Al,
Good point. I should have asked if there had been any rasing fixture
failures.
In Gary's defence, he said it should handle the load with no problem and
then mentioned the winch capacity. I'm sure if he had any doubt, he would
have told me.
I would assume that the structure itself was built to handle the load and
beyond. But, you know what they say about the word asssume : ).
Tony KT2Q
----- Original Message -----
From: "Al Williams" <alwilliams@olywa.net>
To: "KT2Q" <dxdx@optonline.net>; "TowerTalk" <towertalk@contesting.com>
Sent: Thursday, August 18, 2005 12:45 PM
Subject: Re: [TowerTalk] Thanks: Rasing fixture strength replies.
> Steve's (k7lxc) prime directive not withstanding (do what the mfr says), I
> think that Garry at U.S. Tower might be correct in stating "...the
> winch...should not be a problem"; However the real concern is the
> tilt-raising fixture assembly strong enough to safely raise the tower.
> Remember that the safe load is usually several time less than the working
> strength load. I hope that some experts will
> correct and/or further explain the following:
>
> 1. It is typical that metal structures bend/bow until they suddenly
> collapse with a little increased load. Does this bending also
> progressively weaken the structure?
>
> 2. What does the winch rating of 1500lbs really mean? One mfr states
> that winches are often rated by their pull capabiliity. The pull
> capability is determined by how much pull can a typical man exert on the
> crank handle multiplied by the leverage of the winch handle and the gear
> ratio of the winch. This has nothing to do with the safe rating. Instead
> the safe rating of the winch concerns how strong is the raising ratcheting
> mechanism and the clutch mechanism of the brake part of the winch when
> lowering, and how do they deteriate with usage?
>
> 3. I read the response of the winches 1500lb rating with only a 900lb +
> 200lb load as leaving a safety margin. However there are two leverages
> not being considered. The first leverage is a linear one caused by not
> lifting the load at the center of gravity. For simplicity assume that the
> tower, antenna, and mast weight are approximately evenly distributed. With
> the winch cable attached to the tower at approximately 7' from one end of
> the tower and approximately 24' from the other end (21 + 10 -7), the
> leverage is 24/7. Of course the actual leverage is less because the weight
> is not evenly distributed but the leverage is still considerable.
>
> 4. The second leverage is an angular one caused by lifting the load at an
> angle away from vertical. In this case the height of the raising fixture
> is about the same as the distance from the bottom of the tower that the
> cable is attached resulting in and angle of about 45 degrees. This means
> that the only .707 of the pull of the cable is applied to lifting the
> tower. Also .707 of the pull of the cable is applied to trying to pull
> the tower towards the concrete base. I need some help here. Does this
> mean that the leverage is 1/.707 or 1/(.707 + .707)?
>
> Now multiplying the 1100lb tower and antenna load by the two leverages,
> say 3:1 for the linear leverage and 1.414 for the angular leverage shows
> that the winch and raising fixture is being stressed to around 4000
> pounds!
>
> Again, will the real experts please correct and explain better my
> analysis?
>
> k7puc
>
> --- Original Message -----
> From: "KT2Q" <dxdx@optonline.net>
> To: "TowerTalk" <towertalk@contesting.com>
> Sent: Tuesday, August 16, 2005 2:48 PM
> Subject: [TowerTalk] Thanks: Rasing fixture strength replies.
>
>
>> All:
>>
>> Thanks for all the informaitve replies on the strength of the TRX80
>> raising
>> fixture. The only "complaint" I recevied is that the structure tends to
>> bow
>> a little with the heavier masts and antennas and that the standard winch
>> should be replaced with one that has more leverage.
>>
>> I called Garry at U.S. Tower and he said that the winch is rated at
>> 1500lbs
>> and should not be a problem with my 900lb tower and 200lbs or so of mast,
>> antennas and rotor.
>>
>> For saftey reasons, the consensus is to support the tower to take some of
>> the load off the cable when working on the anetennas; makes sense to me.
>>
>> Thanks again...
>>
>> 73, Tony KT2Q
>>
>>
>>
>> _______________________________________________
>>
>> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
>> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
>> any questions and ask for Sherman, W2FLA.
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk@contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>
>
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|