Page 357 - Marine Structural Design

Chapter I7 Fatigue Capacity 333

Table 17.1 Comparison of European Standards for Fatigue S-N Curves for Air

Note: For thickness correction, the reference thickness is 32 mm and 25 mm for welded
connections for tubular joints and non- tubular joints, respectively.
In Europe, the UK HSE (1995) replaced the UK DEn (1990). The main change is that m and r
become independent of the S-N curves selected. A weld classification factor f (to be multiplied
to the stress range) has been introduced in UK HSE (1995) so that various S-N curves in UK
Den (1 990) may be expressed in one S-N equation. In other word, the S-N curves in UK HSE
(1995) are unified to a single equation by defining stress range as:
s = f * s, [ tl" (17.5)

where, S, = stress range which includes weld macro-geometry but excludes the peak stress due
to local defects that have been implicitly accounted for in the weld classification factor f.
The relationship between the weld class (B, C, D, . . .) and the weld classification factor f is
B(f=0.64), C(f=0.76), D(f=l), E(f1.14), F(f=1.34), F2 (f=1.52), G (f=1.83) and W (e2.13).
Since 1948 the Norwegian standard NS3472 has been used for design of land and offshore
steel structures in Norway. In 1998, NS3472 was revised and in the same time, NORSOK N-
004 (NTS, 1998) was developed for design of offshore steel structures. NORSOK is a
Norwegian initiative by the industry to develop a design standard for more cost effective
offshore development. Eurocode 3 is a European standard for design of building structures.
Table 17.1 lists the S-N curves used in Europe for air environments.
In the USA, fatigue design is based on API RF' 2A WSD and AWS D1.l. A detailed
background of the AWS code Provisions is given by Marshall (1 992) and outlined by Marshall
(1993). Geyer and Stahl (1986) presented a simplified fatigue design procedure for offshore