Page 37 - Structural Steel Designers Handbook AISC, AASHTO, AISI, ASTM, and ASCE-07 Design Standards

Brockenbrough_Ch01.qxd 9/29/05 4:59 PM Page 1.35

PROPERTIES OF STRUCTURAL STEELS AND EFFECTS OF STEELMAKING AND FABRICATION

STRUCTURAL STEELS, STEELMAKING, AND FABRICATION 1.35

increased carbon and alloy content of the steel, with increased thickness of the steel, and for cuts
having geometries that act as high stress raisers. Most recommendations for minimum preheat tem-
peratures are similar to those for welding.
The roughness of thermally cut surfaces is governed by many factors such as (1) uniformity of
the preheat, (2) uniformity of the cutting velocity (speed and direction), and (3) quality of the steel.
The larger the nonuniformity of these factors, the larger is the roughness of the cut surface. The
roughness of a surface is important because notches and stress raisers can lead to fracture. The
acceptable roughness for thermally cut surfaces is governed by the job requirements and by the mag-
nitude and fluctuation of the stresses for the particular component and the geometrical detail within
the component. In general, the surface roughness requirements for bridge components are more
stringent than for buildings. The desired magnitude and uniformity for surface roughness can be
achieved best by using automated thermal cutting equipment where cutting speed and direction are
easily controlled. Manual procedures tend to produce a greater surface roughness that may be unac-
ceptable for primary tension components. This is attributed to the difficulty in controlling both the
cutting speed and the small transverse perturbations from the cutting direction.
(R. L. Brockenbrough and J. M. Barsom, Metallurgy, Chap. 1.1 in Constructional Steel Design—An
International Guide, R. Bjorhovde et al., eds., Elsevier Science Publishers, New York.)

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