163 Where Pr Factored compressive resistance (kips. c Resistance factor.
𝑃𝑃
𝑚𝑚
= Nominal compressive resistance (kips. To determine the nominal
compressive resistance however, pile strength and buckling failure should be considered, where a step-by-step procedure is presented as follows.
Step 1: Determine the equivalent nominal yield resistance, Po: The equivalent nominal yield resistance, Po, is a function of the material yield stress, cross sectional area and slenderness reduction factor, if applicable. For non-slender
piles in compression, the slenderness reduction factor, Q, is taken as 1.0. However, for slender piles, the full nominal yield strength under uniform axial compression is limited by local buckling. This reduction factor
is governed by section buildup, pile dimensions and material properties, therefore, a further discussion of slender members and direction for calculating Q maybe found in AASHTO (2014) Article 6.9.4.2.2.
𝑃𝑃
𝑐𝑐
= Equation 11-26) Where
𝐴𝐴
𝑔𝑔
= Gross cross-sectional area (in.
Po
= Equivalent nominal axial yield resistance (kips. y Yield stress of steel.
Q
= Slender element reduction factor. To satisfy the slender element
requirement for local buckling, Equation 11-27 is used for H-piles while Equation 11-29 is used for unfilled pipe piles.
𝑏𝑏
𝑓𝑓
2𝑡𝑡
𝑓𝑓
≤ Equation 11-27) and
0.35 ≤ 𝑘𝑘
𝑐𝑐
≤ 0.76 in which
𝑘𝑘
𝑐𝑐
= Equation 11-28)
164 Where
𝑏𝑏
𝑓𝑓
= Flange width (in.
𝑡𝑡
𝑓𝑓
= Flange thickness (in.
𝐹𝐹
𝑦𝑦
= Yield stress of steel (ksi). st Elastic modulus of steel (ksi).
𝑑𝑑
𝑤𝑤
= Web depth (in.
𝑡𝑡
𝑤𝑤
= Web thickness (in.
𝐷𝐷
𝑡𝑡 ≤ Equation 11-29) Where
𝐷𝐷 = Diameter of pipe (in.
𝑡𝑡 = Wall thickness (in. y Yield stress of steel (as per AASHTO). t Elastic modulus of steel (ksi).
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