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Cecil, !5DXP wrote:
"According to Rohn, a single set of guy wires limits the tower to 40 - feet maximum height - sorry about that." Well, it depends on the Model No. and how you will load the tower. It is best to follow thw manufacturer`s recommendations to the letter. There is a length that you can stack which will endure without guys in most cases. Towers usually come in 20-ft. sections. Often one or two sections is all it is safe to use without guys. Windloading the tower is expected to withstand, often determines space between guy points. Wind exerts force on the tower and its appurtences, often expressed in a sum of pounds per square foot on the area facing the wind.. Resistance (drag) produces a differential pressure on items in the wind. Force is proportional to the projected area in the wind, and varies with the shape and roughness of the item in the wind. Windload on a tower is not uniform. The wind usually blows harder at higher altitudes. Wind tries to turn the tower over but until something yields, it is in equilibrium and the summation of of forces about the base of the tower is zero. The summation of torques is zero. Guywires exert force in yje only way they can. They have tension in the direction of the wire. This may be resolved into vertical and horizontal components. This prevents movement and increases base loading when the wind blows. Pressure on items in the wind (pounds per square feet) is a function of the square of the wind velocity (miles per jour). One formula considered useful is named "Ensewiler" which is said to give: 22.5 psf = 85 MPH 45 psf = 134MPH 60 psf = 155MPH 75 psf = 173MPH Best regards, Richard Harrison, KB5WZI |
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