5.
A slab is structural element whose thickness is small
compared to its own length and width.
Slabs in Buildings are usually used to transmit the loads on
floors and roofs to the supporting beams.
7.
A One Way Slab is simply a very wide beam that spans between
supports.
When slab is supported on two opposite sides only, total load is carried
along the perpendicular direction of supporting beams.
When slab is supported at all sides and length/width >2 of a slab
panel, maximum load is carried along the short direction.
shrinkage Reinft.
Main reinforcement is placed along the load carrying direction.
Beam
L
Main Reinft.
Beam
S
8.
The slab is designed as a series of 1’-0” wide beam
“strips”. The analysis is similar to rectangular
beams, except the width b = 12” and the height is
usually on the order of 4” →10”.
The main tension bars are usually #4, #5 or #6 bars.
however, additional bars are placed perpendicular to the
main tension bars to prevent cracking during the curing
process. These bars are referred to as “shrinkage” or
“temperature” bars and are also usually
#4 or #5 bars.
9.
A one-way slab is supported by parallel walls or beams, and the main
tension reinforcing bars run parallel to the span. It looks like the following:
10.
1- Minimum Thickness:
To control deflection, ACI Code specifies minimum thickness values for oneway solid slabs, shown in the following Table.
Element
Simply
supported
One End
continuous
Both end
continuous
Cantilever
One way
slabs
L/20
L/24
L/28
L/10
Where L is the span length in the direction of bending.
11.
2- Design Concept:
One-way solid slabs are designed as a number of
independent 1 ft or 12 “ wide strips which span in the
short direction and supported on crossing beams.
S1
S2
1 ft
L
S1
S2
12.
3- Reinforcement Ratio:
One-way solid slabs are designed as rectangular sections
subjected to shear and moment. Thus, the maximum
reinforcement ratio is
m ax 0.85 1
f c ' u
f y u t
4-Minimum reinforcement
Shrinkage and temperature
„ For fy = 40 to 50 ksi As(S&T) = 0.002bh
„ For fy = 60 ksi As(S&T) = 0.0018bh
„ For fy > 60 ksi As(S&T) = (0.0018x60xbh)/fy >= 0.0014bh
13.
5- Spacing of Reinforcement Bars
S=( 12 * as) / As
here , as = area of the bar used ,
As = area of reinforcement
6- Loads Assigned to Slabs
wu=1.2 D.L + 1.6 L.L
„
7-Minimum cover
ACI 7.7.71 (if not exposed to weather or in contact with soil)„
¾ in. for # 11 and smaller
1.5 in. for # 14 and # 18 bars
14.
1- Select representative 1ft wide design strip/strips to span in the short
direction.
2- Choose a slab thickness to satisfy deflection control requirements.
When several numbers of slab panels exist, select the largest
calculated thickness.
3- Calculate the factored load wu by magnifying service dead and live
loads according to this equation wu=1.20wD +1.60wL .
4- Draw the shear force and bending moment diagrams for each of the
strips.
15.
5- calculate maximum moment Mu.
6- Flexural reinforcement ratio is calculated from the following
equation ,
ρ m ax 0.85 β1
f c ' εu
f y εu εt
7-Compute the area of shrinkage reinforcement,
8-Draw a plan of the slab and representative cross sections
showing the dimensions and the selected reinforcement.
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