Design Guide 8

For CHS and RHS welded joints under fatigue loading



This is the eight handbook in the CIDECT series “Construction with Hollow Steel Sections” and covers the fatigue design of various types of joints between and connections to hollow steel section members. The fatigue phenomenon is characterised by the progressive degradation of strength under the action of time variant stresses that results in the formation and subsequent growth of cracks, which may eventually lead to fracture of a member or even the collapse of the structure.

The fatigue life of a structure depends upon many factors such as: the type of joint, the type of loading, the structural detailing, etc. Several methods, of varying accuracy and complexity, have been developed over the years for the determination of the fatigue life of a structure or structural detail. These methods include the classification method, the punching shear method, the fracture mechanics method, the hot spot stress method, etc.

This handbook concentrates mainly on the hot spot stress method, which is widely regarded as one of the most accurate because it can take into account most of the influencing factors. It uses various parametric formulae to calculate the so called ‘hot spot stress’, which in turn is used to determine the fatigue life of the joint under investigation. The fatigue life determination using the much more restrictive and approximate classification method is also included, but in much less detail.