Page 363 - Marine Structural Design

Chapter I7 Fatigue Capacity 339

17.2.3 Notch Stress Approach

The notch stress approach is based on the determination of peak stress that account for the
weld profile. The notch stress is therefore estimated as the product of the hot-spot stress and
rhe stress concentratio factor for weld profile (so-called weld concentration facyor). The weld
concentratio factor may be estimated from diagrams, parametrci equations, experimental
measurements and finite element analysis. The presence of the welds should be given due
consideration in the notch stress approach.
The IIW (Hobbacher, 1996) recommended the following procedure for the calculation of
notch stresses:

An effective weld root radius of ~lmm to be considerd,
is
The method is restricted to weld joints which are expected to fail from weld toe or weld
root.

. Flank angle of 30 degrees for butt welds and 45 degrees for filler welds may be considerd,
The method is limited to thickness of larger than 5 mm.

17.3 Stress Concentration Factors
17.3.1 Definition of Stress Concentration Factors

The aim of the stress analysis is to calculate the stress at the weld toe (hot spot), chef . The
stress concentration factor due to the geometry effect is defined as,

nhot spot
SCF = - ( 1 7.1 0)
@,lllind
There are three approaches to determining the SCF:
Experimental Data,
Finite Element Analysis, and
Parametric equations based on experimental data or finite element analysis.
The above approaches will be detailed in the following sub-sections.