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Steel Portal Frame EC3 RUNET software
16 Short theoretical overview
16.1 Design Loads EN1991:2005 :
16.1.1 Permanent loads EN1991-1:2005
Weight of the roof system (sheeting+purlins+insulation)
Weight of the ceiling structure (if any)
Self-weight of the portal frame elements (calculated by the program)
16.1.2 Imposed loads EN1991-1:2005
A distributed imposed load qk according to Eurocode 1 EN1991-1-1 Tab 6.1 is considered on top of the roof.
16.1.3 Snow load EN1991-3:2003
Snow load is computed according to Eurocode 1-3 EN1991-3:2003, from the characteristic snow load on the ground and the roof slope.
s=μ i
C e
C t
s k
(EN1991-3:2003 §5.2) [kN/m²]
The three characteristic load arrangements of EN1991-3:2003 §5.3.3 are considered in the load cases. If the frame is flat (α=0
°
) one load arrangement is considered s= 0.80 C e
C t
s k.
The characteristic snow load on the ground s can be defined directly by k selecting the snow region, snow zone and the altitude, according to
EN1991-3:20 Annex C.
The snow load arrangements according to Eurocode 1-3 are
Flat roofs. Load case (I)
Pitched roofs Load cases (I) (II) III)
If the roof slop is low , only snow load arrangement (I) is necessary. The limit slope for this is angle a=2°. You can set this angle to a bigger value at Parameters/Design parameters/ parameters for Portal frames.
16.1.4 Wind load of EN1991-4:2005
Wind load is computed according to of EN1991-4:2005 §7.2.5 from the wind peak velocity pressure q(z).
Wind pressure on surfaces we=q(z)·Cpe [kN/m²]
The wind pressure coefficients Cpe are computed from EN1991-4:2005
Tab.74a for roof surfaces and EN1991-4:2005 Tab 7.1 for the vertical wall surfaces.
The wind peak velocity pressure q(z), can be defined directly from the wind velocity the terrain roughness and the oreography. According to EN1991-
4:2005 §4.5 and Annex A.
The wind pressure or underpressure on roof and wall surface are computed according to Eurocode 1-4. For roof slopes (α<=8
ο
) one load arrangement is considered. For higher slope values two wind load cases are considered according to the pressure coefficients of Table 7.4a of Eurocode 1-4.
The specified internal pressure is always added (increase underpressure) to the external wind pressure situation.
16.1.5 Earthquake loading EN1998-1:2004
The earthquake loading is defined from the ground acceleration and the design spectrum according to Eurocode 8 EN1998-1:2004.
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