AGENDA ITEM: 650-608 Design Loads for Tank Roofs
DATE: January 28, 2008
CONTACT: Randy Kissell, TGB Partnership
PH: 919-644-8250 FX: 919-644-8252, email: randy.kissell@tgbpartnership.com
PURPOSE:
1) To allow reduced live loads for tank roofs where allowed by load standards
2) To include unbalanced snow loads on tank roofs
SOURCE: Committee members’ request
REVISION: 3
IMPACT:
1) Reduce cost where reduced live loads are allowed by load standards;
2) Reduce the likelihood of failures when roofs are subjected to drifting snow loads.
RATIONALE:
General
This version of the ballot addresses comments received in the ballot conducted before the Fall 2007
Refining meeting.
Committee members requested an investigation into more precise loads for tank roofs. The first ballot
addressed only aluminum dome roofs, but committee members requested that any changes to roof loads
apply to all tank roofs. This ballot, therefore, uniformly addresses snow loads, wind loads, and minimum
roof live loads for all tank roofs addressed by API 650.
Loads on tanks were recently revised in agenda item 650-472, which provided more precise loads than
previously required by API 650. For example, API 650 previously specified a 25 psf roof live load for all
tanks in all locations. 650-472 (published in 650’s 10th edition, addendum 4) changed this, providing
rules for determining the uniform snow load for the tank based on its location. Changes were also made
to more accurately determine other loads such as minimum roof live load and wind load, and address load
combinations.
The 650-472 load changes were based on ASCE 7, Minimum Design Loads for Buildings and Other
Structures, but the 650-472 snow load and minimum roof live load were simplified from the ASCE 7
approach. Now that the committee is requesting more precise loads, this ballot proposes to revise 650’s
snow load and minimum roof live load requirements to more closely match ASCE 7.
This will have the benefit of reducing costs in low snow load regions where ASCE 7 provides for lower
minimum roof live loads, and making tank design more consistent with accepted practice for other
structures. Another advantage will be to reduce roof failures due to drifting snow loads by addressing
unbalanced snow loads for the first time in API 650.
650-608 Design Loads for Tank Roofs 1/28/08
1
Minimum Roof Live Load
ASCE 7 section 4.9.1 prescribes minimum roof live loads as a function of the tributary area of a structural
member and the rise-to-span ratio of dome roofs. The largest ASCE 7 minimum roof live load value of
20 psf is conservatively prescribed by API 650 5.2.1(e). ASCE 7 allows this value to be reduced to as
little as 12 psf for structural components with large tributary areas in domes with large rise-to-span ratios.
This ballot proposes to allow lower minimum roof live loads where allowed by ASCE 7, but no less than
15 psf. (AWWA D100 specifies 15 psf as a minimum.) This reduces the design load in regions where
the ground snow load is small.
Wind Loads
This ballot would not change wind loads except that they would be applied to all roofs, including
aluminum dome roofs, which currently have different wind loads based on outdated ASCE 7 arched roof
wind loads. The discussion below provides the rationale for the roof wind load currently in API 650.
ASCE 7-02 (Minimum Design Loads for Buildings and Other Structures) provides wind pressures for
dome roofs in Figure 6-7. Dome pressures are a function of the tank-height-to-diameter ratio, distance
from the windward edge, and roof profile. These were used in agenda item 650-472 to provide the wind
pressure for doubly curved surfaces, and this ballot proposes to apply these to aluminum domes, since the
ASCE 7 pressure is more accurate than the current API 650 G.4.2.2.1 provisions. The ASCE 7 dome
wind pressure approach is briefly reviewed below.
For typical profiles permitted by API 650 (for steel domes, see 5.10.6.1 and for aluminum domes, see
G.6.2) on an 80’ diameter, 48’ tall tank, ASCE 7 Figure 6-7 gives an approximate average Cp = -0.97, so
the design wind pressure is
p = qh (GCp - GCpi)
p = 36.4 (-0.97(0.85) – 0.18) = 36.4 (-0.94) = 36.6 psf
(uplift)
A computation of ASCE 7-02 wind pressure on domes is shown for 3 tanks below, using a dome radius
equal to the tank diameter (D), a typical radius for API 650 tanks (see section 5.10.6 for steel domes and
G.6.2 for aluminum domes), resulting in a dome-height-to-tank-diameter ratio of 0.13:
Dome Roof Wind Pressure Coefficients Cp for 3 Tank Sizes
30’ x 40’h
80’ x 48’h
150’ x 48’h
5,000 bbl
43,000 bbl
151,000 bbl
h/D
1.3
0.6
0.32
Pt. A (windward edge)
-1.6
-1.4
-1.0
Pt. B (center)
-1.0
-1.0
-0.8
Pt. C (leeward edge)
-0.5
-0.5
-0.3
average coefficient
-1.02
-0.97
-0.72
average uplift (psf)
38.1
36.6
28.8
In each case, the uplift on the windward side is about 3 times the uplift on the leeward side, producing a
net horizontal force in a direction opposite to the wind direction. Therefore, the horizontal effect of the
wind counteracts overturning and can be conservatively neglected.
A 30 psf roof uplift pressure was selected as a reasonable average for all roofs based on the above, and
matches that used for steel roofs in 650.
650-608 Design Loads for Tank Roofs 1/28/08
2
Snow Load
The snow load currently given in API 650 5.2.1(g) is solely a balanced (uniform) load. ASCE 7-02
provides, in addition to balanced snow loads, unbalanced snow loads (ASCE 7 Figure 7-3). The ASCE 702 unbalanced snow load on dome roofs varies from 0.5 times the flat roof snow load pf at the roof’s
crown to about 2 times the flat roof snow load at the 30o slope point (see the figure below). In plan, this
load is distributed over a 90o sector and tapers to zero over the 22.5o sectors to either side of the 90o
degree sector.
The ASCE unbalanced distribution can be used to compute an average pressure in the loaded 90o sector of
1.58 times the flat roof snow load, when the area loaded is accounted for. (Arcs further from the roof
center have more area). This ballot proposes for simplicity to use 1.5 times the flat roof snow load for the
unbalanced load, and apply this over a 90o + 2(22.5 o) = 135 o sector (135/360 = 3/8 of the roof’s area).
2.0 pf Cs /Ce
0.5pf
30o slope
Dome
Elevation
This ballot proposes that roof general buckling and tension ring checks for steel and aluminum domes be
based on the unbalanced snow load since its intensity is greater than the balanced snow load, and the
unbalanced load acts over a sufficiently large portion of the roof to cause general buckling and tension
ring failure.
ASCE 7 does not require unbalanced loads for dome roofs with a slope from the eave to the crown of 10o
or less. If a cone roof is considered to be similar to a dome roof, then a cone roof with a slope of ¾ on 12
(3.57o) has a slope less than 10o, for which the only unbalanced load ASCE 7 requires is a partial loading
(the balanced load acting over only part of the roof).
Roof Design
There are four types of fixed roofs addressed by API 650:
Roof Type
Supported Cone Roofs
API 650 Reference
5.10.4
Self-Supporting Cone
5.10.5
650-608 Design Loads for Tank Roofs 1/28/08
Slope θ or Radius r
3.6 o (¾ on 12); may be
greater
9.5 o < θ < 37o
Safety Factor on Buckling
1.67 on column buckling
variable from about 3 to
3
Roofs
less than 2*
Self-Supporting Dome
5.10.6
0.8D < r < 1.2D
4*
and Umbrella Roofs
Self-Supporting
Appendix G
0.7D < r < 1.2D
1.65 on general buckling;
Aluminum Dome Roofs
1.95 on member buckling
*Safety factors for self-supporting cone and self-supporting dome roofs are given in Jawad and Farr,
Structural Analysis and Design of Process Equipment.
Fixed roofs will be more accurately designed as a result of this ballot by including unbalanced snow loads
in their design. The table above shows that steel domes and self-supporting cone roofs have higher safety
factors than the other roofs. This is partially due to the fact that API 650 places no tolerances on out-ofroundness for steel domes and self-supporting cones, so they can have geometric imperfections that
reduce their buckling strength. However, since unbalanced loads will now be considered in their design,
it is reasonable to reduce the steel dome safety factor for unbalanced loads to 3.5 as proposed in this
ballot. The US unit equation for steel dome thickness given in 5.10.6.1 is modified as follows:
Current equation: t =
rr
200
T
+ C.A. > 3/16 in.
45
rr
r
T
+ C.A. and t = r
200 45
230
where T = balanced load and U = unbalanced load
Ballot equations: Use the greater of t =
U
+ C.A. > 3/16 in.
45
Designers may use the balloted equations given in 5.10.5 and 5.10.6 or they may perform more precise
analyses if they wish. An example for a self-supporting steel dome is using 5.10.6 using the current 650
approach and this ballot’s approach is given below:
Given:
Balanced snow load = 20 psf
Unbalanced snow load = 30 psf
Tank diameter D = 80 ft
Dome radius rr = tank diameter D
External pressure = 1” w.c. = 5.2 lb/ft2
C.A. = 0
Assume a thickness of 0.375 in., which weighs 15.3 lb/ft2
Current method:
T = balanced snow + 0.4(external pressure) + dead load = 20 psf + 0.4(5.2 psf) + 15.3 psf = 37.4 psf
r
T
80 37.4
t= r
+ C.A. =
+ 0 = 0.365 in.
200 45
200 45
Ballot method:
U = unbalanced snow + 0.4(external pressure) + dead load = 30 psf + 0.4(5.2 psf) + 15.3 psf = 47.4 psf
r
T
80 47.4
t= r
+ C.A. =
+ 0 = 0.357 in.
230 45
230 45
650-608 Design Loads for Tank Roofs 1/28/08
4
T = balanced snow + 0.4(external pressure) + dead load = 20 psf + 0.4(5.2 psf) + 15.3 psf = 37.4 psf
r
T
80 37.4
t= r
+ C.A. =
+ 0 = 0.365 in.
200 45
200 45
For this example, the current method and the ballot method give the same result.
Aluminum Dome Seismic Load
The aluminum dome seismic load (G.4.2.3) needs to be updated since Appendix E has changed. This
ballot corrects the dome seismic load to correspond with the new Appendix E seismic design
requirements.
Aluminum Dome General Buckling
The aluminum dome general buckling equation is made dimensionless in this ballot to be consistent with
the metric guidelines passed by the committee. The allowable buckling pressure is required to be
compared to the revised loads in G.4.2.1 and G.4.2.2.
Aluminum Dome Tension Ring
The aluminum dome tension ring area equation given in G.4.1.4 has a typo. The US unit version should
be
11D 2
180
 tan  sin(
) Ft

Written in dimensionless form, making the applied load a variable, and using η sin(180o/η) ≈ π, this
equation is
An =
An =
D 2 ( LL  DL)
, which is used in this ballot.
8Ft tan 
BALLOT:
Add unlined words
5.2.1 Loads Loads are defined as follows:
(a) Dead Load (DL): The weight of the tank or tank component, including any corrosion
allowance unless otherwise noted.
(b) Design External Pressure (Pe): Shall not be less than 0.25 kPa (1 in. of water). This standard
does not contain provisions for external pressures greater than 0.25 kPa. Design requirements for vacuum
exceeding this value and design requirements to resist flotation and external fluid pressure shall be a
matter of agreement between the Purchaser and the Manufacturer (see Appendix V).
(c) Design Internal Pressure (Pi): Shall not exceed 18 kPa (2.5 lbf/in2).
(d) Hydrostatic Test (Ht ): The load due to filling the tank with water to the design liquid level.
(e) Minimum Roof Live Load (Lr): 1.0 kPa (20 lb/ft2) on the horizontal projected area of the roof.
The minimum roof live load may alternatively be determined in accordance with ASCE 7, but shall not be
less than 0.72 kPa (15 psf). The minimum roof live load shall be reported to the purchaser.
(f) Seismic (E): Seismic loads determined in accordance with sections E.1 through E.6 (see Data
650-608 Design Loads for Tank Roofs 1/28/08
5
Sheet, Line 8).
(g) Snow (S): The ground snow load shall be determined from ASCE 7 Figure 7-1 or Table 7-1
unless the ground snow load that equals or exceeds the value based on a 2% annual probability of being
exceeded (50 yr mean recurrence interval) is specified by the purchaser.
1) The balanced design snow load (Sb) shall be 0.84 times the ground snow load. Alternately,
the balanced design snow load shall be determined from the ground snow load in accordance
with ASCE 7.
2) The unbalanced design snow load (Su) for cone roofs with a slope of 10o or less shall be
equal to the balanced snow load. The unbalanced design snow load (Su) for all other roofs
shall be 1.5 times the balanced design snow load. Unbalanced design snow load shall be
applied over a 135o sector of the roof plan with no snow on the remaining 225o sector.
Alternately, the unbalanced snow load shall be determined from the ground snow load in
accordance with ASCE 7.
The balanced and unbalanced design snow loads shall be reported to the purchaser.
(h) Stored Liquid (F): The load due to filling the tank to the design liquid level (see 5.6.3.2) with
liquid with the design specific gravity specified by the purchaser.
(i) Test Pressure (Pt): As required by F.4.4 or F.7.6.
(j) Wind (W): The design wind speed (V) shall be 190 km/hr (120 mph), the 3 sec gust design
wind speed determined from ASCE 7 Figure 6-1, or the 3 sec gust design wind speed specified by the
purchaser (this specified wind speed shall be for a 3 sec gust based on a 2% annual probability of being
exceeded (50 yr mean recurrence interval)). The design wind pressure shall be 0.86 kPa [V/190]2, [(18
lbf/ft2)(V/120)2] on vertical projected areas of cylindrical surfaces and 1.44 kPa(V/190)2, [(30
lbf/ft2)(V/120)2] uplift (2) on horizontal projected areas of conical or doubly curved surfaces, where V is
the 3 sec gust wind speed. The 3 sec gust wind speed used shall be reported to the purchaser.
1. These design wind pressures are in accordance with ASCE 7 for wind exposure category C.
As an alternative, pressures may be determined in accordance with ASCE 7 (exposure
category and importance factor provided by purchaser) or a national standard for the specific
conditions for the tank being designed.
2. The design uplift pressure on the roof (wind plus internal pressure) need not exceed 1.6
times the design pressure P determined in F.4.1.
3. Windward and leeward horizontal wind loads on the roof are conservatively equal and
opposite and therefore they are not included in the above pressures.
4. Fastest mile wind speed times 1.2 is approximately equal to 3 sec gust wind speed.
5.10.5.1 Self-Supporting Cone Roofs
For SI units, change:
D
T
Minimum thickness =
> 5 mm
4.8 sin  2.2
Maximum thickness = 12.5 mm, exclusive of corrosion allowance
where
D = nominal diameter of the tank shell (m)
T = greater of load combinations (e)(1)and (e)(2) of Appendix R (kPa)
θ = angle of cone elements to the horizontal (deg)
650-608 Design Loads for Tank Roofs 1/28/08
6
to:
Minimum thickness = greatest of
D
T
D
U
,
, and 5 mm
4.8 sin  2.2 5.5 sin  2.2
where
D = nominal diameter of the tank (m)
T = greater of Appendix R load combinations (e)(1)and (e)(2) with balanced snow load Sb (kPa)
U = greater of Appendix R load combinations (e)(1)and (e)(2) with unbalanced snow load Su (kPa)
θ = angle of cone elements to the horizontal
For US units, change:
D
T
> 3/16 in.
400 sin  45
Maximum thickness = ½ in., exclusive of corrosion allowance
Minimum thickness =
where
D = nominal diameter of the tank (ft)
T = greater of load combinations (e)(1)and (e)(2) of Appendix R (lbf/ft2)
θ = angle of cone elements to the horizontal (deg)
to:
Minimum thickness = greatest of
D
T
D
U
,
, and 3/16 in.
400 sin  45 460 sin  45
where
D = nominal diameter of the tank shell (ft)
T = greater of Appendix R load combinations (e)(1)and (e)(2) with balanced snow load Sb (lbf/ft2)
U = greater of Appendix R load combinations (e)(1)and (e)(2) with unbalanced snow load Su (lbf/ft2)
θ = angle of cone elements to the horizontal
5.10.6.1 Self-Supporting Dome and Umbrella Roofs
For SI units, change:
r
T
Minimum thickness = r
+ C.A. and > 5 mm
2.4 2.2
Maximum thickness = 12.5 mm, exclusive of corrosion allowance
where
D = nominal diameter of the tank shell (m)
T = greater of load combinations (e)(1)and (e)(2) of Appendix R (kPa)
r = roof radius (m)
to:
Minimum thickness = greatest of
rr
r
T
U
+ C.A., r
+ C.A., and 5 mm
2.4 2.2
2.7 2.2
where
D = nominal diameter of the tank shell (m)
650-608 Design Loads for Tank Roofs 1/28/08
7
T = greater of Appendix R load combinations (e)(1)and (e)(2) with balanced snow load Sb (kPa)
U = greater of Appendix R load combinations (e)(1)and (e)(2) with unbalanced snow load Su (kPa)
r = roof radius (m)
For US units, change:
rr
T
+ C.A. > 3/16 in.
200 45
Maximum thickness = ½ in., exclusive of corrosion allowance
Minimum thickness =
where
D = nominal diameter of the tank shell (ft)
T = greater of load combinations (e)(1)and (e)(2) of Appendix R (lbf/ft2)
r = roof radius (ft)
to:
Minimum thickness = greatest of
rr
200
r
T
+ C.A., r
45
230
U
+ C.A., 3/16 in.
45
where
D = nominal diameter of the tank shell (ft)
T = greater of Appendix R load combinations (e)(1)and (e)(2) with balanced snow load Sb (lbf/ft2)
U = greater of Appendix R load combinations (e)(1)and (e)(2) with unbalanced snow load Su (lbf/ft2)
r = roof radius (ft)
APPENDIX R – LOAD COMBINATIONS
R.1 For the purposes of this standard, loads are combined in the following manner. Design rules account
for these load combinations, including the absence of any load other than DL in the combinations:
(a) Fluid and Internal Pressure:
DL + F + Pi
(b) Hydrostatic Test:
DL + (Ht + Pt)
(c) Wind and Internal Pressure:
DL + W + 0.4Pi
(d) Wind and External Pressure:
DL + W + 0.4Pe
(e) Gravity Loads:
1) DL + (Lr or Su or Sb) + 0.4Pe
2) DL + Pe + 0.4(Lr or Su or Sb)
(f) Seismic:
DL + F + E + 0.1Sb + 0.4Pi
 R.2 If the ratio of operating pressure to design pressure exceeds 0.4, the purchaser should consider
specifying a higher factor on design pressure in (c), (d), (e)(1), and (f).
Appendix G
Current (10th edition, 4th addendum)
650-608 Design Loads for Tank Roofs 1/28/08
Replace with:
8
G.4.1.3 Local and general buckling of the dome
roof must be considered with a minimum factor of
safety of 1.65 applied to the buckling equation or
method. General buckling of the dome roof shall
be considered either by using non-linear finite
element analysis or by the following equation:
Wa = allowable total downward load in kPa
G.4.1.3 General buckling The allowable
general buckling pressure pa shall equal or exceed
the maximum pressure given in R.1(e) where
1.6 E I x A
pa =
LR 2 ( SF )
E = modulus of elasticity of the dome frame
members
Ix = moment of inertia of the frame members for
bending in a plane normal to the dome surface
A = cross sectional area of the frame members
R = spherical radius of the dome
L = average length of the frame members
SF = safety factor =1.65
Ix = moment of inertia of frame members against
bending in a plane normal to the dome surface in
cm4
Alternately, pa shall be determined by a non-linear
finite element analysis with a safety factor of 1.65.
In SI units:
Wa =
108 .1  10 6 E I x Ag
LR 2 ( SF )
where
Ag = cross sectional area of beam in cm2
R = spherical radius of the dome in cm
SF = safety factor = 1.65
In US units:
2258  10 6 E I x Ag
Wa =
LR 2 ( SF )
where
Wa = allowable total downward load (lbf/ft2)
Ix = moment of inertia of frame members against
bending in a plane normal to the dome surface (in4)
Ag = cross sectional area of beam (in2)
R = spherical radius of the dome in (in.)
SF = safety factor = 1.65
G.4.1.4 The minimum net tension ring area
(exclusive of bolt holes and top flange protrusions)
shall be determined per the following formula:
In US units:
An =
11D 2
180
 tan (
) Ft

650-608 Design Loads for Tank Roofs 1/28/08
G.4.1.4 Tension Ring The net tension ring area
(exclusive of bolt holes and top flange protrusions)
shall not be less than:
An =
D2 p
8 Ft tan 
where
An = net area of tension ring
9
where
An = net area of tension beam (in.2)
D = nominal tank diameter (ft)
η = number of dome supports
θ = ½ the central angle of the dome or roof slope at
the tank shell
Ft = allowable stress of the tension ring (lbf/in2)
In cases where the total dead load plus live load is
greater than 1.34 kPa (28 lbf/ft2), the above formula
shall be multiplied by W/1.34 (or 28), where W =
the total dead load plus live load for the dome.
Note: this formula does not include factors for
bending stresses due to loads from the panel
attached to the beam. These stresses must also be
considered in the tension ring design, as per G.3.1.
G.4.2 DESIGN LOADS
Dome roofs shall be designed for the loads in 3.2.1,
G.4.2, and G.4.3; and for the load combinations (a),
(b), (c), (e), and (f) of Appendix Y.
D = nominal tank diameter
p = maximum pressure given in R.1(e)
θ = ½ the central angle of the dome or roof slope at
the tank shell
Ft = tension ring allowable stress
Note: this formula does not include bending
stresses due to loads from the panel attached to the
beam. These stresses must also be considered in
the tension ring design per G.3.1.
G.4.2 DESIGN LOADS
Dome roofs shall be designed for:
a) the loads in 5.2.1.
b) the load combinations in Appendix R.1(a),
(b), (c), (e), and (f).
G.4.2.1 Unbalanced Load
The design shall consider one-half of the uniform
downward load required applied to one-half of the
dome with only the dead load on the other half.
G.4.2.2 Wind Load
G.4.2.2.1 For dome structural design, the
minimum wind load shall be the load resulting
from a design wind speed of 190 km/h (120 mph)
which imposes a velocity pressure of 1.48 kPa (31
lbf/ft2)). The following pressure coefficients shall
be used:
G.4.2.1 Unbalanced Load
The design shall consider one-half of the uniform
downward load required applied to one-half of the
dome with only the dead load on the other half.
G.4.2.2 Wind Load
G.4.2.2.1 For dome structural design, the
minimum wind load shall be the load resulting
from a design wind speed of 190 km/h (120 mph)
which imposes a velocity pressure of 1.48 kPa (31
lbf/ft2)). The following pressure coefficients shall
be used:
Windward quarter = -0.9
Center half = -0.7
Leeward quarter = -0.5
Windward quarter = -0.9
Center half = -0.7
Leeward quarter = -0.5
For domes designed for 3 sec gust wind speeds
other than 190 km/h (120 mph), the wind load shall
be multiplied by the following:
For domes designed for 3 sec gust wind speeds
other than 190 km/h (120 mph), the wind load shall
be multiplied by the following:
In SI units: (V/190)2
In SI units: (V/190)2
In US Customary units: (V/120)2
In US Customary units: (V/120)2
650-608 Design Loads for Tank Roofs 1/28/08
10
Where
V = wind speed (3 sec gust) in km/h (mph).
Where
V = wind speed (3 sec gust) in km/h (mph).
Note: The velocity pressure of 1.48 kPa (31 lbf/ft2)
is based on ASCE 7-98, Category II, Exposure C,
with an Importance Factor of 1.0.
G.4.2.2.2 See 3.11 for tank overturning stability.
Note: The velocity pressure of 1.48 kPa (31 lbf/ft2)
is based on ASCE 7-98, Category II, Exposure C,
with an Importance Factor of 1.0.
G.4.2.2.2 See 3.11 for tank overturning stability.
G.4.2.3 Seismic Load
If the tank is designed for seismic loads, the roof
shall be designed for a horizontal seismic force
determined as follows:
F = 0.6 ZIWr
where
F
=
horizontal seismic force.
Z, I, and Wr are as defined in Appendix E.
The force shall be uniformly applied over the
surface of the roof.
G.4.2.1 Seismic Load
If the tank is designed for seismic loads, the roof
shall be designed for
G.4.2.4 Panel Loads
G.4.2.2 Panel Loads
G.4.2.4.1 Roof panels shall be of one-piece
aluminum sheet (except for skylights as allowed by
G.8.4) and shall be designed to support a uniform
load of 3 kPa (60 lbf/ft2) over the full area of the
panel without sustaining permanent distortion.
G.4.2.2.1 Uniform Load Roof panels shall be
one piece aluminum sheet (except for skylights as
per G.8.4). The roof shall be designed to support a
uniform load of 3 kPa (60 lbf/ft2) over the full area
of a panel.
G.4.2.4.2 The roof shall be designed to support
two concentrated loads 1100 N (250 lbf), each
distributed over two separate 0.1 m2 (1 ft2) areas of
any panel.
G.4.2.2.2 Concentrated Load The roof shall be
designed to support two concentrated loads 1100 N
(250 lbf), each distributed over two separate 0.1 m2
(1 ft2) areas of any panel.
G.4.2.4.3 The loads specified in G.4.2.4.1 and
G.4.2.4.2 shall not be considered to act
simultaneously or in combination with any other
loads.
a) a horizontal seismic force Fh = AiWr
b) a vertical seismic force Fv = ±AvWr
where Ai, Av, and Wr are as defined in Appendix E.
Forces shall be uniformly applied over the surface
of the roof. Horizontal and vertical forces need not
be applied simultaneously.
G.4.2.2.3 Application The loads specified in
G.4.2.2.1 and G.4.2.2.2 shall not be applied
simultaneously or in combination with any other
loads.
Appendix L
Change “11. Thickness * _______ In. Snow Load* to
Minimum Roof Live Load _______ psf
Balanced Snow Load _________ psf
Unbalanced Snow Load _______ psf
650-608 Design Loads for Tank Roofs 1/28/08
11