1. Free walls, roofs and billboards
Wind loading and structural response
Lecture 22 Dr. J.D. Holmes
Free walls, roofs and billboards

2. Free walls, roofs and billboards
free-standing walls
elevated walls and billboards
free roofs and canopies

3. Free walls, roofs and billboards
attached canopies
solar panels

4. Free walls, roofs and billboards
free-standing walls
wind at 90o to plane of wall (lecture 8, Chapter 4)
CD = 1.2
TWO-DIMENSIONAL WALL
Ground
SQUARE WALL
CD = 1.1
Ground
reference U taken as Uh (top of wall)

5. Free walls, roofs and billboards
free-standing walls
wind at 90o to plane of wall (lecture 8, Chapter 4)
reference U taken as Uh (top of wall)

6. Free walls, roofs and billboards
free-standing walls
wind at 90o to plane of wall
Mean
Maximum b h
b/h 4 3 2 1
Cpn
Jensen Number (h/zo) = 50 to 160

7. Free walls, roofs and billboards
free-standing walls
wind at 45o to plane of wall
b/h 4 3 2 1
Cpn
Mean
Maximum b h
Jensen Number (h/zo) = 50 to 160

8. Free walls, roofs and billboards
free-standing walls
wind at 45o to plane of wall
mean Cpn
1.6
1.0
1.9
1.4
0.7
1.1
0.8
0.6
0.4
2.2
1.8
2.7
b/h=2
b/h=3
b/h=5
b/h=10
Net pressure difference high for first 1-2 wall heights from windward end

9. Free walls, roofs and billboards
free-standing walls
wind at 45o to plane of wall
mean Cpn
y/h 4 3 2 1
Cpn
no corner 45
corner 45
infinite 45
corner 225
no corner 225 45
225 y
Effect of corner is to reduce largest net pressure

10. Free walls, roofs and billboards
Parallel free-standing walls
(noise barriers on urban freeways) s h
wind at 0o to plane of walls
Shielding
significant shielding effects up to 10 wall heights separation

11. Free walls, roofs and billboards
wind at 0o to plane of board
mean Cpn =
Cpn 1.5
effect of elevation : increase magnitude of mean net pressure coefficient

12. Free walls, roofs and billboards
wind at 45o to plane of board
mean Cpn
45o
1.5
1.1 2c c
Ground

13. Free walls, roofs and billboards
New table proposed for ASCE-7-05
Solid freestanding walls and solid signs
Force coefficients Cf given as function of clearance ratio, s/h, and aspect ratio, B/s

14. Free walls, roofs and billboards
Walls on bridges
wind at 0o to plane of wall
Coefficients based onU at top of wall : little effect of s/h ratio

15. Free walls, roofs and billboards
Free-standing roofs
pnet
flat
pnet
pitched
pnet
troughed
Usual convention : positive net pressure is downwards

16. Free walls, roofs and billboards
Free-standing roofs
pnet

17. Free walls, roofs and billboards
Free-standing roofs
pnet
Effect of stored goods : flow stagnates underneath - pnet goes more negative

18. Free walls, roofs and billboards
Free-standing roofs
pitched - full scale
d=9.3 m
upper surface pressures dominate - especially near the ridge

19. Free walls, roofs and billboards
Free-standing roofs
pitched - model tests 
high positive and negative values for roof pitches of 22.5o and 30o
Cpn averaged over half a roof

20. Free walls, roofs and billboards
Attached canopies (over loading bays etc.)
zero pitch - model scale h hc wc
Canopy height-to-width ratio, hc/wc
hc/h =1
hc/h=0.75
hc/h=0.5
-4.0
-3.0
-2.0
-1.0
0.0
Cpn
or 4.0, whichever is the lesser
or 4.0, whichever is the lesser
when mounted near the top of the wall, uplift force is high

21. Free walls, roofs and billboards
Solar panels
on roofs of buildings
wind loads are affected by many parameters :   l d c e w h1 h2

22. Free walls, roofs and billboards
Solar panels
‘stand-off’ distance reduces net load normal to roof
higher roof pitch produces less uplift force
panel near eaves or gable ends experience higher loads
generally better to mount parallel to roof slope ( = 0)

23. End of Lecture 22 John Holmes 225-405-3789 JHolmes@lsu.edu