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Unformatted text preview: 53 2.1 GENERAL Buildings and other structures shall be designed using
the provisions of either Section 2.3 or 2.4. Where
elements of a structure are designed by a particular
material standard or speciﬁcation, they shall be
designed exclusively by either Section 2.3 or 2.4. 2.2 SYMBOLS ‘g A, a load or load effect arising from extra ordinary
event A
D = dead load
D, = weight of ice
E = earthquake load
F = load due to ﬂuids with well—deﬁned pressures
and maximum heights
F,1 = flood load
H = load due to lateral earth pressure, ground water
pressure, or pressure of bulk materials
. L = live load
L, = roof live load
R = rain load
S = snow load
T = selfstraining load
W = wind load
W, = windon—ice determined in accordance with
Chapter 10 2.3 COMBINING FACTORED LOADS USING
STRENGTH DESIGN 2.3.1 Applicability
The load combinations and load factors given in Section 2.3.2 shall be used only in those cases in _
which they are speciﬁcally authorized by the appli—
cable material design standard. 2.3.2 Basic Combinations
Structures, components, and foundations shall be designed so that their design strength equals or
exceeds the effects of the factored loads in the following combinations: 1. 1.41) 2. 1.20 + 1.6L + 0.5(L, or S or R) 3. 1.20 +1.6(L, or S or R) + (L or 05W)
:: 4. 1.2.0 «1 LOW + L" + 0.505., or S or R) Chapter 2
COMBENATIQNS QF LOADS 6. 0.9D + LOW
7. 0.919 + 1.0E 5. 1.2Dt— 1.0E+L+0.2S E EXCEPTIONS: l. The load factor on L in combinations 3, 4, and 5 is
permitted to equal 0.5 for all occupancies in which
L0 in Table 41 is less than or equal to 100 psf,
with the exception of garages or areas occupied as
places of public assembly. 2. In combinations 2, 4, and 5, the companion load S
shall be taken as either the ﬂat roof snow load (pf) or the sloped roof snow load (pg). Where ﬂuid loads F are present, they shall be
included with the same load factor as dead load D in
combinations 1 through 5 and 7. ' Where load H are present, they shall be included as follows: 1. where the effect of H adds to the primary variable
load effect, include H with a load factor of 1.6; 2. where the effect of H resists the primary variable
load effect, include H with a load factor of 0.9
where the load is permanent or a load factor of 0
for all other conditions. Effects of one or more loads not acting shall be
investigated. The most unfavorable effects from both
wind and earthquake loads shall be investigated,
where appropriate, but they need not be considered to
act simultaneously. Refer to Section 12.4 for speciﬁc
deﬁnition of the earthquake load effect E.1 Each relevant strength limit state shall be investigated. 2.3.3 Load Combinations Including Flood Load
When a structure is located in a ﬂood zone (Section 5.3.1), the following load combinations shall be considered in addition to the basic combinations in Section 2.3.2: 1. In V—Zones or Coastal AZones, 1.0W in combina«
tions 4 and 6 shall be replaced by LOW + 2.015}. 2. In noncoastal A—Zones, LOW in combinations 4
and 6 shall be replaced by 0.5W + 1.0Fa. 'The same E from Sections 1.4 and 12.4 is used for both Sections
2.3.2 and 2.4.1. Refer to the Chapter ll Commentary for the Seismic Provisions. CHAPTER 2 COMBINATIONS OF LOADS 2.3.4. Load Combinations Including Atmospheric
Ice Loads . When a structure is subjected to atmospheric ice
and windon—ice loads, the following load combina.
tions shall be considered: 1. 0.5(L, or S or R) in combination 2 shall be replaced
by 0.2D, 4 0.5.9. 2. LOW + 0.505, or S or R) in combination 4 shall be
replaced by D, + W; + 0.58. 3. LOW in combination 6 shall be replaced by
D; “l" m. ;: 2.3.5 Load Combinations Including
SelfStraining Loads Where applicable, the structural effects of load T shall be considered in combination with other loads.
The load factor on load T shall be established consid—
ering the uncertainty associated with the likely
magnitude of the load, the probability that the _, maximum effect of T will occur simultaneously with
other applied loadings, and the potential adverse '; consequences if the effect of T is greater than
assumed. The load factor on T shall not have a value
3: less than 1.0. :: 2.3.6 Load Combinations for Nonspecified Loads Where approved by‘ the Authority Having Jurisdiction, the Responsible Design Professional is j permitted to determine the combined load effect for i strength design using a method that is consistent with
the method on which the load combination require— ; ments in Section 2.3.2 are based. Such a method must
be probabilitybased and must be accompanied by
documentation regarding the analysis and collection
of suppmting data that is acceptable to the Authority 3 Having Jurisdiction. 2.4 COMBINING NOMINAL LOADS USING
ALLOWABLE STRESS DESIGN 2.4.1 Basic Combinations Loads listed herein shall be considered to act in
the following combinations; whichever produces the
most unfavorable effect in the building, foundation, or
structural member being considered. Effects of one or
more loads not acting shall be considered. 1. D
2. 0+1.
3. D+(L,orSorR) 4. D + 0.751. + 0.7502, or S or R) 5. D + (0.6W or 0.7E)
6a. D + 0.75L + 0.75(0.6W) + 0.75(L, or S or R)
6b. D + 0.75L + O.75(0.7E) + 0.755 7. 0.6D + 0.6W
8. 0.60 + 0.713
EXCEPTIONS: 1. In combinations 4 and 6, the companion load S
shall be taken as either the ﬂat roof snow load (pf)
or the sloped roof snowload (19,). 2. For nonbuilding structures, in which the wind load
is determined from force coefﬁcients, Cf, identiﬁed
in Figures 29.51, 29.52 and 2953 and the
projected area contributing wind force to a founda
tion element exceeds 1,000 square feet on either a
vertical or a horizontal plane, it shall be permitted
to replace W with 0.9W in combination 7 for
design of the foundation, excluding anchorage of
the structure to the foundation. 3. It shall be permitted to replace 0.61) with 0.9D in
combination 8 for the design of Special Reinforced
Masonry Shear Walls, where the walls satisfy the
requirement of Section 14.4.2. Where ﬂuid loads F are present, they shall be
included in combinations 1 through 6 and 8 with the
same factor as that used for dead load D. Where load H is present, it shall be included as
follows: 1. where the effect of H adds to the primary variable
load effect, include H with a load factor of 1.0; 2. where the effect of H resists the primary variable
load effect, include H with a load factor of 0.6
where the load is permanent or a load factor of 0
for all other conditions. The most unfavorable effects from both wind
and earthquake loads shall be considered; where
appropriate, but they need not be assumed to act
simultaneously. Refer to Section 1.4 and 12.4
for the speciﬁc deﬁnition of the earthquake load
effect E? Increases in allowable stress shall not be used
with the loads or load combinations given in this
standard unless it can be demonstrated that such an
increase is justiﬁed by structural behavior caused by
rate or duration of load. 2The same E from Sections 1.4 and l2.4 is used for both Sections
2.3.2 and 2.4.1. Refer to the Chapter ll Commentary for the Seismic
Provisions. 2 Load Combinations Including Flood Load
When a structure is located in a ﬂood zone, e, following load combinations shall be onsidercd in addition to the basic combinations in ection 2.4.1: _ In V—Zoncs or Coastal AZones (Section 5.3.1),
1,5Fa shall be added to other loads in combinations ' 5 6, and 7, and E shall be set equal to zero in 5 s __ and 6.
. In noncoastal A—Zones, 0.75Fa shall be added to ' combinations 5, 6, and 7, and E shall be set equal
I to zero in 5 and 6. ' .4.3 Load Combinations Including Atmospheric
ce Loads When a structure is subjected to atmospheric ice
and windon—ice loads, the following load combina ' tions shall be considered: "1. 0.7Di shall be added to combination 2. '12. (L, or S or R) in combination 3 shall be replaced '2' by 0.7D; + 0.7% + S. "3. 0.6W in combination 7 shall be replaced by 0.7D; +
0.7Wi. 2.4.4 Load Combinations Including
ShelfStraining Loads Where applicable, the structural effects of load T
Shall be considered in combination with other loads.
Where the maximum effect of load '1‘ is unlikely to
occur simultaneously with the maximum effects of
other variable loads, it shall be permitted to‘reduce
the magnitude of T considered in combination with
;_ these other loads. The fraction of T considered in :: combination with other loads shall not be less than
0.75. MINIMUM DESIGN LOADS 2.5 LOAD COMBINATIONS FOR
EXTRAORDINARY EVENTS 2.5.1 Applicability Where required by the owner or applicable code,
strength and stability shall be checked to ensure that
structures are capable of withstanding the effects of
extraordinary (i.e., low—probability) events, such as
ﬁres, explosions, and vehicular impact without
disproportionate collapse. 2.5.2 Load Combinations 2.5.2.1 Capacity
For checking the capacity of a structure or structural element to withstand the effect of an extraordinary
event, the following gravity load combination shall be considered: (09 or 1.2)1) + A. + 0.5L + 0.23 (2.51) in which Ak = the load or load effect resulting from
extraordinary event A. 2.5.2.2 Residual Capacity For checking the residual loadcarrying capacity
of a structure or structural element following the
occurrence of a damaging event, selected loadbearing
elements identified by the Responsible Design
Professional shall be notionally removed, and the
capacity of the damaged structure shall be evaluated
using the following gravity load combination: (0.9 or 1.2)D + 0.5L + 0.2(L, or S or R) (2.52) i 2.5.3 Stability Requirements
Stability shall be provided for the structure as a whole and for each of its elements. Any method that
considers the inﬂuence of secondorder effects is permitted. ...
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