## 1 Introduction
The AISC-358 [6] standard governs metallic connections, and it also describes the limitations, scope, and requirements to apply this type of links, so that the structures can work stably in the inelastic range and adequately dissipate energy. However, many structures currently built do not conform to such regulations. Fillet welding is applied instead of full penetration welding (as required by the regulations) [18]. Steel connections are the most expensive items, so the total cost of a structure is affected by the type of connection you apply. For this reason, this is usually an influential factor in the decision on the model to apply models, seeking simplicity and lower costs [19]. After the 2011 earthquake in the Tohoku region, Japan, it was found that structures with rigid beam-column connections, in moment frames, with tubular columns and I-type beams, adequately resisted this event (consult, for example, in [[https://repositorio.uchile.cl/handle/2250/147494](https://repositorio.uchile.cl/handle/2250/147494)]([https://repositorio.uchile.cl/handle/2250/147494](https://repositorio.uchile.cl/handle/2250/147494)) (accessed on January 2024)). However, it has been documented in different investigations that these connections are weak and can present fractures that result in significant damage, in the event of events such as earthquakes or similar, if they are not correctly implemented [1; 20]. Ecuador is a country located in a region of high seismic risk, and for safety, it is essential to study the behavior of construction systems and their connections. The results of these studies will provide the national market with connection options for tubular, concrete-filled, circular, and rectangular column sections, that promote simple assembly, reduce total costs, and increase the process efficiency. Particularly, the connection of steel beam with tubular steel column, filled with concrete, using flange-web welded plate connection, has not been fully studied in the country. In this context, the article reports on a study of the seismic behavior of flange-web welded plate connections in tubular columns filled with concrete and type I beam, by simulation with the finite element method. For this, the SMF is analyzed, under the guidelines of the AISC/ANSI 360-341 [4; 5] standards, and a study of its inelastic behavior against cyclic loads. Four metallic connections were analyzed in different configurations with CFST columns, connected with steel beams. For example, in [21; 22] it is reported tests for six different types of circular CFST welded connections, using the quasi-static test method. The connections were fabricated using different elements: diaphragms, plates, embeddable weldable corrugated bars, continuous flanges, and continuous steel tubes. On the other hand, [PERSON], [PERSON] and [PERSON] performed tests under cyclic loading on five circular CFST welded connections [23]. These authors tested four types of connections, characterized by the arrangement of the weld from the flange of the beam to the external diaphragm, and by the tubular walls of the columns. The obtained results showed that all the connections failed due to the fracture of the weld during the non-linear behavior. The residual stresses accumulated in the tube wall because of diaphragm welding, reducing the deformation capacity of the column. In this investigation, three-dimensional connections were modeled and analyzed until failure. In this case, for the AISC 358-16 code for seismic applications, only two prequalified connections are considered, which use tubular columns (ConXL and SidePlate) that have a high cost in the market. There are no known recommendations for obtaining rigid connections such as those proposed in this study, which allow the generation of plastic hinges to obtain stable hysteretic curves.