Per ASCE 7-05 Code - Chapter 10
for Ice Loads Due to Freezing Rain on C and MC Shapes
|Member Size =|
|Building Classification =||[?]||Table 1-1, page 3|
|Nominal Ice Thickness, ti =||in.||Figures 10-2 through 10-6, pages 104-108|
|Topographic Factor, Kzt =||[?]||Section 6.5.7 & Figure 6-4|
|Height Above Ground, z =||ft.|
Occupancy Category of Buildings and Other Structures for Flood, Wind, Snow, Earthquake, and Ice Loads
Nature of Occupancy
|Buildings and structures that represent a low hazard to human life in the event of failure including, but not limited to:
- Agriculture facilities
|Buildings and other structures except those listed in Categories I, III and IV||II|
| Buildings and other structures that represent a substantial hazard to human life in the event of failure including, but not limited to:
- Buildings and other structures where more than 300 people congregate in one areaBuildings and other structures, not includes in Occupancy Category IV, with potential to cause substantial economic impact and/or mass disruption of day-to-day civilian life in event of failure, including, but not limited to:
- Power generating stations, water treatment facilities, sewage treatment facilities, and telecommunication centers
| Buildings and other structures designated as essential facilities including, but not limited to:
- Hospitals and health care facilities having surgery or emergency treatment facilities
The Topographic Factor, Kzt, accounts for effect of wind speed-up over isolated hills and escarpments (Sect. 6.5.7 and Fig. 6-4).
Kzt = (1+K1*K2*K3)^2 (Eq. 6-3), where:
H = height of hill or escarpment relative to the upwind terrain, in feet.
Lh = Distance upwind of crest to where the difference in ground elevation is half the height of hill or escarpment, in feet.
K1 = factor to account for shape of topographic feature and maximum speed-up effect.
K2 = factor to account for reduction in speed-up with distance upwind or downwind of crest.
K3 = factor to account for reduction in speed-up with height above local terrain.
x = distance (upwind or downwind) from the crest to the building site, in feet.
z = height above local ground level, in feet.
The effect of wind speed-up shall not be required to be considered (Kzt = 1.0) when H/Lh < 0.2, or H < 15' for Exposures 'C' and 'D', or H < 60' for Exposure 'B'.
|IMPORTANCE FACTOR, I, (ICE LOADS)|
Atmospheric ice loads due to freezing rain, snow, and in-cloud icing shall be considered in the design of ice-sensitive structures. In areas where records or experience indicate that snow or in-cloud icing produces larger loads than freezing rain, site-speciﬁc studies shall be used. Structural loads due to hoarfrost are not a design consideration.
FREEZING RAIN: Rain or drizzle that falls into a layer of subfreezing air at the earth’s surface and freezes on contact with the ground or an object to form glaze ice
Disclaimer: This calculator is not intended to be used for the design of actual structures, but only for schematic (preliminary) understanding of structural design principals. For the design of an actual structure, a competent professional should be consulted.
‘Calculations courtesy of Alex Tomanovich, PE ’