 end cont. L/28 ----- L/21
cantilever L/8 L/5.6 ...
13
14
Fcu= 25 N/mm2
Fy= 360 N/mm2
F.C= 1.5 KN/m2
L.L= 3.0 KN/m2
Solved examples by different codes
15
th.b 250 mm 250 mm 250 mm 300
tS 50 mm 50 mm 50 mm 50 mm
h 200 200 200 250
Mu (Kn.m/rib)
19.187 19.187 17.75 23.5
AS 29...
16
One & two way slab Solved examples
One way
slab
Two way
slab
Fcu= 25 N/mm2
Fy= 360 N/mm2
F.C= 1.5 KN/m2
L.L= 3.0 KN/m2
17
th.b. 320 mm 250 mm
h 250 mm 200 mm
ts 70 mm 50 mm
Mu (KN.m/rib) 45.64
α dir. β dir.
15.68 15.68
As 529.255 mm2/ rib
23...
Effect of cross ribs on deflection
 In The previous example the effect of cross ribs on deflection will be
discussed on s...
19
■ Case of one cross rib:
Effect of cross ribs
20
■ Case of two cross rib:
Effect of cross ribs
The two cases have the same deflection value so it is more economic to us...
Modeling

21
22
Modeling
■ Model 1
The ribs are frame elements with cross section as T-section and connected
together with a virtual sl...
23
The moment on the ribs=19.3675 KN.m
24
Modeling
■ Model 2
The ribs are frame elements with cross section as T-section and connected
together with frame elemen...
25
Modeling
■ Model 3
The ribs are converted to a thickness on the whole slab and use virtual slab to
connect between elem...
26
The moment on the ribs= 19.0767 KN.m
27
Modeling
■ Model 4
The ribs are represented as frame elements with rectangle section and the
connecting element is fram...
 This table shows the differences between the models and the manual
solution .
28
Manual4321Model
19.187519.155519.076719...
Case study
 Introduction:
Different case study for hollow block slabs and ribbed slabs.
■ Case 1
29
Ordinary one way holl...
30
Case study
.
31
Case study
■ Case 2
Cantilever hollow block slabs
32
Case study
■ Case 3
Two way hollow block slabs
Ribbed slabs one way and two way ( waffle ) and how the blocks are
placed .
33
Case study
■ Case 4
34
Case study
35
Case study
■ Case 5
In this case foam blocks are used
Clay blocks are used in this case.
36
Case study
■ Case 6
Questions
37
38
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Hollow block and ribbed slabs

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Hollow block and ribbed slabs

  1. 1. 1
  2. 2. 2 Under supervision of Dr . Mohamed Nabil This report has been prepared by :  Mohamed Mohsen Mohamed Hussein  Mohamed Nabil Ali Kamel  Mohamed Youssef Mahmoud Youssef  Ahmed Hamdy Mohamed Hassan Hollow block & Ribbed slabs
  3. 3. Outlines ■ Introduction. ■ Comparison between different codes. ■ Solved example by different codes. ■ One & two way slab solved example. ■ Effect of cross ribs on deflection. ■ Modeling. ■ Case study. 3
  4. 4. 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.  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 ).  Types hollow block slab are one way and two way slabs . 4
  5. 5. Introduction The advantages of Ribbed and Hollow block slabs are as follows: ■ They provide an economical, versatile lightweight monolithic slab system and this its main advantage reduction of weight by removing the part of the concrete below the neutral axis. ■ Components are relatively light and no mechanical handling is necessary there is ease of construction.  Economic for spans more than 5m with light or moderate live loads, such as hospitals, office or residential buildings. 5
  6. 6. ACI 318 ECP 203 BS 8110 Euro code 2 Comparison between different codes 6
  7. 7. 7 ■ 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. Comparison between different codes Egyptian code (ECP 203)  Limitations of Hollow block slabs :
  8. 8. 8 ■ 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) ■ 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.  Limitations of Ribbed slabs:
  9. 9. 9 Comparison between different codes 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. t b e b t b ≤ t/4
  10. 10. Euro code (En2) ■ 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. 10 Comparison between different codes  Limitations of Hollow block slabs :  Limitations of Ribbed slabs: ■ One limitation will change from ribbed slab The minimum flange thickness of 50 mm may be reduced to 40 mm.
  11. 11. 11 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 Comparison between different codes  Limitations of Hollow block slabs & Ribbed slab:
  12. 12. 12 Simply sup. L/20 L/20 ----------- L/16 1 end cont. L/25 L/20.8 L/18.5 2 end cont. L/28 ----- L/21 cantilever L/8 L/5.6 L/8 e ≤ 700 mm e ≤ 1500 mm e ≤ 1500 mm e ≤ 750 mm b ≤ t/4 b ≤ t/4 b ≥ 100 mm L.L ≤ 3 KN/m2 , Ls> 5 L.L > 3 KN/m2 , Ls→(4:7) L.L > 7m. ------- If L ≥ 10th.b ------- One X rib One X rib 3 X ribs Comparison between different codes
  13. 13. 13
  14. 14. 14 Fcu= 25 N/mm2 Fy= 360 N/mm2 F.C= 1.5 KN/m2 L.L= 3.0 KN/m2 Solved examples by different codes
  15. 15. 15 th.b 250 mm 250 mm 250 mm 300 tS 50 mm 50 mm 50 mm 50 mm h 200 200 200 250 Mu (Kn.m/rib) 19.187 19.187 17.75 23.5 AS 293.30 mm2 255.72 mm2 322.005 mm2 226.67 mm2 Main ribs dim. 100 × 200 mm 100 × 200 mm 100 × 200 mm 100 × 250 mm Cross ribs No cross ribs No cross ribs One cross rib No cross ribs Solid part Short dir. long dir. Short dir. long dir. Short dir. long dir. Short dir. long dir. 0.3 m. 0.3 m. 0.3 m. 0.3 m. 0.25 m. 0.3 m. 0.3 m. 0.3 m. Conc. Quantities 2.806 m3 2.806 m3 2.934 m3 3.07 m3 Solved examples by different codes
  16. 16. 16 One & two way slab Solved examples One way slab Two way slab Fcu= 25 N/mm2 Fy= 360 N/mm2 F.C= 1.5 KN/m2 L.L= 3.0 KN/m2
  17. 17. 17 th.b. 320 mm 250 mm h 250 mm 200 mm ts 70 mm 50 mm Mu (KN.m/rib) 45.64 α dir. β dir. 15.68 15.68 As 529.255 mm2/ rib 239.68 mm2/ rib. For α dir. And 251.09 mm2/ rib. for β dir. Ribs dim. 0.12 * 0.25 m 0.1 * 0.2 m NO. of main ribs 11 12 No. of cross ribs 1 12 Conc. quantities 5.6854 m3 5.234 m3 RFT 1017.79 mm2 /m 981.54 mm2/m One & two way slab Solved examples It is obvious that the RFT and concrete quantities in the two way hollow block slab is more economic however the execution of the two way hollow block slab is harder than the one way hollow block slab.
  18. 18. Effect of cross ribs on deflection  In The previous example the effect of cross ribs on deflection will be discussed on sap program.  At first one cross rib is put in the mid span of the slab.  Then two cross ribs are put at 1/3 of the span from each side. 18
  19. 19. 19 ■ Case of one cross rib: Effect of cross ribs
  20. 20. 20 ■ Case of two cross rib: Effect of cross ribs The two cases have the same deflection value so it is more economic to use one cross rib at mid span
  21. 21. Modeling  21
  22. 22. 22 Modeling ■ Model 1 The ribs are frame elements with cross section as T-section and connected together with a virtual slab with very small thickness.
  23. 23. 23 The moment on the ribs=19.3675 KN.m
  24. 24. 24 Modeling ■ Model 2 The ribs are frame elements with cross section as T-section and connected together with frame elements with cross section as rectangular section . The moment on the ribs= 19.1793 KN.m
  25. 25. 25 Modeling ■ Model 3 The ribs are converted to a thickness on the whole slab and use virtual slab to connect between elements with very small thickness.
  26. 26. 26 The moment on the ribs= 19.0767 KN.m
  27. 27. 27 Modeling ■ Model 4 The ribs are represented as frame elements with rectangle section and the connecting element is frame element with rectangle section. The moment on the ribs= 19.1555 KN.m
  28. 28.  This table shows the differences between the models and the manual solution . 28 Manual4321Model 19.187519.155519.076719.179319.3675M (ultimate) KN .m Rectangular section Rectangular section T-sectionT-sectionCross section of ribs FramesVirtual slabFramesVirtual slabConnecting elements W (rib)On slabW (rib)On slabLoads 0101Self weight multiplier Modeling
  29. 29. Case study  Introduction: Different case study for hollow block slabs and ribbed slabs. ■ Case 1 29 Ordinary one way hollow block slab
  30. 30. 30 Case study
  31. 31. . 31 Case study ■ Case 2 Cantilever hollow block slabs
  32. 32. 32 Case study ■ Case 3 Two way hollow block slabs
  33. 33. Ribbed slabs one way and two way ( waffle ) and how the blocks are placed . 33 Case study ■ Case 4
  34. 34. 34 Case study
  35. 35. 35 Case study ■ Case 5 In this case foam blocks are used
  36. 36. Clay blocks are used in this case. 36 Case study ■ Case 6
  37. 37. Questions 37
  38. 38. 38

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