PowerFrame Part 3 - Wind and Snow Loads.pdf

7/22/2019 PowerFrame Part 3 - Wind and Snow Loads.pdf

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Part 3:

PowerFrameWind & snow loads

generators(Eurocode 1)


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PowerFrame Manual Wind & snow loads generators 2

BuildSoft nv

All rights reserved. No part of this document may be reproduced ortransmitted in any form or by any means, electronic or manual, for anypurpose, without the prior written consent of BuildSoft.

The programs described in this manual are subject to copyright by BuildSoft.They may only be used by the licensee and may only be copied for thepurpose of creating a security copy. It is prohibited by law to copy them forany other purpose than the licensees own use.

Although BuildSoft has tested the programs described in this manual and hasreviewed this manual, they are delivered As Is, without any warranty as totheir quality, performance, merchantability or fitness for any particular

purpose. The entire risk as to the results and performance of the programs,and as to the information contained in the manual, lies with the end-user.


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1 Table of contents1 TABLE OF CONTENTS ......................................................................................3

2 WIND LOADS GENERATOR ............................................................................4

2.1 WIND LOADS GENERATOR (EC1) .......................................................................4

2.1.1 Introduction ...............................................................................................4

2.1.2 General principles .....................................................................................42.1.2.1 Application limitations .................... ...................... ..................... ..................... ..................... ...................... ..............42.1.2.2 Wind direction....................... ..................... ..................... ...................... ..................... ..................... ..................... ....42.1.2.3 Wind load cases..................... ..................... ..................... ...................... ..................... ..................... ..................... ....52.1.2.4 Wind velocity ...........................................................................................................................................................52.1.2.5 Reference wind pressure qref.....................................................................................................................................6 2.1.2.6 Wind pressure on surfaces...................... ...................... ..................... ..................... ...................... ..................... .......72.1.2.7 Exposure coefficient ce(z).........................................................................................................................................7 2.1.2.8 Roughness coefficient cr(z).......................................................................................................................................8 2.1.2.9 Topography coefficient ct(z).....................................................................................................................................9 2.1.2.10 Example ...............................................................................................................................................................92.1.2.11 Dynamic coefficient (Cd)....................................................................................................................................10 2.1.2.12 External pressure coefficient (Cpe) .....................................................................................................................10

2.1.2.12.1 External pressure coefficient Cpe for vertical walls.........................................................................................102.1.2.12.2 External pressure coefficient Cpe for roofs......................................................................................................13

2.1.2.13 Internal pressure coefficient (Cpi).......................................................................................................................14

2.1.3 Examples..................................................................................................15

2.1.4 Country-specific maps and values...........................................................212.1.4.1 Direction factor (Belgium)......................................................................................................................................212.1.4.2 Maps.................... ..................... ...................... ..................... ..................... ..................... ...................... ...................22

2.1.4.2.1 The Netherlands................................................................................................................................................232.1.4.2.2 France ................... ..................... ...................... ..................... ..................... ..................... ...................... ............24

3 SNOW LOADS GENERATOR..........................................................................24

3.1 SNOW LOADS GENERATOR (EC1) ......................................................................24

3.1.1 Introduction .............................................................................................24

3.1.2 General principles ...................................................................................253.1.2.1 Snow load on the ground (sk)..................................................................................................................................25 3.1.2.2 Snow load on roofs (s)............................................................................................................................................253.1.2.3 Snow load cases......................................................................................................................................................253.1.2.4 Snow loads on snowguards and obstacles...............................................................................................................25

3.1.3 Examples..................................................................................................263.1.3.1 Example 1...............................................................................................................................................................263.1.3.2 Other examples........ ..................... ..................... ..................... ...................... ..................... ..................... ................29

3.1.4 Maps ........................................................................................................313.1.4.1 Austria ..................... ..................... ..................... ..................... ...................... ..................... ..................... ................313.1.4.2 Belgium ................... ..................... ..................... ..................... ...................... ..................... ..................... ................323.1.4.3 Denmark..................... ..................... ...................... ..................... ..................... ..................... ...................... ............323.1.4.4 Finland....................................................................................................................................................................32 3.1.4.5 France ...................... ..................... ..................... ..................... ...................... ..................... ..................... ................333.1.4.6 Germany..................... ..................... ...................... ..................... ..................... ..................... ...................... ............343.1.4.7 Greece.....................................................................................................................................................................35 3.1.4.8 Italy.........................................................................................................................................................................36 3.1.4.9 Luxemburg .............................................................................................................................................................373.1.4.10 The Netherlands................... ...................... ..................... ..................... ..................... ...................... ...................373.1.4.11 Portugal...................... ..................... ..................... ..................... ...................... ..................... ..................... .........373.1.4.12 Spain ..................................................................................................................................................................373.1.4.13 Sweden........ ...................... ..................... ..................... ...................... ..................... ..................... ..................... ..39

3.1.4.14 Switzerland.........................................................................................................................................................39 3.1.4.15 United Kingdom.................................................................................................................................................41


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2 Wind loads generator2.1 Wind loads generator ( EC 1)

2.1.1 IntroductionPowerFrame includes several wind loads generators corresponding todifferent Standards (EC1, NBN 1991-2-4, BS 6399, NV 65, NEN 6702). Thispart of the manual deals with the generation of wind loads as per Eurocode 1.This document is not a substitute to this Standard, but provides a betterinsight on the effective use of PowerFrames wind loads generator.

2.1.2 General principles2.1.2.1 Application limitationsThe application of the wind loads generator has only one limitation relateddirectly to the prescriptions of Eurocode 1.

Eurocode 1 is not applicable to buildings characterized by a dynamiccoefficient (Cd) exceeding the value of 1.2. The dynamic coefficient Cd takesinto account the reduction effects due to the lack of correlation of pressures

over large surfaces as well as the increasing effects due to the frequencycontent of turbulence close to the fundamental frequency of the structure. Itdepends on the overall dimensions and the type of structure (steel, timber,concrete,...). For instance, a reinforced concrete building not higher than 100meter or a steel construction lower than 35 meter have a dynamic coefficientCd lower than or equal to 1. The dynamic coefficient of a building can beobtained using the diagram given in section 9 of Eurocode 1 part 2-4, orthrough the application of the formula given in annex B of Eurocode 1 part 2-4.

The wind loads generators as implemented in PowerFrame are applicable tobuildings, and are not necessarily appropriate for other types of structures, aseg. bridges,

2.1.2.2 Wind directionThe Eurocode proposes a method to model the effects of wind blowingperpendicular to the vertical surfaces of a building. PowerFrame will enable togenerate wind loads over planes parallel to the XY and ZY planes.


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2.1.2.3 Wind load casesPowerFrame allows to generate wind loads in case wind acts from the left tothe right, or from the right to the left. In addition, EC1 specifies 2 possibilitiesfor each case, related to the angle between the wind direction and the

horizontal plane (?15). In other words, PowerFrame allows to handle bothupward or downward winds. Normally, a building should be able to resistwind loads in all possible cases.

2.1.2.4 Wind velocityThe reference wind velocity vrefis defined as 10 minutes mean wind velocity,at a height of 10 meter above ground level on a terrain of category II (seefurther for more background information), having a mean return period of 50years.

It shall be determined from

0,refALTTEMDIRref vCCCv ????

wherevref,0: basic value of reference wind velocity;CDIR: direction factor (taking into account wind direction);CTEM: reduction factor for temporary or provisional structures.CTEM

= 1, unless otherwise specified in annex A of Eurocode 1part 2-4

CALT: altitude factor (taking into account the altitude of the buildinglocation).

The values of above parameters are specified for each country and eachregion:

? in Belgium, vref,0 is fixed at 26.2 m/s, CTEM and CALT both equal 1. A

table defines CDIR as a function of wind direction. CDIR = 1 for windsblowing from the North, West or South but varies between 1 and 0.837for wind directions between North and East, and between East andSouth.

? in the Netherlands, a distinction is made between 3 regions for whichthe basic reference wind velocity is 25.0, 27.5 and 30 m/s. The 3regions are illustrated on the map included in the Country-specific mapsand values. section. The parameters CDIR, CTEMand CALTare all equalto 1.


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? in Luxemburg, vref,0is taken equal to 26.0 m/s. CDIR, CTEMand CALTareall equal to 1.

? In France, 4 zones are specified for which different basic referencewind velocities are applicable (24.0, 26.0, 28.0, 30.5 m/s). The zones

are defined as shown on the map in this manuals section Country-specific maps and values. The parameters CDIR, CTEMand CALTare allequal to 1.

? Germany is divided in 4 zones in which the basic reference windvelocity varies between 24.3 and 31.5 m/s. In zones 1 and 2, for whichthe average wind velocity is relatively low, the CALTcoefficient is to beused for all constructions located at an altitude of more than 800 meter.

o In zone 1, CALT= 0.65 + altitude /2270 for an altitude ranging from

800 to 1100 meter. Above an altitude of 1100 meter,measurements are required to determine the appropriate value forCALT.

o In zone 2, measurements are required for altitudes from 800meter onwards.

For buildings designed for a life time of max. 4 years, a reduction of thedesign wind pressures is allowed and can be introduced through thefactor CTEM.

Should parameters referring to other countries be required, please checkEurocode Part 2-4 Annex A.

2.1.2.5 Reference wind pressure qrefThe reference wind pressure qref, expressed in N/m

2, is calculated as:

2

2

ref

ref

vq

??

?

wherevref: reference wind velocity in m/s

? : air density in kg/m3. Air density is affected by the altitude anddepends on the temperature and pressure to be expected in theconsidered region during wind storms. Unless otherwise specified

in annex A of Eurocode 1 part 2-4, the value of ? shall be takenequal to 1.25 kg/m3.

For instance: in Belgium, the reference wind pressure is equal to 429 N/m

2

incase CALT= CTEM= CDIR= 1.


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2.1.2.6 Wind pressure on surfacesThe net value of the wind pressure on a surface corresponds to the differencebetween the external and internal pressure on this surface.

The wind pressure acting on the external surfaces of a structure (we) is givenby:

peeerefe Czcqw ??? )(

whereqref: reference wind pressure;ce(ze): exposure coefficient;cpe: external pressure coefficient.

The wind pressure acting on the internal surfaces of a structure (wi) is givenby:

piierefi Czcqw ??? )(

whereqref: reference wind pressure;ce(zi): exposure coefficient;

cpi: internal pressure coefficient.

2.1.2.7 Exposure coefficient ce(z)The exposure factor ce(z) takes into account the impact of several parameterson the average wind velocity. For example : terrain characteristics, presenceor absence of obstacles, topography and height above ground level. Thisfactor can be derived from the following formula:

?

?

?

?

?

?

?

?????

)()(

71)()()( 22

zczc

kzczczc

tr

Ttre

where kT: terrain factor (see table below) ;cr(z) roughness coefficient (see section Roughness coefficient

cr(z)of this manual) ;ct(z) topography coefficient (see section Topography coefficient

ct(z)of this manual).

Following terrain categories are considered :

I rough open sea, lakes with at least 5 km fetch upwind and smooth flatcountry without obstacles.


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II farmland with boundary hedges, occasional small farm structures,houses or trees.

III suburban or industrial areas and permanent forests.

IV urban areas in which at least 15% of the surface is covered by buildingshaving a height exceeding 15 meter.

The parameters kT, z0 and zmin are defined as a function of the followingterrain categories :

Terrain category kT z0[m]

zmin[m]

IIIIIIIV

0.170.190.220.24

0.010.050.31

248

16

The parameters z0 and zmin (minimum height) allow to determine theroughness coefficient cr(z).

2.1.2.8 Roughness coefficient cr(z)cr(z) , as a function of height z, is given by:

)200(ln)( min0

mzzz

zkzc Tr ???

?

?

?

??

?

???

)(ln)()( min0

minmin zz

z

zkzczc Trr ??

?

?

?

??

?

????

Calculation example cr(z):

Consider a terrain of category III on which a 4 meter high building willbe erected. Based on the previous table, it is derived that:

kT= 0.22z0 = 0.3mzmin = 8m

The height z is equal to 4m and is thus lower than the minimum height.

Thus:


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cr(z) = cr(zmin) = cr(8) = 0.22 * ln(8/0.3) = 0.722

2.1.2.9 Topography coefficient ct(z)

The topography coefficient ct(z) accounts for the increase of the mean windspeed over isolated hills and escarpments (not undulating and mountainousregions). It is related to the wind velocity at the base of the hill orescarpment. It shall be considered for locations closer than half the length ofthe hill slope from the crest or 1,5 times the height of the cliff. It is defined by:

ct= 1 in case ?< 0.05

ct= 1 + 2 . s . ? in case 0.05 < ?< 0.3

ct= 1 + 0.6 . s in case ?> 0.3

where

s : a factor derived from diagrams 8.1 & 8.2 of EC1, part 2-4

?: upwind slope of terrain in wind direction [%].

2.1.2.10 Example

Hypotheses: Terrain of category III, situated in Belgium.

Construction height and length: 1 meter.

Suppose the construction is situated on top of a hill which is 30 m high, andhas a slope of 30% in all directions.

Calculation of wind pressure:

? the roughness coefficient cr(z) has the same value as in the previousexample :

KT= 0.22cr(z) = 0.722


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? topography coefficient ct(z):

?= 0.3Le = Lu = 100mZ/Le = 0.3

Diagram 8.2 of the Eurocode shows s = 0.5, which finally yields toct(z) = 1.3

? exposure coefficient ce(z)

ce(z) = 2.328

Hence, the wind pressure on the vertical surface at the left hand side in the

above picture is equal to:

2.328 x 429 = 999N/m2.

2.1.2.11 Dynamic coefficient (Cd)The pressure calculated in accordance with the principles outlined above, stillneeds to be multiplied by a factor cd, to take into account the possible risk ofa dynamic excitation of the structure. The dynamic coefficient of a building

can be obtained using the diagram given in section 9 of Eurocode 1 part 2-4,or through the application of the formula given in annex B of Eurocode 1 part2-4.

2.1.2.12 External pressure coefficient (Cpe)

2.1.2.12.1 External pressure coefficient Cpe forvertical walls

Cpe for buildings and individual parts of buildings depends on the size of theloaded area A:

Cpe,1 in case the loaded area A is smaller than or equal to 1m2

Cpe,10 in case the loaded area A is larger than or equal to 10 m2

Cpe= Cpe,1+ (Cpe,10 Cpe,1) . log10A,

in case the loaded area A is larger than 1 m2

but smaller than 10 m2

.


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The value of Cpealso depends on the ratio d/h, where d corresponds to thedepth of the building (in the wind direction) and h corresponds to the height ofthe building.

The table below shows the values that correspond to the front and rearvertical walls of a rectangular building:

Zone D E

d/h Cpe,10 Cpe,1 Cpe,10 Cpe,1

? 1

? 40.80.6

11

-0.3-0.3

In case the ratio d/h is between 1 and 4, the values of Cpeare obtained byinterpolation.

In the previously presented example, the wind pressure on the vertical wallscan now be calculated.

? wind pressure on front wall (windward side):

429 x 1.634 X 1.0 = 701 N/m2

? wind pressure on rear wall (leeward side):

429 x 1.634 x (-0.3) = -210 N/m2.

Using the same hypotheses as in the previous example, assume aconstruction of 4 meter high. The surface exposed to the wind is thus 4m

2.

Cpe = Cpe,1+ (Cpe,10 Cpe,1) . log10A

= 1.0 + (0.8 1.0) . log104 = 0.880



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429 x 1.634 X 0.880 = 616 N/m2


429 x 1.634 x (-0.3) = -210 N/m2.

Again using the same hypotheses, considering a building with a depth of 2meter in the direction of the wind:

d/h = 2

The value of Cpe,10is obtained through interpolation:

Cpe,10= 0.8 0.2/3 = 0.733

Cpe = Cpe,1+ (Cpe,10 Cpe,1) . log10A= 1.0 + (0.733 1.0) . log104= 0.840


429 x 1.634 X 0.840 = 589 N/m2


429 x 1.634 x (-0.3) = -210 N/m2.

Note: the reference heigt zefor walls of rectangular buildings depends on the

aspect ratio h/b (height over width):? buildings whose height h is less than b shall be considered to be one

part

? buildings whose height h is larger than b but less than 2b, shall beconsidered to be of 2 parts, comprising: a lower part extending upwardsfrom the ground to a height equal to b and an upper part

? buildings whose height h is larger than 2b shall be considered to be inmultiple parts, comprising: a lower part extending upwards from theground to a height equal to b; an upper part extending downwards from

the top by a height equal to b and a middle region, between the upperand lower parts, divided into as many horizontal strips as desired,eachone with a maximum height of b.


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2.1.2.12.2 External pressure coefficient Cpe forroofs

The Eurocode considers two different types of roof. Hereafter, the calculationof the external wind pressure will be discussed and presented in detail for 2specific roof types. It should be outlined that PowerFrame can handle othertypes of roof than those discussed hereafter, in order to meet the Eurocoderequirements as closely as possible.

2.1.2.12.2.1 Flat roof

All roofs with a slope smaller than 4% are qualified as flat roofs. A flat roofcan be divided in different zones, as outlined in the plan view given below :

The parameter e is the minimum of 2h and b, h being the height of the flatroof above ground level.

The factors given in the following table apply to the different zones indicatedin the above diagram :

f g h iZone

Cpe,10 Cpe,1 Cpe,10 Cpe,1 Cpe,10 Cpe,1 Cpe,10 Cpe,1

Sharp eaves -1.8 -2.5 -1.2 -2.0 -0.7 -1.2 ?0.2

Withparapets

Hp/h = 0.025Hp/h = 0.05Hp/h = 0.1

-1.6-1.4-1.2

-2.2-2.0-1.8

-1.1-0.9-0.8

-1.8-1.6-1.4

-0.7-0.7-0.7

-1.2-1.2-1.2

?0.2

?0.2

?0.2

The values of Cpe in zone i can be positive or negative. Therefore, 2 casesneed to be considered (corresponding to positive pressure and suction).

An example will be presented further in this manual.

2.1.2.12.2.2 Duopitch roof


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A duopitch roof can be divided in different zones, as presented in the diagrambelow:

The height ze= h is the height above ground level of the highest point of theroof (roof crest). The parameter e is the minimum of 2h and b.

For a wind blowing in the direction of the roof slope, the values of Cpecan bederived from the table below:

Zone f g h i j

Slope Cpe,10 Cpe,1 Cpe,10 Cpe,1 Cpe,10 Cpe,1 Cpe,10 Cpe,1 Cpe,10 Cpe,1

515

30

456075

-1.7 -2.5-0.9 -2.0

0.2-0.5 -1.5

0.7

0.70.70.7

-1.2 -2.0-0.8 -1.5

0.2-0.5 -1.5

0.7

0.70.70.8

-0.6 -1.2-0.30.2-0.20.4

0.60.70.8

-0.3-0.4

-0.4

-0.2-0.2-0.2

-0.3-1.0 -1.5

-0.5

-0.3-0.3-0.3

An example will be presented further in this manual.

2.1.2.13 Internal pressure coefficient (Cpi)The theoretical background given below can easily be understood by usingPowerFrames dialogue window related to the internal pressure

coefficient.The user is to select the corresponding case in the dialoguewindow to directly view the value of Cpi.

Eurocode 1 part 2-4 considers several cases.

? The first case relates to nearly square buildings, characterized by ahomogeneous distribution of openings. In this case, Cpi is equal to 0.25.

? The second case corresponds to closed buildings with internalpartitions, and opening windows. In this case, Cpiis to be taken equal to0.8 or 0.5. Both possibilities have to be considered.


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? The third case includes all situations not covered by the first andsecond case described above. First, the opening ratio needs to bedetermined as follows:

Taking into account the area of temporary openings, 2 values for need to be determined (a maximum value and a minimum value).

Once both limit values have been determined, the graph below shouldbe used to derive the related value of Cpi :

Consequently, 2 values are obtained for Cpi. Both of them must beconsidered during the calculation of wind pressure.

2.1.3 ExamplesThe use of PowerFrames wind loads generator will now be explained througha number of practical examples.

First, the user defines the model geometry and boundary conditions as heusually does in PowerFrame. Then, the user selects the contour of the frameon which the wind load is to be defined, and should keep in mind that the

selected frame must always be in one plane, either parallel to the XY- orthe XZ-plane.

The user will then focus on the 2D frame contour as shown below :

Column height : 4mTotal height : 8mFrame width: 16m


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This frame is part of a larger model, representing a structure with a totallength of 18 meter and a distance of 6 meter between the frames.

In the Loads-window, the user first selects the appropriate load group in theicon toolbox before starting the definition of the wind loads. He should checkthat the frame shown above has been properly selected, and will then notice

that the icon has become active.

Using the icon, the following dialogue window will appear on the screen :

At this point, PowerFrame offers the user a choice between differentStandards. In the context of this manual, the Eurocode 1 will be used.Confirming the selection of Eurocode 1, the following dialogue will appear onthe screen:


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The user first starts to specify whether the wind blows from left to right or fromright to left. He will notice that a possible choice exists between an upward ordownward wind. The external pressure coefficients can effectively changedepending on this condition. The structure needs to be analyzed for bothconditions.

The external pressure coefficients do depend on the position of the selectedframe within the whole building. The Eurocode makes a difference betweenthe frames that can be considered as located in the middle of the building, atthe front side or at the rear side. For example, a frame with a duopitch roof is

considered to be at the edge of the building, if its distance D from the edgemeets the following condition :

D < 0.25 * min (2H , B), where

? B: width of the building (in the direction of the wind)

? H: height of the building

In the case of a canopy roof, a frame is considered to be at the edge if thedistance D between the edge and the frame meets the following condition:

D < 0.1 L, where

? L: length of the building exposed to the wind


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The next entry in the dialogue window allows to specify the width of thebuilding or that part of the building to be analyzed. When the building consistsof 2 blocks with different dimensions, it is recommended that both blocks beconsidered separately when using the wind loads generator, defining the

width to be equal to the width of the part the user is currently working on.

The distance between frames needs to be indicated in the line below. Thisdistance is actually used to define the roof surface that will transmit windloads to the frame. The user should therefore remember to divide the actualdistance by a factor 2 for both end frames.

The dynamic coefficient is filled in in the next editor field. The user is to referto section 9 of Eurocode 1 part 2-4, or to annex B of Eurocode 1 part 2-4 for

more information.

In the open dialogue window, two buttons allow to open secondary dialogue

boxes. First, the user has to click on to open the dialogueboxbelow:

The user should now enter the terrain parameters as specified in the first partof this manual. ce(z), ct(z) and cr(z) will be calculated automatically using thevalues the user has entered in the dialogue window.

At this stage, to have a good understanding of the considered example, theuser should fill in the dialogue tab as shown in the above figure.

Using the button, the user has to go back to the main dialogue

window and then click on the button to open the dialoguewindow shown below:


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This dialogue window helps to choose the most appropriate internal pressurecoefficient depending on the effective frontal area of the structure. The userwill continuously see in this dialogue window the value of Cpi depending on

the selection that has been made and on the values that have been defined.Indeed, the current value is always shown in the field at the bottom of thedialogue window, corresponding to the option User-defined value.

For this example, the user fills in the dialogue tab as shown above.

Using the button, he then returns to the main dialogue window andchecks that all parameters have been defined as shown previously. Thefollowing results will then be displayed:

Should the internal pressure coefficient Cpi have not been considered, thepressure distribution would be:


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A second example looks into the calculation of Cpein case of a building with aflat roof. The global procedure being the same as the one outlined in theprevious example, the user now considers Cpi to be equal to zero (byselecting the option : Do not take internal pressures into account).

The frame is 5 meter high and 8 meter wide. It is part of a construction with atotal length of 18 meter, and frames every 6 meter.

In this case, the results are:

These results can easily be verified manually using the information that waspreviously given in the Eurocode.

In the last example, a canopy roof will be handled.

In this particular case, the user will have only to select the roof girders todefine the wind loads, as the open walls will of course take no wind load.

Users selection will thus look as follows:

Height: 5mWidth : 8m


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As a result, two important changes in the dialogues will be noticed. The firstchange will be observed in the main dialogue window of the wind loadsgenerator. An extra editor field will request to define the height above groundlevel of the lower roof edge. The second change is related to the internalpressure coefficient, as this coefficient no longer needs to be defined(Eurocode 1 part 2-4 directly specifies the net pressure coefficients). Indeed,if the user presses the button Internal pressure , he will get the followingmessage:

If the user proceeds to the calculation of wind pressure, having defined allparameters as in the previous example and specified a total height of 6meter, the following results will be displayed:

2.1.4 Country-specific maps and values

2.1.4.1 Direction factor (Belgium)

Direction Direction factor0 (North)22.5

1.01.0


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37.754556.2590 (East)120

150180 (South)270 (West)

0.9490.8940.8370.8940.894

0.9491.01.0

For intermediate directions,interpolate between the givenvalues.

2.1.4.2 Maps


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2.1.4.2.1 The Netherlands


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2.1.4.2.2 France

3 Snow loads generator3.1 Snow loads generator (EC1)

3.1.1 IntroductionPowerFrame includes several snow loads generators corresponding todifferent Standards (EC1, NBN ENV 1991-2-3, BS 6399 Part 3, N 84, NV 65,NEN 6702). This part of the manual is dedicated to the generation of snow

loads based on Eurocode 1 part 2-3. This document is not a substitute to thisStandard, but is aimed at providing a better insight on the effective use ofPowerFrames snow loads generator.


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3.1.2 General principles

3.1.2.1 Snow load on the ground (sk)The snow load on the ground is the reference value to be taken into accountfor the calculation of the snow load on roofs. This reference snow loaddepends on the geographical position and the altitude of the building.Eurocode 1 part 2-3 annex A gives characteristic values for the snow load onthe ground for most of the European countries.

3.1.2.2 Snow load on roofs (s)The snow load on a roof shall be determined using the following formula:

ktei sCCs ???? ?

where

? i: snow load shape coefficient, function of the type of roofCe: exposure coefficient (generally taken equal to 1) ;Ct: thermal coefficient (for normal standards of thermal insulation,

taken equal to 1. A reduction in the snow load on the roof may be

permitted by the introduction of values of the thermal coefficientsmaller than 1, to take account of the effect of heat loss throughthe roof).

The snow load is assumed to act vertically and shall refer to the horizontal

projection of the area of the roof. ? i is determined automatically byPowerFrame, using section 7 of Eurocode 1 part 2-3 concerning snow onbuildings.

3.1.2.3 Snow load casesThe Eurocode specifies different snow load situations depending on the typeof roof. PowerFrame schematizes those situations by means of sketches. Asa result, the user can easily see all possible load situations by going throughthe example that is presented further in this manual.

3.1.2.4 Snow loads on snowguards and

obstaclesThe Eurocode does not specify any change in snow loads depending on thepresence or absence of snowguards. Nevertheless, a formula is given to


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determine the force exerted by a sliding mass of snow in the direction of theslope, per unit width .

???? sinbsF

where :

? s: snow load on the roof

? ? : roof pitch measured from the horizontal

? b: distance on plan from the guard or obstacle to the ridge.

This force is not considered or calculated by PowerFrame. If the user wantsto account for those forces in the PowerFrame model, they need to beintroduced manually in the model.

Note : PowerFrames snow loads generator has not been designed forcylindrical roofs. Therefore, it will not always produce snow loads whichcomply completely with the Eurocode standard for those types of roof.Nevertheless, by selecting the most frequent load cases, the user will be ableto obtain appropriate snow load models.

3.1.3 Examples

3.1.3.1 Example 1In this section, the snow loads generator will be further explained through apractical example. The snow loads generator only becomes available in theicon toolbox of the Loads-window after a frame contour has been selected.This frame contour should be in a (vertical) plane parallel to the XY- or XZ-plane.

The following frame contour will be considered.

To apply the snow loads generator, it is not necessary that the boundaryconditions or cross-section properties have been designed already. The usershould go to the Loads-window and be certain to select a load group with the

Column height: 5mTotal height: 8mFrame width: 10m


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appropriate load factors. He should then select the frame contour, and the

icon becomes active, and then click on the icon to make the followingdialogue window appear:

Eurocode 1 is then to be selected by the user to launch the actual snow loadsgenerator.

It should be noted that in the dialogue tab which comes up, PowerFrame willpresent the frame contour that is considered, as a confirmation of then users

selection.


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The first line allows to define the width of the building on which snow loadsare applied and transferred to the selected frame.

The snow load on the ground (sk) is to be defined manually to allow the use ofthe snow loads generator in as many countries as possible. Please refer to

annex 1 of this manual or to annex A of Eurocode 1 to get more informationon the most appropriate value of sk.

Eurocode specifies the concentrated loads to take into account the effect ofsnow overhanging the edge of a roof. By selecting or unselecting the option inthe dialogue tab, this can be taken into account.The thermal coefficient and the exposure coefficient can be taken equal to 1as a default. However, in particular situations, different values can be used.Please refer to Eurocode 1.

Finally, at the bottom of the dialogue window, a button is available for theselection of the most appropriate load situation. This button gives access tothe following scheme, from which the most relevant situation can be selected:

In general, the design standard requires the building to be able to support allpossible cases. Once the load case has been selected, the user is to returnto the main dialogue, and confirm to get results as shown in the figure below(distributed loads are shown in Newton/meter).


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3.1.3.2 Other examplesFinally, additional examples are presented, which can be set up very similarlyto the first example.


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A final example relates to the situation in which snow overhangs the edge ofa cantilever roof. The load due to the overhang will be assumed to act alongthe edge of the roof and will be introduced as a concentrated load on theframe, as clearly shown in the figure below


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3.1.4 Maps

3.1.4.1 Austria

Zone A

Altitude(m) < 200 300 400 500 600 700 800 900 1000 1100 1200sk(kN/m

2) 0.75 0.85 1.00 1.20 1.45 1.75 2.10 2.55 3.00 3.50 4.05

Zone B

Altitude(m) < 200 300 400 500 600 700 800 900 1000 1100 1200sk(kN/m

2) 1.55 1.55 1.60 1.75 2.00 2.30 2.65 3.10 3.65 4.25 4.95

Zone C

Altitude(m) < 200 300 400 500 600 700 800 900 1000 1100 1200sk(kN/m

2) - - 2.15 2.35 2.70 3.10 3.60 4.20 4.95 5.75 6.65

Zone D

Altitude(m) < 200 300 400 500 600 700 800 900 1000 1100 1200sk(kN/m

2) - - - - 1.00 1.20 1.45 1.75 2.10 2.50 3.00


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3.1.4.2 BelgiumThe characteristic snow load on the ground is to be calculated using theformulae below:

sk= 0.50 (kN/m2) altitude (m) A ? 100sk= 0.50 + 0.007(A 100)/6 (kN/m

2) altitude (m) 100 < A ? 700

3.1.4.3 Denmark

The characteristic snow load on the ground is sk= 1.0 kN/m2.

3.1.4.4 Finland


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3.1.4.5 France

Zones

1A 1B 2A 2B 3 4sk(kN/m

2) 0.45 0.45 0.55 0.55 0.65 0.90sA(kN/m

2) - 1.00 1.00 1.35 1.35 1.80

Zone 1A: Aisne, Ardennes, Aube, Calvados, Charente-Maritime, Cher, CtedOr, Ctes dAmor, Eure, Eure-et-Loire, Finistre, Ile et Viliane, Indre, Indre-et-Loire, Loi-et-Cher, Loire-Atlantique, Loiret, Maine-et-Loire, Manche, Marne,Haute-Marne, Mayenne, Meurthe-et-Moselle*, Meuse, Morbihan, Moselle*,Nivre, Nord, Oise, Orne, Pas-de-Calais, Sarthe, Seine-Maritime, Deux-

Svres, Somme, Vende, Vienne, Vosges*, Yonne.Rgion Ile-de-France: Ville de Paris, Seine-et-Marne, Yvelines,

Essonne, Hauts-de-Seine, Seine-Saint-Denis, Val-de-Marne, Val dOise.

Zone 1B: Allier, Alpes-Maritimes, Bouches-du-Rhne, Cantal, Corrze,Haute-Corse, Corse-Sud, Creuse, Dordogne, Haute-Garonne, Gers, Gironde,Landes, Lot, Lot-et-Garonne, Puy-de-Dme, Pyrnes-Atlantiques, Hautes-Pyrnes, Sane-et-Loire*, Tarn-et-Garonne, Var*, Haute-Vienne.

Zone 2A: Ain, Alpes-Hautes-Provence, Hautes-Alpes, Arige, Aveyron,Doubs, Jura, Loire, Haute-Loire, Lozre, Meurthe-et-Moselle*, Moselle*, Bas-


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Rhin, Haut-Rhin, Rhne, Haute-Sane, Sane-et-Loise*, Tarn*, Var*,Vosges*.

Zone 2B: Gard, Hrault*, Vaucluse.Zone 3: Ain*, Ardche, Arige*, Aude*, Drme, Hrault*, Isre, Pyrnes-

Orientales*, Savoie, Haute-Savoie, Tarn*, Var*, Belfort (Territoire).

Zone 4: Aude*, Pyrnes-Orientales.

* only partially.

3.1.4.6 Germany

Zone I

Altitude (m) > 200 300 400 500 600 700 800 900 1000sk(kN/m

2) 1.13 1.13 1.13 1.13 1.28 1.58 1.88 2.25 2.70


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Zone II

Altitude (m) > 200 300 400 500 600 700 800 900 1000sk(kN/m

2) 1.13 1.13 1.13 1.35 1.73 2.25 2.78 3.45 4.20

Zone III

Altitude (m) > 200 300 400 500 600 700 800 900 1000sk(kN/m

2) 1.13 1.13 1.50 1.88 2.40 3.00 3.83 4.65 5.70

Altitude (m) 1100 1200 1300 1400 1500sk(kN/m

2) 6.95 8.20 9.60 11.10 12.70

Zone VI

Altitude (m) > 200 300 400 500 600 700 800 900 1000

sk(kN/m2

) 1.50 1.73 2.33 3.15 3.90 4.88 5.85 6.98 8.25

Altitude (m) 1100 1200 1300 1400 1500sk(kN/m

2) 9.40 10.60 11.75 12.90 14.10

3.1.4.7 GreeceZone I :

Zone II :


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3.1.4.8 Italy

Zone Isk= 1.60 kN/m

2 A ? 200 m

sk= 1.60 + 3 (A-200)/1000 kN/m2 200? A ? 750 m

sk= 3.25 + 8.5 (A-750)/1000 kN/m2 A > 750 m

Zone II

sk= 1.15 kN/m2 A ? 200 m

sk= 1.15 + 2.6 (A-200)/1000 kN/m2 200? A ? 750 m

sk= 2.58 + 8.5 (A-750)/1000 kN/m2 A > 750 m

Zone III

sk= 0.75 kN/m2 A ? 200 m

sk= 0.75 + 2.2 (A-200)/1000 kN/m2 200? A ? 750 m

sk= 1.96 + 8.5 (A-750)/1000 kN/m2 A > 750 m


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3.1.4.9 LuxemburgThe characteristic snow load on the ground should be determined based onfollowing formulae:

sk= 0.50 (kN/m2) altitude (m) A ? 100

sk= 0.50 + 0.007 (A 100)/6 (kN/m2) altitude (m) 100 < A ? 700

3.1.4.10 The Netherlandssk= 0.70 kN/m

2.

3.1.4.11 PortugalFor the following regions: Viana do Castelo, Braga, VilaReal, Braganda,Porto, Aveiro, Viseu, Guarda, Coimbra, Leiria, Castelo Branca, Portalegre ,and at altitudes above 200m:

sk= (A 50)/400 kN/m2.

Elsewhere, snow loads do not have to be considered.

3.1.4.12 Spain

Zone I

Altitude (m) : 200 400 500 600 700 800 900 1000 1100 1200 1300sken kN/m

2: 0.2 0.2 0.3 0.3 0.5 0.6 0.7 1.1 1.6 1.8 1.9


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Altitude (m) : 1400 1500 1600 1700 1800 1900 2000sken kN/m

2: 2.2 3.2 3.8 4.5 5.3 6.3 7.4

ZoneIIAltitude (m) : 200 400 500 600 700 800 900 1000 1100 1200 1300sken kN/m

2: 0.4 0.5 0.6 0.6 0.7 1.0 1.1 1.7 1.9 2.1 2.4


2: 2.6 3.6 4.0 4.5 5.0 5.6 6.2

Zone IIIAltitude (m) : 200 400 500 600 700 800 900 1000 1100 1200 1300sken kN/m

2: 0.2 0.2 0.2 0.3 0.3 0.5 0.6 0.9 1.0 1.2 1.4


2: 1.6 2.2 2.6 3.0 3.5 4.1 4.8

Zone IV

Altitude (m) : 200 400 500 600 700 800 900 1000 1100 1200 1300sken kN/m

2: 0 0 0 0 0 0 0 0.9 1.0 1.2 1.4Altitude (m) : 1400 1500 1600 1700 1800 1900 2000sken kN/m

2: 1.6 2.2 2.6 3.0 3.5 4.1 4.8


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3.1.4.13 SwedenSnow zone : 4 3 2.5 2 1.5 1sk(kN/m

2) : 4.0 3.0 2.5 2.0 1.5 1.0

3.1.4.14 SwitzerlandAt altitudes below 1500 m :

2

2

/350

0.14.0 mkNA

s ref

k?

?

?

?

?

?

?

?

??

?

?

??

?

????

where

? sk is the snow load on the ground, with a minimum value of 0.9 kN/m2.

? Arefis the reference altitude from the map below.


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3.1.4.15 United Kingdom

sk= sb+ (0.1 sb+ 0.09)(A 100)/100 (kN/m2)

with sbbased on the map below:

PowerFrame Part 3 - Wind and Snow Loads.pdf

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Transcript of PowerFrame Part 3 - Wind and Snow Loads.pdf