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## Re: [TowerTalk] Rohn Torque Bar confusion

 To: "Tower (K8RI)" , Re: [TowerTalk] Rohn Torque Bar confusion kr7x@comcast.net Tue, 03 Aug 2004 18:12:51 +0000
 ```Roger etal: You are partially correct and partially incorrect. You can't eliminate basic vector statics from the argument of the usefullness of torque arms. I specifically mean the style used for 55g and larger and made of channel. If you can imagine the tower in section as a rigid triangle with the guy attachments at the verticies (points) and the line of the guys extending outward from the verticies in line with the center of gravity of the triangle.( the intersection of the perpendicular bisectors of the opposite sides). When the wind or other forces are a linear vector in the plane of the triangle and through the center of gravity, the tower section will try to displace laterally. This lateral displacement is resisted by the guys as the vector summation of the forces in the guys. Equal and opposite total reaction. The tower section is in equilibrium and will not translate in its plane. Remeber guys only resist tension and cannot resist a lateral load to their line of action. When you translate the plane triangle section in rotation in its plane, twist or torque load, initally the guys cannot resist the lateral displacement as the guy's line of action is perpendicular to theaction direction of the load. As the triangular section twists additionally then there is created an angle between the line of force and the guy line of action which can develop a vector resistance to the movement of the triangular section. This value of resistance is a function of the sine of the angle created. It wil start at 0 degrees at rest, sine of 0 degrees is 0. This explains why the torsional resistance of the standard guying scheme is so low and why if significant torsional forces are present in a tower they twist. In this case the farther away from the center the guy attachment point is really doesn't help with the torsional strength the angle between the guy and the line of force of the torque is what matters. When you star guy or 6 point guy a tower with a torque arm mechanism then you have guys that are better aligned to initally resist the twist from the onset. Therefore this type of system is better able to resist torsional loadings. In a normal tower torsion is input into the tower by the antenna and the rotator mounting plate as the rotator needs something to push against to work. The top of the tower is one of the best places to put a 6 point guying system if that is were the rotator is located. Newton's laws and vector mechanics will always explain how these things work. Regards Lonberg Design Group, Ltd. Hank Lonberg, P.E.,S.E. / KR7X President > I've noted a bit of confustion on the effectiveness of torque bars. > > First, torque bars do work when rigidly installed. > Second they work without resorting to 6 point guys (2 per arm) > Third, they are more effective with the 6 point guy system than a 3 point. > > For those who say they don't work all you have to do is the math. > > When the arm moves it translates to linear pull on the guy. An 18 inch arm > is going to pull more on the guy than when the guy is anchored directly to > the tower leg. With Kevlar guys this is substantial force as there is so > little catenary and give in the guy line. > > The big question is; Do you need them? > "My own opinion" is , It all depends. If the tower load is some long beams > I'd certainly use torque arms. If the antenna/wind load is minimal I'd not > bother. > > On my system which is most likely not typical > http://www.rogerhalstead.com/ham_files/Tower29.htm and > http://www.rogerhalstead.com/ham_files/Tower26.htm I do use the torque arms > at the top. I do not use them at the middle and bottom levels. > > The top guys are tensioned to a bit over 600# while the bottom two tiers are > about 450# > > I've been up there in winds near 30 mph and the top of that tower does not > appear to move. > However, looking up through the antennas at the clouds when the wind is > blowing like that creates a tendency to leave fingerprints in the tower > legs. > > > Roger Halstead (K8RI, EN73 & ARRL Life Member) > N833R, World's Oldest Debonair (S# CD-2) > www.rogerhalstead.com > > > _______________________________________________ > > 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 ```
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