# The structural stress concept for hot spots

The **structural stress concept (SSK)** is an extension of the nominal Stress concept dar. It applies to complex geometry forms application, where the nominal stresses can no longer be determined by the elementary strength of materials. In particular for welded hollow section structures the structural stress concept of advantage, which goes back to an approach by HAIBACH proves. It detects the stress of increases due to the component structure in the weld base point calculated by applying a notional structure stress is at the critical point (also called **hot spot**) was determined.

The determination of the structural stress s_{S} is done by measurement or calculation of stresses at specified intervals to the base point of the weld, the weld to the base point then be extrapolated linear or quadratic. Structure in the fictitious stress increases are included in the geometry of the structure (structural discontinuities). However, local stress effects due to the weld geometry are not recognized.

The right figure shows the definition of structural stress compared to the rated Stress and the local stress on the example of a strut connection. For each notch detail to be considered a **stress concentration factor (SCF)** as a function of the load type is specified (axial compression, bending in the plane, bending out of the plane) is generally used to describe the relationship between structural stress and nominal stress. The evaluation of the fatigue strength is then carried out by comparing the existing structural stress with structural stress SN curves.