At the end of this week student should be able to: a)
Adapt the procedure in the EC2 to design RC Solid slabs(CO2).
b)
Adopt new parameter to design the Solid slabs(CO2).
c)
Construct the detail of Solid slabs.(CO2)
A slab is a flat two dimensional planar structural element which its overall depth (h) is relatively less than its width (b) It primarily transfer the load by bending in one or two directions. RC slabs are used in floors, roofs and walls of buildings and as the decks of bridges Design formulas for slab design is similar to the design of beam
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There are various types of slab
Selecting the most effective floor system can be vital to achieving overall economy ď‚ž In general, rectangular one way and two way Solid slabs are widely used because they are easier to construct and cheaper compared to the other types of slabs ď‚ž
Determine Design criteria
Assess Actions on Slab
Determine Material Properties
Determine Nominal Concrete Cover
Verify Shear
Design for flexural reinforcement
Analyze Slab for Med & Ved
Determine the thickness of the Slab
Verify Cracking
Produce detailed sketch/drawing
Verify Deflection
The analysis of reinforced concrete slab to determine bending moment and shear force may be done either by using elastic analysis or by considering plastic collapse methods. Hence one of the following methods can be use. Elastic analysis (Classical Method) Yield line method Moment and shear coefficient from Code of practice or handbook Numerical Method Hillerborg strip method
One-way solid slab may come in simply supported or continuous form One-way slab can be visualized in terms of the deflected shape of the loaded surface One-way slab may be supported in only two opposite edges or on the four edges The distribution of the flexural reinforcements are depends on the flexural spanning
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One-way solid slab supported in two opposite edges
One-way solid slab supported at all four edges
The main reinforcement of a two-way spanning slab is designed to carry bending moments in both directions This occurs when a slab is supported at its four sides and its Ly ratio to Lx is less or equal than 2 Two-way spanning slabs can be designed either as a simply supported slab or as a restrained slab Restrained slab are slab where the corners are prevented from lifting and provision for torsion are made. This will depends on the condition of connections between the slab and the supporting elements
Two-way spanning simply supported solid slab
The bending moments Mx and My for a rectangular slabs simply supported on all four edges with corners free to lift or the slabs do not having adequate provisions to prevent lifting of corners are obtained using Mx = x W l2x My = y W l2x Where, x and y are coefficients given in Table 1 below W- Total load /unit area lx & ly – lengths of shorter and longer span.
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Two-way spanning continuous (restrained) solid slab
EC 2 has two alternative methods for checking deflection, either a limiting span-to-depth ratio or the theoretical deflection calculation. The span-todepth ratio should ensure that deflection is limited to span/250.
ď ą To resist cracking of the concrete slabs, EC2 specify details such as minimum area of reinforcement required in a section and limits to the maximum and minimum spacing of bar. ď ą The minimum area of principal reinforcement is As,min = 0.26fctmbtd/fyk but not less than 0.0013btd, where bt is the mean width of the tension zone.
Figure below shows part of the first floor plan of a reinforced concrete office building. During construction, slabs and beams are cast together. The finishes, ceiling and services form a characteristic permanent action of 1.5 kN/m2 (excluding self-weight). The characteristic variable action is 4.0 kN/m2. The floor is inside enclosed building and subjected to 1 hour fire resistance requirements. The construction materials consist of Grade C25 concrete and Grade 500 steel reinforcement. Base on the information provided, design slab panel B-C/ 1-2. A
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