Associating SCFs with Tubular Joints Associating SCFs with Tubular Joints

Like SN curves a set of stress concentration factors (SCFs) must be associated with each fatigue point. The details differ based on the type of fatigue being computed. For tubular joint fatigue, the SCFs will normally be computed based on the joint geometry and the load path and is controlled by a set of options on the point definition or ED_POINT command, and the default for all of these parameters is specified on similar options of the &DEFAULT command. The applicable options are:


     -CO_SCF, SCF_TYPE

     -LEN_FACTOR, FRACHOL

     -MAX_CHD_LEN, MAXCHOL

     -CHD_FIXITY, CHD_FIX

     -SCF_BOUNDS, MIN_SCF, MAX_SF

This computation is controlled by the -CO_SCF option. The valid values for SCF_TYPE are K&S, API, MARSHALL, and EFTHYMIOU. With the automatic computation of SCFs, two values are computed: one for the root of the weld on the brace side, and one for the root of the weld on the chord side. The -LEN_FACTOR, -MAX_CHD_LEN, and -CHD_FIXITY options define parameters which are used by some of the methods in computing the SCFs. For some methods, the SCFs depend upon the length of the chord. FRACHOL is a fraction of the actual chord length which will be used. The default value of FRACHOL is one. MAXCHOL is the maximum length which will be used and its default value is "infinite". Suppose that the chord length was 200. If FRACHOL is set to .5 and MAXCHOL is 50, the program will first set the length to be used to .5*200. It will then take the maximum of 100 and 50 and use this value in the computation. The -CHD_FIXITY, option defines the "chord flexibility" CHD_FIX. This is a measure of the bending support at the ends of the chord. It should be a number between .5 and 1. The first of these corresponds to the chord ends being pinned and the later fixed. The -SCF_BOUNDS option defines minimum and maximum values for SCFs. Any computed SCF smaller than MIN_SCF or greater than MAX_SCF will be replaced with the limit.

If stiffeners are associated with either of the two chord classes, then they will be used in computing the "crushing" of the joint, in computing the code check for the joint, and in computing the stress concentration factor for the joint. The number of stiffeners will be the sum of the number for both chord segments. For situations where two classes define the chord with different stiffener attributes, then the properties of the last one encountered will be used. Here, the stiffeners are "smeared" over the effective length (or true brace footprint of the joint). The SCFs computed by whichever method are reduced according to "Lloyd's Register of Shipping Recommended Parametric Stress Concentration Factors for Ring_Stiffened Tubular Joints".