EN 1991-1-3 DK NA:2015

Statistical analysis of snow data Not relevant 4.2(1) Other representative values - Load combination values ... National choices DS/EN 1991-1-3 DK NA:...

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DS/EN 1991-1-3 DK NA:2015 - 2nd edition National Annex to Eurocode 1: Actions on structures Part 1-3: General actions - Snow loads _______________________________________________________________________

Foreword This national annex (NA) is a revision oqf DS/EN 1991-1-3 DK NA:2012 and replaces the latter on 2015-10-15. No technical changes have been made. The changes are purely editorial and are a consequence of the publication of DS/EN 1991-1-3+A1:2015; they consist in changes of µ subscripts and renumbering of figures. Previous versions of and addenda to this NA as well as an overview of all NAs can be found at www.eurocodes.dk This NA lays down the conditions for the implementation in Denmark of DS/EN 1991-1-3 for construction works in conformity with the Danish Building Act or the building legislation. Other parties can put this NA into effect by referring thereto. A National Annex contains national provisions, viz. nationally applicable values or selected methods. The Annex may furthermore give complementary, non-contradictory information. This NA includes:    

an overview of possible national choices and clauses containing complementary information; national choices; complementary, non-contradictory information; text replacing clauses 5.3.6 and 6.2, respectively.

Page 1 of 15 Foreword

DS/EN 1991-1-3 DK NA:2015 – 2nd edition

Overview of possible national choices and complementary information The list below identifies the clauses where national choices are possible and the applicable/not applicable informative annexes. Furthermore, clauses giving complementary information are identified. Complementary information is given at the end of this document. Clause

Subject

National choice1)

1.1(2)

Not relevant

3.3(1)

Scope Snow loads for altitudes above 1500 m Scope Application of Annex A Scope Application of Annex B Classification of actions Definition of exceptional snow loads Classification of actions Conditions for loads due to exceptional snow drifts Exceptional conditions

3.3(2)

Exceptional conditions

Not relevant

3.3(3)

Exceptional conditions

Not relevant

4.1(1) NOTE 1 4.1(1)

Characteristic values Snow load on the ground Characteristic values European ground snow load map Characteristic values Statistical analysis of snow data Other representative values Load combination values Treatment of exceptional snow loads on the ground Load arrangements Application of Annex B Load arrangements Guidance on determining the load arrangements in connection with artificial removal or redistribution of snow loads

National choice

1.1(3) 1.1(4) 2(3)

2(4)

4.1(2) 4.2(1) 4.3(1) 5.2(2) 5.2(5)

Not relevant

Complementary information

No exceptional loads are applied

Not applicable Not relevant

No exceptional loads are applied

Not relevant

No exceptional loads are applied

Not relevant

No exceptional loads are applied No exceptional loads are applied No exceptional loads are applied

Not relevant Not relevant National choice Not relevant Not relevant No guidance

No exceptional loads are applied No exceptional loads are applied Removal of snow should not be assumed in the design

Page 2 of 15 Overview, national choices and complementary information.

DS/EN 1991-1-3 DK NA:2015 – 2nd edition

Clause

Subject

National choice1)

5.2(6)

Load arrangements Further complementary guidance in connection with rainfalls at the same time as snow loads Load arrangements Exposure coefficient Ce Load arrangements Thermal coefficient Ct Roof shape coefficients. General Alternative load arrangements for snow drift Shape coefficients for roofs

No complementary guidance

No complementary guidance Not relevant; no exceptional loads are applied Unchanged

Complementary information

Monopitch roofs - drifted snow load arrangements Snow load shape coefficients. Pitched roofs Snow load shape coefficients. Multi-span roofs Application of Annex B Snow load shape coefficients. Multi-span roofs Further guidance Snow load shape coefficients. Cylindrical roofs Upper limit of shape coefficients for cylindrical roofs Snow load shape coefficients. Cylindrical roofs Consideration of snow fences Snow load shape coefficients. Cylindrical roofs Drifting load arrangement Snow load shape coefficients. Roofs abutting and close to taller construction works as well as drifting at projections and obstructions Snow load shape coefficients. Roofs abutting and close to taller construction works Range for µw

Unchanged

But see Annex F

5.2(7) 5.2(8) 5.3.1(1)

5.3.1(3), Table 5.2 5.3.2(3) 5.3.3(4) 5.3.4(3)

5.3.4(4)

5.3.5(1) NOTE 1

5.3.5(1) NOTE 2 5.3.5(3)

5.3.6

5.3.6(1) NOTE 1

Complementary information

National choice

National choice Not relevant

No exceptional loads are applied

No guidance

Unchanged

National choice

National choice

The entire clause is replaced by a new clause Cf. above, new clause

Page 3 of 15 Overview, national choices and complementary information.

DS/EN 1991-1-3 DK NA:2015 – 2nd edition

Clause

Subject

National choice1)

5.3.6(1) NOTE 2

Snow load shape coefficients. Roofs abutting and close to taller construction works Range for drift length Snow load shape coefficients. Roofs abutting and close to taller construction works Drifted snow Local effects

Cf. above, new clause

5.3.6(3)

6.2

6.2(2) 6.3(1)

Local effects. Drifting at projections and obstructions Local effects. Snow overhanging the edge of a roof

6.3(2)

Cf. above, new clause

The entire clause is replaced by a new clause 5.3.6 Cf. above, new clause Unchanged

Local effects. Snow overhanging the edge of a roof Coefficient k Annex A Design situations and load arrangeTable A.1 ments to be used for different locaNOTE 2 tions Annex B Snow load shape coefficients for exceptional snow drifts Annex C European Ground Snow Load Maps

Not applicable

Annex D

Adjustment of the ground snow load according to return period

Unchanged

Annex E

Bulk weight density of snow

No choice made

Annex F

Alternative drifted snow load arrangements Roof valleys

Annex G

Complementary information

Not applicable

Not applicable

Snow overhanging the edge of a roof is not applied Snow overhanging the edge of a roof is not applied, k=0 No exceptional loads are applied No exceptional loads are applied

Not applicable

The recommended values are applied Complementary information Complementary information

1)

Unchanged: The recommendation in the Eurocode is followed. No choice made: The Eurocode does not recommend values or methods, but allows the option of determining national values or methods. Not applicable The Annex is not applicable. Applicable: The Annex is applicable in Denmark and has the same status as specified in the Eurocode. National choice: A national choice has been made. Not relevant: Not applicable in Denmark.

Page 4 of 15 Overview, national choices and complementary information.

DS/EN 1991-1-3 DK NA:2015 – 2nd edition

National choices 4.1 (1) NOTE 1 Characteristic values - Snow load on the ground Characteristic ground snow load value sk = 1,0 kN/m2. 4.2 (1) Other representative values - Load combination factors Values equal to those specified in the Danish National Annex to DS/EN 1990 are chosen. 5.2(7) Load arrangements – Exposure coefficient Ce The exposure coefficient, Ce, depends on the topography of the surroundings and the size of the structure, and is determined by: Ce = CtopCs where Ctop is the topography coefficient Cs is the size coefficient. The coefficient Ctop is obtained using Table 5.1.a NA. Table 5.1.a NA – Recommended values of Ctop for different topographies Topography 𝑪𝐭𝐨𝐩 a) Windswept 0,8 Normal b) 1,0 c) Sheltered 1,25 a)

Windswept topography: Flat unobstructed areas exposed on all sides without, or little shelter afforded by terrain, higher construction works or trees. The topography can be taken as windswept when the structure is at least 15 m higher than local shelters in the surrounding terrain. It is particularly decisive to evaluate the conditions in the case of exposure to wind from eastern directions – see Figure 5.2.c NA. b)

Normal topography: Areas where there is no significant removal of snow by wind on construction works because of terrain, other construction works or trees. c)

Sheltered topography: Areas in which the construction being considered is considerably lower than the surrounding terrain or surrounded by high trees and/or by higher construction works.

The coefficient Cs is obtained by: For sheltered topography: Cs = 1,0 Page 5 of 15 National choices

DS/EN 1991-1-3 DK NA:2015 – 2nd edition

For windswept and normal topographies, where l1 and l2 are the lengths of the longer and shorter sides, respectively, of the building: For 2h > l1 (cf. Figure 5.0.b NA): Cs = 1,0 For 2h ≤ l1 (cf. Figure 5.0.b NA): 𝐶s = 1 𝑙 −10ℎ 𝐶s = 1 + 0,025 ∙ 2 ℎ 𝐶s = 1,25

for l2 ≤ 10h for 10h < l2 < 20h for l2 ≥ 20h

Figure 5.0.b NA – Building dimensions

5.3.3(4) Snow load shape coefficients. Pitched roofs For structures exposed to wind and snow, an additional load arrangement is taken into account by applying a shape factor of zero for the windward side and µw for the leeward side of the roof as shown in Figure 5.2.b NA. The load arrangement allows for an exceptional amount of drifted snow due to wind on the leeward side of the roof when all of the conditions mentioned below are fulfilled:  the orientation of the building shall be as shown in Figure 5.2.c NA;  the height of the windward side of the building does not exceed 10 m;  2 times the ridge height, h, is smaller than the crosswind dimension of the building, l, see Figure 5.2.c NA, i.e. 2h < l;  the depth of the building, b, is larger than the ridge height of the building, h, see Figure 5.2.b NA, i.e. b > h;  the windward terrain is an open area which corresponds to a terrain roughness of category II according to DS/EN 1991-1-4 (Table 4.1) at a distance of 400 m. The rules in clause 5.3.3(4) are not to be combined with the rules for roof valleys specified in Annex G. Page 6 of 15 National choices

DS/EN 1991-1-3 DK NA:2015 – 2nd edition

Figure 5.2.b NA – Snow load shape coefficient for leeward side depending on roof slope The shape coefficient, µw, obtained from Figure 5.2.b NA, may be calculated using the following expressions: µw = 0,8 µw = 0,6 + 0,04α µw = 1,2 µw = 2,4 – 0,04α µw = 0

for 0º ≤ α ≤ 5º for 5º < α < 15º for 15º ≤ α ≤ 30º for 30º < α < 60º for 60º ≤ α

Figure 5.2.c NA – Drifted snow on leeward side of the roof (hatched area) is assumed to occur only when the windward side faces directions from NNE to SE, corresponding to significant drifting when wind comes from easterly directions only Page 7 of 15 National choices

DS/EN 1991-1-3 DK NA:2015 – 2nd edition

5.3.5(1) NOTE 2 Snow load shape coefficients. Cylindrical roofs – Consideration of snow fences Where snow fences or other structural parts prevent snow from sliding down the roof, the snow load should be increased.

5.3.5(3) Snow load shape coefficients. Cylindrical roofs - Drifted snow load arrangement For cylindrical roofs, the drifted snow load arrangement in figure 5.6 in DS/EN 1991-1-3:2007 is supplemented by the following load arrangement shown in Figure 5.5.b NA and Figure 5.5.c NA. For β0 ≤ 60º, triangular drifting distribution is assumed, taken as zero at the ridge and using the shape coefficients µ4 and µ4/2, respectively, at the line separating the roof and the vertical faces. For β0 >60º, triangular drifting distribution is assumed, taken as zero at the ridge and using the shape coefficients µ4 and µ4/2, respectively, where β = 60°. For β > 60°, the shape coefficient is 0.

Figure 5.5.b NA – Snow load shape coefficient for a cylindrical roof slope  0 > 60º

Figure 5.5.c NA – Snow load shape coefficient for a cylindrical roof slope  0  60º Page 8 of 15 National choices

DS/EN 1991-1-3 DK NA:2015 – 2nd edition

5.3.6 Snow load shape coefficients. Roofs abutting and close to taller construction works as well as drifting at projections and obstructions (1)NA The structure afforded shelter from the wind is illustrated in Figure 5.6.a NA. It is assumed that αw > -5 and αl > -5. Global shelters have a decisive effect on the wind flow around the entire structure. Local shelters only affect the wind flow around the shelter. The rules given in this clause apply when 2 times the height of the shelter is smaller than the horisontal crosswind dimension of the shelter. If this condition is not fulfilled, the wind will primarily flow around the shelter and drifting be reduced. NOTE - Equivalent rules also apply to smaller buildings abutting or close to cylindrical buildings.

(2)NA The parameter a determines whether the shelter is local (a ≤ 0,2) or global (a ≥ 0,4) and is obtained using the expression 𝑎 = max {

2 ℎ𝑠𝑤 𝑏𝑤 , } 𝑏𝑤 ℎw 25ℎw

where (see also Figure 5.6.a NA): hw bw hsw

is the height of the windward face; hw is not taken as lower than 1,5 m; is the distance from the height of the windward face of the shelter; is the height of the face of the shelter for αsw ≤ 60°. For αsw = 90°, hsw is taken as the ridge height. For 60 ° < αsw < 90°, hsw is obtained by interpolation.

(3)NA Snow load shape coefficients for structures with shelters are given by the following expressions and are shown in Figure 5.6.a NA: µ2 is taken from table 5.2 of DS/EN 1991-1-3/A1, applying the roof slopes considered µ3 = µs+ µw where µs µw

(5.7) is the snow load shape coefficient due to snow sliding from the upper roof; is the snow load shape coefficient due to wind. This shape coefficient depends on the specific weight density of snow, γ, which is taken as 2 kN/m3 for this calculation.

(4)NA For the windward face of a shelter the following applies, see Figure 5.6.a NA: lsw = min{bw;2hsw} 𝛾

𝜇ww = ℎsw 𝑠

k

but 5 m ≤ lsw ≤ 15 m but µww ≥ µ1 Page 9 of 15

National choices

DS/EN 1991-1-3 DK NA:2015 – 2nd edition

µww ≤ 2 µww ≤ 10a µww ≤ 4

but a ≤ 0,2 but 0,2 < a < 0,4 but a ≥ 0,4

(5)NA For the leeward face of a shelter the following applies, see Figure 5.6.a NA: but 5 m ≤ lsl ≤ 15 m og lsl ≤ b1

lsl = 5 hsl 𝛾

𝜇wl = ℎsl 𝑠

but µ ≤ µwl ≤ 2

µwl = 0

if hsl < 0,5 m

µsl = 0

if hsl < 0,5 m

µsl = 0 µsl = µ1(αsl) bsl / lsl

for αsl ≤ 15° for αsl > 15°

k

NOTE - NOTE - For low values of hsw, the load case in Annex F, F(3), may govern the design.

Figure 5.6.a NA Structure with shelter where the windward face height is hsw and the leeward face height is hsl

Page 10 of 15 National choices

DS/EN 1991-1-3 DK NA:2015 – 2nd edition

(6) NA If the leeward side of a roof has several local shelters, the leeward load shall be increased in certain cases. This is taken into account by applying an additional load arrangement when all of the conditions mentioned below are fulfilled:      

the orientation of the building shall be as shown in Figure 5.2.c NA; the height of the windward side of the building does not exceed 10 m; 2 times the ridge height, h, is smaller than the crosswind dimension of the building, l, see Figure 5.7.a NA, i.e. 2h < l; the shelters are at least 0,5 m high; the free distance, lv, between shelters is between 3 and 7 times their width, v; shelters are located on the leeward side.

The shape coefficient, µw, for the additional load arrangement is obtained from: µw = 1,0 µw = 1 – (α-35)/25 µw = 0

for 0º ≤ α ≤ 35º for 35º < α < 60º for 60º ≤ α

The load is applied to the leeward face of the shelters, see Figure 5.7.a NA.

Figure 5.7.a NA Closely spaced local shelters with wind from easterly directions, cf. Figure 5.2.c NA Page 11 of 15 National choices

DS/EN 1991-1-3 DK NA:2015 – 2nd edition

If the free distance between the shelters is 10 times the shelter width, (lv ≥ 10v), the load case in Figure 5.7.a NA may be disregarded. If the free distance is between 7 and 10 times the shelter width, (7v < lv < 10v), the shape coefficient, µw, is determined by linear interpolation.

If the free distance is 0, the shape coefficient, µw, is determined by applying the rules in clause 5.3.6(5) NA. If the free distance is between 0 and 3 times the shelter width, (0 < lv < 3v), the shape coefficient, µw, is determined by linear interpolation. The rules regarding local shelters are to be combined neither with the rules in clause 5.3.3(4), nor the rules for roof valleys specified in Annex G.

Annex A, Table A.1, Note 2 Design situations and load arrangements to be used for different locations – Application of Annex B ( (exceptional snow loads) Exceptional snow falls or snow drifts are not assumed for Denmark; therefore no instructions are given for cases B1 and B3.

Page 12 of 15 National choices

DS/EN 1991-1-3 DK NA:2015 – 2nd edition

Complementary (non-contradictory) information 5.3.1(1) Shape coefficients. General. Alternative snow drift load arrangements NOTE - Drifted snow loads are furthermore to include the specifications in Annex F.

Annex F Alternative drifted snow load arrangements (1)NA For structures susceptible to snow load variations, e.g. cantilevered structures and structures susceptible to torsion, a load case is examined where half of the snow load is taken as a fixed action and the other half of the snow load is taken as a free action. (2)NA The same partial coefficient is applied for the fixed part and the free part of the snow load. For cantilevered roofs, examples include the following load cases:

Figure F.1 NA Structure with cantilever

For a structure susceptible to torsion, examples include the following load cases:

Figure F.2 NA Structure susceptible to torsion

NOTE - μ = μ1 (3)NA For a roof where the slope is reduced from α2 to α3, see Figure F.3 NA, the risk of snow loads due to drifting can be taken into account as illustrated in the figure. Case (ii) is equivalent to case (ii) in DS/EN 1991-1-3, clause 5.3.4 (3), which is applied if α3 < 0.

Page 13 of 15 Complementary information

DS/EN 1991-1-3 DK NA:2015 – 2nd edition

Figure F.3 NA – Shape coefficient for roofs with change of slope

Annex G Roof valleys (1)NA At roof valleys, drifting may occur both at the windward and the leeward sides. The rules given below apply for buildings where the horisontal projection of the roof valley l ≥ 10 m, and where b1 ≥ 2h1 or b2 ≥ 2h2; the symbols appear from Figure G.1 NA. (2)NA Drifting is assumed in the hatched area in Figure G.1 NA. Drifting may occur on both sides simultaneously or on one side only. (3)NA Within the hatched area the shape coefficient is increased from µ2 to µ3 as shown in Figure G.1.NA, where µ2 and µ3 are the shape coefficients according to clause 5.3.3(2). For µ3, the value of the larger of the angles of roof pitch is applied. NOTE 1 - The rule applies to monopitch as well as pitched roofs. NOTE 2 - For structures that are not susceptible to asymmetric snow loads (e.g. structures not susceptible to torsion), it will be conservative to take the shape coefficient as µ3 for the entire hatched area.

Page 14 of 15 Complementary information

DS/EN 1991-1-3 DK NA:2015 – 2nd edition

Figure G.1 NA Structure with roof valleys. The area for which increased shape coefficients apply is marked

Page 15 of 15 Complementary information

DS/EN 1991-1-3 DK NA:2015 – 2nd edition