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August 31, 1989

Refer to: HNG-14/SS-13

Mr. Mark S. Granger
Sign Post Sales Manager
Marion Steel Company
912 Cheney Avenue
Marion, Ohio 43302

Dear Mr. Granger:

This is in response to your letter of August 8 to Mr. James Hatton requesting Federal Highway Administration (FHWA) acceptance of your company's Rib-Bak sign posts in sizes from 2 to 4 pound-per-foot when used with a lap splice connection. You referenced a study done by the Texas Transportation Institute for the State of Arizona (Arizona Research Study HPR-PL-1-31 (202), "Small Sign Support Analysis"). The report contained dimensions and installation details, which are repeated here in the enclosure.

The full-scale crash-testing phase of the study included four tests of triple post supports using 1,800 pound cars. The results of those four tests are as follows:

Test No.

Size of Posts in Installation

Impact Speed

Vehicle Change in Velocity

Occupant Impact Speed

Occupant Ridedown Accel.

7024-24

4 lbs/ft

20.6 mph

28.0 fps

21.9 fps

2.7 g

7024-25

4 lbs/ft

62.6 mph

13.2 fps

13.2 fps

0.6 g

7024-26

3 lbs/ft

21.7 mph

12.6 fps

12.5 fps

0.5 g

7024-27

3 lbs/ft

61.6 mph

9.1 fps

No contact

No contact

Test 7024-24 did not meet the FHWA requirements for breakaway supports. An analysis of the energy expended during that test, however, allows us to accept the use of two 4 pound-per-foot posts within a 7-foot span. Tests of the 3 pound-per-foot posts did meet breakaway requirements for change in velocity; therefore triple post installations of sizes from 2 to 3 pounds-per-foot are acceptable.

It is noted that the sign supports were only tested in the "strong" soil described in the NCHRP 230. If you desire to offer this hardware to States for use in soil equivalent to the "weak" soil described in the NCHRP 230, we recommend additional tests be conducted in that soil type.

In Summary, your company's Rib-Back posts in "strong" soil using a stub/sign post where the stub is 4 inches high or less are acceptable for use on Federal-aid highway projects, if requested by a State, in the configurations shown in the matrix below. Installations using one or two posts, or those using lighter weight posts than those tested will result in less severe accelerations and velocity changes. Therefore, we are extending out acceptance to cover installations down to a single 2 pound-per-foot post.

Post Size

Acceptable Single

Applications Dual

Triple

2 lbs.

Yes

Yes

Yes

2 ½ lbs.

Yes

Yes

Yes

2 lbs.

Yes

Yes

Yes

3 lbs.

Yes

Yes

Yes

4 lbs.

Yes

Yes

No

This acceptance is limited to breakaway characteristics of the system and does not cover is structural features. Presumably, you will supply potential users with sufficient information on structural design and installation requirements to ensure proper performance. We anticipate that the States will require certification from Marion Steel company that the hardware furnished has essentially the same chemistry, mechanical properties, and geometry as that used in the tests, and that it will meet the FHWA change in velocity requirements.

Sincerely yours,

L. A. Staron, Chief
Federal-Aid and Design Division

Enclosure

Federal Highway Administration
HNG-14:NArtimovich:gm:8-23-89:61331
copies to:
HED-1 HNG-1 HNG-10 HNG-14 Reader, 3212
Reader, 3128 Reader, 3206 File, 3128
M. Hargrave, HSR-20 H. Taylor, HHS-12
RAs w/enclosure


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