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Chapter 2
LOADS ON BUILDINGS AND STRUCTURES
2.1 INTRODUCTION
2.1.1 SCOPE
This chapter specifies the minimum design forces including dead load, live load, wind and earthquake loads,
miscellaneous loads and their various combinations. These loads shall be applicable for the design of buildings
and structures in conformance with the general design requirements provided in Chapter 1.
2.1.2 LIMITATIONS
Provisions of this chapter shall generally be applied to majority of buildings and other structures covered in this
code subject to normally expected loading conditions. For those buildings and structures having unusual
geometrical shapes, response characteristics or site locations, or for those subject to special loading including
tornadoes, special dynamic or hydrodynamic loads etc., site‐specific or case‐specific data or analysis may be
required to determine the design loads on them. In such cases, and all other cases for which loads are not
specified in this chapter, loading information may be obtained from reliable references or specialist advice may
be sought. However, such loads shall be applied in compliance with the provisions of other parts or sections of
this Code.
2.2 DEAD LOADS
2.2.1 GENERAL
The minimum design dead load for buildings and portions thereof shall be determined in accordance with the
provisions of this section. In addition, design of the overall structure and its primary load‐resisting systems shall
conform to the general design provisions given in Chapter 1.
2.2.2 DEFINITION
Dead Load is the vertical load due to the weight of permanent structural and non‐structural components and
attachments of a building such as walls, floors, ceilings, permanent partitions and fixed service equipment etc.
2.2.3 ASSESSMENT OF DEAD LOAD
Dead load for a structural member shall be assessed based on the forces due to :
- weight of the member itself,
- weight of all materials of construction incorporated into the building to be supported permanently by
the member,
- weight of permanent partitions,
- weight of fixed service equipment, and
- net effect of prestressing.
Part 6
2.2.4 WEIGHT OF MATERIALS AND CONSTRUCTIONS
In estimating dead loads, the actual weights of materials and constructions shall be used, provided that in the
absence of definite information, the weights given in Tables 2.2.1 and 2.2.2 shall be assumed for the purposes
of design.
Table 2.2.1 : Unit Weight of Basic Materials
Material
Unit weight
(kN/m
3
) Material
Unit
Weight
(kN/m
3
)
Aluminium
Asphalt
Brass
Bronze
Brick
Cement
Coal, loose
Concrete ‐ stone aggregate (unreinforced)
‐ brick aggregate (unreinforced)
Copper
Cork, normal
Cork, compressed
Glass, window (soda‐lime)
22.8*
20.4*
Granite, Basalt
Iron ‐ cast
‐ wrought
Lead
Limestone
Marble
Sand, dry
Sandstone
Slate
Steel
Stainless Steel
Timber
Zinc
5.9‐11.
- for reinforced concrete, add 0.63 kN/m
3 for each 1% by volume of main reinforcement
2.2.5 WEIGHT OF PERMANENT PARTITIONS
When partition walls are indicated on the plans, their weight shall be considered as dead load acting as
concentrated line loads in their actual positions on the floor. The loads due to anticipated partition walls, which
are not indicated on the plans, shall be treated as live loads and determined in accordance with Sec 2.3.2.4.
2.2.6 WEIGHT OF FIXED SERVICE EQUIPMENT
Weights of fixed service equipment and other permanent machinery, such as electrical feeders and other
machinery, heating, ventilating and air‐conditioning systems, lifts and escalators, plumbing stacks and risers etc.
shall be included as dead load whenever such equipment are supported by structural members.
2.2.7 ADDITIONAL LOADS
In evaluating the final dead loads on a structural member for design purposes, allowances shall be made for
additional loads resulting from the (i) difference between the prescribed and the actual weights of the
members and construction materials; (ii) inclusion of future installations; (iii) changes in occupancy or use of
buildings; and (iv) inclusion of structural and non‐structural members not covered in Sec 2.2.2 and 2.2.3.
2.3 LIVE LOADS
2.3.1 GENERAL
The live loads used for the structural design of floors, roof and the supporting members shall be the greatest
applied loads arising from the intended use or occupancy of the building, or from the stacking of materials and
the use of equipment and propping during construction, but shall not be less than the minimum design live
loads set out by the provisions of this section. For the design of structural members for forces including live
loads, requirements of the relevant sections of Chapter 1 shall also be fulfilled.
Part 6
Table 2.3.1 Minimum Uniformly Distributed Live Loads, And Minimum Concentrated Live Loads
Occupancy or Use Uniform
kN/m
2
Conc.
kN
Apartments (see Residential )
Access floor systems
Office use
Computer use
Armories and drill rooms 7.
Assembly areas and theaters
Fixed seats (fastened to floor)
Lobbies
Movable seats
Platforms (assembly)
Stage floors
Balconies (exterior)
On one‐ and two‐family residences only, and not exceeding 19.3 m
2
Bowling alleys, poolrooms, and similar recreational areas 3.
Catwalks for maintenance access 1.92 1.
Corridors
First floor
Other floors, same as occupancy served except as indicated
Dance halls and ballrooms 4.
Decks (patio and roof)
Same as area served, or for the type of occupancy accommodated
Dining rooms and restaurants 4.
Dwellings (see Residential )
Elevator machine room grating (on area of 2,580 mm
2 )
Finish light floor plate construction (on area of 645 mm
2 )
Fire escapes
On single‐family dwellings only
Fixed ladders See Section 2.3.
Garages (passenger vehicles only) Trucks and buses
a , b
Grandstands (see Stadiums and arenas, Bleachers )
Gymnasiums—main floors and balconies 4.
Handrails, guardrails, and grab bars See Section 2.3.
Hospitals
Operating rooms, laboratories
Patient rooms
Corridors above first floor
Hotels (see Residential )
Libraries
Reading rooms
Stack rooms
Corridors above first floor
c
Manufacturing
Light
Heavy
Marquees 3.
Office Buildings
File and computer rooms shall be designed for heavier loads based on anticipated
occupancy
Lobbies and first‐floor corridors
Offices
Corridors above first floor
Chapter 2
Table 2.3.1 Minimum Uniformly Distributed Live Loads, And Minimum Concentrated Live Loads (Contd.)
Penal Institutions
Cell blocks
Corridors
Residential
Dwellings (one‐ and two‐family)
Uninhabitable attics without storage
Uninhabitable attics with storage
Habitable attics and sleeping areas
All other areas except stairs and balconies
Hotels and multifamily houses
Private rooms and corridors serving them
Public rooms and corridors serving them
Reviewing stands, grandstands, and bleachers
d
Roofs
Ordinary flat, pitched, and curved roofs
Roofs used for promenade purposes
Roofs used for roof gardens or assembly purposes
Roofs used for other special purposes
Awnings and canopies
Fabric construction supported by a lightweight rigid skeleton structure
All other construction
Primary roof members, exposed to a work floor
Single panel point of lower chord of roof trusses or any point along primary
structural members supporting roofs over manufacturing, storage
warehouses,and repair garages
All other occupancies
All roof surfaces subject to maintenance workers
h
i
0.24(nonreduceable)
i
Schools
Classrooms
Corridors above first floor
First‐floor corridors
Scuttles, skylight ribs, and accessible ceilings 0.
Sidewalks, vehicular driveways, and yards subject to trucking
e
f
Stadiums and arenas
Bleachers
Fixed seats (fastened to floor)
d
d
Stairs and exit ways
One‐ and two‐family residences only
g
Storage areas above ceilings 0.
Storage warehouses (shall be designed for heavier loads if required for
anticipated storage)
Light
Heavy
Stores
Retail
First floor
Upper loors
Wholesale, all floors
Vehicle barriers See Section 2.3.
Walkways and elevated platforms (other than exit ways) 2.
Yards and terraces, pedestrian 4.
a Floors in garages or portions of a building used for the storage of motor vehicles shall be designed for the uniformly
distributed live loads of Table 2.3.1 or the following concentrated load: (1) for garages restricted to passenger vehicles
accommodating not more than nine passengers, 13.35 kN acting on an area of 114 mm by 114 mm footprint of a jack;
and (2) for mechanical parking structures without slab or deck that are used for storing passenger car only, 10 kN per
wheel.
Chapter 2
2.3.7 MORE THAN ONE OCCUPANCY
Where an area of a floor is intended for two or more occupancies at different times, the value to be used from
Table 2.3.1 shall be the greatest value for any of the occupancies concerned.
2.3.8 MINIMUM ROOF LIVE LOADS
Roof live loads shall be assumed to act vertically over the area projected by the roof or any portion of it upon a
horizontal plane, and shall be determined as specified in the following sections :
2.3.8.1 REGULAR PURPOSE FLAT, PITCHED AND CURVED ROOFS
Live loads on regular purpose roofs shall be the greatest applied loads produced during use by movable objects
such as planters and people, and those induced during maintenance by workers, equipment and materials but
shall not be less than those given in Table 2.3.2.
2.3.8.2 SPECIAL PURPOSE ROOFS
For special purpose roofs, live loads shall be estimated based on the actual weight depending on the type of
use, but shall not be less than the following values :
a) roofs used for promenade purposes ‐ 3.0 kN/m
2
b) roofs used for assembly purposes ‐ 5.0 kN/m
2
c) roofs used for gardens ‐ 5.0 kN/m
2
d) roofs used for other special purposes‐ to be determined as per Sec 2.3.
2.3.8.3 ACCESSIBLE ROOF SUPPORTING MEMBERS
Roof trusses or any other primary roof supporting member beneath which a full ceiling is not provided, shall be
capable of supporting safely, in addition to other roof loads, a concentrated load at the locations as specified
below :
a) Industrial, Storage and Garage Buildings ‐ Any single panel point of the
lower chord of a roof truss, or any point of other primary roof supporting
member
9.0 kN
b) Building with Other Occupancies ‐ Any single panel point of the lower chord
of a roof truss, or any point of other primary roof supporting member
1.3 kN
2.3.9 LOADS NOT SPECIFIED
Live loads, not specified for uses or occupancies in Sec 2.3.3, 2.3.4 and 2.3.5, shall be determined from loads
resulting from :
a) weight of the probable assembly of persons;
b) weight of the probable accumulation of equipment and furniture, and
c) weight of the probable storage of materials.
2.3.10 PARTIAL LOADING AND OTHER LOADING ARRANGEMENTS
The full intensity of the appropriately reduced live load applied only to a portion of the length or area of a
structure or member shall be considered, if it produces a more unfavourable effect than the same intensity
applied over the full length or area of the structure or member.
Where uniformly distributed live loads are used in the design of continuous members and their supports,
consideration shall be given to full dead load on all spans in combination with full live loads on adjacent spans
and on alternate spans whichever produces a more unfavourable effect.
Part 6
Table 2.3.2 : Minimum Roof Live Loads(
1 )
Type and Slope of Roof Distributed
Load, kN/m
2
Concentrated
Load, kN
I Flat roof (slope = 0) 1.5 1.
II 1. Pitched or sloped roof (0 < slope < 1/3)
2 Arched roof or dome (rise < 1/8 span)
1.0 0.
III 1. Pitched or sloped roof (1/3 ≤ slope < 1.0)
- Arched roof or dome (1/8 ≤ rise < 3/8 span)
0.8 0.
IV 1. Pitched or sloped roof (slope ≥ 1.0)
- Arched roof or dome (rise ≥ 3/8 span)
0.6 0.
V Greenhouse, and agriculture buildings 0.5 0.
VI Canopies and awnings, except those with
cloth covers
same as given in I through IV
above based on the type and
slope.
Note : (1) Greater of this load and rain load as specified in Sec 2.6.3 shall be taken as the design live load
for roof. The distributed load shall be applied over the area of the roof projected upon a horizontal plane
and shall not be applied simultaneously with the concentrated load. The concentrated load shall be
assumed to act upon a 300 mm x 300 mm area and need not be considered for roofs capable of laterally
distributing the load, e.g. reinforced concrete slabs.
2.3.11 OTHER LIVE LOADS
Live loads on miscellaneous structures and components, such as handrails and supporting members, parapets
and balustrades, ceilings, skylights and supports, and the like, shall be determined from the analysis of the
actual loads on them, but shall not be less than those given in Table 2.3.3.
2.3.12 IMPACT AND DYNAMIC LOADS
The live loads specified in Sec 2.3.3 shall be assumed to include allowances for impacts arising from normal
uses only. However, forces imposed by unusual vibrations and impacts resulting from the operation of installed
machinery and equipment shall be determined separately and treated as additional live loads. Live loads due to
vibration or impact shall be determined by dynamic analysis of the supporting member or structure including
foundations, or from the recommended values supplied by the manufacture of the particular equipment or
machinery. In absence of a definite information, values listed in Table 2.3.4 for some common equipment, shall
be used for design purposes.
2.3.13 REDUCTION OF LIVE LOADS
Except for roof uniform live loads, all other minimum uniformly distributed live loads, Lo in Table 2.3.1, may be
reduced according to the following provisions.
2.3.13.1 GENERAL
Subject to the limitations of Sections 2.3.13.2 through 2.3.13.5, members for which a value of K LL
A
T is 37.16 m
or more are permitted to be designed for a reduced live load in accordance with the following formula:
ସ.ହ
ඥ ಽಽ
where, L = reduced design live load per m
2
of area supported by the member; L 0
= unreduced design live load
per m
2
of area supported by the member (see Table 2.3.1); K LL = live load element factor (see Table 2.3.5); A T
tributary area in m
2
. L shall not be less than 0.50 L 0 for members supporting one floor and L shall not be less than
0.40 L
0
for members supporting two or more floors.
Part 6
2.3.13.2 HEAVY LIVE LOADS.
Live loads that exceed 4.79 kN/m
2
shall not be reduced.
EXCEPTION: Live loads for members supporting two or more floors may be reduced by 20 percent.
2.3.13.3 PASSENGER CAR GARAGES.
The live loads shall not be reduced in passenger car garages.
EXCEPTION: Live loads for members supporting two or more floors may be reduced by 20 percent.
2.3.13.4 SPECIAL OCCUPANCIES.
2
or less shall not be reduced in public assembly occupancies.
- There shall be no reduction of live loads for cyclone shelters.
2.3.13.5 LIMITATIONS ON ONE WAY SLABS.
The tributary area, A T , for one‐way slabs shall not exceed an area defined by the slab span times a width normal
to the span of 1.5 times the slab span.
2.3.14 REDUCTION IN ROOF LIVE LOADS
The minimum uniformly distributed roof live loads, L o
in Table 2.3.1, are permitted to be reduced according to
the following provisions.
2.3.14.1 FLAT, PITCHED, AND CURVED ROOFS.
Ordinary flat, pitched, and curved roofs are permitted to be designed for a reduced roof live load, as specified
in Eq.2.3.2 or other controlling combinations of loads, as discussed later in this chapter, whichever produces
the greater load. In structures such as greenhouses, where special scaffolding is used as a work surface for
workmen and materials during maintenance and repair operations, a lower roof load than specified in Eq. 2.3.
shall not be used unless approved by the authority having jurisdiction. On such structures, the minimum roof
live load shall be 0.58 kN/m
2
L
r
= L
o
R
1
R
2 where 0_._ 58 ≤ L r
where
L
r = reduced roof live load per m
2
of horizontal projection in kN/m
2
The reduction factors R 1 and R 2 shall be determined as follows:
R
1 = 1 for A t ≤ 18_._ 58m
2
= 1. 2 − 0. 011 A
t for 18_._ 58m
2
< A
t < 55_._ 74m
2
= 0_._ 6 for A t ≥ 55_._ 74m
2
where A t = tributary area in m
2
supported by any structural member and
R
2 = 1 for F ≤ 4
= 1_._ 2 − 0_._ 05 F for 4 < F < 12
= 0_._ 6 for F ≥ 12
Chapter 2
where, for a pitched roof, F = 0.12 × slope, with slope expressed in percentage points and, for an arch or dome,
F =rise‐to‐span ratio multiplied by 32.
2.3.14.2 SPECIAL PURPOSE ROOFS.
Roofs that have an occupancy function, such as roof gardens, assembly purposes, or other special purposes are
permitted to have their uniformly distributed live load reduced in accordance with the requirements of Section
Table 2.3.5 Live Load Element Factor, K LL
Element
K
LL
Interior columns
Exterior columns without cantilever slabs
4
4
Edge columns with cantilever slabs 3
Corner columns with cantilever slabs
Edge beams without cantilever slabs
Interior beams
2
2
2
All other members not identified including:
Edge beams with cantilever slabs
Cantilever beams
One‐way slabs
Two‐way slabs
Members without provisions for continuous
shear transfer normal to their span
1
a In lieu of the preceding values, K LL is permitted to be calculated.
2.4 WIND LOADS
2.4.1 GENERAL
Scope: Buildings and other structures, including the Main Wind‐Force Resisting System (MWFRS) and all
components and cladding thereof, shall be designed and constructed to resist wind loads as specified herein.
Allowed Procedures: The design wind loads for buildings and other structures, including the MWFRS and
component and cladding elements thereof, shall be determined using one of the following procedures:
(1) Method 1—Simplified Procedure as specified in Section 2.4.4 for buildings and structures meeting the
requirements specified therein;
(2) Method 2—Analytical Procedure as specified in Section 2.4.5 for buildings and structures meeting the
requirements specified therein;
(3) Method 3—Wind Tunnel Procedure as specified in Section 2.4.18.
Wind Pressures: Acting on opposite faces of each building surface. In the calculation of design wind loads for
the MWFRS and for components and cladding for buildings, the algebraic sum of the pressures acting on
opposite faces of each building surface shall be taken into account.
2.4.1.1 MINIMUM DESIGN WIND LOADING
The design wind load, determined by any one of the procedures specified in Section 2.4.1, shall be not less than
specified in this section.
Main Wind‐Force Resisting System: The wind load to be used in the design of the MWFRS for an enclosed or
partially enclosed building or other structure shall not be less than 0.5 kN/m
2
multiplied by the area of the
Chapter 2
BUILDING OR OTHER STRUCTURE, REGULAR SHAPED: A building or other structure having no unusual
geometrical irregularity in spatial form.
BUILDING OR OTHER STRUCTURES, RIGID: A building or other structure whose fundamental frequency is
greater than or equal to 1 Hz.
BUILDING, SIMPLE DIAPHRAGM: A building in which both windward and leeward wind loads are transmitted
through floor and roof diaphragms to the same vertical MWFRS (e.g., no structural separations).
COMPONENTS AND CLADDING: Elements of the building envelope that do not qualify as part of the MWFRS.
DESIGN FORCE, F : Equivalent static force to be used in the determination of wind loads for open buildings and
other structures.
DESIGNPRESSURE, p : Equivalent static pressure to be used in the determination of wind loads for buildings.
EAVE HEIGHT, h : The distance from the ground surface adjacent to the building to the roof eave line at a
particular wall. If the height of the eave varies along the wall, the average height shall be used.
EFFECTIVE WIND AREA, A : The area used to determine GC p
. For component and cladding elements, the
effective wind area in Figs. 2.4.11 through 2.4.17 and 2.4.19 is the span length multiplied by an effective width
that need not be less than one‐third the span length. For cladding fasteners, the effective wind area shall not be
greater than the area that is tributary to an individual fastener.
ESCARPMENT: Also known as scarp, with respect to topographic effects in Section 2.4.9, a cliff or steep slope
generally separating two levels or gently sloping areas (see Fig. 2.4.4).
FREE ROOF: Roof (monoslope, pitched, or troughed) in an open building with no enclosing walls underneath the
roof surface.
GLAZING: Glass or transparent or translucent plastic sheet used in windows, doors, skylights, or curtain walls.
GLAZING, IMPACT RESISTANT: Glazing that has been shown by testing in accordance with ASTM E1886 and
ASTM E1996 or other approved test methods to withstand the impact of wind‐borne missiles likely to be
generated in wind‐borne debris regions during design winds.
HILL: With respect to topographic effects in Section 2.4.9, a land surface characterized by strong relief in any
horizontal direction (see Fig. 2.4.4).
HURRICANE PRONE REGIONS: Areas vulnerable to hurricanes; in Bangladesh these areas include the
Sundarbans, southern parts of Barisal and Patuakhali, Hatia, Bhola, eastern parts of Chittagong and Cox’s Bazar
IMPACT RESISTANT COVERING: A covering designed to protect glazing, which has been shown by testing in
accordance with ASTM E1886 and ASTM E1996 or other approved test methods to withstand the impact of
wind‐borne debris missiles likely to be generated in wind‐borne debris regions during design winds.
IMPORTANCE FACTOR, I : A factor that accounts for the degree of hazard to human life and damage to property.
MAIN WIND‐FORCE RESISTING SYSTEM (MWFRS): An assemblage of structural elements assigned to provide
support and stability for the overall structure. The system generally receives wind loading from more than one
surface.
MEAN ROOF HEIGHT, h : The average of the roof eave height and the height to the highest point on the roof
surface, except that, for roof angles of less than or equal to 10
o
, the mean roof height shall be the roof heave
height.
OPENINGS: Apertures or holes in the building envelope that allow air to flow through the building envelope and
that are designed as “open” during design winds as defined by these provisions.
RECOGNIZED LITERATURE: Published research findings and technical papers that are approved.
Part 6
RIDGE: With respect to topographic effects in Section 2.4.9, an elongated crest of a hill characterized by strong
relief in two directions (see Fig. 2.4.4).
WIND‐BORNE DEBRIS REGIONS: Areas within hurricane prone regions located:
- Within 1.6 km of the coastal mean high water line where the basic wind speed is equal to or greater than 180
km/h or
- In areas where the basic wind speed is equal to or greater than 200 km/h.
2.4.3 SYMBOLS AND NOTATION
The following symbols and notation apply only to the provisions of Section 2.4:
A = effective wind area, in m
2
A
f = area of open buildings and other structures either normal to the wind direction or projected on a plane
normal to the wind direction, in m
2
.
A
g
= the gross area of that wall in which A o
is identified, in m
2
.
A
g i
= the sum of the gross surface areas of the building envelope (walls and roof) not including A g
, in m
2
A
o
= total area of openings in a wall that receives positive external pressure, in m
2
.
A
oi
= the sum of the areas of openings in the building envelope (walls and roof) not including A o
, in m
2
A
og
= total area of openings in the building envelope in m
2
A
s
= gross area of the solid freestanding wall or solid sign, in m
2
a = width of pressure coefficient zone, in m.
B = horizontal dimension of building measured normal to wind direction, in m.
b = mean hourly wind speed factor in Eq. 2.4.14 from Table 2.4.
= 3 ‐s gust speed factor from Table 2.4.
C
f
= force coefficient to be used in determination of wind loads for other structures
C
N
= net pressure coefficient to be used in determination of wind loads for open buildings
C
p
= external pressure coefficient to be used in determination of wind loads for buildings
c = turbulence intensity factor in Eq. 2.4.5 from Table 2.4.
D = diameter of a circular structure or member in m.
D’ = depth of protruding elements such as ribs and spoilers in m.
F = design wind force for other structures, in N.
G = gust effect factor
G
f
= gust effect factor for MWFRSs of flexible buildings and other structures
GC
pn
= combined net pressure coefficient for a parapet
GC
p
= product of external pressure coefficient and gust effect factor to be used in determination of wind loads
for buildings
GC
pf = product of the equivalent external pressure coefficient and gust‐effect factor to be used in determination
of wind loads for MWFRS of low‐rise buildings
Part 6
q i = velocity pressure for internal pressure determination, in N/m
2
q p = velocity pressure at top of parapet, in N/m
2
q z = velocity pressure evaluated at height z above ground, in N/m
2
R = resonant response factor from Eq. 2.4.
R
B
, R
h
, R
L = values from Eq. 2.4.
R
i = reduction factor from Eq. 2.4.
R
n = value from Eq. 2.4.
s = vertical dimension of the solid freestanding wall or solid sign from Fig.2.4.20, in m.
r = rise‐to‐span ratio for arched roofs.
V = basic wind speed obtained from Fig.2.4.1 or Table 2.4.1, in m/s. The basic wind speed corresponds to a 3 ‐s
gust speed at 10 m above ground in Exposure Category B having an annual probability of occurrence of
V
i
= unpartitioned internal volume m
3
Z
V
= mean hourly wind speed at height ҧݖ, m/s.
W = width of building in Figs. 2.4.12 and 2.4.14A and B and width of span in Figs. 2.4.13 and 2.4.15, in m.
X = distance to center of pressure from windward edge in Fig. 2.4.18, in m.
x = distance upwind or downwind of crest in Fig. 2.4.4, in m.
z = height above ground level, in m.
z = equivalent height of structure, in m.
z g = nominal height of the atmospheric boundary layer used in this standard. Values appear in Table 2.4.
z min = exposure constant from Table 2.4.
α = 3 ‐s gust‐speed power law exponent from Table 2.4.
ߙො = reciprocal of α from Table 2.4.
ߙത= mean hourly wind‐speed power law exponent in Eq. 2.4.14 from Table 2.4.
β = damping ratio, percent critical for buildings or other structures
א = ratio of solid area to gross area for solid freestanding wall, solid sign, open sign, face of a trussed tower, or
lattice structure
λ = adjustment factor for building height and exposure from Figs. 2.4.2 and 2.4.
= integral length scale power law exponent in Eq. 2.4.7 from Table 2.4.
η = value used in Eq. 2.4.13 (see Section 2.4.10.2)
θ = angle of plane of roof from horizontal, in degrees
v = height‐to‐width ratio for solid sign
Chapter 2
2.4.4 METHOD 1—SIMPLIFIED PROCEDURE
2.4.4.1 SCOPE
A building whose design wind loads are determined in accordance with this section shall meet all the conditions
of Sections 2.4.4.2 or 2.4.4.3. If a building qualifies only under 2.4.4.2 for design of its components and
cladding, then its MWFRS shall be designed by Method 2 or Method 3.
Limitations on Wind Speeds : Variation of basic wind speeds with direction shall not be permitted unless
substantiated by any established analytical method or wind tunnel testing.
2.4.4.2 MAIN WIND FORCE RESISTING SYSTEMS
For the design of MWFRSs the building must meet all of the following conditions:
- The building is a simple diaphragm building as defined in Section 2.4.2.
- The building is a low‐rise building as defined in Section 2.4.2.
- The building is enclosed as defined in Section 2.4.2 and conforms to the wind‐borne debris provisions of
Section 2.4.11.3.
- The building is a regular‐shaped building or structure as defined in Section 2.4.2.
- The building is not classified as a flexible building as defined in Section 2.4.2.
- The building does not have response characteristics making it subject to across wind loading, vortex
shedding, instability due to galloping or flutter; and does not have a site location for which channeling effects or
buffeting in the wake of upwind obstructions warrant special consideration.
- The building has an approximately symmetrical cross‐section in each direction with either a flat roof or a
gable or hip roof with θ ≤ 45
◦
- The building is exempted from torsional load cases as indicated in Note 5 of Fig. 2.4.10, or the torsional load
cases defined in Note 5 do not control the design of any of the MWFRSs of the building.
2.4.4.3 COMPONENTS AND CLADDING
For the design of components and cladding the building must meet all the following conditions:
- The mean roof height h must be less than or equal to 18.3 m ( h ≤ 18.3 m).
- The building is enclosed as defined in Section 2.4.2 and conforms to the wind‐borne debris provisions of
Section 2.4.11.3.
- The building is a regular‐shaped building or structure as defined in Section 2.4.2.
- The building does not have response characteristics making it subject to across wind loading, vortex
shedding, instability due to galloping or flutter; and does not have a site location for which channeling effects or
buffeting in the wake of upwind obstructions warrant special consideration.
- The building has either a flat roof, a gable roof with θ ≤ 45
o
, or a hip roof with θ ≤ 27
o
2.4.4.4 DESIGN PROCEDURE
- The basic wind speed V shall be determined in accordance with Section 2.4.6. The wind shall be assumed to
come from any horizontal direction.
- An importance factor I shall be determined in accordance with Section 2.4.7.
- An exposure category shall be determined in accordance with Section 2.4.8.3.
Chapter 2
- The building or other structure does not have response characteristics making it subject to across wind
loading, vortex shedding, instability due to galloping or flutter; or does not have a site location for which
channeling effects or buffeting in the wake of upwind obstructions warrant special consideration.
The provisions of this section take into consideration the load magnification effect caused by gusts in resonance
with along‐wind vibrations of flexible buildings or other structures. Buildings or other structures not meeting
the requirements of Section 2.4.4, or having unusual shapes or response characteristics shall be designed using
recognized literature documenting such wind load effects or shall use the wind tunnel procedure specified in
Section 0.
2.4.5.2 SHIELDING.
There shall be no reductions in velocity pressure due to apparent shielding afforded by buildings and other
structures or terrain features.
2.4.5.3 AIR PERMEABLE CLADDING
Design wind loads determined from Section 2.4.5 shall be used for air permeable cladding unless approved test
data or recognized literature demonstrate lower loads for the type of air permeable cladding being considered.
2.4.5.4 DESIGN PROCEDURE
- The basic wind speed V and wind directionality factor K d
shall be determined in accordance with Section
- An importance factor I shall be determined in accordance with Section 2.4.7.
- An exposure category or exposure categories and velocity pressure exposure coefficient K z
or K h
, as
applicable, shall be determined for each wind direction in accordance with Section 2.4.8.
- A topographic factor K zt shall be determined in accordance with Section 2.4.9.
- A gust effect factor G or G f , as applicable, shall be determined in accordance with Section 2.4.10.
- An enclosure classification shall be determined in accordance with Section 2.4.11.
- Internal pressure coefficient GC pi shall be determined in accordance with Section 2.4.12.1.
- External pressure coefficients C p or GC pf , or force coefficients C f , as applicable, shall be determined in
accordance with Section 2.4.12.2 or 2.4.12.3, respectively.
- Velocity pressure q z
or q h
, as applicable, shall be determined in accordance with Section 2.4.11.5.
- Design wind load p or F shall be determined in accordance with Sections 2.4.13.
2.4.6 BASIC WIND SPEED
The basic wind speed, V, used in the determination of design wind loads on buildings and other structures shall
be as given in Fig.2.4.1 except as provided in Section 2.4.6.1. The wind shall be assumed to come from any
horizontal direction.
2.4.6.1 SPECIAL WIND REGIONS
The basic wind speed shall be increased where records or experience indicate that the wind speeds are higher
than those reflected in Fig. 2.4.1. Mountainous terrain, gorges, and special regions shall be examined for
unusual wind conditions. The authority having jurisdiction shall, if necessary, adjust the values given in Fig. 2.4.
to account for higher local wind speeds. Such adjustment shall be based on adequate meteorological
information and other necessary data.
Part 6
2.4.6.2 LIMITATION
Tornadoes have not been considered in developing the basic wind‐speed distributions.
2.4.6.3 WIND DIRECTIONALITY FACTOR
The wind directionality factor, K d
, shall be determined from Table 2.4.5. This factor shall only be applied when
used in conjunction with load combinations specified in Chapter 2 of Part 6 of this code.
2.4.7 IMPORTANCE FACTOR
An importance factor, I , for the building or other structure shall be determined from Table 2.4.2 based on
building and structure categories listed in Section 1.2.4.
2.4.8 EXPOSURE
For each wind direction considered, the upwind exposure category shall be based on ground surface roughness
that is determined from natural topography, vegetation, and constructed facilities.
2.4.8.1 WIND DIRECTIONS AND SECTORS
For each selected wind direction at which the wind loads are to be evaluated, the exposure of the building or
structure shall be determined for the two upwind sectors extending 45
o
either side of the selected wind
direction.
The exposures in these two sectors shall be determined in accordance with Sections 2.4.8.2 and 2.4.8.3 and the
exposure resulting in the highest wind loads shall be used to represent the winds from that direction.
2.4.8.2 SURFACE ROUGHNESS CATEGORIES
A ground surface roughness within each 45
o
sector shall be determined for a distance upwind of the site as
defined in Section 2.4.8.3 from the categories defined in the following text, for the purpose of assigning an
exposure category as defined in Section 2.4.8.3.
Surface Roughness A : Urban and suburban areas, wooded areas, or other terrain with numerous closely spaced
obstructions having the size of single‐family dwellings or larger.
Surface Roughness B: Open terrain with scattered obstructions having heights generally less than 9.1 m. This
category includes flat open country, grasslands, and all water surfaces in hurricane prone regions.
Surface Roughness C: Flat, unobstructed areas and water surfaces outside hurricane prone regions. This
category includes smooth mud flats and salt flats.
2.4.8.3 EXPOSURE CATEGORIES
Exposure A: Exposure A shall apply where the ground surface roughness condition, as defined by Surface
Roughness A, prevails in the upwind direction for a distance of at least 792 m or 20 times the height of the
building, whichever is greater.
EXCEPTION: For buildings whose mean roof height is less than or equal to 9.1 m, the upwind distance may be
reduced to 457 m.
Exposure B : Exposure B shall apply for all cases where Exposures A or C do not apply.
Exposure C : Exposure C shall apply where the ground surface roughness, as defined by Surface Roughness C,
prevails in the upwind direction for a distance greater than 1,524 m or 20 times the building height, whichever
is greater. Exposure C shall extend into downwind areas of Surface Roughness A or B for a distance of 200 m or
20 times the height of the building, whichever is greater.
