HF Tower Collapse ! We re not the only ones. NSARC HF Operators 1 KFI KRBC-TV

Transcription

1 HF Tower Collapse! We re not the only ones. KFI KRBC-TV NSARC HF Operators 1

2 Building the Original! 24 foot Aluminum tower! TH6 3 element tri-band (20/15/10M) yagi! Restrictions " No guy points no guy wires " No roof mounts no compromising roof performance! Self supporting structure! Face mounted tower to building strut system NSARC HF Operators 2

3 NSARC Installation NOTES Mast = 1-1/2" dia extend X" feet above top of tower 36 inches A. NO GUY WIRES ON TOWER B. TOWER MATERIAL TH6DX HF Yagi 24 foot boom 12 inches Top Section 93 inches Tower sections, 8 foot Heights Aluminum Tower C. ANTENNA HY Gain TH6DX Tri Band Yagi D. MAST MATERIAL 1-1/2" dia x 8 foot Steel or Aluminum pipe tower joint E. ROTOR SCALE = 1/4" to 1 foot 186 inches Ham IV mounted internally to tower in mid-section "Unistruts" 2 places Mid Section 93 inches F. "C" STRUT CLAMPS Use existing clamps (2) at post supporting flat top antenna. Add 2 more clamps to complete tower clamping ~ 20 inches ~ 14 inches tower joint Bottom Section actual 7' 9" 93 inches overall height 374 inches 31 feet, 2 inches ~0.46 wavelength at 14 MHz clamp ~ 40 inches ~ 174 inches 114 inches 9' 6" SOUTH MECHANICAL ROOM ~ 12 inches clamp 188 inches 15 feet 8 inches optional bottom section, base secured to room structure TRI-BAND YAGI and TOWER MOUNTING EMO ROOF - SOUTH MECHANICAL ROOM Rev 2 - added optional bottom section. ROOF NSARC HF Operators 3

4 The Tower! Heights aluminum tower donated by VE7PO.! Included rotor and bearing! TH6 Yagi from VE7QH estate NSARC HF Operators 4

5 The Site! Mechanical Room - note mounting struts! Face mount tower to struts Struts NSARC HF Operators 5

6 The Strut! Unistrut P /8" square 4" 2" Weld Weld Strut Screwed to steel on ~ 10" centers. Self tapping screws Weld aprox 7-3/4" 2-1/2" Heights Tower Leg OD 1.31" One only shown 16 " Approx 42 " 39-1/2" center to center 1/8" x 2" x 4" Tubing 3/16" -2-1/2" x 2-1/2" Angle 2-1/2" 13-1/4"! Strut connection to building structural Clamp Bolt Mast to Strut Clamp similar to a Sinclair Type CLAMP015 4 places 1/4" galv steel Detail A Unistrut P /8 x 1-5/8 12 gauge 1/8" x 3 x 4" Tubing NSARC HF Operators 6

7 The Clamps! Clamps used to connect the tower legs to the Unistrut This side To Unistrut This side To Tower Leg! Two struts two legs 4 clamps NSARC HF Operators 7

8 The Connection! Tower Legs Clamp - Strut NSARC HF Operators 8

9 Mounting Lower Section! Bottom 8 section of tower! Clamping tower face to struts! Tower supported on two legs! Four places NSARC HF Operators 9

10 Mid and Top Sections! Mid and top section of tower joint being inspected! Rotor and Thrust bearing installed NSARC HF Operators 10

11 Mounting Mid Section! Heavy mid section in place NSARC HF Operators 11

12 Raising Top Section! Top section and mast! 1-1/2 Aluminum pipe mast! Lateral bearing on top section of tower! Jason Timmis VE7AG rigger NSARC HF Operators 12

13 The Yagi! TH6 yagi pre-assembled on roof NSARC HF Operators 13

14 Lifting Yagi.. NSARC HF Operators 14

15 Rotating & Supervising NSARC HF Operators 15

16 Sliding Up & Bolting NSARC HF Operators 16

17 Laying out Cables! Coax! Rotor NSARC HF Operators 17

18 Installing Cables Outside! Cables bundled and supported along struts! Cable supported on messenger guy wire between buildings NSARC HF Operators 18

19 Cable Entrance Room! Cables terminated with lightning surge protectors in equipment room on roof! Note copper grounding plates NSARC HF Operators 19

20 Installing Cables Inside! Cable supported on cable trays and in conduits inside ceiling and between floors NSARC HF Operators 20

21 Connecting to Antenna NSARC HF Operators 21

22 Finished. NSARC HF Operators 22

23 The Storm! Storm on 15 Dec 2007! Installation calculated to have survived to 100 km/hr! Winds to 97 km/hr at YVR! Wide open exposure to the West! Wind gusts in excess of 100 km/hr " 85 feet above ground " High rise buildings to South and North Venturi effect? NSARC HF Operators 23

24 What Happened?! Tower broke off at the top of the bottom section, above the connections to the building! Struts and clamps to building undamaged! Tower joint (bottom to mid section) did not fail! Bottom tower section, outer leg, collapsed! Tower hinged, toppled and severed; antenna hit the deck! Yagi boom broke in half; elements on one side all destroyed! Mast broke in half at boom mounting connection NSARC HF Operators 24

25 Bottom Section! The failure point! Legs broken off below section joint and above clamps! Cross bracing has collapsed! Unsupported leg is pushed sideways and down NSARC HF Operators 25

26 Clamps and Struts! Clamps and Struts do not appear to be altered or distorted! Conclusion " Building attachment mechanism did not fail NSARC HF Operators 26

27 Mid Section! Note section joint is intact! Note one leg has collapsed! Collapsed leg is part of the unsupported leg of bottom section! Unsupported tower leg buckled to the East and was pushed up until bottom section failed NSARC HF Operators 27

28 Top and Mid Section! Top and mid sections have no apparent damage! Section joints are undamaged! No distortion of cross bracing! Rotor and bearing have no apparent damage! Conclusion " No failure in top or mid sections NSARC HF Operators 28

29 Mast Failure! Mast broke at bolt hole that locked the boom to the mast! This was not the supporting mechanism for the boom! Boom to mast clamp is intact & clamp acts above and below where the mast broke.! Conclusion " Mast broke when boom impacted roof as tower collapsed NSARC HF Operators 29

30 Yagi Failure! Asymmetrical damage! Boom broke in half on impact & punctured roof (only instance)! Conclusion " Yagi fell on end & side and hit roof as a result of tower collapse NSARC HF Operators 30

31 Analysis! Wind was from the west / tower collapsed to the East! Failure occurred in the bottom section above supports! Cross bracing failed! Both West tower legs acted as a hinge point.! East leg buckled and tower fell Eastwards! All legs severed under the rotation and load! Yagi was destroyed on impact with the roof NSARC HF Operators 31

32 What Induced the Failure?! Most likely TORQUE applied to lower section induced failure " Torque as a result of yagi whipping back and forth " Unsupported leg free to move " Restrained only by cross bracing " X braces solid aluminum rod soft material " Leg was pushed off center by torquing! West wind, so East leg takes all the compression " Equal tension is shared by the two West legs (stronger)! East leg then fails due to bending moment and tower collapses to the east destroying the yagi and breaking the mast and boom on impact with roof! This analysis is that of VA7JW. Other opinions may exist. NSARC HF Operators 32

33 What Now?! REBUILD!! NSEMO opened a Task Number to cover expenses incurred by them due to 15 Dec 06 Wind Storm! NSEMO will include our claim for loss of tower and antenna! Claim to be submitted to NSEMO by noon tomorrow 26 Jan 07! Will take 2 months for a ruling to be handed down! We do not expect to be covered for this event NSARC HF Operators 33

34 Plan A Tower Replacement Mast. note D NOTES A. GUY WIRES SteppIR HF Yagi note C ~ 12 inches Element, 3 places None allow ed B. TOWER DETAIL 60" mast ~ 15 inches Trylon Three 8 foot tower sections ~ 33" ~ 9" rotor Top plate bearing equipped Mid plate rotor equipped Top Section ~ 94 inches Height of Tower abov e bottom of tower ~ 294" C. ANTENNA SteppIR 3 element Yagi. 6.1 sq ft max w ind area Weight 45 lbs Wind survivablilty 100 mph D. MAST MATERIAL Trylon 1.9" OD x 6 foot schedule 40 galv. steel pipe 3 section TRYLON tower Tower joint Mid plate diaphram Ef f ectiv e height of Tower above anchor point, ~ 226" Mid Section ~ 91 inches E. ROTOR Ham IV mounted internally in top section F. "C" UNISTRUT & CLAMPS Tyco - Unistrut type P /4" square x 12 gauge galv steel rail mounted to building strucutral steel. Unistrut to tow er leg clamp is Sinclair type "Clamp015" Clamping to tower leg requires review. ~ 20 inches Tower joint Height of Yagi above Roof ~ 380 inches ~ 31 f eet, 8 inches ~0.45 wavelength at 4 MHz G. Diaphrams Use modified "plates" as stiffening diaphrams at locations indicated ~ 40 inches ~ 174 inches "Unistruts" 2 places Ty pe P-1000 clamps 4 places Note F Bottom Section ~ 94 inches ~ 68" f rom tower bottom to top anchor point ~ 28 " ~114 inches 9' 6" SOUTH MECHANICAL ROOM View of South end, looking North Stif f ening Diaphrams Two. One at each building attachement point. Note G ~ 86" SteppIR YAGI and TRYLON TOWER MOUNTING EMO ROOF - SOUTH MECHANICAL ROOM SCALE = approx 1/4" to 1 foot DATE: 9 January 2007 DRAWN BY: JOHN WHITE, VA7JW REV: Proposed ROOF NSARC HF Operators 34

35 Trylon Tower! Same configuration as previous design! Steel tower much heavier design! Engineered by Trylon! Face mounting system not yet designed by Trylon! Outside engineering approvals may be required! Replacement Antenna " TH7 for claim purposes (TH6 no longer available) " 3 element SteppIR but club pays incremental cost! Costs " Claim for tower / TH6 $8,730 " Club incremental for SteppIR ~ $1,200! Excessive, uncertain, unaffordable abandon this approach NSARC HF Operators 35

36 Plan B - The Pipe NOTES A. GUY WIRES SteppIR HF Yagi Note C Rotor Mast. Note D Element, 3 places None allow ed B. MAIN MAST DETAIL Boom Mast Rotor Clamp Rotor Note E ~ 8" extension ~ 11" mast ~ 15" rotor Galv Steel Pipe. Nominal 4", schedule 40 Actual 4-1/2" OD / 0.237" wall X 15 feet long C. ANTENNA Rotor Plate Pipe Mast. Note B ~ 5" transition Height of Yagi abov e Main Roof ~ 319 inches / ~ 26-1/2 f eet ~0.4 wav elength at 14 MHz SteppIR 3 element Yagi. 6.1 sq ft published w ind area Weight 45 lbs Wind survivablilty 100 mph 180" 15 f oot pipe 211" 145" ~ 12 f eet abov e mech room roof D. ROTOR MAST MATERIAL Galv Steel Pipe. Nominal 1.5" schedule 40 Actual 1.9" OD / w all x 24" long 161" E. ROTOR ~ 20 inches ~ 4" ~ 16" Ham IV mounted internally in top section Wind area measured 0.7 sq ft Weight measured 15 lbs ~ 40 inches ~ 174 inches "Unistruts" 2 places Ty pe P-1000 Unistrut clamps 4 places Note F ~ 6 " ~ 50" 174" F. UNISTRUT & ANGLE BRACKET SRUCTURE Mast Pipe clamped to angle bracket structure. Angle brackets 1/4" x 4-1/2' x 4-1/2" x 24 inches Two back to back angles form one rail between mtg centers Angle brackets bolted to building Unistrut on 18 inch centers ~114 inches 9' 6" SOUTH MECHANICAL ROOM View of South end, looking North ~ 108" ROOF SteppIR YAGI and PIPE MAST MOUNTING EMO ROOF - SOUTH MECHANICAL ROOM SCALE = approx 1/4" to 1 foot DATE: 25 January 2007 DRAWN BY: JOHN WHITE, VA7JW REV: Proposed NSARC HF Operators 36

37 The Pipe! Mount a 4-1/2 diameter steel pipe on face " 4 nominal / schedule 40 / wall! Pipe about 15 feet in total length! Bolt pipe to angle brackets! Bolt angles to existing clamps! About half weight of tower solution! Significantly less wind loading! Very strong in Torque no unsupported leg issues! Design to be strong in bending - hence 4-1/2 pipe! Simple and unobtrusive compared to tower! Design supported by NSEMO Communications consultant NSARC HF Operators 37

38 How to Put Up?! Tilt Up Crank up approach! Mount a winch on angle brackets! Assemble pipe, rotor and yagi on main roof " support pipe at an angle with a stand! Attach winch cable to pipe mast! Pull into upright position against mounting brackets! Install pipe clamps not tight! Attach winch cable to bottom of mast! Crank mast up to height! Tighten pipe clamps! All done from ladders, no tower climb NSARC HF Operators 38

39 Estimated Cost to Club! Pipe Mast $1600! SteppIR $2,460! P Eng Services $1,700! Contigency $ 565! Total $6,325 " Taxes, shipping, duties, all in! $8,000 allocated funds are for this purpose " Cannot apply to Gaming for emergency funds as we have declared the $8k for exactly this purpose! Cannot use $11,900 Gaming funds specific to grant NSARC HF Operators 39

40 Discussion! Should we put the yagi back up?! Do we want to spend $6,000?! BOD to approve (or disapprove) prior to any club expenditure NSARC HF Operators 40