Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined...

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Design Ribbed and Flat Slabs

Transcript of Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined...

Page 1: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,

Design Ribbed and Flat Slabs

Page 2: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,

Ribbed Slabs

• Introduction:

• In long span, solid reinforced concrete slabs, e.g. greater than 5 m, the self-weight becomes excessive when compared to the applied dead and imposed loads, resulting in an uneconomic method of construction. One method of overcoming this problem is to use

ribbed slabs which are suitable for longer spans supporting light loading.

Page 3: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,

• Ribbed slabs are reinforced concrete slabs in which some of the volume of concrete

below the neutral axis (i.e. the area in tension) is removed and replaced with block formers or left as voids, as shown in Figures

Page 4: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 5: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 6: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 7: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,

• Example: Single Span Hollow-Tile Floor

• A hollow-tile floor, in which the permanent blocks are not jointed in a cement : sand mortar, is to be designed as a series of simply supported spans as indicated in Figures. Using the design data given and assuming that the blocks do not contribute to the strength of the floor, determine:

• i) the suitability of the slab thickness,

• ii) the reinforcement required.

Page 8: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 9: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,

• Design Data: • Characteristic dead load (including self-weight)

5.0 kN/m2 • Characteristic imposed load 4.0 kN/m2 • Characteristic concrete strength (fcu) 40 N/mm2 • Characteristic of reinforcement (fy) 460 N/mm2 • Exposure condition mild • Fire rating Minimum 1 hour • Span of slab 4.0 m • Nominal maximum aggregate size 14 mm

Page 10: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 11: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 12: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 13: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 14: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 15: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 16: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 17: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 18: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 19: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,

FLAT SLABS

• Definition:

• The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,

supported generally without beams by columns with or without column heads.

Page 20: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 21: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 22: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 23: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 24: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,

Traditionally, drop caps and panels around columns are used for two principal reasons:

1. Column capitals, or drop caps, are used to improve the punching shear capacity of the

column/slab joint only.

2. Drop panels are used to increase the bending moment capacity of the joint, reduce deflection, and increase the punching shear capacity.

Page 25: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 26: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,

General Code Provisions

1. The ratio of the longer to the shorter span should not exceed 2.

2. Design moments may be obtained by

(a) equivalent frame method

(b) simplified method

(c) finite element analysis

Page 27: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 28: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 29: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,

Analysis

• (a) Frame analysis method:

The structure is divided longitudinally and transversely into frames consisting of columns

and strips of slab. Either the entire frame or sub-frames can be analysed by frame analysis

programs

Page 30: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,

Division of Panels

Page 31: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,

(b)Simplified method:

• In this method, for structures where lateral stability does not depend on slab-column connections, moments and shears are taken from Table 3.12 of the code for one-way spanning continuous slabs. The total moment across the full width of the panel is calculated and the proportion resisted by the column strip and middle strip are taken from Table 3.18 of the

code.

Page 32: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 33: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,

deformation

Page 34: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,

Moment distribution

Page 35: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 36: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 37: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,

• Punching shear occurs where a two-way concrete fl at slab or plate is connected to a column without beams. It is the tendency of the slab to drop as a unit around the column

Page 38: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 39: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 40: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 41: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 42: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 43: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 44: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 45: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 46: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 47: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 48: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 49: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 50: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 51: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 52: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 53: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 54: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 55: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 56: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 57: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,
Page 58: Design Ribbed Slabs · Design Ribbed and Flat Slabs . Ribbed Slabs ... •The flat slab is defined in BS8110: Part 1, clause 1.3.2.1, as a slab with or without drops,