Variable actions snow loads

In persistent or transient situations, snow load on a roof, s, is defined as being: <bs EN 1991-1-3 5.2(3)>

S - PjCeCtsk where

Sk -where snow load shape factor p1 - undrifted snow shape factor p2 - drifted snow shape factor

For flat roofs, 0° - a (with no higher structures close or abutting), P1 - P2 - 0.8

For shallow monopitch roofs, 0°< a < 30° (with no higher structures close or abutting), p1 - 0.8, p2 - 0.8 (1 + a/ 30) For other forms of roof and local effects refer to BS EN 1991-1-3 Sections 5.3 and 6

exposure coefficient

For windswept topography Ce - 0.8

For normal topography Ce - 1.0

For sheltered topography Ce - 1.2

thermal coefficient, Ct - 1.0 other than for some glass-covered roofs, or similar characteristic ground snow load kN/m2 0.15(0.1Z + 0.05) + (4+100) / 525

Z = zone number obtained from the map in BS EN 1991-1-3 NA

Figure NA.1 A = site altitude, m

Figure NA.1 of the NA to BS EN 1991-1-3 also gives figures for sk at 100 m a.m.s.l. associated with the zones. For the majority of the South East, the Midlands, Northern Ireland and the north of England apart from high ground, sk = 0.50 kN/m2. For the West Country, West Wales and Ireland the figure is less. For most of Scotland and parts of the east coast of England, the figure is more. See Figure 2.1 Snow load is classified as a variable fixed action. Exceptional circumstances may be treated as accidental actions in which case reference should be made to BS EN 1991-1-3

England Snow Load
HI Zone 1 = 0.25kN/m' at 100 m a.m.6,1. E) Zone 3 =i O.AOMIm' at-100 m a.m.s.l. El Zone 1 = 0.50kN/m"' at 100 rti a.m.s.l. H] Zone 1 = O.eOkW/m'' at 100 m a.m.s.l. H] Zone t = 0.70kN/m"' at 100 m a.m.s.l.

Figure 2.1

Characteristic ground snow load map

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    Is snow load a variable action?
    8 years ago
  • lacey
    When to use undrifted/ drifted snow loading?
    2 months ago

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