144 Ductility

Ductility is the ability of a material to undergo large inelastic deformation before failure. It is an important material property because ductility allows for early warnings of incipient failure and permits force redistribution to occur in statically indeterminate structures. One of the drawbacks of high-strength steels is the reduction in ductility when compared to lower-strength steels, such as A36, A572, and A992 structural steels. However, it has been reported that all HPS steels can achieve uniaxial elongations in the range of 18-30% (Bjorhovde 2004), which is more than adequate for engineering applications. Moreover, tests on HPS wide-plate (8 x 0.75 in., or 20 x 2 cm) specimens with holes (Dexter et al. 2002) under tension have shown that the tensile ductility capacity of HPS70W steels is well within the required range for structural steel. The study also indicates that adequate ductility is achieved for members under tension when t) (!) *1 0 <14' ■»

where An is the net sectional area, Ag is the gross sectional area, Fy is the yield strength, and Fu is the tensile strength.

Statistical analysis of the mill report tensile properties of more than 2400 heats of HPS70W has shown that Fy/Fu « 0.84, with a coefficient of variation of 0.06. This means in accordance with Equation 14.1, adequate ductility is expected if An/Ag > 0.84.

Because the current American Institute of Steel and Concrete (AISC) and American Association for State Highway and Transportation Officials (AASHTO) provisions for tension members with holes require that the member be proportioned so that

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