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Why U.S. Tower is the Best Choice for Small Wind Turbines
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U.S. Tower, Inc. is the best choice for small wind turbines. Our towers are designed specifically for small wind turbines and the needs of wind turbine owners. Our tower designs have a proven track record and have been installed throughout the U.S. Following are some specific comparisons with the Rohn SSV (TM).
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Larger Tower Spread Reduces Stress and Cost
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Broader tower sections mean lower tower and foundation stress. For any given tower height, the greater the distance between the tower legs at the base, the lower the stress will be on the legs and foundation attachment points. The image at the right shows the dimensions for the 120' US Tower, Inc. Model W and 120' Rohn SSV Tower. The larger base dimension of our tower is clearly visible. In fact, the spread dimension of our tower is larger than the SSV for the base of each 20' section running up the tower. These larger dimensions result in a lighter weight and less expensive tower with no sacrifice in strength.
An additional benefit of a larger distance between tower legs is that the tower tends to be stiffer. This means that when the turbine runs in a strong wind the tower tends to move less. A stiffer tower can also lead to a higher natural frequency for the structure which can help to reduce vibration from turbine rotor exitation. Tower vibration can cause rattling of the braces and noise.
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| Tower Base Spread - 120' Tower |
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Engineered Brace Attachment
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| US Tower Engineered Brace Attachment |
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| SSV Tower Top Section |
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The US Tower, Inc. engineered brace attachement design results in more efficient tower aseembly and can save the installer many hours of labor when installing the tower. A 120' SSV tower uses approximately 426 brace bolts. The US Tower. Inc. Model W uses 252 brace bolts. Because two diagonals are attached using a single brace bolt the number of bolts is nearly halved. When a single brace is attached using one bolt an engineer would call this "single shear". When two braces are attached using a single bolt, an engineer would call this "double shear". A bolt in double shear can handle twice the load of a bolt in single shear so there is virtually no difference in strength between the SSV method and our design. However, because only a fraction of the number of bolts is used, The US Tower, Inc. design can save hours of labor when assembling the tower. Each bolt not only requires a nut, but it also requires a lock nut so reducing the number of bolts saves a great deal of time. Time reduction results in lower installation cost to the owner.
Another benefit of our design is a reduction of leg warping. The above image at the right shows an SSV top tower section being assembled. The curve in the tower legs is clearly visible. This curve is caused when the brace tabs are welded to the pipe leg. When steel is welded and cooled, the steel in the weld area contracts. Because the opposite side of the pipe is not heated nearly as much it retains its original shape. Because of the differential heating, the metal contraction causes the pipe to bow. When the tower is assembled it is necessary to remove this bow and straighten the legs. Because the pipe is very strong and stiff, it is sometimes necessary to use a "come along" or winch to pull the legs apart so the braces can be installed. For sections with short braces such as the top section, this can be difficult and time consuming. The US Tower, Inc. design uses short individual brace tabs so there is less welding and substantially less distortion. This results in time and cost savings for the owner and installer.
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| All towers are Made in America (100' Model W, Taunton, MA) |
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