Rectangular hollow sections – bending fatigue tests and finite element models

Abstract

The cold formed rectangular hollow sections (RHS) are used frequently to build the joints for the modern steel structures (buildings, steel bridges, offshores) and especially for the structural joints made of hollow sections with large width ratios b1/b0 it is often necessary to weld in the areas close to the edges.
Welding in cold formed areas is not only an open question for statically loaded sections (brittle fracture) but also for dynamically loaded structures (fatigue resistance). A lot of structures presented above are subjected to dynamic loadings and unfortunately a very small number of informations about the influence of welding in the cold formed areas on fatigue resistance are available.
In order to establish the fatigue behaviour of welded and non-welded rectangular hollow sections specimens, a large number of 4-point bending tests are performed at the University Friedericiana of Karlsruhe, Laboratory for Steel, Timber and Masonry.
Because these tests are very expansive, and because of the large number of parameters regarding the RHS to be investigated (steel grade, wall thickness, load distribution, boundary conditions), a number of finite element models for these specimens are made. By modeling the specimens with different types of finite elements (shells, solids) and taking into account some types of loading distributions
and boundary conditions, the obtained results (stresses, strains, displacements) from a static analysis are compared with those obtained from the real 4-points bending tests.
In this way, the obtained conclusions would lead to decrease of the number of the specimens need to be tested and in the same time of the costs of the project.
Simultaneous, by using finite element analysis, many factors with direct influence on the fatigue resistance can be considered.