This article addresses the structural behavior of the connection between circular hollow steel tubular columns and I-section beams in civil construction. As a strategy to improve the stiffness of this connection, external diaphragms are used — flat components incorporated at the interface between the column and the beam. It is noteworthy that the Brazilian standard ABNT NBR 16239:2013 does not cover the design of this type of connection. The objective of this study is to numerically analyze the behavior of welded connections between a circular hollow section column and I-section beams, using external diaphragms in X-type and XX-type connections. These connections were subjected to compression and bending loads, and variations in the column diameter and wall thickness were also considered. Numerical modeling was performed using the finite element method and showed agreement with the numerical and experimental results obtained by Winkel (1998). The performance of the external diaphragm proved to be satisfactory, as it resulted in a considerable increase in stiffness, enhancing the connection’s load-bearing capacity, as well as the positive effects of increasing the column’s diameter and wall thickness.
