PROBABILISTIC-BASED HURRICANE RISK ASSESSMENT AND ...

for both the potential impacts of climate change and the effects degradation may have ondistribution pole failure. In the following, an overview of distribution pole design isprovided, including the degradation function implement to account for the effects ofageing.1.1.4.1 Design of Timber Distribution PolesHistorically, distribution poles were designed using the deterministic method prescribedin the NESC standard (NESC 2002). The Allowable Stress Design (ASD) method isbased on specific load factors and strength factors that are combined with zonal loadingmaps (Wolfe et al. 2001). The load and strength factors are determined based on thegrade of the construction of the distribution poles.In order to maintain consistent (or uniform) reliabilities for distribution poles, the LoadResistance Factor Design (LRFD) method was developed by the ASCE (Bhuyan and Li2006, Dagher 2001), and is now typically used in distribution (utility) pole design(ASCE-111 2006). LRFD is used to assess the performance of a distribution pole atvarious limit states. Limit states are used to describe a condition at which a structurestops fulfilling its intended purpose. Limit states are categorized as: Strength andServiceability. Strength limit states define load-carrying capacity and include fracture,buckling, and excessive yielding,. Serviceability limit states define performance andinclude deflection, cracking, and vibration (McCormac 2008).The two design methods vary as they are based on different design principles. Thefollowing formulation can be used for both methods.R n > γ S ∅n (1.5)where R n is the design (nominal) strength of the poles (e.g. design bending moment) andidentified using design standards, ø is the strength factor, S n is the design (nominal) load,and γ is the load factor.When designing distribution poles, the design method should be specified and thecorresponding load conditions identified (i.e. values for ø and γ). Then the design load(S n ) is determined, and consequently the required design strength is determined by using22