Behavior and design of built-up compressed steel members composed of concentric hot rolled circular hollow sections

This research presents a study of the behavior of built-up compressed steel members composed of concentric hot rolled circular hollow sections. The use of these members is an innovative solution of practical interest for situations in which a single member does not reach the required compressive strength. Some technically and economically viable design and fabrication solutions to built-up members composed of concentric hot rolled circular hollow sections are presented. For the validation of numerical results, models of singular hollow sections are made and compared to the EN 1993-1-1, and the results obtained with numerical models were satisfactory. The compression resistance of these numerical models differs less than 9% from the EN 1993-1-1 values. Once the numerical modeling was validated, the study of built-up members was made, considering the tubes always united at the extremities by end plates, and along the length by fixed interconnections or sliding interconnections or, furthermore, without interconnections. For these three different conditions, several numerical models using FEM via Abaqus software were simulated to obtain and compare the compression resistance. The results show that these built-up sections with fixed and sliding interconnections have very similar behavior to the results obtained with European Standard procedure, when considering equivalent areas and inertias for the built-up section. Also, it shows that this observation does not apply to the sections without interconnections. Comparative graphs of compression resistance curves were generated, as also some graphs that show the distribution of the compressive force between each member of the built-up section. Finally, a formulation for the design of built-up sections without interconnections along the tubes was proposed to avoid robust computational methods.