Determination of snow bag for height changes on roofs according to EN 1991-1-3

Technical Article

This article was translated by Google Translator View original text

Annexes are often found on buildings. If the roof levels are not at the same depth, this elevation jump (if more than 0.5 m) must additionally be considered for the snow load assumption.

In addition to the normal snow load, which is applied to the roof below, an additional load from slipping and blown snow has to be considered. These two additional loads are distributed triangularly over the length of the flywheel l s .

Additional impact loads due to the snow slipping off the higher roof may also have to be taken into account.

γ = weight of snow = 2 kN/m³

h = depth of the eavesdropping

s k = characteristic value of the snow load on the ground in kN/m²

l s = drift length = $ 2 \; \ cdot \; \ mathrm h \; \ left \ {\ begin {array} {l} \ geq \; 5 \; \ mathrm m \\ leq \; 15 \; \ mathrm m \ end {array} \ right. $
If the length of the underlying roof b 2 is shorter than the length of the gougule wedge l s , then the load ordinates must be cut off at the edge of the roof.

μ 1 = 0.8 (assuming the lower roof is flat)

μ 2 = μ s + μ w

μ s = shape coefficient for derived snow
α ≤ 15 °: μ s = 0
α> 15 °: μ s results from an additional load that is distributed triangular to length l s . As an additional load, 50% of the resulting snow load is applied to the adjoining roof side of the higher roof.

μ = shape coefficient of the roof at a higher level = 0.8 (regardless of the roof inclination)

μ w = shape coefficient for snow with consideration of wind = $ \ frac {{\ mathrm b} _1 \; + \; {\ mathrm b} _2} {2 \; \ cdot \; \ mathrm h} \ le \ \ ; \ frac {\ mathrm \ gamma \; \ cdot \; \ mathrm h} {{\ mathrm s} _ {\ mathrm k}} $

In addition, the sum of the shape coefficients μ w + μ s can be limited by the National Annex (Germany) as follows.

Common case:
0.8 ≤ μ w + μ s ≤ 2.4

Canopies open at the side and accessible for evacuation (b 2 ≤ 3 m):
0.8 ≤ μ w + μ s ≤ 2

For snow regions s k ≥ 3.0 kN/m², the upper limit applies for the alpine region according to DIN EN 1991-1-3: 2010-12 and DIN EN 1991-1-3/A1: 2015-12, Figure C.2 Limitation:
1.2 ≤ μ w + μ s ≤ (6.45/s k 0.9 )

Exceptional actions (North German Plain) in general:
0.8 ≤ μ w + μ s ≤ 2.4

When arranging snow guards or similar structures, it is not necessary to use μ s .

Example:

b 1 = 10 m
b 2 = 5 m
h = 3 m
Roof inclination of the roof at a higher level = 30 °
A = 100 m
Snow Load Zone 2
μ 1 = 0.8
s k = 0.25 + 1.91 ⋅ ((A + 140)/760) ² ≥ 0.85 → 0.85 kN/m²

Uniformly distributed snow load on the roof below:
μ 1 ⋅ s k = 0.8 ⋅ 0.85 kN/m² = 0.68 kN/m²

Length of drift wedge:
${\mathrm l}_{\mathrm s}\;=\;2\;\cdot\;\mathrm h\;\left\{\begin{array}{l}\geq\;5\;\mathrm m\\\leq\;15\;\mathrm m\end{array}\right.=\;2\;\cdot\;3\;\mathrm m\;=\;6\;\mathrm m$

Shape coefficient for derived snow:
μ s = 0.67

Shape coefficient for snow with consideration of wind:
$µ_{\mathrm w}\;=\;\frac{{\mathrm b}_1\;+\;{\mathrm b}_2}{2\;\cdot\;\mathrm h}\;\leq\;\frac{\mathrm\gamma\;\cdot\;\mathrm h}{{\mathrm s}_{\mathrm k}}\;\\µ_{\mathrm w}\;=\;\frac{10\;\mathrm m\;+\;5\;\mathrm m}{2\;\cdot\;3\;\mathrm m}\;\leq\;\frac{2\;\mathrm{kN}/\mathrm m³\;\cdot\;3\;\mathrm m}{0,85\;\mathrm{kN}/\mathrm m²}\;=\;2,50$

Limitation of shape coefficients (general case):
0.8 ≤ μ w + μ s ≤ 2.4
μ 2 = μ w + μ s = 2.5 + 0.67 = 3.17 → 2.4

μ 2 ⋅ s k = 2.4 ⋅ 0.85 kN/m² = 2.04 kN/m²

In RFEM and RSTAB, it is possible to conveniently apply the load arising from drifted snow and shifting snow as a linearly variable surface load. For frameworks, for example, you can apply the load with the load generator.

Keywords

Snow Snow bag Drifted snow load Snow accumulation Vertical rise

Reference

[1]   Eurocode 1: Actions on structures - Part 1‑3: General actions - Snow actions; EN 1991‑1‑3:2003 + AC:2009
[2]   National Annex - Nationally determined parameters - Eurocode 1: Actions on structures - Part 1‑3: General actions - Snow actions; EN 1991‑1‑3/NA:2019‑04
[3]   Albert, A.: Schneider - Bautabellen für Ingenieure mit Berechnungshinweisen und Beispielen, 23. Auflage. Köln: Bundesanzeiger, 2018

Downloads

Links

Contact us

Contact Dlubal Software

Do you have questions or need advice?
Contact our free e-mail, chat, or forum support or find various suggested solutions and useful tips on our FAQ page.

(267) 702-2815

info-us@dlubal.com

Contact us

Contact Dlubal Software

Did you find your question?
If not, contact us via our free e-mail, chat, or forum support, or send us your question via the online form.

(267) 702-2815

info-us@dlubal.com

RFEM Main Program
RFEM 5.xx

Main Program

Structural engineering software for finite element analysis (FEA) of planar and spatial structural systems consisting of plates, walls, shells, members (beams), solids and contact elements

Price of First License
3,540.00 USD
RSTAB Main Program
RSTAB 8.xx

Main Program

The structural engineering software for design of frame, beam and truss structures, performing linear and nonlinear calculations of internal forces, deformations, and support reactions

Price of First License
2,550.00 USD