5 FACTORY FINISH
5.1.1 In the absence of other specific requirements, all materials shall be galvanized (see Annex A).
22.214.171.124 Structural Materials -- Structural materials shall be galvanized in accordance with ASTM A123 (hot-dip). Exceptions may be made when galvanizing in accordance with ASTM A123 would be potentially detrimental to the structure or its components. Examples include applications utilizing certain high-strength and/or proprietary steels and weldments. In these cases, an alternative method of corrosion control shall be specified.
126.96.36.199 Hardware t Hardware shall be galvanized in accordance with ASTM A153 (hot-dip) or ASTM B695 Class 50 (mechanical).
188.8.131.52 Guy Strand -- Zinc-coated guy strand shall be galvanized in accordance with
ASTM A475 or ASTM A586.
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PLANS, ASSEMBLY TOLERANCES, AND MARKING
6.1.1 Complete plans, assembly drawings, or other documentation shall be supplied showing
the necessary marking and details for the proper assembly and installation of the material,
including the design yield strength of the structural members and the grade of structural bolts
6.1.2 Tolerances for the proper layout and installation of the material; and the foundations and
anchors shall be shown on the plans.
184.108.40.206 Plumb -- The horizontal distance between the vertical centerlines at any two
elevations shall not exceed .25 percent of the vertical distance between the two elevations.
220.127.116.11 Twist -- The twist (angular rotation in the horizontal plane) between any two
elevations shall not exceed 0.5 degrees in 10 feet [3 m] and the total twist in the structure shall not
18.104.22.168 Length -- For tubular steel pole structures with
telescoping joint, butt welded or
flanged shaft connections, the overall length of the assembled structure shall be within plus 1
percent or minus 1/2 percent of the specified height.
(Note: Horn reflectors and other types of offset-feed antennas have polarization
performance requirements, which are sensitive to angular displacement from boresight
direction. Special consideration must be given to the mount, attachment hardware,
installation practice, as well as the support structure; to 'minimize all contributing factors to
initial skew or offset.) --"
6.1.3 All structural members or welded structural assemblies, except for hardware, shall have a part number. The part numbers shall correspond with the assembly drawings. The part number is to be permanently attached (stamped, welded lettering, stamped on a plate that is welded to the member, etc.) to the member before all protective coatings (galvanizing, paint, etc.) are applied. The part number shall have a minimum character height of 1/2 in. [13 mm], be legible and clearly visible to an inspector after erection.Back to Contents
7 FOUNDATIONS AND ANCHORS
7.1.1 Standard Foundations and Anchors w Structures designed to support the specified loads defined in Section 2 for normal soil conditions as defined in 7.1.3. Pile construction, roof installations, foundations or anchors designed for submerged soil conditions, etc., are not to be considered as standard.
7.1.2 NonStandard Foundations and Anchors -- Structures designed to support the specified loads defined in Section 2 in accordance with site specific conditions.
7.1.3 Normal Soil -- A cohesive soil with an allowable net vertical bearing capacity of 4000 pounds per square foot [192 kPa] and an allowable net horizontal pressure of 400 pounds per square foot per lineal foot of depth [63 kPa per lineal meter of depth] to a maximum of 4000 pounds per square foot [192 kPa].
(Note: Rock, noncOhesive soils, saturated or submerged soils are not to be considered normal soil.)
7.2.1 Standard foundations and anchors may be used for bidding purposes and for construction when actual soil parameters equal or exceed normal soft parameters.
7.2.2 When standard foundations and anchors are utilized for final designs, it shall be the responsibility of the purchaser to verify by geotechnical investigation that actual site soil parameters equal or exceed normal soil parameters. (See Annex A.)
7.2.3 Foundations and anchors shall be designed for the maximum structure reactions resulting from the specified loads de£med in Section 2 using the following criteria:
22.214.171.124 When standard foundations and anchors are to be used for construction, "normal soil" parameters from 7.1.3 shall be used for design.
126.96.36.199 When nonstandard foundations and anchors are to be used for construction, the soil parameters recommended by the geotechnical engineer should incorporate a minimum factor of safety of 2.0 against ultimate soil strength (see Annexes A and I).
188.8.131.52 Standard foundations, anchors, or drilled and belled piers shall be assumed to resist uplift forces by their own weight plus the weight of earth enclosed within an inverted pyramid or cone whose sides form an angle of 300 with the vertical. The base of the cone shall be the base of the foundation if an undercut or toe is present or the top of the foundation base in the absence of the foundation undercut. Earth shall be considered to weigh 100 pounds per cubic foot [16 k.N/m3] and concrete 150 pounds per cubic foot [24 kN/m3].
184.108.40.206 Straight shaft drilled piers for standard foundations shall have an ultimate skin friction of 200 pounds per square foot per lineal foot of depth [31 kPa per lineal meter of depth] to a maximum of 1000 pounds per square foot of shaft surface area [48 kPa] for uplift or download resistance.
7...4.3 Nonstandard foundations, anchors, and drilled piers shall be designed in accordance with the recommendations of a geotechnical report (see Annex I).
220.127.116.11 Foundations, anchors, and drilled piers shall be proportioned in accordance with the following:
(WR/2.0) + (Wc/1.25) > Ur and (WR+Wc)/1.5 > Up where: WR = soil resistance from 18.104.22.168, 22.214.171.124 or 126.96.36.199
WC TM weight of concrete
Up = maximum uplift reaction
188.8.131.52 A mat or slab foundation for a self-supporting structure shall have a minimum safety factor against overturning of 1.5.
7.2.5 The depth of standard drilled foundations subjected to lateral or overturning loads shall be proportioned in accordance with the following:
LD > 2.0 + S/(3d) + 2 [82/(18d2)+ 8/2 + M/(3d)]1/2 (fl)
LD > .61 + S/(143d) + 2 [82/(41333d2) + 8/96 + M/(143d)]1/2 [mi
where: LD = Depth of drilled foundation below ground level (ft) [m] d = Diameter of drilled foundation (ft) [m]
S = Shear reaction at ground level (kips) [kN]
M = Overturning moment at ground level (fl-kips) [m-kN]
Reference: Broms, B., "Design of Laterally Loaded Piles", Journal of the Soil Mechanics and Foundation Division Proceedings of the American Society of Civil Engineers, May, 1965.
7.3 Special Conditions
7.3.1 When a support is to be designed by other than the manufacturer, the manufacturer will be responsible for furnishing the reactions, weights, and interface details for the purchaser's engineer to provide the necessary attachment.
7.3.2 The effects of the presence of water shall be accounted for in the design of nonstandard foundations. Reduction in the weight of materials due to buoyancy and the effect on soil properties under submerged conditions shall be considered.
7.4 Foundation Drawings
7.4.1 Foundation drawings shall indicate structure reactions, material strengths, dimensions, reinforcing steel, and embedded anchorage material type, size, and location. Foundations designed for normal soil conditions shall be so noted.
(Note: Normal soil design parameters and methods are presented to
obtain uniform standard
foundation and anchor designs for bidding purposes. Design methods for other conditions and
other foundation types must be consistent with accepted engineering practices.)
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8 SAFETY FACTOR OF GUYS
8.1.1 Guy Connection -- The guy connection is defined as the hardware or mechanism by which a length of guy strand is connected to the tower, insulator, or guy anchor. The connection may include, but is not limited to, the following: shackles, in-line insulators, thimbles, turnbuckles, twin base clips, u-bolt cable clips, poured socket fittings, and grip- type dead-end connections. Twin base and u-bolt clips used on guy strand through 7/8-in. diameter shall be considered to have a maximum efficiency factor of 90 percent. In all other cases, clips on strand shall be considered to have a maximum efficiency factor orS0 percent. For all other types of end connections, manufacturer's recommendations should be followed when determining the connection efficiency factor.
8.1.2 Safety Factor of Guys t The safety factor of guys shall be calculated by dividing the published breaking strength of the guy or guy connection strength, whichever is lower, by the maximum calculated tension design load.
8.2.1 For structures under 700 ft [213 m] in height, the safety factor of guys and their connections shall not be less than 2.0.
8.2.2 For structures 1200 ft [366 m] or greater in height, the safety factor of guys and their connections shall not be less than 2.5.
8.2.3 For structures between 700 ft [213 m] and 1200 ft [366 m] in height, the minimum safety factor of guys and their connections shall be determined by linear interpolation between 2.0 and 2.5.
(Note: A 1/3 increase in stress for wind-loading conditions does not apply to the published breaking strength of guys and their connections.)
8.2.4 Structure height, for purposes of determining the required safety factor of all guys and their connections, shall be based on total structure height including tubular or latticed poles mounted on the structure.
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9 PRESTRESSING AND PROOF LOADING OF GUYS
9.1.1 Prestressing of Guys -- The removal of inherent constructional looseness of the guy under a sustained load.
9.1.2 Proof Loading -- The assurance of mechanical strength of factory assembled end connections.
9.2.1 Prestressing and proof loading are not normally required. When specified, prestressing and proof loading shall be performed in accordance with the recommendations of the guy manufacturer.
(Note: For tall, guyed structures, consideration should be given to prestressing and proof loading.)
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10 INITIAL GUY TENSION
10.1.1 Initial Guy Tension -- The specified guy tension in pounds [newtons] under no wind load conditions, at the guy anchor at the specified temperature (see 10.2).
10.2.1 Initial tension in the guys, for design purposes, is normally 10 percent of the published breaking strength of the strand with upper and lower limits of 15 and 8 percent respectively. Values of initial tension beyond these limits may be used provided consideration has been given to the sensitivity of the structure to variations in initial tension and, ff necessary, to dynamic behavior (see note below). Consideration shall be given to the site ambient temperature range. In the absence of site specific data, the initial tensions shall be based upon an ambient temperature of 60°F.
(Note: The stated 8-15 percent initial tension extreme values are provided as recommended guidelines only. Specific site and terrain conditions may necessitate initial tension values outside this range. When using initial tension values above 15 percent, consideration should be given to the possible effects of aeolian vibration. Likewise, when using initial tension values less than 8 percent, consideration should be given to the effects of galloping and slack-taut pounding.)
10.3 Method of Measurement
10.3.1 Initial tension may be measured by vibration frequency, mechanical tensiometers, measurement of guy sag, or by other suitable methods (see Annex E).
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11 OPERATIONAL REQUIREMENTS
11.1.1 Twist -- The angular rotation of the antenna beam path in a horizontal plane from the no-wind load position at a specified elevation.
11.1.2 Sway -- The angular rotation of the antenna beam path in a vertical plane from the no-wind load position at a specified elevation.
11.1.3 Displacement -- The horizontal translation of a point relative to the no-wind load position of the same point at a specified elevation.
11.2 Standard (See Annex A)
11.2.1 The minimum standard shall be based on a condition of no ice and a wind load based on a
50 mph basic wind speed [22.4 m/s] calculated in accordance with 2.3. The operational requirements shall be based on an overall allowable 10 dB degradation in radio frequency signal level.
11.2.2 Unless otherwise specified, the operational requirements for microwave antenna/ reflector systems shall be determined using Annexes C and D.
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12 PROTECTIVE GROUNDING
12.1.1 Grounding -- The means of establishing an electrical connection between the structure and the earth, adequate for lightning, high voltage, or static discharges.
12.1.2 Primary Ground -- A conducting connection between the structure and earth or some conducting body, which serves in place of the earth.
12.1.3 Secondary Ground -- A conducting connection between an appurtenance and the structure.
(Note: Ground wire should not be encased in the foundation.)
12.2 Standard (See Annex A)
12.2.1 Structures shall be directly grounded to a primary ground.
12.2.2 A minimum ground shall consist of two 5/8 in. [16 mm] diameter galvanized steel ground rods driven not less than 8 ft [2.5 m] into the ground, 180° apart, adjacent to the structure base. The ground rods shall be bonded with a lead of not smaller than No. 6 [5 mm] tinned bare copper connected to the nearest leg or to the metal base of the structure. A similar ground rod shall be installed at each guy anchor and similarly connected to each guy at the anchor.
12.2.3 Self-supporting towers exceeding 5 ft [1.5 m] in base width shall have one ground rod per leg installed as above.
12.2.4 All equipment on a structure shall be connected by a secondary ground.
12.2.5 Remote passive reflectors are exempt from the grounding requirements specified herein.
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13 CLIMBING AND WORKING FACILITIES
13.1.1 Climbing Facilities -- Components specifically designed or provided to permit access, such as fixed ladders, step bolts, or structural members.
13.1.2 Climbing Safety Devices -- Equipment devices other than cages, designed to minimize accidental falls, or to limit the distance of such falls. The devices permit the person to ascend or descend the structure without having to continually manipulate the device or any part of the device. The climbing safety device usually consists of a carrier, safety sleeves, and safety belts.
13.1.3 Working Facilities -- Work platforms and access runways.
13.1.4 Hand or Guardrails -- Horizontal barriers erected along the sides or ends of working facilities to prevent falls.
13.2.1 Climbing and working facilities, hand or guardrails, and climbing safety devices shall be provided when specified by the purchaser. (See Annex A.)
13.2.2 Climbing facilities shall be designed to support a minimum 250 [1.1 kN] pound concentrated live load.
184.108.40.206 When fixed ladders are specified as the climbing
facility, they shall meet the -
following minimum requirements:
a. Side rail spacing -- 12 in. [300 mm] minimum clear width.
b. Rung spacing -- 12 in. [300 mm] minimum center-to-center, 16 in. [410 mm] maximum.
c. Rung diameter -- 5/8 in. [16 mm] minimum.
220.127.116.11 When step bolts are specified, they shall meet the following requirements:
a. Clear Width -- 4 1/2 in. [110 mm] minimum.
b. Spacing -- 12 in. minimum [300mm] center to center, alternately spaced, 18 in. [460 mm] maximum.
c. Diameter -- 5/8 in. [16 mm] minimum.
13.2.3 Climbing safety devices shall meet the design requirements of the American National Standards Institute (ANSI) A14.3-1984, "Safety Requirements for Fixed Ladders", Section 7.
13.2.4 Support structures for working facilities shall be designed to support a uniform live load of 25 lb/ft2 [1.2 kPa], but in no case shall the support structure be designed for less than a total live load of 500 pounds [2.2 kN]. Working surfaces, such as grating, shall be designed to support two 250-pound [ 1.1 kN] loads. These loads are not to be applied concurrenfiy with wind and ice loads.
13.2.5 Hand or guardrails shall be designed to support a minimum concentrated live load of 150 pounds [0.67 kN], applied in any direction.
(Note: 13.2 is intended to provide minimum requirements for new structures. It is not intended to replace or supersede applicable laws or codes.)
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14 MAINTENANCE AND INSPECTION
14.1.1 Maintenance and inspection of steel antenna towers and antenna supporting structures should be performed by the owner on a routine basis.
(Note 1: It is recommended that all structures be inspected after severe wind and/or ice storms or other extreme loading conditions.)
(Note 2: Recommended inspection and maintenance procedures for towers are provided in Annex E.)
(Note 3: Shorter inspection intervals should be considered for
structures in coastal salt water
environments, in corrosive atmospheres, and in areas subject to frequent vandalism.)
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15 ANALYSIS OF EXISTING TOWERS AND STRUCTURES
15.1.1 Steel antenna towers and other supporting structures should
be analyzed when changes
occur to the original design or operational loading conditions. Recommended criteria for the
analysis of existing structures are provided in Annex F.
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