Free walls, roofs and billboards Wind loading and structural response Lecture 22 Dr. J.D. Holmes Free walls, roofs and billboards
Free walls, roofs and billboards free-standing walls elevated walls and billboards free roofs and canopies
Free walls, roofs and billboards attached canopies solar panels
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)
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)
Free walls, roofs and billboards free-standing walls wind at 90o to plane of wall Mean Maximum b h 0.1 1 10 100 b/h 4 3 2 1 Cpn Jensen Number (h/zo) = 50 to 160
Free walls, roofs and billboards free-standing walls wind at 45o to plane of wall 0.1 1 10 100 b/h 4 3 2 1 Cpn Mean Maximum b h Jensen Number (h/zo) = 50 to 160
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
Free walls, roofs and billboards free-standing walls wind at 45o to plane of wall mean Cpn 0.1 1 10 100 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
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
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
Free walls, roofs and billboards wind at 45o to plane of board mean Cpn 45o 1.5 1.1 2c c Ground
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
Free walls, roofs and billboards Walls on bridges wind at 0o to plane of wall Coefficients based onU at top of wall : little effect of s/h ratio
Free walls, roofs and billboards Free-standing roofs pnet flat pnet pitched pnet troughed Usual convention : positive net pressure is downwards
Free walls, roofs and billboards Free-standing roofs pnet
Free walls, roofs and billboards Free-standing roofs pnet Effect of stored goods : flow stagnates underneath - pnet goes more negative
Free walls, roofs and billboards Free-standing roofs pitched - full scale d=9.3 m upper surface pressures dominate - especially near the ridge
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
Free walls, roofs and billboards Attached canopies (over loading bays etc.) zero pitch - model scale h hc wc 0.0 0.5 1.0 1.5 2.0 2.5 3.0 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
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
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)
End of Lecture 22 John Holmes 225-405-3789 JHolmes@lsu.edu