WIND LOAD CALCULATION

STRUCTURE DETAILS

Details ValueTilt angle 45

Height(feet) 3.33Length(feet) 10Width(feet) 4

Lower end clearance(feet) 0.5

STAGE 1WIND FORCE

F = Qd*A where,

Symbol Description ValueF Wind Force(pounds) 4996.144Qd Design Wind Pressure(psf) 124.9036A Area of PV structure(ft^2) 40

DESIGN WIND PRESSURE

Qd = Q*G*Cpi where,

Symbol Description ValueQd Design Wind Pressure(psf) 124.9036G Gust factor 0.85Cpi Internal Pressure Coefficient 4.7θ Tilt Angle 45

WIND PRESSURE

where,

Symbol Description ValueQ Wind Pressure (psf) 31.26Kz Velocity Pressure Coefficient 0.85Kzt Topographic Effect Factor 1

Q = 0.00256*Kz*Kzt*Kd*V2*I

Kd Wind Directionality Factor 1I Importance Factor 1.15V Design Wind Speed(mi/h) 111.9

VELOCITY PRESSURE COEFFICIENT

Kz = 2.01*(Z/Zg)^(2/α) or Kz = 2.01*(15/Zg)^(2/α)

To find the coefficient, please enter values below from sheet 2

Factor ValueExposure C

Height of Structure (feet) 3.33Zg 900α 9.5

Kz 0.85

TOPOGRAPHIC EFFECT FACTOR

This factor helps in adjusting wind pressure if our PV structure is located in hill stationsIf the PV structure is located in plains, we simply take this factor as 1I have not included calculation method for hilly areas because it is quite complicated. If need arises please let me know, I will provide a solution

Kzt 1

WIND DIRECTIONALITY FACTOR

This factor accounts for change in wind direction. This value varies from 0 to 1. We take the maximum value for maximum safety

Kd 1

IMPORTANCE FACTOR

Importance factor takes care of risk caused to human life if this structure fails because of wind force

Category Importance factor4 1.15

BASIC WIND SPEED

Zone (Colour Code) Wind Speed(m/s) Wind Speed(mi/h)LIGHT PINK 50 111.9

WIND LOAD CALCULATION

STAGE 2UPLIFT FORCE

In this force, we need to consider Lift coefficients from sheet 5-Design Wind PressureUse the table below to calculate uplift force

Symbol Description ValueF Wind Force(pounds) 3614.23Qd Design Wind Pressure(psf) 90.36A Area of PV structure(ft^2) 40

Tilt Angle Lift coefficient45 3.4

Total Downward Force = Weight of Structure

Item Value(Kg) Value(pounds)Weight of Structure(Kg) 3827.6912 8436.23Weight of 1 module(Kg) 120 264.48Number of modules(kg) 5 5.00Weight of Concrete(Kg) 250 551.00

Weight of metal frame(Kg) 300 661.20

Factor of Safety is 1.2

FOS 2.3 SAFE

SLIDING FORCE

If force acting on the structure is greater than downward(weight) of the structure then entire structure slides creating problem

Friction Force = Weight*Friction coefficient

Item Value(Kg) Value(pounds)Weight of Structure(Kg) 3827.69 8436.23

Friction coefficient 0.65 0.65Friction force 2488.00 5483.55

Factor of Safety is 1.2

FOS 1.1 NOT SAFE

OVERTURNING MOMENT

This force tries to overturn our structure

Overturning Moment = Force*Perpendicular Distance(height)

Overturning Moment 16629.303

Factor of Safety is 1.4

FOS 0.5 NOT SAFE

Importance factor takes care of risk caused to human life if this structure fails because of wind force

VELOCITY PRESSURE COEFFICIENT

NOTES:There are 2 factors which determine Velocity Pressure Coefficient, they are

1) Surface Roughness, and2) Ground Exposure type

What is Surface Roughness and how to calculate ?

Surface roughness denotes the terrain aroung our PV structures. This is again divided into three categories, they are,

Number Surface Roughness type Description1) Surface Roughness B This category represents urban areas which are closely packed, something like cities, towns etc2) Surface Roughness C This region has buildings less than 10m tall and distributed. This is in between region B and D. Something like villages fall under this category3) Surface Roughness D This region usually represents desert type terrain with no obstruction to wind. Very open space

What is Ground Exposure type and how to calculate ?

Ground exposure denotes the type of terrain, wind travels before hitting our PV structures. This is divided into 3 categories

Number Ground Exposure Type Description1) Exposure B2) Exposure D3) Exposure C If condition does not satisfy both B and D, this is used

How to find Velocity Pressure Coefficient from above tables?

Steps:1) We need to find Exposure type2) We need to find height of structure

There are two different formulas depending on the height of PV structure

If height is greater than 15ft then use

Kz = 2.01*(Z/Zg)^(2/α)

If height is less than 15ft then use

Kz = 2.01*(15/Zg)^(2/α)

where, α and Zg are taken from the table below

Exposure Category Zg (feet) α

If SURFACE EXPOSURE B prevails for 800m or 20 times the height of PV structure (higher value among the 2).If SURFACE EXPOSURE D prevails for 1524m or 20 times the height of PV structure (higher value among the 2).

B 1200 7C 900 9.5D 700 11.5

Surface roughness denotes the terrain aroung our PV structures. This is again divided into three categories, they are,

DescriptionThis category represents urban areas which are closely packed, something like cities, towns etcThis region has buildings less than 10m tall and distributed. This is in between region B and D. Something like villages fall under this categoryThis region usually represents desert type terrain with no obstruction to wind. Very open space

Ground exposure denotes the type of terrain, wind travels before hitting our PV structures. This is divided into 3 categories

Description

If condition does not satisfy both B and D, this is used

prevails for 800m or 20 times the height of PV structure (higher value among the 2). prevails for 1524m or 20 times the height of PV structure (higher value among the 2).

DescriptionThis category represents urban areas which are closely packed, something like cities, towns etcThis region has buildings less than 10m tall and distributed. This is in between region B and D. Something like villages fall under this categoryThis region usually represents desert type terrain with no obstruction to wind. Very open space

Description

If condition does not satisfy both B and D, this is used

Importance Factor

Importance factor is divided into 4 categories. Please follow the table below and use this in sheet 1 to find wind force

Occupancy Category Nature of occupancy1 Temporary sheds, structures as those used during construction and those structures which possess low risk to human life2 Buildings and structures possessing low risk to human life and property in the event of failure. This does not include residential buildings3 All general buildings ,structures and residential buildings4 Important buildings such as hospitals, communication buildings, power plant structures etc.

Based on the occupancy category, select the Importance factor to find wind force. In sheet 1 just enter occupancy category, it will automatically collect data from this sheetI have included this table here just for your reference

Occupancy Category Importance factor1 0.872 13 1.154 1.15

Importance factor is divided into 4 categories. Please follow the table below and use this in sheet 1 to find wind force

Nature of occupancyTemporary sheds, structures as those used during construction and those structures which possess low risk to human lifeBuildings and structures possessing low risk to human life and property in the event of failure. This does not include residential buildingsAll general buildings ,structures and residential buildingsImportant buildings such as hospitals, communication buildings, power plant structures etc.

Based on the occupancy category, select the Importance factor to find wind force. In sheet 1 just enter occupancy category, it will automatically collect data from this sheet

Basic Wind Speed

Please use this map to find the appropriate wind speed for any location.I have included 6 colour codes to make it clear. Use the drop down list box in page 1 to input basic wind speed

I have included 6 colour codes to make it clear. Use the drop down list box in page 1 to input basic wind speed

DARK PINK

LIGHT PINKGREEN

LIGHT BLUE

YELLOW

DARK BLUE

Design Wind Pressure

This is the pressure that is actually acting on our PV structures. We make a small assumption here. Our PV structures are considered to be completely open and henceexternal pressure coefficients are zero and we have only internal presure coefficients

In the following table, I have mentioned pressure coefficients for various tilt angles. Please use the closest possible tilt angle to calculate design wind pressure

Roof Angle Pressure Coefficients Lift Pressure coefficients0 1.5 1.5

7.5 2.4 1.615 2.9 2.2

22.5 3.5 3.130 4.2 3.6

37.5 4.3 3.645 4.7 3.4

Gust factor:

This factor accounts for loading effect of wind turbulence on structures. This is different for rigid and flexible structures. PV structures are rigid and henceGust factor is taken as a constant value of 0.85 always

This is the pressure that is actually acting on our PV structures. We make a small assumption here. Our PV structures are considered to be completely open and henceexternal pressure coefficients are zero and we have only internal presure coefficients

In the following table, I have mentioned pressure coefficients for various tilt angles. Please use the closest possible tilt angle to calculate design wind pressure

This factor accounts for loading effect of wind turbulence on structures. This is different for rigid and flexible structures. PV structures are rigid and hence