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Hang tough & enjoy your tower Charlie!
If it breaks, fix it. Otherwise enjoy it! Some day I may get brave and post the pictures of my fold over-crank up mast with the CushCraft A3 beam on it. It waves around in the wind like a sailboat mast and flexes the I-beam gantry enough to scare the clueless when it is time to do antenna work. When mine breaks, I will either fix or replace, just as I have always done... My current worries are lightning and ice. It has only been up about five years, time will tell. On Wed, 13 Jul 2005 03:43:15 -0700, "Ed Price" wrote: "Charlie" wrote in message ... The images are the same yeah...DUH!! Since there was no damage.....except perhaps your brain damage. You don't catch on too fast do you? -- Charlie Ham Radio - AD5TH www.ad5th.com Deep South 2 Meter SSB Net www.deepsouthnet.net Well, this will be my last post on this thread. I think Charlie has burnt his last shred of credibility by using identical images for "before" and "after" evidence. I'm sure everyone noted that not even a single tree leaf was lost during that disaster, so I suppose Charlie could also claim that his tower is as strong as a leaf, maybe even stronger! Since Charlie doesn't seem to worry too much about factual evidence, his request for technical comments must have been posted for entertainment value, and in that, he certainly has succeeded. Can we look forward to annual updates posting the same original image, thereby proving that Chuckie has not only built a strong, but an eternal tower? |
"John Ferrell" bravely wrote to "All" (13 Jul 05 14:47:06)
--- on the heady topic of " AD5TH Tower - Storm Damage Photos" JF From: John Ferrell JF Xref: aeinews alt.ham-radio.vhf-uhf:8238 JF Hang tough & enjoy your tower Charlie! JF If it breaks, fix it. Otherwise enjoy it! JF Some day I may get brave and post the pictures of my fold over-crank JF up mast with the CushCraft A3 beam on it. It waves around in the wind JF like a sailboat mast and flexes the I-beam gantry enough to scare the JF clueless when it is time to do antenna work. JF When mine breaks, I will either fix or replace, just as I have always JF done... JF My current worries are lightning and ice. JF It has only been up about five years, time will tell. There is a thing called metal fatigue of which I was abruptly reminded of this spring. I was raking the lawn as I usually do and the aluminum handle just snapped in half without any provocation. No way I could have casually seen it but the rake was some decades old and probably flexed all it would flex. So there you go, time is against us! A*s*i*m*o*v .... Give me that old time religion. Hail, Zeus! |
Asimov wrote:
"There is a thing called metal fatigue of which I was strongly reminded this spring." Yes. It usually begins with a microscopic crack. The greater the stress, the shorter the life. Damage is cumulative. It is affected by temperature and surface finish. Some metals such as steel and titanium have lower stress limits below which they are mostlly im,mune to failure from repeated flexing. Other metals such as aluminum and its alloys have no such immunity and eventually fail under repeated flexing. In these, designs are kept below the fatigue threshold for the number of stress cycles expected within their lives. Or, a lifetime is specified and replacement is required. Another technique is non-destructive testing to find cracks and the piece is retired for cause. Best regards, Richard Harrison, KB5WZI |
I rarely get caught with the antenna fully extended when the wind is
gusting.Thank goodness for electric winches! Crank up masts are an entirely different kind of antenna mount. I would not bet on it withstanding 110 mph winds in the up position, but I am betting it will do more than that retracted! Wednesday, 13 Jul 2005 23:14:08 -500, "Asimov" wrote: "John Ferrell" bravely wrote to "All" (13 Jul 05 14:47:06) --- on the heady topic of " AD5TH Tower - Storm Damage Photos" JF From: John Ferrell JF Xref: aeinews alt.ham-radio.vhf-uhf:8238 JF Hang tough & enjoy your tower Charlie! JF If it breaks, fix it. Otherwise enjoy it! JF Some day I may get brave and post the pictures of my fold over-crank JF up mast with the CushCraft A3 beam on it. It waves around in the wind JF like a sailboat mast and flexes the I-beam gantry enough to scare the JF clueless when it is time to do antenna work. JF When mine breaks, I will either fix or replace, just as I have always JF done... JF My current worries are lightning and ice. JF It has only been up about five years, time will tell. There is a thing called metal fatigue of which I was abruptly reminded of this spring. I was raking the lawn as I usually do and the aluminum handle just snapped in half without any provocation. No way I could have casually seen it but the rake was some decades old and probably flexed all it would flex. So there you go, time is against us! A*s*i*m*o*v ... Give me that old time religion. Hail, Zeus! |
In all honesty to those that ridiculed the tower and it's associated riggings etc...I have posted photos of the damage incurred from the category 4 hurricane Dennis. According to my map you weren't hit by hurricane Dennis..... maybe a bit of tropical storm.... maybe. Ed |
http://www.wunderground.com/history/...2/MonthlyHisto ry.html#calendar DATE High Avg Gusts Events 9 24 3 59 Rain , Thunderstorm 10 37 8 28 Rain 11 21 13 20 Rain 12 16 2 30 Thunderstorm Damn! gusts to 59 and they get Federal disaster assistance? Hell, we had gusts that high in the past couple months on the Oregon coast. Maybe we ought to appy too? Ed K7AAT |
Asimov wrote:
"Richard Harrison" bravely wrote to "All" (14 Jul 05 12:04:53) --- on the heady topic of " AD5TH Tower - Storm Damage Photos" RH From: (Richard Harrison) RH Xref: aeinews rec.radio.amateur.antenna:34153 RH Some metals such as steel and titanium have lower stress limits below RH which they are mostlly im,mune to failure from repeated flexing. Other RH metals such as aluminum and its alloys have no such immunity and RH eventually fail under repeated flexing. In these, designs are kept RH below the fatigue threshold for the number of stress cycles expected RH within their lives. Or, a lifetime is specified and replacement is RH required. Another technique is non-destructive testing to find cracks RH and the piece is retired for cause. How can one estimate stress cycles from a wind load? A*s*i*m*o*v Believe it or not, but from historical weather data. Historical wind profiles do exist. Statistical analysis will yield an 80 percentile, 90 percentile or even 99 percentile probability of all wind being below the profile limit. |
Asimov wrote:
"How can one estimate stress cycles from a wind load?" Tower failure usually results from a single event or cycle of overstress. Radio towers are rated according to the mph or wind load ( pounds per square foot) they will withstand while carrying all their other loads, dead or live. Towers do vibrate in a breeze as any tower climber can affirm. Resonant frequency depends on construction. Wind vibration has brought down structures. A famous example is "Galloping Gertie", a suspension bridge in the western U.S.A. Deflection is limited in radio towers and elastic limits are not exceeded. The tower section returns to its original form after each flexing. Stress cycles enlarge certain microscopic cracks. Examples are the Comet airliner. Three aircraft flew apart in mid-air. It was determined that stress cracks in the angular corners of its windows were enlarged by pressurization / depressurization cycles. This was fixed by rounded corners but it was too late. The first jet airliner was scrubbed. Another example is found in high pressurre gas pipelines. Their internal pressure cycles and this tends to enlarge microscopic cracks, if any, in the pipe. Pipes are hydrostatically tested before placed in service (no energy storage in water as it is incompressible) so a pipe blow out of water won`t likely hurt a bystander. After the pipe is put in service it is retested each year. Radio towers are not usually flexed beyond limits by vibration but come down due to an accident and / or extreme wind. Best regards, Richard Harrison, KB5WZI |
Yes, the Tacoma Narrows Bridge !
They forgot to design it for torsional forces. Expensive lesson to learn. It was rebuilt without the solid sides, this allows the winds to pass between the steel members instead of against them. jake Richard wrote: Asimov wrote: "How can one estimate stress cycles from a wind load?" Tower failure usually results from a single event or cycle of overstress. Radio towers are rated according to the mph or wind load ( pounds per square foot) they will withstand while carrying all their other loads, dead or live. Towers do vibrate in a breeze as any tower climber can affirm. Resonant frequency depends on construction. Wind vibration has brought down structures. A famous example is "Galloping Gertie", a suspension bridge in the western U.S.A. Deflection is limited in radio towers and elastic limits are not exceeded. The tower section returns to its original form after each flexing. Stress cycles enlarge certain microscopic cracks. Examples are the Comet airliner. Three aircraft flew apart in mid-air. It was determined that stress cracks in the angular corners of its windows were enlarged by pressurization / depressurization cycles. This was fixed by rounded corners but it was too late. The first jet airliner was scrubbed. Another example is found in high pressurre gas pipelines. Their internal pressure cycles and this tends to enlarge microscopic cracks, if any, in the pipe. Pipes are hydrostatically tested before placed in service (no energy storage in water as it is incompressible) so a pipe blow out of water won`t likely hurt a bystander. After the pipe is put in service it is retested each year. Radio towers are not usually flexed beyond limits by vibration but come down due to an accident and / or extreme wind. Best regards, Richard Harrison, KB5WZI |
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