Free walls, roofs and billboards

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

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. CD = 1.2 CD = 1.1 Ground Ground TWO-DIMENSIONAL WALL SQUARE 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)

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. 4 3 2 1 0 Maximum Cpn Mean b h 0.1110 100 b/h Free walls, roofs and billboards free-standing walls • wind at 90o to plane of wall Jensen Number (h/zo) = 50 to 160

7. 4 3 2 1 0 Maximum Cpn b h Mean 0.1 1 10100 b/h Free walls, roofs and billboards free-standing walls • wind at 45o to plane of wall Jensen Number (h/zo) = 50 to 160

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

9. 4 3 2 1 0 225 no corner 45 y 45 Cpn corner 45 infinite 45 corner 225 no corner 225 0.1 1 10 100 y/h Free walls, roofs and billboards free-standing walls • wind at 45o to plane of wall mean Cpn Effect of corner is to reduce largest net pressure

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

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

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

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

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

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

18. d=9.3m Free walls, roofs and billboards Free-standing roofs pitched - full scale 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. -4.0 -3.0 -2.0 -1.0 0.0 wc Cpn hc/h =1 h hc or 4.0, whichever is the lesser hc/h=0.75 or 4.0, whichever is the lesser hc/h=0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Canopy height-to-width ratio,hc/wc Free walls, roofs and billboards Attached canopies (over loading bays etc.) zero pitch - model scale when mounted near the top of the wall, uplift force is high

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

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 22John Holmes225-405-3789 JHolmes@lsu.edu