Page 378 - Forensic Structural Engineering Handbook

STEEL STRUCTURES 11.9

FIGURE 11.2 Scanning electron micrograph showing microvoid coalescence on the surface of
a ductile facture.

FIGURE 11.3 Brittle, low-energy fracture of a jumbo wide flange section used in the tension
chord of a roof truss. Fracture initiated from a preexisting weld-prep flaw (arrow).

trusses, and gas pipelines where thick intersecting plates have been welded together. The
intersection of thick plates creates a local region of high constraint—that is, a triaxial stress
state wherein the three principal stresses are approximately equal—which limits the defor-
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mation capacity of the steel at the plate intersection. In fact, the level of constraint at the
notch tip, in general, governs the brittle behavior of steels. The apparent reduction in notch