Hollowblock slabs.pdf

7/27/2019 Hollowblock slabs.pdf

http://slidepdf.com/reader/full/hollowblock-slabspdf 1/9

Hollow Block Slabs

2

R C D e s i g n 2 - D r . H a n y N e s s i m

M o n d a y ,

O c t o b e r

1 5 ,

2 0 1 2

Hollow Block Slabs (definitions) Hollow blocks are used

to fill portions of theslab thickness; thisresults in deeper armfor the reinforcement while saving theamount of concreteand hence the own

weight of the slab.The reinforcement is located between the

blocks inside the ribs.Blocks may be concrete blocks or styro-foam



3


M o n d a y ,

O c t o b e r 1 5 ,

2 0 1 2

Hollow Block Slabs (definitions)

When the ribs are inone direction then it isa one-way hollow block

slab, regardless of therectangularity; r.

When ribs are in bothdirections then it is atwo-way hollow block

slab.

4


M o n d a y ,

O c t o b e r

1 5 ,

2 0 1 2

Advantages & Disadvantages Advantages

Reducing slab weight by reducing amount of concrete below neutral axis.

Ease of construction, especially when all beamsare hidden beams.

Economic for spans > 5m with moderate liveload: hospitals, office and residential buildings.

Improved insulation for sound and heat.

Disadvantages Not economic for small spans Not suitable for heavy loads or dynamic loads. Difficult to repair or strengthen



5


M o n d a y ,

O c t o b e r 1 5 ,

2 0 1 2

One-Way Hollow Block Slabs

8282520Clear span (Ln /t)

cantileverContinuous

both ends

Continuous

one end

Simply

supportedSupport condition

Ribs are in one direction only

For spans less than 10m or cantilevers less than 2m long.

St. 400/600; for other grades divide values by

+

6504.0

y f

b e

ts

t

6


M o n d a y ,

O c t o b e r

1 5 ,

2 0 1 2

Cross ribs Cross ribs are used when the live load ≥

3kN/m2 or Span > 5m.

Threecross ribs

One crossrib

One crossrib

NoCross Sibs

>3kN/m2> 3kN/m2≤ 3kN/m2≤ 3kN/m2Live Load

>7m4m – 7m>5m≤ 5mSpan



7


M o n d a y ,

O c t o b e r 1 5 ,

2 0 1 2

Minimum Dimensions

e ≤ 700mm b = t/3 ≥ 100mm t s = e/10 ≥ 50mm

b e

ts

t

8


M o n d a y ,

O c t o b e r

1 5 ,

2 0 1 2

Loading

Own weight including blocks’ weight. Flooring Live Load

b e

ts

t



9


M o n d a y ,

O c t o b e r 1 5 ,

2 0 1 2

Loading

Own Weight including blocks’ weight (kN/m2)

1.200.704.784.103.803.303.363.03

Twoway

Oneway

Twoway

Oneway

Twoway

Oneway

Twoway

Oneway

Foam Blocks500x400x200

Concrete Blocks400x200x250



b e

ts

t

10


M o n d a y ,

O c t o b e r

1 5 ,

2 0 1 2

Load Distribution Factors for Two-way When LL ≤ 5 kN/m2 or when the compression

flange is incomplete.

0.0530.0630.0770.0930.1130.1400.1720.2120.2620.3330.396β

0.8490.8300.8060.7780.7460.7060.6600.6060.5430.4730.396α

2.01.91.81.71.61.51.41.31.21.11r



11


M o n d a y ,

O c t o b e r 1 5 ,

2 0 1 2

Load Distribution Factors for Two-way

When LL > 5 kN/m2

0.0590.0720.0860.1070.1330.1660.2030.2580.3280.4050.500β

0.9410.9280.9140.8930.8670.8340.7970.7420.6720.5950.500α

2.01.91.81.71.61.51.41.31.21.11r

12


M o n d a y ,

O c t o b e r

1 5 ,

2 0 1 2

Calculate Bending Moments Two spans

When LL ≤ DL, andthe difference betweenspans is not more than20%; then the bendingmoment could becalculated as following.

W = wu for limit statedesign method.

& w = w for allowablestresses designmethod.

w



13


M o n d a y ,

O c t o b e r 1 5 ,

2 0 1 2

More than two spans

Spans differences are not more than 20%

LL ≤ DL

Calculate Bending Moments

W

14


M o n d a y ,

O c t o b e r

1 5 ,

2 0 1 2

Using Design Aids Charts (flexure)



15


M o n d a y ,

O c t o b e r 1 5 ,

2 0 1 2

Design for Shear

Shearing stresses should be less than the concrete shear capacityand, hence, minimum shear reinforcement could be used.

)(q

q.

4.0Aent;reinforcemshearMinimum

) / (q16.0qcapacity;shearConcrete

.qstress;Shearing

2

cu

umins,

2

ucu

u

mmsb f

mm N f

t b

Q

y

c

cu

u

=

≥=

=

γ

16


M o n d a y ,

O c t o b e r

1 5 ,

2 0 1 2

Minimum Reinforcement

5φ6mm/m’ perpendicular to ribs.

4φ6mm/m’ parallel to ribs.

Bottom reinforcement = rib mainreinforcement.

Top reinforcement = ½ bottomreinforcement

Stirrups

Rib reinf.

Slab reinf.

In top slab

In Cross rib



17


M o n d a y ,

O c t o b e r 1 5 ,

2 0 1 2

Minimum Reinforcement

Stirrups

Rib reinf.

Slab reinf.

In Main rib

(as beams)

≥

≥

=

s t e e l

s t e e ls t e e l

s t e e ld e f o r m e d

d e f o r m e d d e f o r m e d

d e f o r m e d f o r

f o r f o r

f o r b d ;

b d ;b d ;

b d ;

1 0 0

1 0 0 1 0 0

1 0 0

0 . 1 5

0 . 1 5 0 . 1 5

0 . 1 5

s t e e l

s t e e ls t e e l

s t e e lm i l d

m i l d m i l d

m i l d f o r

f o r f o r

f o r b d ;

b d ;b d ;

b d ;

1 0 0

1 0 0 1 0 0

1 0 0

0 . 2 5

0 . 2 5 0 . 2 5

0 . 2 5

A

AA

A

A

A A

A 1 . 3

1 . 3 1 . 3

1 . 3

f

ff

f

1 . 1

1 . 1 1 . 1

1 . 1

b d

b d b d

b d

f

ff

f

f

ff

f

0 . 2 2 5

0 . 2 2 5 0 . 2 2 5

0 . 2 2 5

m i n .

m i n .m i n .

m i n .A

AA

A

m i n

m i n m i n

m i n s ,

s ,s ,

s ,

s

ss

s

y

yy

y y

yy

y

c u

c u c u

c u

m i n

m i n m i n

m i n s ,

s ,s ,

s ,

Example

Hollowblock slabs.pdf

Documents

Transcript of Hollowblock slabs.pdf