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Friction Coefficient Test

Subject: Report of Testing HDPE Base Friction Coefficient Test
Advanced Support Products, Inc.
Tomball, Texas
Date: March 8, 2000

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Testing done by:
Russ Engineering Group, Inc.
7600 GSRI Avenue
Baton Rouge, La. 70820


Test Configurations Test Performed Test Results Table Test Conclusions Recommendations

Test Configurations

Eight (8) base assemblies were tested for coefficient of static friction. The tests were performed by Professional Service Industries, Inc. in their laboratory in Pittsburgh, Pa. Three configurations were tested on four different surfaces.

The three assemblies were:

  • HDPE Base
  • HDPE Base on Rubberized Bearing Pad (Epoxied to the base)
  • HDPE Base on Rubberized Bearing Pad (Non-Epoxied)

The four surfaces were:

  • Dry Concrete
  • Wet Concrete
  • Dry Rubber Membrane
  • Wet Rubber Membrane

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Test Performed

A fifty (50) pound weight was placed on the center of the base assembly. A Chantillon Digital Force Gauge, Model #DRC 100, was used to pull the base. The horizontal force required to put the base into motion was then recorded. The coefficient of static friction is simply the horizontal force in pound divided by 50 pounds.

Test Results Table

The results of the above test are tabulated as follows:

HDPE Base
Test No. Surface Condition Force Applied Coefficient of Friction
1 Dry Concrete 32.2 0.64
2 Dry Concrete 30.8 0.62
3 Dry Concrete 30.9 0.62
4 Dry Concrete 29.1 0.58
5 Dry Concrete 29.3 0.59
Average   30.5 0.61

HDPE Base/Rubberized Pad (Epoxied)
Test No. Surface Condition Force Applied Coefficient of Friction
1 Dry Concrete 51.4 1.03
2 Dry Concrete 49.8 1.00
3 Dry Concrete 50.5 1.01
4 Dry Concrete 52.6 1.05
5 Dry Concrete 50.6 1.01
Average   51.0 1.02

HDPE Base/Rubberized Pad (Non-Epoxied)
Test No. Surface Condition Force Applied Coefficient of Friction
1 Dry Concrete 37.7 0.75
2 Dry Concrete 38.4 0.77
3 Dry Concrete 39.3 0.79
4 Dry Concrete 38.1 0.76
5 Dry Concrete 37.5 0.75
Average   38.2 0.76

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HDPE Base
Test No. Surface Condition Force Applied Coefficient of Friction
1 Wet Concrete 30.3 0.61
2 Wet Concrete 28.3 0.57
3 Wet Concrete 26.6 0.53
4 Wet Concrete 30.0 0.60
5 Wet Concrete 26.7 0.53
Average   28.4 0.57

HDPE Base/Rubberized Bearing Pad (Epoxied)
Test No. Surface Condition Force Applied Coefficient of Friction
1 Wet Concrete 34.8 .070
2 Wet Concrete 36.3 0.73
3 Wet Concrete 38.1 0.76
4 Wet Concrete 37.5 0.75
5 Wet Concrete 38.3 0.77
Average   37.0 0.74

HDPE Base/Rubberized Bearing Pad (Non-Epoxied)
Test No. Surface Condition Force Applied Coefficient of Friction
1 Wet Concrete 36.7 0.73
2 Wet Concrete 38.2 0.76
3 Wet Concrete 38.3 0.77
4 Wet Concrete 39.4 0.79
5 Wet Concrete 39.1 0.78
Average   38.3 0.77

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HDPE Base
Test No. Surface Condition Force Applied Coefficient of Friction
1 Dry Rubber 52.2 1.04
2 Dry Rubber 52.8 1.06
3 Dry Rubber 50.6 1.01
4 Dry Rubber 51.1 1.02
5 Dry Rubber 52.1 1.04
Average   51.8 1.04

HDPE Base/Rubberized Bearing Pad (Epoxied)
Test No. Surface Condition Force Applied Coefficient of Friction
1 Dry Rubber 46.9 0.94
2 Dry Rubber 43.4 0.87
3 Dry Rubber 43.9 0.88
4 Dry Rubber 43.2 .086
5 Dry Rubber 43.5 0.87
Average   44.2 0.88

HDPE Base/Rubberized Bearing Pad (Non-Epoxied)
Test No. Surface Condition Force Applied Coefficient of Friction
1 Dry Rubber 36.5 0.73
2 Dry Rubber 40.4 0.81
3 Dry Rubber 37.8 0.76
4 Dry Rubber 41.6 0.83
5 Dry Rubber 39.4 0.79
Average   39.1 0.78

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HDPE Base
Test No. Surface Condition Force Applied Coefficient of Friction
1 Wet Rubber 35.5 0.71
2 Wet Rubber 37.5 0.75
3 Wet Rubber 38.2 0.76
4 Wet Rubber 35.1 0.70
5 Wet Rubber 34.4 0.69
Average   36.1 0.72

HDPE Base/Rubberized Bearing Pad (Epoxied)
Test No. Surface Condition Force Applied Coefficient of Friction
1 Wet Rubber 35.7 0.71
2 Wet Rubber 34.1 0.68
3 Wet Rubber 33.4 0.67
4 Wet Rubber 33.8 0.68
5 Wet Rubber 34.1 0.68
Average   34.2 0.68

HDPE Base/Rubberized Bearing Pad (Non-Epoxied)
Test No. Surface Condition Force Applied Coefficient of Friction
1 Wet Rubber 37.4 0.75
2 Wet Rubber 37.8 0.76
3 Wet Rubber 38.7 0.77
4 Wet Rubber 38.3 0.77
5 Wet Rubber 37.3 0.75
Average   37.9 0.76

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Test Conclusions

From these results, it is clear that a coefficient of static friction of .053 is conservative. The lowest individual reading of any of the 60 test pulls has a coefficient of .053. This is in the case of a bare HDPE base on wet concrete. It is the understanding of this engineering firm that the bare base is never in contact with the roof. A bearing pad is always utilized.

The highest average reading for a bare HDPE Base with Rubberized Epoxied Bearing Pad was 1.02 on dry concrete. The lowest average reading was .076 on wet rubber. This assembly was very consistent

Recommendations

Applying epoxy to the pad did not improve the friction factor for all of the utilizations that the product is likely to encounter. It is therefore recommended that the pad not be epoxied to the base. This is the typical application.

Using a coefficient of static friction of .053 is conservative. Using a coefficient of .070 is recommended.

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