# Windload on Ground PV Structures

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02-Dec-2014Category

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WIND LOAD CALCUSTRUCTURE DETAILS Details Tilt angle Height(feet) Length(feet) Width(feet) Lower end clearance(feet) Value 45 3.33 10 4 0.5

STAGE 1 WIND FORCE F = Qd*A where, Symbol F Qd A Description Wind Force(pounds) Design Wind Pressure(psf) Area of PV structure(ft^2) Value 4996.14 124.904 40

DESIGN WIND PRESSURE Qd = Q*G*Cpi where, Symbol Qd G Cpi WIND PRESSURE Q = 0.00256*Kz*Kzt*Kd*V *I where, Symbol Q Kz Kzt Kd I Description Value Wind Pressure (psf) 31.26 Velocity Pressure Coefficient 0.85 Topographic Effect Factor 1 Wind Directionality Factor 1 Importance Factor 1.152

Description Value Design Wind Pressure(psf) 124.904 Gust factor 0.85 Internal Pressure Coefficient 4.7 Tilt Angle 45

V

Design Wind Speed(mi/h)

111.9

VELOCITY PRESSURE COEFFICIENT Kz = 2.01*(Z/Zg)^(2/) or Kz = 2.01*(15/Zg)^(2/)

To find the coefficient, please enter values below from sheet 2 Factor Exposure Height of Structure (feet) Zg Kz TOPOGRAPHIC EFFECT FACTOR This factor helps in adjusting wind pressure if our PV structure is located in hill stations If the PV structure is located in plains, we simply take this factor as 1 I 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 Value C 3.33 900 9.5 0.85

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 IMPORTANCE FACTOR Importance factor takes care of risk caused to human life if this structure fails because of wind force Category Importance factor 4 1.15 BASIC WIND SPEED Zone (Colour Code) LIGHT PINK Wind Speed(m/s) 50 Wind Speed(mi/h) 111.9 1

ND LOAD CALCULATION

STAGE 2 UPLIFT FORCE In this force, we need to consider Lift coefficients from sheet 5-Design Wind Pressure Use the table below to calculate uplift force Symbol F Qd A Tilt Angle 45 Description Wind Force(pounds) Design Wind Pressure(psf) Area of PV structure(ft^2) Lift coefficient 3.4 Value 3614.23 90.36 40

Total Downward Force = Weight of Structure Item Weight of Structure(Kg) Weight of 1 module(Kg) Number of modules(kg) Weight of Concrete(Kg) Weight of metal frame(Kg) Factor of Safety is 1.2 FOS 2.3 SAFE Value(Kg) Value(pounds) 3827.6912 8436.23 120 264.48 5 5.00 250 551.00 300 661.20

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 Weight of Structure(Kg) Friction coefficient Friction force Factor of Safety is 1.2 FOS OVERTURNING MOMENT This force tries to overturn our structure Overturning Moment = Force*Perpendicular Distance(height) Overturning Moment Factor of Safety is 1.4 FOS 0.5 NOT SAFE 16629.303 1.1 NOT SAFE Value(Kg) Value(pounds) 3827.69 8436.23 0.65 0.65 2488.00 5483.55

n hill stations

mplicated.

ils because of wind force

-Design Wind Pressure

t) of the structure then entire

VELOCITY PRESSURE COEFFICIENT NOTES: There are 2 factors which determine Velocity Pressure Coefficient, they are 1) 2) Surface Roughness, and 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 Number 1) 2) 3) Surface Roughness type Surface Roughness B Surface Roughness C Surface Roughness D

This category represents urban areas which are closely packed, This region has buildings less than 10m tall and distributed. Th This region usually represents desert type terrain with no obstru

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 Number 1) 2) 3) Ground Exposure Type Exposure B Exposure D Exposure C

If SURFACE EXPOSURE B prevails for 800m or 20 times th If SURFACE EXPOSURE D prevails for 1524m or 20 times If condition does not satisfy both B and D, this is used

How to find Velocity Pressure Coefficient from above tables? Steps: 1) 2) We need to find Exposure type 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/) If height is less than 15ft then use Kz = 2.01*(15/Zg)^(2/) where, and Zg are taken from the table below

Exposure Category Zg (feet) B 1200 C 900 D 700

7 9.5 11.5

ain divided into three categories, they are,

Description areas which are closely packed, something like cities, towns etc han 10m tall and distributed. This is in between region B and D. Something like villages fall under this category esert type terrain with no obstruction to wind. Very open space

r PV structures. This is divided into 3 categories

Description 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). h B and D, this is used

r this category

Importance Factor Importance factor is divided into 4 categories. Please follow the table below and use this in sheet 1 Occupancy Category 1 2 3 4

Nature of occupa Temporary sheds, structures as those used during construction and those structures Buildings and structures possessing low risk to human life and property in the eve All general buildings ,structures and residential buildings Important buildings such as hospitals, communication buildings, power plant struc

Based on the occupancy category, select the Importance factor to find wind force. In sheet 1 just enter occu I have included this table here just for your reference Occupancy Category Importance factor 1 0.87 2 1 3 1.15 4 1.15

below and use this in sheet 1 to find wind force

Nature of occupancy struction and those structures which possess low risk to human life n life and property in the event of failure. This does not include residential buildings ings n buildings, power plant structures etc.

orce. 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 s

in page 1 to input basic wind speed

DARK PINK LIGHT PINK GREEN LIGHT BLUE YELLOW DARK BLUE

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 external 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

Roof Angle 0 7.5 15 22.5 30 37.5 45 Gust factor:

Pressure Coefficients 1.5 2.4 2.9 3.5 4.2 4.3 4.7

Lift Pressure coefficients 1.5 1.6 2.2 3.1 3.6 3.6 3.4

This factor accounts for loading effect of wind turbulence on structures. This is different for rigid and flex Gust factor is taken as a constant value of 0.85 always

small assumption here. Our PV structures are considered to be completely open and hence

lt angles. Please use the closest possible tilt angle to calculate design wind pressure

his is different for rigid and flexible structures. PV structures are rigid and hence