Appendix J

Purpose

The purpose of this experiment was to evaluate the strength of detachable steps on T&D poles; and to compare the strength of the step attachment with a threaded rod passed through both sides of the pole versus attachment with a carriage bolt through one wall of the pole only

The "Specifications for Pole Steps" developed and issued by the Transmission and Distribution and Committee for the Edison Electric Institute require that "the maximum permanent deflection of any detachable steps shall not be greater than 1/8 inch at a point 4-1/2 inches from the support under a load of 300 lbs. applied at this point."
Test Procedure and Results

Three tests were conducted in this experiment. In each test, a section of pole was strapped in the pole test fixture, a detachable step was installed and a load was applied approximately 4-1/2 inches from the step support (one inch from the outermost end of the step). The load was applied parallel to the axis of the pole in all tests.

The first pole test was conducted with a step mounted on a section of the T5D25 T&D pole. This pole section was taken from midpole where there was minimum wall thickness and no turnaround in the rovings. The step was installed using threaded rods with the same hardware used on production Shakespeare T&D poles as supplied to Montana Power. At a load of 300 lbs., the deflection of the step at 4-1/2 inches from the support was 1/8 inch. As the load increased, the step continued to deflect. At a load of 750 lbs., the deflection was 3/4 inch. At this point it was obvious that the deflection was occurring because the pole was becoming oval from the compressive forces being generated by the action of the step pivoting on the restraining nut, putting the threaded rod in tension. At a load of 850 lbs., the step pivoted on the restraining nut so much that it slipped off. Neither the step nor pole were damaged, however.

The second test was conducted with a step mounted at the top step location on a section of a T4D40 T&D pole (one of the test poles for the first Montana Power order). This step was mounted to one wall of the pole only, using a 1/2 inch carriage bolt with a modified step plate, and a square curved washer and hex nut inside the pole. Load was applied to this step as in the first test. At a load of 300 lbs., deflection of the step was negligible, The load was increase to 1000 lbs., still with negligible deflection, at which point the pole began to slip in the straps of the test fixture. The load was then reduced to 700 lbs. and held at this level for two hours before being released.

The third test was conducted with a step mounted three feet above the midpole turnabout of the same T4D40 T&D pole used in the previous test. This location was chosen because the wall thickness is minimum at this point. The step was mounted in the same manner as in the second test, but the pole was secured more tightly in the test fixture. The load was taken all the way to 1200 lbs., which was the maximum limit of the test setup, again with negligible deflection. The load was then released.

Discussion

Both methods of mounting detachable steps met the strength and deflection requirements. However, mounting the steps with an attachment to one wall of the pole offers several advantages over mounting them with a threaded rod passed through both walls. To begin with, the above tests showed that the one wall mounting system is significantly stronger. And only half as many holes have to be drilled in the poles to install the step mounting hardware. The one wall mounting system would save weight, also; approximately 20 lbs. per pole for the Montana Power poles.

The problem with mounting detachable step hardware to one wall of the pole is the difficulty of installing a fastener from the inside of the pole. For the above tests, this problem was overcome by cutting the pole into sections so that the step attachment inside of the pole was within an arm's length of the end of the section. Three possible solutions to this problem are currently under investigation.

It is recommended that the one-wall method of step attachment should be adopted for production as soon as the inside fastener problem is satisfactorily solved.

Test Date: 6 AUG 93

 

Item Tested SINGLE WALL STEP BOLT WITH STEP	Test Report No.
Type Test: CANTILEVER LOAD TEST	Page No. 1 OF 1
Purpose of Test DETERMINE STRENGTH OF STEP MOUNTED TO A T5D25 POLE WITH DOUBLE WALL STEP BOLT	Drawing No.

Results of Test

   

Load (lbs.)	Deflection
50	0
100	0
150	1/32"
200	1/16"
250	3/32"
300	1/8"
400	7/32"
500	9/32"
600	13/32"
700	9/16"
800
850	*Step jumped off nut

Tested By: D. BRADLEY

Reported By: D. BRADLEY

Approved By: JOHN F. BOOZER III

Test Date: 6 AUG 93
 

Item Tested SINGLE WALL STEP BOLT WITH STEP	Test Report No. 1575
Type Test CANTILEVER LOAD TEST	Page 1 OF 1
Purpose of Test DETERMINE STRENGTH OF STEP MOUNTED TO A T4D40 POLE WITH SINGLE WALL STEP BOLT	Drawing No. X-3725-STBLT-1

Results of Test

Load (lbs.)

• Test 2 - 1000 lbs. - Backed off to 700 lbs.; held for 2 hours and released.
• Test 3 - 1200 lbs. - Pulled to 1200 lbs. and released

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Shakespeare Composite Structures

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