t 3 

U.S.Lkpartment 

of Transportation 

’ Feda~~lHighway 

Aclrrrinistmtlon 

OCT 1 cl 1991 

Refer to: HNG-14 

David L. Christensen, P.E. 

Chief Structural Engineer 

Utah Department of Transportation 

4501 South 2700 West 

Salt Lake City, Utah 84119-5998 

Dear Mr. Christensen: 

Thank you for your September 12 letter to Mr. Thomas 0. Willett in which you 

requested federal Highway Administration (FHWA) acceptance for the four bolt 

slip-base used for luminaire support poles. These bases are currently in use 

in Utah, Montana, Idaho, Wyoming, and Nevada. In support of this request, you 

submitted reports dated August 1991 of tests conducted at the Midwest Roadside 

Safety Facility at the University of Nebraska at Lincoln. The tests were 

conducted to determine if the bases and poles met the FHWA breakaway 

requirements which reference the American Association of State Highway and 

Transportation Official's (AASHTO) Standard Soecifications for Structural 

SupDorts 

Details of the tested hardware are shown in the enclosed drawing of the 

slip-base. Test results and significant design details are summarized below: 

Test Number USBLM-1 USBLM-2 

Impact Speed 24.15 km/h (15.0 mph) 92.60 km/h (57.5 mph) 

Vehicle Velocity Change 1.86 m/s (6.1 fps) 4.11 m/s (13.5 fps) 

Occupant Velocity Change 2.32 m/s (7.6 fps) 4.33 m/s (14.2 fps) 

Data 

Vehicle Mass (Weight) 795 kg (1,750 pounds) 

Test Article Configuration Dual Mast Arm 

(Single or dual mast arm configuration will be acceptable.) 

Stub Height 1OOmm (4.0 inches) 

Weight of Test Article 410 kg (902 pounds) 

(Pole mast arm and luminaire weights of up to 450 kg (1,000 pounds) each will 

be acceptable.) 

Luminaire Mounting Height 15.85m (52.0 feet) 

(Up to 17.25 m (56.5 feet) will be acceptable.) 

Bolt Circle Diameter 330mm (13 inches) 

, (This is the minimum acceptable bolt circle.) 
2 

( Clamping Bolt Force four l-inch bolts @ 19,126 N (4,300 

pounds) each. 

(The four slip-bolts were torqued to 108 Newton-meters (80 foot-pounds) each, 

and then released and retorqued to 95 Newton-meters (70 foot-pounds.)) 

Pole Wall Thickness 11 gage 

(Minimum wall thickness for a 25Otmn (IO-inch) diameter pole to be considered 

breakaway is 11 gage. This is consistent with FHWA guidelines for 3-bolt 

slip-bases.) 

Keeper Plate Thickness 28 gage steel 

(This is the maximum acceptable thickness.) 

The above information shows that the tested pole-base combination meets the 

change in velocity and stub-height requirements adopted by the FHWA. 

Therefore, the subject four-bolt slip-base for luminaire supports, as shown in 

the enclosed drawing, is acceptable for use on Federal-aid projects when 

requested by a State. Our acceptance is limited to bases where the corrosion 

protection of the fastener hardware is the same as the tested hardware. It is 

our understanding that all hardware was hot-dip galvanized except for the 

clamping bolts and their'nuts which were cadmium plated. Galvanized clamping 

bolts will be acceptable if procedures are followed during their installation 

to assure that the same clamping~force is developed in the bolts. Care must 

be taken during installation of the anchor bolts that the tops of the bolts do 

not extend above the slip-plane. The slip-base itself may not extend more 

than 1001~1 (4 inches) above a 60-inch chord, as specified by AASHTO. 

I 

This acceptance is limited to breakaway characteristics of the bases and does 

not cover the structural features of the bases nor the poles. Presumably, you 

will supply potential users with sufficient information on structural design 

and installation requirements to ensure proper performance. You should 

request certification from the manufacturer that the poles and slip-bases 

furnished have essentially the same chemistry, mechanical properties, and 

geometry as those used in the tests, and that they will meet the FHWA change 

in velocity requirements. 

Sincerely yours, 

L. A. Staron 

Chief, Federal-Aid and Design Division 

Enclosure 

Roadside and Geometric Design Acceptance Letter LS-25 
LIGHT POLE BASE PLATE 

ANCHOR PLATE ASSEHB _--v-- 

I. IGHT POLE BASE WCTION A - A 

____-__ _.__- - .--- 

.-___ ---- -z 

_.._.-. -..- 

_._- .._- - 

3. 

4. 

5. 

6. 

I. 

8. 

9. 

SLIP BOLT GASKET --- 

(28 tA. GNYANlLED SHEET HElALl 

-..-we - 

____-_.___“__l_--I._I-___-_- _- . . ._^. - ., 

_~._ ~~ .~ 

.__...-. .~. 

UTAH DEPARTMENT 

LUIIINAIRE 

BREAKAWAY BASE