TIA/EIA-222-G, the national standard´s seventh revision for Steel Antenna Towers and Antenna Supporting Structures, became effective January 1, 2006. REV. F wind loading is calculated according to the Fastest-Mile Wind Speed for the structure´s location as recorded from the 1-in-50-year wind speeds encountered at that location that were constant over a distance of one mile. REV. G requires that wind loading be calculated according to the three-second-gust wind speed, allowing the tower´s design to accommodate instantaneous loads. Loadings will be determined by specific local county criteria from wind, ice, and seismic maps.
Tower and foundation installations should be performed by qualified and experienced personnel using construction drawings. This document is to serve as a guide for sizing and buying the 45GSR tower. All types of antenna installations should be thoroughly inspected by qualified personnel and re-marked with appropriate danger and anti-climb labels at least twice a year to ensure safety and proper performance.
Wind Loading, Antenna Loading and Wind Survivability ratings vs. Height Documentation Provided by ROHN is available here as a Resource, but is by no means complete by itself or a susbstitution for Engineering Conducted Specific to your Application. Contact Us with any Questions you may have regarding Use prior to Purchase. All Information regarding the ROHN 45GSR Tower line, Parts and Accessories is as accurate and complete as we can possibly provide given that this Resource Offering is subject to change without Notice and is beyond Our Control.
Wind speed is a function of height, topology and ground cover. Generally speaking, a better picture of the wind resource is gained from towers closest to the height of the turbine that is being contemplated for the installation. A small variation in wind speed has a significant impact on energy capture. Data needs to be collected at a minimum of two levels (three levels are preferred) to determine the turbulence and shear within the wind. This is accomplished by having more than one anemometer mounted to the tower at prescribed intervals. Dual anemometers are recommended at the highest metering point. Anemometers are placed at various levels to determine the wind shear and the magnitude of wind turbulence which may fatigue the rotor blades over time. Wind speed has a functional relationship to elevation. As a general rule, the higher a turbine rotor is placed above ground, the greater the velocity and power of the wind. Turbine generators placed on higher towers will produce more electrical energy. Wind speed over the first 500 meters above ground tends to increase with an exponential factor (a friction coefficient derived for ground cover resistance) in proportion with the height. For every 20 meter increase in elevation, the velocity of the wind increases 5% to 15% depending on type of ground cover. The type of ground cover in the region tends to offer a certain degree of resistance to the movement of wind as ground level is approached. The opposition that ground cover offers to wind can be given a value, known as the "coefficient of friction", that may be used in projecting wind speed at higher altitudes when the speed of the wind is known at a certain height above ground level.
These Pre-Engineered Tower Kits are for 110 MPH - 3 Second Gust (No Ice) / 50 MPH - 3 Second Gust (3/4" Radial Ice) as a Structure Class II in Exposure Category C on Topographical Category I. Towers for use in higher Ice zones will need to be Custom Engineered by ROHN. Contact us for Details.
I. PURPOSE AND INTENT
a) The intended purpose of these guidelines is to assist the customer and/or owner to retain the services of a Geotechnical Engineer.
b) It is not ROHN´s purpose or intent to supercede the Geotechnical Engineer´s knowledge, judgement and/or experience. It is the Geotechnical Engineer´s responsibility to add or delete from these items, based on local site conditions and other factors.
c) Additional information is provided in ANSI/TIA-222-G Annex G "Geotechnical Investigations".
a) ROHN will not accept any liability, either expressed or implied, for the use of, and omissions in, these guidelines.
III. EXPLORATORY BORINGS
a) Borings should be taken at tower legs for self-supporting towers and at the base and anchor points for guyed towers. For small self-supporting towers, two borings may suffice. For large self-supporting towers, one boring should be taken at each tower leg. A "small" self-supporting tower is assumed to have a face width less than 20 feet and a compression load less than 50 kips per leg. For pole structures, one boring may suffice.
b) The minimum boring depth should be 30 feet for pole structures, self-supporting towers and guyed tower bases. For guyed tower anchors, the minimum depth should be 15 feet. The actual depth of boring must be determined by the Geotechnical Engineer based on reactions, soil conditions and the type of foundation recommended.
c) If borings cannot be advanced to the desired depth, rock corings should be taken. Rock Quality Designation (RQD) values and compressive strengths should be determined.
IV. GEOTECHNICAL REPORT
a) The following properties, for each soil layer encountered, should be determined by field or laboratory testing and summarized in the geotechnical report:
1. Soil classification and elevations
2. Standard penetration values
3. Unconfined compression strength
4. Angle of internal friction
6. "In-Situ" soil density and moisture content
7. Rock quality designation (RQD) and percent rock sample recovered
8. Other properties unique to site conditions
b) The following items should be discussed in the geotechnical report:
1. Geological description of site
2. Observed and expected ground water conditions
3. Expected frost penetration depth
4. Corrosion potential of soil and corrosion protection recommendations
5. Site access and potential construction difficulties
6. Dewatering or site drainage requirements
7. Backfill material recommendations
8. Settlement considerations
9. Additional information to aid foundation designer
10. Recommended types of foundations
11. Design parameters for uplift, download and lateral load
12. Factor of safety considered when allowable vs. ultimate design parameters are provided
13. Recommended construction techniques and inspections