AASHTO - Std. Spec for Structural Supports for Highway Signs....

[ARS97]

My company is dabbling with some small prototype models of monopole structures that support various appurtenances such as antennas, solar panels, etc. The customer requires that these towers be AASHTO compliant. (AASHTO Standard Specifications for Structural Supports or Highway Signs, Luminaries, and Traffic Signals)

I'm not terribly familar with this specification, but I'm catching on. I have a question regarding the detailed analysis requirement in Section 4.8.2.

I'm not sure I fully understand the reasoning behind the 1.45 multipler. You multiply the primary service loads by 1.45, perform the analysis, and divide the results by 1.45 for actual code-checking purposes. However, it seems a little vague as to what type of analysis is needed with the multipler. The wording allows me to read it two ways:

1) Use the multiplier and a SECOND order analysis
2) Use the multiplier and a FIRST order analysis in order to mimic a SECOND order effect.

If it's #1, then once again, why? Why factor it up and divide it back to where it started? What purpose does it serve? How is this applied practically?

If it's #2, then it makes more sense to me. Although, if a robust second order analysis was available (Staadpro or similar), why not just use it....

Hoping someone can shed some light onto this issue.

 

[ARS97]

Upon further thought, if you interpret it as #2 (see above), then dividing the results to use in code-checking procedures basically cancels out the approximate second order effect. This surely wouldn't be the case.....

Based on that, it seems like #1 is the correct interpolation. But once again, what would you be accomplishing?

 

[ARS97]

ttt