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FIGURE 4.3 Definition of x for selected cross-sections.

4.3.1.2 Load and Resistance Factor Design

According to the LRFD Specification (AISC 1999), tension members designed to resist a factored axial force of Pu calculated using the load combinations shown in Table 4.3 must satisfy the condition of f tPn > Pu (4.9)

The design strength f tPn is evaluated as follows:

Yielding in gross section:

where 0.90 is the resistance factor for tension, Fy is the specified minimum yield stress of the material, and Ag is the gross cross-sectional area of the member.

Fracture in effective net section:

where 0.75 is the resistance factor for fracture in tension, Fu is the specified minimum tensile strength, and Ae is the effective net area given in Equation 4.5. Block shear: If FuAnt > 0.6FuAnv (i.e., shear yield-tension fracture)

ftPn = 0.75[0.60FyAgv + FuAnt] < 0.75[0.6FuAnv + FuAm] (4.12a)

and if FuAnt < 0.6FuAnv (i.e., shear fracture-tension yield)

ftPn = 0.75[0.60FuAnv + FyAgt] < 0.75[0.60FuAnv + FuAnt] (4.12b)

where 0.75 is the resistance factor for block shear, Fy, Fu are the specified minimum yield stress and tensile strength, respectively, Agv is the gross shear area, Ant is the net tension area, Anv is the net shear area, and Agt is the gross tension area.

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