Codes and Standards

Back to Contents

ANNEX E: TOWER MAINTENANCE AND INSPECTION PROCEDURES

Owners of towers should perform initial and periodic tower inspection and maintenance to assure safety and to extend service life. It is recommended that major inspections be performed, at a minimum, every 3 years for guyed towers and every 5 years for self-supporting towers. See section 14. Ground and aerial procedures should be performed only by authorized personnel, experienced in climbing and tower adjusmaents.

Some of the items listed below may apply only to initial construction of new towers.

I. Tower Conditions (guyed and self-supporting)

A. Members

1. Bent members (legs and lacing)

2. Loose members

3. Missing members

4. Climbing facilities, platforms, catwalks -- all secure

5. Loose and/or missing bolts

B. Finish

1. Paint and/or galvanizing condition

2. Rust and/or corrosion conditions

3. FAA or ICAO color marking conditions

4. Water collection in members (to be remedied, e.g., unplug drain holes, etc.)

C. Lighting

1. Conduit, junction boxes, and fasteners weather tight and secure

2. Drains and vents open

3. Wiring condition

4. Controllers functioning

a. Flasher
b. Photo control
c. Alarms

5. Light lenses

6. Bulb condition (Option: change all bulbs at one time)

D. Grounding

1. Connections checked and secure

2. Corrosion observed and remedied

3. Lightning protection secure (as required)

E. Tower Base Foundation

1. Ground Conditions

a. Settlements or movements
b. Erosion
c. Site condition (standing water, drainage, trees, etc.)

2. Base condition

a. Nuts and lock nuts tight
b. Grout condition

3. Concrete Condition

a. Cracking, spalling, or splitting
b. Chipped or broken concrete
c. Honeycombing
d. Low spots to collect moisture
e. Anchor-bolt corrosion

F. Tower Assembly Pro£fie (See Figures E1 and E2)

1. Antennas and feedlines (each)

a. Frequency
b. Elevation
c. Type
d. Size
e. Manufacturer
f. Connectors and hangers

2. Optional appurtenances (walkways, platforms, sensors, floodlights, etc.)

a. Elevation
b. Arrangement
c. Drawings or sketches

3. Foundation and anchors

a. Plan
b. Elevations (relative or mae)
c. Size
d. Depths
e. Soil type (if known or necessary)

G. Tower Alignment (See Figures E3, E6, and E7)

1. Tower Plumb and Twist (See 6.1.2.1 and 6.1.2.2)

H. Insulators (As Required)

1. Insulator Condition

a. Cracking and chipping
b. Cleanliness of insulators
c. Spark gaps set properly
d. Isolation transformer condition
e. Bolts and connections secure
f. Manufacturer type and part numbers for future replacements

II. Guyed Towers

A. Anchors

1. Settlement, movement or earth cracks

2. Backffil heaped over concrete for water shedding

3. Anchor rod condition below earth (Maintain required structural capacity of anchor during exploration, inspection and maintenance. Attachment to temporary anchorage may be required.)

4. Corrosion control measures (galvanizing, coatings, concrete encasement, cathodic protection systems, etc., refer to Annex J.)

5. Grounding (Paragraph I-D)

6. Anchor head clear of earth

B. Tower Guys (see Figures E4 and E5)

1. Strand

a. Type (lx7 EHS, lx19 bridge Strand, etc.)
b. Size
c. Breaking strength
d. Elevation
e. Condition (corrosion, breaks, nicks, kinks, etc.)

2. Guy Hardware

3. Elements

a. Bent, broken, cracked or bullet damaged
b. Loose
c. Missing
d. Loose and/or missing fasteners

4. Corrosion condition

5. Radomes and/or cover conditions

B. Feed Lines (waveguide, coax, etc.)

1. Hangers and supports

a. Condition
b. Quality
c. Corrosion condition

2. Flanges and seals (check integrity)

3. Line Condition

a. Dents
b. Abrasions
c. Holes
d. Leaks
e. Jacket condition

4. Grounds

a. Top ground strap bonded both ends
b. Bottom ground strap bonded both ends

5. Feedline support (ice shields)

a. Properly attached
b. Loose and/or missing bolts
c. Members straight and undamaged

TOWER ELEVATION

Show the following:

-- Tower Height above ground	-- Location of feed lines
-- Location of antennas	-- Location of platforms, ladders, etc.

Click for Figure E1

PLOT PLAN

Show the following:

-- Tower layout relative to North	-- Access roads and buildings
-- Anchors and assign letter designation	-- Power lines and poles
-- Relative or true anchor and base elevations

Click for Figure E2

TOWER LEG VERTICAL ALIGNMENT

1. Check with transit. Two transit setups are required. Line transit parallel to one face and center on leg. Second setup should be at 90° on same leg. Show on sketch below the locations used for transit setup. Indicate North.

Click for Table E8

Approximate wind speed during measurements mph

Note: This procedure is not sufficient to determine both twist and out of plumb.

IV. Methods For Measuring Guy Initial Tensions
There are two basic methods of measuring guy initial tensions in the field: the direct method
and the indirect method.

A. The Direct Method (see Figure E8)

A dynamometer (load cell) with a length adjustment device, such as a come-along, 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 the original turnbuckle begins to slacken. At this point the dynamometer carries all of the guy load to the anchor, and the guy tension may be read direcfiy off the dynamometer dial.

One may use this method 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.

B. The Indirect Method (see Figures E8 and E9)

There are two common techniques for the indirect measurement of guy initial tensions: the pulse or swing method (vibration) (Figure E8) and the tangent intercept or sag method (geometry) (Figure E9).

1. The Pulse Method (see Figures E8 and E10)

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 the 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:

equation.gif (4709 bytes)

in which (see Figure E10)
T_A = Guy tension at anchor (lb) .....
T_M = Guy tension at mid-guy (lb)
W = Total weight of guy, including insulators, etc. (lb)
L = Guy chord length (ft)

V = Vertical distance from guy attachment on tower to guy attachment at anchor (ft)
H = Horizontal distance from guy attachment on tower to guy attachment at anchor
fit)
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.

2. The Tangent Intercept Method (see Figure E9)
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:

equation3.gif (2251 bytes)

in which

C = Distance from guy attachment on tower to the center of gravity of the weight W (ft)

I = The tangent intercept (ft)

ff the weight is uniformly distributed along the guy cable, C will be approximately equal to 1-I/2. If the weight is not uniformly disWibuted, the guy may be subdivided into n segments and the following equation may be used: