1. PRESENTATION OUTLINE
Definition Of Slab
Definition Of One-Way Slab
Deflection
Design Concept
Minimum Thickness Of One-Way Slab
Load Assigned To Slabs
Temperature And Shrinkage Reinforcement
Temperature And Shrinkage Reinforcement Ratio
Design Procedure
11/25/2013 2
2. DEFINITION OF SLAB
Layer of reinforce-concrete with uniform/variable
thickness supported by restraints
Figure:
11/25/2013 3
3. The ratio of the longer to the shorter side (L/B) of the slab
is at least equal to 2.0
Support conditions is an important impact.
Deflection is another important factor
Load is distributed to the direction perpendicular of the
supporting restraints.
4
DEFINITION OF ONE WAY SLAB
11/25/2013
9. For the purpose of analysis and design, a unit strip of a
slab is cut out at right to the supported beams.
The method here is used for rectangular beams.
Figure
10
DESIGN CONCEPT
11/25/2013
10. To control deflection, ACI Code 9.5.2.1 specifies
minimum thickness values for one-way solid slabs,
shown in Table.
10
MINIMUM THICKNESS OF SLAB
Element Simply
Supported
One-End
Continuous
Both-End
Continuous
Cantilever
One-way
Slab
L/20 L/24 L/28 L/10
L is the span length direction of bending.
If Wc ≈ 90 – 120 psf factor will be applied by ( 1.65-0.005Wc)
If Fy ≠ 60 ksi factor will be ( 0.4 + Fy/100000)
11/25/2013
14. Concrete gets shrinks and results cracking
Cracks known as Hairline cracks.
provide special reinforcement for shrinkage and
temperature contraction in the direction perpendicular to
the main reinforcement.
Maximum lateral spacing 5h or 8″
14
TEMPERATURE AND
SHRINKAGE REINFORCEMENT
11/25/2013
15. TEMPERATURE AND SHRINKAGE
Based on the Gross Concrete Area
Slabs with 40 or 50 grade reinforcement-0.002
Slabs with 60 grade reinforcement-0.0018
Slabs where reinforcement with yield stress exceeding 60 KSI
at 35% yield-(0.0018*60000)/Fy
15
REINFORCEMENT RATIO
11/25/2013
16. Step-1: From given panel find out the Tmin.
Step-2: Find out the Factored Load.(Wu = 1.2*DL + 1.6*LL)
Step-3: Find out Moments of the panel.
(M = Moment Coefficients*Wu*L²)
Step-4: Find out maximum steel ratio
(ρmax = 0.85*β1*(f´c/fy)*(εu/ εu + 0.004)
Step-5: Find dreq. ( )
Step-6: As and a. (
)
Step-7: Temperature and shrinkage reinforcement
Step-7: Reinforcement Detailing.
16
DESIGN PROCEDURE
11/25/2013
A flat, horizontal (or nearly horizontal) molded layer of plain of reinforced concrete, usually of uniform but sometimes of variable thickness, positioned either on the ground or supported by beams, columns, walls, or other framework.
More specifically when slabs are supported on the two opposite sides beams only in which cases the structural action of the slab is one-way. Total load is carried in the direction perpendicular to supporting beams.
And intermediate beam are provided on the slab, If then the ratio of the length and width of slab panel is at least equal to 2 the slab panel is then acting as an one-way slab.
The structural action of a one-way slab may be visualized in terms of the deformed shape of the loaded surface. Figure 2 shows a rectangular slab, simply supported along its two opposite long edges and free of any support along the two opposite short edges. If a uniformly distributed load is applied to the surface, the deflected shape will be as shown by the solid lines. Curvatures, and consequently bending moments, are the same in all strips s spanning in the short direction between supported edges, whereas there is no curvature, hence no bending moment, in the long strips I parallel to the supported edges. The surface approximately cylindrical
The structural action of a one-way slab may be visualized in terms of the deformed shape of the loaded surface. Figure 2 shows a rectangular slab, simply supported along its two opposite long edges and free of any support along the two opposite short edges. If a uniformly distributed load is applied to the surface, the deflected shape will be as shown by the solid lines. Curvatures, and consequently bending moments, are the same in all strips s spanning in the short direction between supported edges, whereas there is no curvature, hence no bending moment, in the long strips I parallel to the supported edges. The surface approximately cylindrical
Since concrete is weak in tension, these temperature and shrinkage stresses are likely to result in cracking. Cracks of this nature are not detrimental, provided their size is limited to what are known as Hairline cracks. it is necessary to provide special reinforcement for shrinkage and temperature contraction in the direction perpendicular to the main reinforcement. This added steel is known as temperature or shrinkage reinforcement, or distribution steel .
Minimum Lateral Spacing is 5h or 8.
