slab (by engg.mohammad asim nosherwani buet khuzdar)
TRANSCRIPT
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PROJECT TITLE : SLAB
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GROUP MEMBERS SAJJAD ASLAM
SABIR BALOCH
MOHAMMAD ASIM
WAHEED AHMED
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In reinforced concrete construction, slabs are used to provide flat, useful surfaces.
A reinforced concrete slab is a broad, flat plate, usually horizontal, with top and bottom surfaces parallel or nearly so.
It may be supported by reinforced concrete beams by masonry or reinforced concrete walls, by structural steel members, directly by columns, or continuously by the ground.
INTODUCTION
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A concrete slab is common structural element of modern buildings. Horizontal slabs of steel reinforced concrete, typically between 4 and 20 inches (100 and 500 millimeters) thick, are most often used to construct floors and ceilings, while thinner slabs are also used for exterior paving.
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TYPES OF SLABS SLAB
ONE WAY
TWO WAY
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1. One way slab is supported by beams in only 2 side.2. The ratio of longer span panel (L) to shorter span panel (B)
is equal or greater than 2. Thus, L/B >= 2.3. Main reinforcement is provided in only one direction for
one way slabs.4. One way slabs will behave in the same manner as a
support beam.5. Main steel is only provided parallel to span
ONE WAY SLAB
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One Way Slab Bending
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• Examples of one way slab…Shades in the roofing system(cantilever). Slab of stairs. Footings.
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Check whether the slab is one-way or two-way. Calculate h(min).
◦ Not less than 110 mm for rooms◦ Not less than 75 mm for sunshades
Calculate dead load acting on the slab◦ Calculate dead load acting on the slab
Calculate live load acting on the slab. Calculate total factored load per unit strip (KN/m)
Design procedure for One Way Slab
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Calculate the moments either directly (simply supported) or by using coefficient for continuous slabs
Calculate effective depth.d = h – (20 + (½)db)db = 10, 13, 15 generally used
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Minimum Slab Thickness: For solid nonprestressed slabs overall slab thickness h, shall
not be less than the limits in the table.
One Way Slab (Design Limits)
Support Condition Minimum h
Simply Supported l/20
One end continuous l/24
Both end continuous l/28
Cantilever l/10
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Two way slab is supported by beams in all four sides. The ratio of longer span panel (L) to shorter span panel (B) is
less than 2 Thus, L/B < 2. Main reinforcement is provided in both the directions for two
way slabs. Two way slabs will reduce bending and shifting.
TWO WAY SLAB
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3D MODEL OF TWO WAY SLAB
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TYPES OF TWO WAY SLAB
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ADVANTAGES OF TWO WAY SLAB
Flexibility in room layout
Reinforcement placement is easier
Ease of Framework installation
Building height can be reduced
Less construction time
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DISADVANTAGES OF TWO WAY SLAB Span length is medium.
Not suitable for supporting brittle (masonry) partitions
Higher slab thickness
Critical middle strip deflection
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For each applicable factored load combination, design
strength at all sections shall satisfy:1. ∅Sn≥U2. ∅Mn≥Mu3. ∅Vn≥Vu
DESIGN STRENGTH
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The Direct Design method consists of a set of rules for distributing moments to slabs and beam sections to satisfy requirements and most serviceability requirements simultaneously. These fundamental steps are involved as follows:
Determination of the total factored static moment. Determination of the total factored static moment to negative
and positive sections
Distribution of the negative and positive factored moments to the column and middle strips and to the beams, if any.
DESIGN OF TWO WAY SLAB BY DIRECT DESIGN METHOD
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LIMITATIONS There shall be a minimum of three continuous spans in
each direction.
Panels shall be rectangular, with the ratio of longer to shorter span not greater than two.
All loads shall be due to gravity only and uniformly distributed over an entire panel. The unfactored live load shall not exceed two times the unfactored dead loads.
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