Page 399 - 2018_Complete_14_Collection (1)_Neat

STRUCTURAL DESIGN

2. 60 percent for members supporting two or L = L R R 2 (Equation 16-26)
1
r
o
more floors. where: 12  L  20
3. R as determined by the following equation: r
For SI: L = L R R
r o 1 2
R = 23.1(1+ D/L ) (Equation 16-25) where: 0.58  L  0.96
o
r
2
where: L = Unreduced roof live load per square foot (m ) of
o
A = Area of floor supported by the member, square horizontal projection supported by the member
2
feet (m ). (see Table 1607.1).
2
L = Reduced roof live load per square foot (m ) of
D = Dead load per square foot (m ) of area r horizontal projection supported by the member.
2
supported.
The reduction factors R and R shall be determined as
L = Unreduced live load per square foot (m ) of 1 2
2
o follows:
area supported.
2
R = 1 for A  200 square feet (18.58 m )
R = Reduction in percent. 1 t
(Equation 16-27)
1607.12 Distribution of floor loads. Where uniform floor R = 1.2 - 0.001A for 200 square feet
live loads are involved in the design of structural members 1 t
arranged so as to create continuity, the minimum applied < A < 600 square feet (Equation 16-28)
t
loads shall be the full dead loads on all spans in combination For SI: 1.2 - 0.011A for 18.58 square meters < A <
t
t
with the floor live loads on spans selected to produce the 55.74 square meters
greatest load effect at each location under consideration. R = 0.6 for A  600 square feet (55.74 m )
2
Floor live loads are permitted to be reduced in accordance 1 t
with Section 1607.11. (Equation 16-29)
where:
1607.13 Roof loads. The structural supports of roofs and
marquees shall be designed to resist wind and, where applica- A = Tributary area (span length multiplied by effective
t
2
ble, snow and earthquake loads, in addition to the dead load width) in square feet (m ) supported by the
of construction and the appropriate live loads as prescribed in member, and
this section, or as set forth in Table 1607.1. The live loads R = 1 for F  4 (Equation 16-30)
2
acting on a sloping surface shall be assumed to act vertically R = 1.2 - 0.05 F for 4 < F < 12
on the horizontal projection of that surface. 2 (Equation 16-31)
R = 0.6 for F  12 (Equation 16-32)
1607.13.1 Distribution of roof loads. Where uniform 2
roof live loads are reduced to less than 20 psf (0.96 kN/m ) where:
2
in accordance with Section 1607.13.2.1 and are applied to F = For a sloped roof, the number of inches of rise
the design of structural members arranged so as to create per foot (for SI: F = 0.12 × slope, with slope
continuity, the reduced roof live load shall be applied to expressed as a percentage), or for an arch or
adjacent spans or to alternate spans, whichever produces dome, the rise-to-span ratio multiplied by 32.
the most unfavorable load effect. See Section 1607.13.2 1607.13.3 Occupiable roofs. Areas of roofs that are occu-
for reductions in minimum roof live loads and Section 7.5 piable, such as vegetative roofs, roof gardens or for assem-
of ASCE 7 for partial snow loading. bly or other similar purposes, and marquees are permitted
1607.13.2 General. The minimum uniformly distributed to have their uniformly distributed live loads reduced in
live loads of roofs and marquees, L , in Table 1607.1 are accordance with Section 1607.11.
o
permitted to be reduced in accordance with Section 1607.13.3.1 Vegetative and landscaped roofs. The
1607.13.2.1. weight of all landscaping materials shall be considered
1607.13.2.1 Ordinary roofs, awnings and canopies. as dead load and shall be computed on the basis of satu-
Ordinary flat, pitched and curved roofs, and awnings ration of the soil as determined in accordance with Sec-
and canopies other than of fabric construction sup- tion 3.1.4 of ASCE 7. The uniform design live load in
ported by a skeleton structure, are permitted to be unoccupied landscaped areas on roofs shall be 20 psf
2
designed for a reduced uniformly distributed roof live (0.958 kN/m ). The uniform design live load for occu-
load, L as specified in the following equations or other pied landscaped areas on roofs shall be determined in
r,
controlling combinations of loads as specified in Sec- accordance with Table 1607.1.
tion 1605, whichever produces the greater load effect. 1607.13.4 Awnings and canopies. Awnings and canopies
In structures such as greenhouses, where special shall be designed for uniform live loads as required in
scaffolding is used as a work surface for workers and Table 1607.1 as well as for snow loads and wind loads as
materials during maintenance and repair operations, a specified in Sections 1608 and 1609.
lower roof load than specified in the following equa- 1607.13.5 Photovoltaic panel systems. Roof structures
tions shall not be used unless approved by the building that provide support for photovoltaic panel systems shall
official. Such structures shall be designed for a mini- be designed in accordance with Sections 1607.13.5.1
2
mum roof live load of 12 psf (0.58 kN/m ). through 1607.13.5.4, as applicable.
372 2018 INTERNATIONAL BUILDING CODE ®
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