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Anonymous Poster

Calculating Wind Resistance

07/31/2008 6:27 AM

hello guys.Am ravin from mauritius. need your help about calculating the wind speed an aluminium door with glass panes can resist.

is there any standard to obey? i have a little company manufacturing aluminium doors and windows. Only two days ago a client of mine asked me this simple question. ' what wind speed can the door resist?'

Any idea how i can calculate this value?

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#1

Re: Calculating Wind Resistance

07/31/2008 6:32 PM

Hello Ravin,

Wind pressure is a better measure of door strength than wind speed. You can calculate the capacity of the aluminum members and the glass panels. Alternatively, you can test the door to destruction and see how much it can carry.

The test setup has to emulate the actual support conditions of the door in place. Doors can be loaded from the exterior or the interior, so they are not necessarily continuously supported along each vertical edge. Put the door flat on the floor or bench, then place one support at each hinge and one at the latch. The gap between the door and floor should be adequate to allow for deflection. Now, slowly add load uniformly over the area of the door until failure.

The relationship between wind speed and wind pressure is complex and depends on too many variables including air density, height, shape of building, gust factor and location of openings in the building.

It is preferable and more informative to tell your clients how much pressure your doors can safely sustain before failure.

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#2

Re: Calculating Wind Resistance

08/01/2008 1:40 AM

The following is a complete comprehensive text showing how to calculate the wind loading as per code ANSI/ASCE 7-88 & ANSI A58.1-82. This procedure is recommended by the code to be used for any structure, building, equipment, ... etc., and I used to use this procedure as a code requirement for calculating the forces and its stresses due to wind load in our piping systems, pressure vessels, distillation towers, flare stacks, .... etc. And I recommend this procedure to be used in your calculations.

Design Wind Force, F = qz * Gh * Cf * Af , lb. [Table 4]

Where,

qz = Velocity pressure = 0.00256 kz (I V)2, lb/ft2. [Equation 3] [6.5]

kz = Velocity pressure exposure coefficient, [see Table 6]. Evaluated at height z above grade & exposure categories. [6.5.3]

I = Importance factor, [see Table 5 & Category Table 1]. Depend on the classification of buildings and other structures for wind, snow, and earthquake loads. Categories I, II, III, and IV related to the nature of occupancy.

V = Basic wind speed, mph, [see Table 7 & Fig. 1]

Gh = Gust response factor, [see Table 8]. The gust response factor is employed to account for the fluctuating nature of wind and its interaction with buildings and other structures, i.e. accounts for the additional loading effects due to wind turbulence over the fastest-mile wind speed. [6.6 & 6.5.3]

Cf = Force coefficient. [Table 12] [6.7]

Af = Area of structures or components and cladding thereof projected on plane normal to wind direction, ft2

Min. Design Wind Loading, [see 6.4.2.1]. The wind load used in design of the main wind-force resisting system for buildings and other structures shall be not less than 10 lb/ft2 multiplied by the area of the building or structure projected on a vertical plane that is normal to the wind direction.

1.4 Classification of Buildings and Other Structures. Buildings and other structures shall be classified according to Table 1 for the purpose of determining wind, snow, and earthquake loads.

Table 1. Classification of Buildings and Other Structures for Wind, Snow, and Earthquake Loads.

Nature of Occupancy

Category

All buildings and structures except those listed below.

I

Buildings and structures where the primary occupancy is one in which more than 300 people congregate in one area.

II

Buildings and structures designated as essential facilities, including, but not limited to :

- Hospital and other medical facilities having surgery or emergency treatment areas.

- Fire or rescue and police stations.

- Structures and equipment in government.

- Communication centers and other facilities required for emergency response.

- Power stations and other utilities required in an emergency.

- Structures having critical national defense capabilities.

- Designated shelters for hurricanes.

III

Buildings and structures that represent a low hazard to human life in the event of failure, such as agricultural buildings, certain temporary facilities, and minor storage facilities.

IV

Table 5. Importance Factor, I (Wind Loads)

I

Category*

100 miles from hurricane oceanline and in other areasAll hurricane oceanline

I

1.001.05

II

1.071.11

III

1.071.11

IV

0.951.00

* See 1.4 and Table 1.

Table 6. Velocity Pressure Exposure Coefficient, Kz

Height above

Kz

ground level, z

(ft)

Exposure

A

Exposure

B

Exposure

C

Exposure

D

0 - 15

20

25

30

40

50

60

70

80

90

100

120

140

160

180

200

250

300

350

400

450

500

0.12

0.15

0.17

0.19

0.23

0.27

0.30

0.33

0.37

0.40

0.42

0.48

0.53

0.58

0.63

0.67

0.78

0.88

0.98

1.07

1.16

1.24

0.37

0.42

0.46

0.50

0.57

0.63

0.68

0.73

0.77

0.82

0.86

0.93

0.99

1.05

1.11

1.16

1.28

1.39

1.49

1.58

1.67

1.75

0.80

0.87

0.93

0.98

1.06

1.13

1.19

1.24

1.29

1.34

1.38

1.45

1.52

1.58

1.63

1.68

1.79

1.88

1.97

2.05

2.12

2.18

1.20

1.27

1.32

1.37

1.46

1.52

1.58

1.63

1.67

1.71

1.75

1.81

1.87

1.92

1.97

2.01

2.10

2.18

2.25

2.31

2.36

2.41

Table 8. Gust Response Factors, Gh and Gz

Height above

Gh and Gz

ground level, z

(ft)

Exposure

A

Exposure

B

Exposure

C

Exposure

D

0 - 15

20

25

30

40

50

60

70

80

90

100

120

140

160

180

200

250

300

350

400

450

500

2.36

2.20

2.09

2.01

1.88

1.79

1.73

1.67

1.63

1.59

1.56

1.50

1.46

1.43

1.40

1.37

1.32

1.28

1.25

1.22

1.20

1.18

1.65

1.59

1.54

1.51

1.46

1.42

1.39

1.36

1.34

1.32

1.31

1.28

1.26

1.24

1.23

1.21

1.19

1.16

1.15

1.13

1.12

1.11

1.32

1.29

1.27

1.26

1.23

1.21

1.20

1.19

1.18

1.17

1.16

1.15

1.14

1.13

1.12

1.11

1.10

1.09

1.08

1.07

1.06

1.06

1.15

1.14

1.13

1.12

1.11

1.10

1.09

1.08

1.08

1.07

1.07

1.06

1.05

1.05

1.04

1.04

1.03

1.02

1.02

1.01

1.01

1.00

Table 12. Force Coefficients for Chimneys, Tanks and Similar Structures, Cf

Cf for h/D values of :

Shape

Type of surface

1

7

25

• Square (wind normal to a face)

•• Square (wind along diagonal)

•••Hexagonal or octagonal [D*qz1/2 > 2.5]

♣ Round [D*qz1/2 > 2.5]

♦ Round [D* qz1/2 ≤ 2.5]

• All

•• All

••• All

♣ Moderately smooth

♣ Rough (D'/D≈0.02)

♣ Very rough (D'/D≈0.08)

♦ All

1.3

1.0

1.0

0.5

0.7

0.8

0.7

1.4

1.1

1.2

0.6

0.8

1.0

0.8

2.0

1.5

1.4

0.7

0.9

1.2

1.2

6.5.3. Exposure Categories.

6.5.3.1. General. An exposure category that adequately reflects the characteristics of ground surface irregularities shall be determined for the site which the building or structure is to be constructed.

Account shall be taken of large variations in ground surface roughness that arise from natural topography and vegetation as well as from constructed features. The exposure in which a specific building or structure is sited shall be assessed as being one of the following categories :

1. Exposure A. A large city centers with at least 50% of the buildings having a height in excess of 70 feet. Use of this exposure category shall be limited to those areas for which terrain representative of Exposure A prevails in the upwind direction for a distance of at least one-half mile or 10 times the height of the building or structure, whichever is greater. Possible channeling effects or increased velocity pressures due to the building or structure being located in the wake of adjacent buildings shall be taken into account.

2. Exposure B. Urban and suburban areas, wooded areas, or other terrain with numerous closely spaced obstructions having the size of single-family dwellings or larger. Use of this exposure category shall be limited to those areas for which terrain representative of Exposure B prevails in the upwind direction for a distance of at least 1500 feet or 10 times the height of the building or structure, whichever is greater.

3. Exposure C. Open terrain with scattered obstructions having heights generally less than 30 feet. This category includes flat open country and grasslands.

4. Exposure D. Flat, unobstructed areas exposed to wind flowing over large bodies of water. This exposure shall apply only to those buildings and other structures exposed to the wind coming from over the water. Exposure D extends inland from the shoreline a distance of 1500 feet or 10 times the height of the building or structure, whichever is greater.

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#5
In reply to #2

Re: Calculating Wind Resistance

08/01/2008 1:06 PM

As usual, a comprehensive outstanding answer! Rated a GA from me...

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#6
In reply to #2

Re: Calculating Wind Resistance

08/01/2008 5:55 PM

Hello Abdel Halim Galala

from me

Excellent and complete answer.

Kind Regards....

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#7
In reply to #6

Re: Calculating Wind Resistance

08/04/2008 5:21 AM

My dear friend EnviroMan thank you very much.

And my dear friend Sparkstation, thank you very much for your excellent and fantastic animation.

With my best regards,,,

from me

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#11
In reply to #2

Re: Calculating Wind Resistance

10/18/2008 3:00 AM

To Eng. Abdel Halim Galala and to all my colleagues here in CR4:

Thank you very much for your suggestions. It helps & gives me a lot of support and confidence in making my calculations. I appreciate it very much.

To all who make good comments & suggestions; thank you guys, keep up the good work in helping one another.

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#12
In reply to #2

Re: Calculating Wind Resistance

06/21/2009 12:58 AM

Dear Abdel,

Your info on calculating wind loads was excellent. I am calculating the wind loading on a array of solar panels and need more info on TABLE 12, Force Coefficients:

Cf for h/D values of :

Shape

Type of surface

1

7

25

• Square (wind normal to a face)

•• Square (wind along diagonal)

•••Hexagonal or octagonal [D*qz1/2 > 2.5]

♣ Round [D*qz1/2 > 2.5]

♦ Round [D* qz1/2 ≤ 2.5]

• All

•• All

••• All

♣ Moderately smooth

♣ Rough (D'/D≈0.02)

♣ Very rough (D'/D≈0.08)

♦ All

1.3

1.0

1.0

0.5

0.7

0.8

0.7

1.4

1.1

1.2

0.6

0.8

1.0

0.8

2.0

1.5

1.4

0.7

0.9

1.2

1.2

What does h/D stand for? CAn you explain this table a little more?

Do you have more info on the surface type; the table gives '1'.7', and '25' which do not mean anything to me. What surface type would a glass solar panel be?

Thanks very much,

John

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#13
In reply to #12

Re: Calculating Wind Resistance

06/21/2009 3:24 AM

Table 12 was extracted from ANSI/ASCE 7-88 (ANSI A58.1-82), and the following notes are subscribed to that table:

Notes:

1. The design wind force shall be calculated based on the area of the structure project on a plane normal to the wind direction. The force shall be assumed to act parallel to the wind direction.

2. Linear interpolation may be used for h/D values other than shown.

3. Notation:

D: diameter or least horizontal dimension, in feet;

D': depth of protruding elements such as ribs and spoilers, in feet; and

h: height of structure, in feet.

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#14
In reply to #13

Re: Calculating Wind Resistance

06/21/2009 3:42 PM

Thanks Abdel. I appreciate your time.

John

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#15
In reply to #12

Re: Calculating Wind Resistance

10/26/2009 1:16 PM

hi, have you found answers to your question?

I have the same problem with applying this explanation to my practical situation (panels on a flat roof.)

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#16
In reply to #15

Re: Calculating Wind Resistance

10/26/2009 4:42 PM

Table 12. Force Coefficients for Chimneys, Tanks and Similar Structures, Cf

Cf for h/D values of :

Shape

Type of surface

1

7

25

• Square (wind normal to a face)

•• Square (wind along diagonal)

•••Hexagonal or octagonal [D*qz1/2 > 2.5]

♣ Round [D*qz1/2 > 2.5]

♦ Round [D* qz1/2 ≤ 2.5]

• All

•• All

••• All

♣ Moderately smooth

♣ Rough (D'/D≈0.02)

♣ Very rough (D'/D≈0.08)

♦ All

1.3

1.0

1.0

0.5

0.7

0.8

0.7

1.4

1.1

1.2

0.6

0.8

1.0

0.8

2.0

1.5

1.4

0.7

0.9

1.2

1.2

Table 12 is prepared to find the values of force coefficient Cf at different values of h/D = 1, h/D = 7 and h/D = 25. For example: for Shape Square (wind normal to a face) at h/D = 25, the force coefficient Cf = 2.0.

Suppose that you have h/D = 20, by looking at Table 12 we find that there is no direct indication to figure 20, here it is allowed to proceed an interpolation between the lower h/D = 7 and and the higher h/D = 25.

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#17
In reply to #16

Re: Calculating Wind Resistance

10/27/2009 5:44 PM

Abdel,

Thank you very much for publishing the code. With careful reading it is really self explanatory. Two questions to you:

- I have found a very similar wind load calculation method referring to ASCE 7-98 at http://web.dcp.ufl.edu/chini/courses/bcn5584/pp/3.ppt#1. Author there advocates different value of coefficients. Which code is current?

- How can I use the method you presented to assess wind load created by multiple rows of inclined solar panels on a roof? Though I am not a structural engineer, my gut feeling tells me that wind will provide press differently on different rows due to turbulence.

Thank you.

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#20
In reply to #2

Re: Calculating Wind Resistance

01/14/2015 11:03 AM

Thank you for this thread, excellent information and very helpful. I am using this for a gravity vent hood (picture below). My concern is that my hood will have an extended curb adapter making the unit approximately 115" above the roof, which is 25' above ground level. Fortunately I have buildings on the south and east side to give protection from the wind. The Hood will be on extended roof curb that will go approximately 6 inches below the roof and determining the strength of my foundation as it relates to the equipment is what I'm trying to do using wind resistance as my force.

Top of Curb adapter to top of hood - 42"

Foundation hood, 6" below roof to 12" above roof

Curb adapter connects at bottom to the existing curb "12" above the roof and spans upwith a height of 63" where it connects to the hood cap. Any thoughts or advice would be greatly appreciated.

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#21
In reply to #2

Re: Calculating Wind Resistance

11/28/2016 8:59 AM

Abdel Halim Galala, I tip my hat to you. Excellent answer.

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Anonymous Poster
#3

Re: Calculating Wind Resistance

08/01/2008 6:41 AM

thanks for all these information guys. i ll use these in my designs as from now on.

but one more thing, the specification of the material used is not taken into consideration into any of the above equation. i.e density of material, stress,....

Dont these parameters come into play when calculating the wind force the object is going to withstand before collapse?

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#4

Re: Calculating Wind Resistance

08/01/2008 10:21 AM

One other factor to consider. I had a door with a damper/closer attached. During a fairly strong wind (35 mph = 60 kph or so) the door blew open. The wind did not damage the door, but the closer bent, preventing it from closing again. If flapped open and closed, hitting the bent closer each time, until the lower hinge broke. The next morning, the door was laying on the ground. It was barely damaged, but the hinges were trashed.

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#8

Re: Calculating Wind Resistance

08/13/2008 6:48 AM

thanks for all the info. has helped me a lot. I want to do it the other way now.

i now want my doors and windows to be able to withstand wind speeds of 56 m/s, ie a dynamic wind pressure of 1.92 KN/m2

so if i want a window of length 1m and width 1 m with the ability to withstand a load of 1.92 KN/m2, how must i proceed from here?

i want to know the deflection that will be caused under such load and i want to calculate the stress in the door.

plz help

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#10
In reply to #8

Re: Calculating Wind Resistance

08/23/2008 1:56 PM

This article addresses thickness and deflection of glass windows. Note that the strength of glass is highly variable.

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#9

Re: Calculating Wind Resistance

08/23/2008 12:36 PM

That all depends of the quality of the door. There are doors and there are DOORS; glass is the same.

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Anonymous Poster
#18

Re: Calculating Wind Resistance

08/13/2010 12:43 AM

Hi guys, Thank you very much for all of the information. I have a similar question to a previous post. does this code and coefficients apply to a solar panel attached to the roof of a building with an inclination? if so, is there a way of taking into consideration the Venturi effect pressure differences induced through the change in area? Thanks, Matthew

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#19

Re: Calculating Wind Resistance

04/06/2013 5:04 AM

Dear Friend,

Pl. refer Post No.1 as the comment for your posting. True, it is the PRESSURE that counts which is opposed by the Door.

The empirical Formula used for calculating the WIND PRESSURE in psi is 0.0004 x V^2, where V is the VELOCITY of AIR in Ft/Sec. If you are NOT conversant with Pressure psi, and Velocity in Ft/Sec., to convert psi to Kg/cm^2, devide psi by 14.2, and to convert Ft/Sec. to M/Sec. devide by 3.28.

DHAYANANDHAN.S

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