Free walls, roofs and billboards
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Free Walls, Roofs, and Billboards: Wind Loads and Pressures, Slides of Environmental Law and Policy
An in-depth analysis of wind loads and pressures on free-standing walls, roofs, and billboards. It covers various aspects such as wind direction, jensen number, net pressure coefficients, shielding effects, and wall spacing. The document also discusses the impact of corner geometry and the effect of elevation on billboards.
Typology: Slides
2012/2013
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- free-standing walls
- elevated walls and billboards
- free roofs and canopies
2 2 a h
1
w L pn
ρ U
p p
C
2 2 a h
1
U L pn
ρ U
p p
C
free-standing walls
- wind at 90o^ to plane of wall (lecture 8, Chapter 4)
CD = 1.
TWO-DIMENSIONAL WALL
Ground
SQUARE WALL
CD = 1.
Ground
reference U taken as Uh (top of wall)
free-standing walls
- wind at 90o^ to plane of wall (lecture 8, Chapter 4)
reference U taken as Uh (top of wall)
free-standing walls
- wind at 45o^ to plane of wall
Jensen Number (h/zo) = 50 to 160
b/h
Cpn
Mean
Maximum
b h
free-standing walls
- wind at 45o^ to plane of wall
Net pressure difference high for first 1-2 wall
heights from windward end
mean Cpn
1.9 1.4^ 0.
b/h=
b/h=
b/h=
b/h=
Parallel free-standing walls (noise barriers on urban freeways)
wall spacing/wall height
Net pressure coefficients
Mean r.m.s. Maximum Minimum
Shielding
significant shielding effects up to 10 wall heights separation
s
- wind at 0 h o (^) to plane of walls
Billboards
- wind at 0o^ to plane of board
effect of elevation : increase magnitude of mean net pressure coefficient
=
Cpn 1.5 =
mean Cpn
s
B
h
SOLID SIGN OR FREESTANDING WALL
GROUND SURFACE
CASE A
WIND NORM AL TO WALL
New table proposed for ASCE-7-
- Solid freestanding walls and solid signs
- Force coefficients Cf given as function of clearance ratio, s/h, and aspect ratio, B/s
CASE B
WIND AT 45° TO WALL
Walls on bridges
- wind at 0o^ to plane of wall
s/h
Cp
upwind
wall
Mean
r.m.s.
Maximum s
Coefficients based onU at top of wall : little effect of s/h ratio
Free-standing roofs
pnet
Free-standing roofs
Effect of stored goods : flow stagnates underneath - pnet goes more negative
pnet
Free-standing roofs
Cpn averaged over half a roof
pitched - model tests
angle of attack (degrees)
Cp (mean)
5 degrees pitch 10 degrees pitch 15 degrees pitch 22.5 degrees pitch 30 degrees pitch
high positive and negative values for
roof pitches of 22.5o^ and 30o
Attached canopies (over loading bays etc.)
when mounted near the top of the wall, uplift force is high
zero pitch - model scale
h (^) hc
wc
Canopy height-to-width ratio, hc/wc
hc/h =
hc/h=0.
hc/h=0.
Cpn
or 4.0, whichever is the lesser
c
c
pn w
h
- Cˆ 1.0 1.
or 4.0, whichever is the lesser
c
c pn (^) w
h
- Cˆ 1.0 0.