Slab Design
System Loading
Tributary Areas
Many floor systems consist of a reinforced concrete slab supported on a rectangular grid of beams. Such a grid of beams reduces the span of the slab and thus permits the designer to reduce the slab thickness. The distribution of floor loads on floor beams is based on the geometric configuration of the beams forming the grid.
1
3
Tributary area of columns A1,
B2 and C1 shown shaded
2
Girders on all four sides
Theoretical Tributary Areas
3
Theoretical Tributary
Beam Areas
4
Theoretical Tributary
Beam Areas
5
Typical Floor Framing System
Floor Beam
Girder
Simplified Floor Beam and
Girder Loadings
6
Example Load
Distribution Problem
The floor system of a library consists of a 6-in thick reinforced concrete slab resting on four floor steel beams, which in turn are supported by two steel girders. Cross-sectional areas of the floor beams and girders are 14.7 in2 and 52.3 in2, respectively as shown on the next page figure.
Determine the floor loads on the floor beams, girders, and
7
columns.
Floor Slab – Floor Beam –
Girder – Column Schematic
8
Building Live Load
Reduction
Recognizing that the probability of supporting a large, fully loaded tributary area is small; building codes permit reductions in the standard (L0) design live loads when the influence area (AI =
KLLAT) is larger than 400 ft2
(37.2 m2) as given in the following formulas:
9
⎛
⎞
15
L = L0 ⎜ 0.25+
⎜
KLL AT ⎠
⎝
US Units
⎛
4.57 ⎞
L = L0 ⎜ 0.25+
⎜
KLL AT ⎠
⎝
SI Units
L ≡ reduced live load
0.50 L0 ≤ L ≤ L0 for single floor members
0.40 L0 ≤ L ≤ L0 for multi-floor members
AT ≡ tributary area ft2 (m2)
10
KLL- element live load factors
(IBC2000 – Table 1607.9.1)
Type of Element
Interior column
Exterior column without cantilever slabs
Edge columns with cantilever slabs Corner columns with cantilever slabs
Edge beams without
Tributary Areas
Many floor systems consist of a reinforced concrete slab supported on a rectangular grid of beams. Such a grid of beams reduces the span of the slab and thus permits the designer to reduce the slab thickness. The distribution of floor loads on floor beams is based on the geometric configuration of the beams forming the grid.
1
3
Tributary area of columns A1,
B2 and C1 shown shaded
2
Girders on all four sides
Theoretical Tributary Areas
3
Theoretical Tributary
Beam Areas
4
Theoretical Tributary
Beam Areas
5
Typical Floor Framing System
Floor Beam
Girder
Simplified Floor Beam and
Girder Loadings
6
Example Load
Distribution Problem
The floor system of a library consists of a 6-in thick reinforced concrete slab resting on four floor steel beams, which in turn are supported by two steel girders. Cross-sectional areas of the floor beams and girders are 14.7 in2 and 52.3 in2, respectively as shown on the next page figure.
Determine the floor loads on the floor beams, girders, and
7
columns.
Floor Slab – Floor Beam –
Girder – Column Schematic
8
Building Live Load
Reduction
Recognizing that the probability of supporting a large, fully loaded tributary area is small; building codes permit reductions in the standard (L0) design live loads when the influence area (AI =
KLLAT) is larger than 400 ft2
(37.2 m2) as given in the following formulas:
9
⎛
⎞
15
L = L0 ⎜ 0.25+
⎜
KLL AT ⎠
⎝
US Units
⎛
4.57 ⎞
L = L0 ⎜ 0.25+
⎜
KLL AT ⎠
⎝
SI Units
L ≡ reduced live load
0.50 L0 ≤ L ≤ L0 for single floor members
0.40 L0 ≤ L ≤ L0 for multi-floor members
AT ≡ tributary area ft2 (m2)
10
KLL- element live load factors
(IBC2000 – Table 1607.9.1)
Type of Element
Interior column
Exterior column without cantilever slabs
Edge columns with cantilever slabs Corner columns with cantilever slabs
Edge beams without