Unguyed Structure Response
The focus of this category of tests is to confirm that the basic pole model behaves as expected to create the correct deflections and stresses from known input loads. Testing both deflections and stresses are critical in evaluating if Pole Loading Results "reasonably represent how a real pole behaves". In addition, the amount of stress created for a specific amount of deflection is a key indicator that the "Stiffness" of the pole segments is accurate. The relative stiffness of the pole segments in relation to the location of the applied loads and the stiffness and location of guying, are the major items that determine the pole's behaviour along its length (stresses & deflection).
It is assumed that all software tools utilize Finite Element Analysis. That means that the pole is assumed to be modeled into many different pole segments and assembled together to represent the whole pole. The tests listed here will validate that these assembled pole segments do in fact come together and are modeled accurately enough to provide reasonably accurate results. This model is tested across the longest distance possible of the pole in order to ensure any model inaccuracies are exposed that may not appear on shorter distance tests.
Most of these tests were modeled after the Pole Class Definitions in the ANSI O5.1 standard. The amount and location of the applied load matches exactly with how the pole classes were defined to create its dimensions. This means that the fibre stress utilization should be very close to 100%, recognizing that the pole dimensions for the groundline were rounded to the nearest 1/2 inch.
In some cases the CSA 015 standard suggests lower maximum fibre strength ratings and slightly different dimensions for the same pole. For this reason one of these tests will be dedicated to a CSA standard-based pole to ensure that the software can properly address Canadian as well as US poles.
It is important to validate that the pole model does not produce different results when loads are placed at different angles and that the results change appropriately to different lengths, classes and species of pole. It is also important to ensure that the pole's deflections and stresses are consistent with each other and the established baseline.
The following tests are suggested:
- Use a 40ft pole; class range: 4 to 1 dimensioned and rated in accordance with the ANSI O5.1 Standard. Species to be Red Pine
- Apply to each pole, the published rated load for the Class at 2 feet from the top of each pole.
- Repeat the above with the applied load shifted by 90 degrees.
- Using western Red Cedar poles of lengths 45ft, 50ft and 60 ft and for classes 2 and 3, repeat the above tests but from one direction only. Use the same Depth of Setting.
- Evaluate a 40ft class 4 Red Pine pole using dimensions, strength and Modulus of Elasticity values from the CSA standard. This confirms that CSA values can be used in Canadian designs.
- No wind or storm loads
- Measure the Pole Top Deflection and the Fiber Stresses at the Groundline.
- Depth of Setting is to be 6 feet(1.828 meters) for all tests.
- This is a Linear Analysis with loads applied without additional load factors applied. If non-factored loads are not possible, divide the proposed load by the load factor before it is applied to the pole.
- Constant Fibre Strength and Modulus of Elasticity at all points along the pole are required and should match the published values in ANSI O5.1 standard, CSA Standard and RUS sources.
These tests are very important since they test a software's Finite Element Analysis Model. In these specific tests however, direct solutions through formulas are possible assuming round tapered beams modeled the same way.
Even though the ANSI and CSA poles often have different fibre stress ratings, as long as the pole dimensions are the same, a different Modulus of Elasticity has no impact on the resulting Groundline Fibre Stress values. This is because the Groundline Moments are the same (a basic statics computation); so as long as the dimensions are the same, the stress calculation should also be the same. The moral of this story is that both fibre stress and deflection need to be evaluated against different scenarios to ensure the software's basic model is performing correctly. The deflection part is particularly important (as seen in later tests) as it is the shared deflection of the pole and attached guys that determine how the applied loads are shared between them. Excessive pole deflection will make the guys carry more load and insufficient pole deflection will make the pole carry more load.