GDOT Section 920: Lighting Standards and Towers

SECTION 920 — Lighting Standards and Towers

920.1General Description

This section includes the requirements for the structural components of poles, towers, bases, anchor bolts, luminaires, and other attachments used for roadway, high mast, or other lighting. In particular, the section covers the following: • Steel lighting standards and towers • Aluminum lighting standards • Prestressed concrete standards • Support and lowering assemblies • Grounding 920.1.01 Related References

A.Standard Specifications

SECTION 105 — Control of Work

SECTION 501 — Steel Structures

SECTION 645 — Repair of Galvanized Coatings

SECTION 682 — Electrical Wire, Cable, and Conduit

SECTION 865 — Manufacture of Prestressed Concrete Bridge Members

B.Referenced Documents

ASTM AASHTO A 27/A 27M A 53/A 53M A 123/A 123M A 153/A 153M A 193/A 193M A 588/A 588M A 709/A 709M B 108 M 222/M 222M M 314 MIL-W-83420 AISI 304 AISI 1020 AASHTO Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals, with Interims (SLTS) ANSI C136.30, American National Standard for Roadway and Area Lighting Equipment-Pole Vibration 1770

SECTION 920 — Lighting Standards and Towers

920.1.01 Submittals Submit to the Engineer shop drawings and design calculations for each type of lighting standard, or tower to be used, for review and approval. Submission should be made electronically in a portable document format (pdf) and include an index. Format all drawings to fit 11 in. x 17 in. (279 mm x 432 mm) paper. Present calculations to fit 8.5 in. x 11 in. (216 mm x 297 mm) paper. The submission shall be prepared and stamped by the Design Engineer who shall be registered as a Professional Engineer in the State of Georgia. The Engineer will distribute submitted documents to the Bridge Engineer (SLTS@dot.ga.gov) for review.

920.2Materials

Design lighting assemblies consisting of standard, tower, bracket arms, lowering assembly, and luminaire support and assemblies according to AASHTO SLTS 920.2.01 Steel Lighting Standards and Towers

A.Requirements

1.Design

Poles shall be designed to the following wind speeds using a 1700 Mean Recurrence Interval (MRI) with Fatigue Category 1 for the listed counties: 150 mph: Bryan, Camden, Chatham, Effingham, Glynn, Liberty, McIntosh 140 mph: Brantley, Bulloch, Charlton, Evans, Long, Screven, Tattnall, Wayne 130 mph: Appling, Bacon, Brooks, Burke, Candler, Clay, Clinch, Decatur, Early, Echols, Emanuel, Grady, Jeff Davis, Jenkins, Lowndes, Miller, Pierce, Seminole, Thomas, Toombs, Ware 120 mph: For all counties not listed above

2.Include the following in the makeup of lighting standards and towers:

• A pole and bracket arms as required on the Contract. • A steel base welded to the other end complete with bolts for use as an anchor base pole, or attached to an approved breakaway device, such as slip base, aluminum transformer base, breakaway couplings, etc., when so specified.

3.Steel Structures

Use structural carbon or structural low alloy steel that meets the requirements of AASHTO SLTS. However, do not use ASTM A 588/A 588M steel.

4.Steel Pipe

When steel pipe is used, use steel pipe complying with ASTM A 53/A 53M Grade B or approved equal. No hydrostatic test is required.

B.Fabrication

1.Roadway Standards

Unless otherwise specified, do the following:

a.Make the shaft or appropriate shape continuously tapered with a base welded to the lower end.

b.The welds of the base flange to the shaft shall be configured such that the weld joints are loaded in shear,

never in tension.

c.Construct the standard of steel at least 11 gauge (3.1 mm) thick to the dimensions required for the

specified mounting height. Form the standard from one piece with one electrically full penetration welded longitudinal joint and no intermediate horizontal joints.

d.After forming and welding, cold-roll the shaft longitudinally under sufficient pressure to flatten the weld

and increase the physical characteristics of the metal in the shaft.

e.Ensure that the shaft has a reinforced handhole with a cover, except where a transformer base is

specified. 1771

SECTION 920 — Lighting Standards and Towers

1) Provide a 0.5 in. (13 mm) approved grounding connector in the shaft or base. 2) Equip the top of the shaft with a removable pole cap held securely in place. 3) Galvanize the shaft, base plate, bracket arm(s), handhole cover, and all elements of the pole with the hot-dipped method in ASTM A 123/A 123M.

f.Equip the top of the shaft with a removable pole cap held securely in place with set screws. Cap shall

match material and meet the same requirements as the pole.

2.Lighting Towers

a.Make the shaft to meet the requirements of the roadway standard (Subsection 920.2.1.B.1).

b.Construct the standard to continuously taper 0.14 to 0.40 in./ft. (12 to 33 mm/m).

c.Ensure that the standard has the necessary dimensions and metal quality to meet the requirements for

the specified mounting height.

d.The shaft may be formed in sections with each section having no more than two longitudinal welded

seams. Sections shall be a minimum of 30 feet in length.

e.Use intermediate horizontal welds only at section joints.

f.Make telescoped joints overlap at least 1-1/2 pole diameters, measured at the minimum diameter of the

inner telescoping section.

g.Have field welding performed only by an approved certified welder who represents the manufacturer.

Ensure the welding follows the requirements of Section 501.

h.Repair any damage to galvanized coating according to Section 645.

i.Match-mark all sections of the shaft so that the tapered sections are assembled properly.

3.Post Top or Other Standards for Special Installation

a.Make the post top and other standards meet the requirements for roadway standards (Subsection

920.2.01.B.1).

b.Make the top diameter of the shaft 2 in. (50 mm) or include a 2 in. (50 mm) tenon, unless otherwise

specified, to insert the shaft or tenon into the luminaire.

4.Anchor Base

Do the following, unless otherwise specified:

a.Secure a steel base to the lower end of the shaft with two continuous electric welds. Ensure that the base

develops the full strength of the adjacent shaft section to resist bending.

b.Provide removable cast or pressed steel covers with each base. Appropriately attach each cover to

the base.

5.Steel Bracket Arms

Do the following, unless otherwise specified:

a.Use the design dimensions from the Contract.

b.Bracket arms shall be of the same material and meet the same requirements as the pole shaft.

c.Ensure that the installed bracket connects securely with the shaft and has a smooth wiring raceway.

d.Use stainless steel bolts and nuts that meet the requirements of ASTM A 193/A 193M, Type B8C or AISI

304 to attach the bracket arm assembly.

6.Transformer Bases

Do the following, unless otherwise specified:

a.Use the dimensions on the Contract to build the bases.

1) Make top and bottom plates that meet the requirements of ASTM A 709/A 709M, Grade 36 (250), and are fabricated to receive the shaft, anchor bolts, and the foundation bolts. 2) Make the side panels meet the requirements of AISI 1020. 3) Create a base thick enough for the height of the standard.

b.Fit the base with a handhole and cover that can be securely fastened.

1772

SECTION 920 — Lighting Standards and Towers

7.Anchor Bolts

a.Provide bolts as follows:

Lighting standard 4 anchor bolts (minimum) Lighting tower 8 anchor bolts (minimum)

b.Use the size indicated on the Contract or as required by the manufacturer’s shop drawings.

c.Use anchor bolts, nuts, and washers that meet the requirements of AASHTO M 314, Grade 55(370).

Supplementary requirementS 1 of AASHTO M 314 also applies. NOTE: Do not use Grade 105 (724).

d.Install anchor bolts with a leveling nut and a flat washer between the leveling nut and the base plate.

1) Use a template to install the bolts. 2) Place a flat washer on top of the base plate. 3) Use a lock washer on top of the flat washer and secure the nut. 4) Fully grout the space between the shoe base and the top of the footing with non-shrink grout.

e.Galvanize threaded ends of anchor bolts, hexagonal nuts, flat washers, and lock washers according to

ASTM A 153/A 153M and Contract details.

8.Finish

Unless otherwise specified, galvanize all steel lighting standards and towers, including pole, base, transformer base, and bracket arm assembly according to ASTM A 123/A 123M.

C.Acceptance

1.The Engineer reserves the right to inspect and run tests as necessary to ensure compliance with these

specifications and to reject items that fail testing.

2.The Engineer will accept the steel lighting standards and towers based on:

• The results of physical and chemical tests made by the Department. • The manufacturer’s certification showing physical and chemical properties of the metal prior to forming.

D.Materials Warranty

General Provisions 101 through 150. 920.2.02 Aluminum Lighting Standards

A.Requirements

1.Design

2.Include the following in making aluminum lighting standards:

a.A pole and bracket arm(s) as required on the Contract.

b.An aluminum base welded or bonded to the lower end, complete with bolts for use as an anchor base

pole or attached to an approved breakaway device such as an aluminum transformer base, breakaway couplings, etc., when so specified. 1773

SECTION 920 — Lighting Standards and Towers

B.Fabrication

Use aluminum materials that meet the requirements of AASHTO SLTS

3.Roadway Standards

a.Make the shaft with a continuous taper formed from an extruded blank (preferably 6063-T6). Weld a base

plate to the lower end.

b.Give the shaft a reinforced handhole with a cover, except when a transformer base is specified.

c.Provide a 0.5 in. (13 mm) approved grounding connection in the shaft or base.

d.Equip the top of the shaft with a removable pole cap held securely in place with set screws. Cap shall

match material and meet the same requirements as the pole.

4.For Post Top or Other Standards for Special Installation,

Do the following, unless otherwise specified:

a.Build the standard to meet the requirements for roadway standards (Subsection 920.2.01.B.1).

b.Make the top diameter of the shaft 3 in. (75 mm) or include a 3 in. (75 mm) tenon to insert the shaft or

tenon into the luminaire.

5.Anchor Base

Do the following, unless otherwise specified:

a.Secure the one-piece aluminum base to the lower end of the shaft by using two continuous welds.

b.Ensure that the base develops the full strength of the adjacent shaft section to resist bending.

c.When the Contract call for a frangible or breakaway base, attach the base to an approved breakaway

device with an approved number and type of bolts, or use a base that is an approved breakaway type.

d.Provide removable cast or pressed aluminum covers with each base. Appropriately attach each cover to

the base.

6.Aluminum Bracket Arms

a.Use the Contract design and dimensions.

b.Ensure that the installed bracket arm connects securely with the shaft and has a smooth wiring raceway.

c.Use stainless steel bolts and nuts that meet the requirements of ASTM A 193/A 193M, Type B8C or

AISI 304, to attach the bracket arm assembly.

7.Transformer Bases

a.Form the base of cast aluminum that meets the requirements of ASTM B 108, Alloy A03560, T6 to

dimensions on the Contract.

b.Make the top so it can receive the anchor base bolts and the bottom so it can receive the anchor bolts.

8.Anchor Bolts

Use bolts as described in Subsection 920.2.01.B.7.

9.Finish all aluminum lighting standards, including pole, base, transformer base, and bracket arm assembly in a

natural aluminum color, unless otherwise specified.

C.Acceptance

1.The Engineer reserves the right to inspect and run tests as necessary to ensure compliance with these

specifications and to reject items that fail tests.

2.The Engineer will accept the aluminum lighting standards based on:

a.The results of physical and chemical tests made by the Department

b.The manufacturer’s certification showing physical and chemical properties of the metal prior to forming

the standard

D.Materials Warranty

General Provisions 101 through 150. 1774

SECTION 920 — Lighting Standards and Towers

920.2.03 Prestressed Concrete Lighting Standard

Concrete poles are only to be used where approved and as specified within the Contract.

A.Requirements

1.Design

Poles shall be designed to the following wind speeds using a 1700 Mean Recurrence Interval (MRI) with

Fatigue Category 1 for the listed counties:

150 mph: Bryan, Camden, Chatham, Effingham, Glynn, Liberty, McIntosh

140 mph: Brantley, Bulloch, Charlton, Evans, Long, Screven, Tattnall, Wayne

130 mph: Appling, Bacon, Brooks, Burke, Candler, Clay, Clinch, Decatur, Early, Echols, Emanuel, Grady,

Jeff Davis, Jenkins, Lowndes, Miller, Pierce, Seminole, Thomas, Toombs, Ware

120 mph: For all counties not listed above

2.Make the pre-stressed concrete lighting standard of the design and dimensions in the Contract. Make the

standard with machines in steel forms by the centrifugal spinning process to ensure maximum density.

3.Use a manufacturing method that produces a smooth cable raceway throughout the length of the standard.

Make the raceway between 1.5 to 2 in. (38 to 50 mm) in diameter when measured at the top of the standard.

B.Fabrication

1.Use materials and manufacturing methods according to Section 865 with the following exceptions:

a.Concrete: Use Class AAA concrete with a maximum aggregate size of 3/8 in. (10 mm) and a maximum

slump of 0.5 in. (15 mm) after the spinning process.

b.De-tension: You may de-tension the standards after 24 hours under a low-temperature steam process.

However, if the standard does not reach a compression strength of 3,500 psi (25 MPa) in this 24-hour

period, the Inspector will reject the standard.

c.Finish: Ensure that the standard has a smooth, uniform finish from a water carborundum mechanical

process that removes the laitance and surface content revealing the aggregate.

2.Bases

a.Furnish the standards with an anchor base or a precast butt base.

NOTE: If using the precast butt base, cast it as an integral part of the standard during the spinning process.

Make a conduit entrance as shown on the Contract.

b.Make the bolt-down anchor base have a cast steel anchor base that meets the requirements of ASTM A

27/A 27M, Grade 70-36 (485-250).

c.Secure the base to the primary pole reinforcement so it is strong enough to transmit the required loads to

the anchor bolts.

d.Fit the base with a handhole and cover that can be securely fastened.

C.Acceptance

1.The Engineer reserves the right to make, inspect and run tests as necessary to ensure compliance with these

specifications and to reject those items failing such tests.

2.The Engineer will accept these standards based on tests made by representatives of the Department during

the manufacturing process.

3.Give sufficient notice to the Engineer prior to manufacture to arrange for the required inspection.

D.Materials Warranty

General Provisions 101 through 150. 1775

SECTION 920 — Lighting Standards and Towers

920.2.04 High Mast Luminaire Support and Lowering Assembly

A.Requirements

1.This assembly shall be a mechanical device capable of supporting the luminaire assembly at the required

operating position and raising the assembly to the operating height and lowering the assembly to ground level

for servicing.

2.Furnish shop and working drawings or illustration sheets according to Section 105.

3.Transfer to the Engineer all guarantees on materials and equipment that the manufacturer normally furnishes,

together with all operating instructions and service manuals.

Include in the guarantees the provision that they are subject to such transfer.

B.Fabrication

1.Use AASHTO SLTS to build the assembly.

2.Support Head Frame

Use a head frame with at least two supports for the suspension cables and a pulley for the power cable.

a.Place the suspension supports 120 degrees apart. Place the power cable pulley midway between two

suspension supports.

b.Attach two pulleys to the inside of each support, one at each end. Construct the pulleys so that the

suspension cables ride freely in the groove of the pulleys.

Provide cable guides and retainers to keep the suspension cables and power cable inside the pulleys.

c.Supply a hood for the support head frame to protect against weather for all working components at the

pole top. Ensure that the hood adequately ventilates the pole.

3.Luminaire Mounting Ring

a.Equip the inner portion of the ring with approved roller-contact, spring loaded centering arms. The arms

should center the luminaire ring while ascending or descending the pole, protect the pole and luminaires,

and prevent jamming during the raising and lowering operations.

Make the rollers for the centering arms of a water-resistant, non-marking composition material.

b.Design the mounting ring to symmetrically mount the number of luminaires indicated on the Contract.

1) Provide a weatherproof junction box and terminal board terminating the power cable and connecting

the luminaire wiring.

2) Provide a weatherproof power receptacle to test the luminaires when the ring is in the

lowered position.

4.Non-Latching Device Design

a.If the design does not have a latching device at the top of the pole, position the luminaire mounting ring

tightly against the support head frame.

NOTE: Use a positive, visible indication that the required force has been applied.

b.Make sure the luminaire mounting ring and support head frame can hold the luminaire mounting ring in

place and prevent rotation and unwanted movement while in the raised position.

c.A spring-loaded arrangement is preferred to provide proper cable tension and hold the luminaire ring

securely in place.

5.Latching Device Design

a.Use a latching device at the top of the pole to latch all three suspension points and support the total

weight of the ring including luminaires.

b.Place all moving parts of the latching device in the luminaire mounting ring.

NOTE: Use a positive, visible indication of the latching position. 1776

SECTION 920 — Lighting Standards and Towers

6.Miscellaneous Hardware

Use non-corrosive miscellaneous fittings, fasteners, and hardware for the support head frame and luminaire

mounting ring. Use an approved means for locking nuts.

7.Hoisting Systems

a.Ensure that each pole has three suspension cables and one hoisting cable.

b.Use cables that have 7 strands of 19 wires each, made of stainless-steel aircraft cable according to

MIL-W-83420, Type 1, Composition B.

c.Use at least 0.2 in. (5 mm) diameter suspension cables and at least a 0.25 in. (6 mm) diameter

hoisting cable.

d.Anchor the ends of the pole’s suspension cables to the top of the suspension cable bracket or transition

plate assembly. Pass the other ends through the pulleys on the support head frame and attach to the

luminaire mounting ring.

e.Secure the hoisting cable at the bottom center of the suspension cable bracket assembly. Attach the

other end to the drum of the motor-driven winch.

Prevent future twisting and eliminate any tension developed during initial installation of the hoisting

cable system.

f.Use a worm-gear reducing winch with a reduction ratio that is self-locking in both raising and

lowering operations.

Completely enclose the worm-gear in a lubricating reservoir.

g.Make the winch operable with either an electric drill motor or a NEMA frame motor as described in

Lowering Device Power Supply Unit.

h.Provide a hand crank for raising and lowering.

i.Include a cable guard/retainer for the winch drum. This will force the cable away from the ends of the

drum for spooling and prevent the cable from coming off the drum.

j.Design the entire hoisting system so that power cable, suspension cables, and hoisting cable may be

replaced from the ground.

8.Lowering Device Power Supply Unit

a.Use a lowering device power supply unit that is either an electric drill motor or a NEMA frame motor.

1) Equip both motors with a factory-set torque limiter. Power each from a weatherproof outlet or

receptacle located in the service area of the pole.

2) You may use a step-down transformer to supply the required motor voltage.

b.Make the transformer an integral part of the power supply unit, when required.

c.Attach and lock in place the drill or motor at the pole handhole. Provide a remote-control system that

works from at least 20 ft. (6 m) away.

9.High Mast Power Cable

a.Use extra heavy-duty power cable in a jacket that resists oil and sunlight. Include in the cable the number

and size of copper insulated conductors required on the Contract.

b.Securely connect the power cable to the luminaire mounting ring and the suspension cable bracket

assembly so it will not damage the cable and supports only its own weight.

10.Pole Disconnect

a.Furnish each pole with a molded case circuit breaker in a NEMA enclosure of the size and type specified

on the Contract.

b.Make the breaker accessible through the pole handhole. Get the breaker from the manufacturer of the

raising and lowering device.

C.Acceptance

General Provisions 101 through 150.

D.Materials Warranty

Submit guarantees on materials and equipment. 1777

SECTION 920 — Lighting Standards and Towers

920.2.05 Grounding

A.Requirements

General Provisions 101 through 150.

B.Fabrication and Construction

1.In accordance with AASHTO recommendations, pole must be grounded independently from power system

ground using a ground rod.

2.Ground rod and equipment must meet provisions set forth within Section 682.6.01 P.

3.Include a grounding conductor with the high mast power cable and connect it to the luminaire mounting ring.

C.Acceptance

General Provisions 101 through 150.

D.Materials Warranty

General Provisions 101 through 150.. 1778

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Source: Standard Specifications for Construction of Transportation Systems, 2021 Edition. Pages 1780–1788 of 2,050. View official source ↗

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920.2Materials

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