4.0 First Line Maintenance
In tower design, it is assumed that the worst case scenario is a total mechanical failure. This can be caused by stress, extreme overload, use of defective and poor quality materials, fatigue, corrosion, poor workmanship, insufficient maintenance, sabotage, as well as any combination of these factors. Every design must attempt to foresee all possible combinations of these that can
occur in the installation environment and incorporate protective answers to them in the design. This is the first line of maintenance.
4.1 Hot Dip Galvanization
Unprotected s teel can be seriously damaged due to environmental factors as rain, salty humid air and extremes of temperature. Corrosion transforms steel back to its natural state of iron, which is very fragile and can prove to be deadly in structures like towers which support heavy pressures. The best way to avoid this phenomenon is through a process called "hot dip galvanization".
This process consists of dipping steel in melted zinc at 450°C. At this
temperature iron and zinc share great affinity, and allow an alloy to form where pure zinc prevails to the outside. The final product is a steel surface protected with a zinc coating.
Due to the difference of electrochemical potential between zinc and steel (cathodic protection), a zinc coating protects steel in such a way that slightly exposed surfaces due to cutting, scratching or piercing are equally protected against corrosion.
What considerably affects the appearance and gauge of galvanization is the contents of alloy elements that are present in steel: carbon, magnesium, and silicon. The greatest effect is produced by silicon in concentrations higher than 0.12%.
Most steels can be galvanized: high-strength steel, low-carbon steel, low-alloy steel, and steels with as much as 0.20% copper content; the most appropriate being low-carbon steels.
4.2 Tower Maintenance
Towers require regular maintenance. Regular maintenance is especially
guyed masts. For masts and towers, maintenance is mandatorily preventive as any breakdown comes usually with catastrophic consequences. Maintenance and inspection of steel antenna towers and antenna supporting structures should be performed by the owner on a routine basis.
Major inspections shall be performed, at a minimum, every 3 years for guyed towers and every 5 years for self -supporting towers.
Ground and aerial procedures should be performed only by authorized personnel, experienced in climbing and tower adjustments.
All structures shall be inspected after severe winds or other extreme loading conditions.
Shorter inspection intervals of 2 years for guyed towers and three years for self supporting towers shall be obligatory for structures in coastal salt water
environments, in corrosive atmospheres, and in areas subject to frequent
vandalisation. At every tower site, the owner shall keep a maintenance log book in a thick cellophane folder. This folder shall be readily accessible to the
regulators inspectors. It shall have the following information: -
• Installation Date
• Inspection due dates
• Painting due dates
• Minor Maintenance due dates
• Major Maintenance due dates
• Name and address of Inspector
For each of the due dates, the log must show whether the inspection or the maintenance was carried out and by whom.
4.3 Maintenance Philosophy
The external condition of Towers and Masts must be regularly inspected with intent to detect deterioration. Necessary maintenance works must be carried out timely.
Periodic checks and inspection of the structure must be carried out: At regular intervals of time during the service life of the structure
After the installation of an additional load like antennas on the structure After each serious climatic event like tempest, hurricane, tornado
The first thorough check of the structure should be carried out 6 months after its installation and erection.
Maintenance checks should be carried out yearly henceforth 4.4 Routine Checks
4.4.1 Main structure
Check that there are no structure components missing
Check that bars are neither warped, holed nor spitted. Replace all defective parts.
Check structure components for corrosion
Check that draining holes on pipe leg members, pipe lattice parts are not blocked.
Check the climbing facilities, platforms, catwalks for integrity
4.4.2 Tower Base Foundation
Check for settlements or movements Check for erosion
Site condition (standing water, drainage, trees, etc.) Check bolts, nuts and lock nuts for tightness
Grout condition 4.4.3 Guy wires
Check that each cable that is part of the guy wire is neither broken nor warped Measure the tension of each guy wire using a strand dynamometer and
compare result with the installer's stated values.
Check guy wires condition (corrosion, breaks, nicks, kinks, etc) Check that the guy wire tightening system is properly greased.
Check backfill heaped over concrete for water shedding Check anchor rod condition below earth
Check for signs of corrosion and take remedial timely steps Ensure anchor head is clear of earth
4.4.4 Bolting parts
Check that no bolts or nuts or any bolting part like washers, pins, etc is missing. Replace these immediately.
Check bolts tightening.
Check bolts, nuts and bolting parts for corrosion. Check anchorage rod in the concrete.
4.4.5 Verticality
Check with the appropriate devices such as theodolite that the structure stands vertical. There shall be no tilts. Take two measurements in two different planes with a 90' angle difference.
4.4.6 Antennas and Accessories
Check antennas and antenna supports good condition Check coaxial cables good condition
Check fixing clamps good condition. 4.4.7 Safety components
Check that access ladder is in good condition
Check rest and work platforms for defects, wear and tear Check that all safety components are existing and complete Check the correct functioning of the fall arrestor system
For a fall arrestor system with cable, check that the cable has not been over tightened.
Check that the anti climbing door is functioning. 4.4.8 Lightning and Earthing system
Check the Earthing connection of coaxial cables,
Measure the resistivity of the Earth and confirm conformity to expected values. 4.4.9 Aviation Safety Lights
Check that all components are in place,
Check condition and well functioning of components (Light bulb, energy cables, fixing parts, photoelectric cell, connections)
Check earthing of the light wiring. 4.4.10 Anti corrosion protection
Check all galvanised members for integrity Check paint condition.
Check for signs of corrosion on the structure, of the bolts, bolting accessories, harnesses, antenna supports, etc
For guyed masts, check for corrosion on the entire guy assembly.
4.4.11 Salty environment
Wash the structure and accessories with clean water once every six months to eliminate residue salt particles which may not be washed away by rain.
4.4.12 Concrete blocks
Check the good condition of above ground concrete block parts.
There must not be any water collection, cracking or splitting, chipped or broken concrete.
Check the condition of anchor setting in the concrete block. Check anchor-bolt corrosion.
4.4.13 Tower loading
Check types, numbers and installed heights of all antennas currently on the structure and confirm that the loading does not exceed structure design load.
4.5 Annual Preventive Maintenance Checks 4.5.1 Structure
Tension of Guy wires using a dynamometer. Geometry of the structure.
Re-tighten main structure and accessories bolted parts (10%) Geometry of the Bars.
Rigidity of Antennas and Accessories. 4.5.2 Safety
Ensure anti climb door can open and close. Clean and grease all hinges.
Ensure the work platform's trap can open and close. Clean and grease all door hinges.
Fixing of the fall arrestor system
Check tower ladder for any signs of weakness, re-tighten all bolts Check the riggers’ safety gear, take inventory and record it
Right placing and right installation of safety components. Test of the fall arrestor system with individual equipment.
4.5.3 Earthing
Physical condition of the lightning rod Physical condition of the lightning arrestor
Physical condition and installation of the copper strip
Connection of the concrete block copper belting onto the copper strip Connection of coaxial cables earthing onto the copper strip
Connection between the bottom coaxial cable earthing and the collection Copper bar fixed on the concrete block
Tightening of the brass bolts of the lightning protection electrodes Resistivity the lightning protection electrodes
Earth resistance
4.5.4 Aviation Safety Lights
Functionality of controllers, flashers, alarms and photo control Condition of electrical wires, connectors and earthing
Condition and fixing of energy cables
Conduit, junction boxes, and fasteners weather tight and secure
Bulb condition - change all bulbs at one time immediately before the rated service hours is achieved.
Condition and fidelity of the power supply systems 4.5.5 Coating
Discrepancies in galvanization
Paint coating. Repaint every three years Rust and/or corrosion conditions
ICAO / NAMA Color marking conditions
Water collection in members - unplug drain holes, etc.
4.6 TESTING
Measurement of Guy Tension
Tension should be measured when wind is relatively still. Measurements in wind velocity above 2 5 m/s (90km/h) will yield misleading results. Tension results can be considered satisfactory if they fall within 15% of the tension value stated by the manufacturer and/or installer. Excessive tension may cause alignment problems and even a cable rupture. It may even cause permanent wrapping of tower structural parts.
a
Dyanamometer
Come - Along
Turnbuckle
4.6.1 The Direct Method (see Figure 4.1)
A dynamometer (load cell) with a come-along (length adjustment device), is attached to the guy system by clamping onto the guy just above the turnbuckle and onto the anchor shaft below the turnbuckle, thus making the turnbuckle redundant. The come-along is then tightened until original turnbuckle begins to slacken. At this point the dynamometer carries the entire guy load to the anchor, and the guy tension may be read directly off the dynamometer dial.
This method is used to set the correct tension by adjusting the come-along until the proper tension is read on the dynamometer.
Two control points are marked, one above the clamping point on the guy and one on the anchor shaft, and the control length is measured. The dynamometer and come-along are then removed, and the original turnbuckle is adjusted to maintain the control length previously measured.
(1) Dynamometer Method As come-along is tightened,
dynamometer carries all the load
V L TA W TM TA TM 2L WV WH 2L
(3) Pulse Method (2) Swing Method
Pulse travels up and Guy swings from a to b and
down the guy N times back N times in p seconds
In p seconds
Figure 4.1
Measurement of Tension of Guy
4.6.2 The Indirect Method
There are two common techniques for the indirect measurement of guy initial tension - the pulse or swing method (vibration) (Figure 4.2) and the tangent intercept method (Figure 4.3).
(a) The Pulse Method
H
Figure 4.2
Relationship between Guy Tension at Anchor and at Mid-Guy
One sharp jerk is applied to the guy cable near its connection to the anchor causing a pulse or wave to travel up and down the cable. On the first return of the pulse to the lower end of the guy cable, a stop watch is started. A number of returns of the pulse to the anchor are then timed, and the guy tension is calculated from the following equations:
where
TA = Guy tension at anchor
TM = Guy tension at mid-guy
W = Total weight of guy, including insulators, etc. L = Guy chord length
N = Number of pulses or swings counted in P seconds
V = Vertical distance from guy attachment on tower to guy attachment at anchor H = Horizontal distance from guy attachment on tower to guy attachment at
anchor
N = Number of pulses or swings counted in P seconds P = Period of time measured for N pulses or swings (s)
Instead of creating a pulse that travels up and down the guy, one may achieve the same result by causing the guy cable to swing freely from side to side while timing N complete swings. The formulas given above will also apply for this approach.
V H I W Line of sight A C T
(b) The Tangent Intercept Method
I V a H Figure 4.3
A line of sight is established which is tangential to the guy cable near the anchor end and which intersects the tower leg a distance (tangent intercept) below the guy attachment point on the mast. This tangent intercept distance is either measured or estimated and the tension is calculated from the following equation:
where
I = The tangent intercept
If the weight is uniformly distributed along the guy cable, C will be approximately equal to 1-I/2. If the weight is not uniformly distributed, the guy may be
subdivided into n segments and the following equation may be used:
where
Wi = Weight of segment i
Ci = Distance from the guy attachment on the tower to the center of gravity of
segment i
If the intercept is difficult to establish, one may use the guy slope at the anchor end with the following equation:
where
cz = Guy angle at the anchor
Note that
and that
and that WC in equation (7) may be replaced with S, as was done in equation (5).
Glossary of Terms
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.
Twist -- The twist (angular rotation in the horizontal plane) between any two elevations shall not exceed 0.5 degrees in 3 m and the total twist in the structure shall not exceed 5".
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.
Normal Soil -- A cohesive soil with an allowable net vertical bearing capacity of 192 kPa and an allowable net horizontal pressure of 63 kPa per linear meter of depth to a maximum of 192 kPa.
Twist -- The angular rotation of the antenna beam path in a horizontal plane from the no-wind load position at a specified elevation.
Sway -- The angular rotation of the antenna beam path in a vertical plane from the no-wind load position at a specified elevation.
Displacement -- The horizontal translation of a point relative to the no-wind load position of the same point at a specified elevation.
Grounding is the means of establishing an electrical connection between the structure and the earth, adequate for lightning, high voltage, or static
discharges.
Primary Ground is the conducting connection between the structure and earth or some conducting body, which serves in place of the earth.
Secondary Ground is the conducting connection between an appurtenance and the structure.
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.
Working Facilities -- Work platforms and access runways.
Guy Connection - the hardware or mechanism by which a length of guy strand is connected to the tower, or guy anchor.
Lux is lumens/sq m
Candela is light intensity. Its unit is the lumen
Alternative Mounting Structure - man made tree, clock tower, church steeple, bell tower, utility pole, light standard, identification pylon, flagpole, or similar structure, designed to support and camouflage or conceal the presence of telecommunications antennas.
Antenna - structure or device used to collect or radiate electromagnetic waves, including directional antennas, such as panels, wireless cable and satellite dishes, and omni-directional antennas, such as whips, but not including satellite earth stations.
Antenna Array - An arrangement of antennas on their supporting structure. Dish Antenna - A parabolic or bowl shaped device that receives and/or transmits signals in a specific directional pattern.
Panel Antenna - An antenna which receives and/or transmits signals in a directional pattern.
Antenna, Stealth - A telecommunications antenna that is effectively camouflaged or concealed from view.
Telecommunications Antenna - An antenna used to provide a telecommunications service.
Whip Antenna - An omni-directional dipole antenna of cylindrical shape which is no more than 15 cm in diameter.
Identification Pylon - A permanent ground mounted sign consisting solely of a single monolithic structure used to identify a development.
Guyed Tower - Any telecommunications tower supported in whole or in part by cables anchored to the ground.
Tower Height - The distance measured from ground level to the highest point of any and all components of the structure, including antennas, hazard lighting, and other appurtenances.
Monopole - A self-supporting telecommunications tower which consists of a single vertical pole fixed into the ground and/or attached to a foundation.
Self-supporting Lattice - A telecommunications support structure which consists of an open network of metal braces forming a tower which is usually triangular or square in plan.
Telecommunications Tower - A self-supporting or guyed structure more than 5 meters in height, built to support one or more telecommunications antennas.
Index A
• Access Ladders 83, 112
• Accidents during the installation period 7
• Aggregate 59, 87
• Air Terminal 75, 80, 88,90
• Airport 6, 55
• Alternative Mounting Structure 13, 122
• Aluminum – polished, anodized and painted finish 86
• Anchor Bolts Template 58
• Angle leg 21, 22
• Annual preventive maintenance checks 113
• Antenna Mounting Frames 101
• Anti Climb Shields 82
• Anti Corrosion protection 112
• Authorization 10
• Aviation Lighting 6, 12
• Aviation safety lights 112, 114
B
• Base Plate 23, 74
• Basic Foundation Design for Slim lattice mast 72
• Basic wind speed 15, 16, 74
• Bi-metallic 88, 98
• Bolting 23, 111, 112, 124
• Bolt-up construction 22
• Bracing 21, 25, 26, 27, 28 29, 33, 35, 49, 62, 86
• Building and roof mounted dish antennas 13
• Bull Dozer 8
C
• Cable and Tape clips 98
• Cable Connectors 97
• Certification 6, 7, 13, 14
• City and Guilds 7
• Clearance certificate 6 • Climbing 24, 81, 82, 83, 84, 110, 111, 112, 121, 122 • Coating 109, 114 • Co-location 10, 122 • Concreting 59 • Copper-Tapes 79, 96 D • Dish Antenna Mounting Standards 13
• Drilled pier Foundation design 67 • Dynamometer 111, 113, 115, 116 E • Earthing 75,76, 78, 88, 89, 91, 92, 93, 94, 112, 114 • Effective height 6 • Elevation Rods 90 • Environmental requirements 9 • Excavators 8 F • Fabricators and Installers 4
• Face width 21, 34, 35, 36, 37, 38, 49, 67, 72. 73 • Factors of safety 61
• Fall Arrest Safety System 81
• Faraday Rod 75
• Finishes 21, 23, 83 • Flat saddle 96
• Flexible copper braid 96
• Footing Assembly 43
• Foundation Design and Loading 40
• Foundation Design 40, 43, 57, 58, 67, 72, 74 • Foundation Engineers 60, 61 • Foundation in swamps 75
G
• Geographical coordinates 6, 7
• Graphite 88
• Ground mounted dish antennas 13
• Guard-rails 81, 84 • Gust factor 16, 35, 36, 126 • Guy Anchor 11, 25, 50, 60, 61, 6, 66, 70, 75, 80,122 • Guy materials 99 • Guy wires 24,25, 111, 113 • Guyed Towers 5, 24, 57, 80, 110 • Guys 6, 11, 25, 66, 87 H • Height of Towers 8 • HF-SSB dipole antennas 50
• High Alumina (HA) 87
• Hot Dip Galvanization 109
• Humic Acid 87 I • ICAO 11, 12, 55, 56, 114 • Inspections 7, 10, 110 • Installation permit 8 • Insulator 93, 118 • Intersecting bracings 86 J • Junction box 12, 114 K • K-bracing 26, 27, 28, 29, 30. 31 • KNm-3 57, 59, 60 • Kpa 57, 59, 121 L
• Lap Link Weight Table 44
• Lattice 5, 21, 22, 24, 26, 27, 34, 37, 38, 44, 45, 73. 86, 67, 111, 123
• Saddle 86, 95
• Lighting 6, 11, 12, 55, 56, 78, 123
• Lightning and Earthing system 112
• Lightning Arrestor 95, 112, 114
• Lightning protection 6, 75, 76, 78, 80, 88, 90, 91, 92, 114
• Log book 7, 110
• Long Boom Arm Crane 8
M
• Magnesium 88, 109
• Maintenance 7, 8, 21, 108, 109, 110, 113
• Maximum compression 35, 36
• Maximum shear 35, 36
• Measurement of Guy Tension 115
• Monopole structures 86, 87
• Monopole Towers 23
• Multi-Point Air Terminal 90
N
• Name plate 7, 60, 61
• Nearness to power lines 12
• Nigeria Airspace Management Authority 6,10
• NAMA 11, 12, 21, 55, 56, 114
• Nigerian Communications Commission 6, 7, 8, 10, 13
• NCC 6, 7, 8, 9, 10, 11, 14
• Nigerian Meteorological Agency 15
• Non-Metallic clips 98
• N-Section Guyed Pole Mast 50
O
• Oblong Box Clamp 91
• Obstruction lamps 55
• Out rigger 50, 52 P • Packer 8 • Painting 55, 110 • Panel Height 26 • Permit Number 7 • Photo sensor 12
• Pier and Pad foundation construction 71
• Piles 56, 61 • Plate Type clamp 92
• Platform height 45
• Platforms 6, 21, 81, 111, 112, 122 • Pointed Air Rod 95
• Post Masts 23 • Property Owner 6 • Protective Grounding 80 • Public Health 9 • Public Safety 4, 8, 13, 82, 109 R • Radio frequency emissions 8
• Raft Foundation 60, 64, 66 • Redundant Diagonal 31
• Reinforcement 59, 60, 61, 65, 66, 80, 88 • Removal of abandoned towers 9
• Residential Areas (towers in) 11, 12, 13 • Resistivity values for different soil types 79
• Resistivity 78, 79, 112, 114 • Rest platforms 21, 81, 83 • Rock Anchors 56, 58 • Roof Mounts 25, 53, 54 • Routine checks 111 S • Safe Working Load (SWL) 58
• Safety Devices 81, 122 • Safety Enhancement 84 • Safety of equipment 4 • Safety of personnel 4 • Salty environment 113 • Screening 9, 13 • Security Fencing 9, 11
• Self Support Lattice 26, 37
• Service Life of Towers 12, 21, 110
• Setbacks of Towers 10, 11
• Side Antenna Mount 103
• Signage 11 • Silver 88