PROBABILISTIC-BASED HURRICANE RISK ASSESSMENT AND ...

where Q is air density factor, k i is terrain exposure coefficient for component i, V is the3-sec gust wind speed, I FW is the importance factor, G RF is the gust response factor, C f isthe force coefficient, and A i is the projected wind surface area normal to the direction ofwind for component i.1.1.4.1.2 Design (Nominal) Resistance (R n )The American National Standards Institute (ANSI 2002) categorizes timber distributionpoles into different classes based on material. ANSI (2002) assigns each class a permittedbending moment at ground line (i.e. 2.0 m from the base of the pole) depending on theheight and the circumference of the poles. The circumference (C g ) of the poles can beestimated from the design load (S n ) of the poles and the fiber stress of the species oftimber (Brown 2008, Wolfe and Kluge 2005):3C g = γ φ S n0.000265∙F 0(1.8)where γ is the load factor, ø is the strength factor, and F 0 is the designated fiber stress(ANSI 2002).1.1.4.1.3 The P-Δ EffectThe P-Δ effect must be accounted for in both design methods. The P-Δ effect refers tothe deflected unbalance that occurs in the tapered distribution pole (ASCE-111 2006).More specifically, the pole “leans over” to resist the load, and results in additionalbending moments that affect the design load (S n ) (Bingel et al. 2003). The ASCE-111(2006) recommends utilizing the Gere-Carter method (1962) to account for the P-Δ effectin utility pole structures; and for simplicity, the Gere-Carter method will therefore beused to estimate the amplification factor (amp) for both design methods.The method involves calculating an amplification factor that should be coupled with thedesign load (S n ) for the distribution pole to account for the deflected unbalance (Eq. 1.6).This method will be utilized in the estimations of the ground line moment for both designmethods.24