It is thought that the earliest practice of civil engineering may have commenced in ancient Egypt (4000 and 2000 BC) when the humans started to abandon a nomadic live to stay on the same place for live, that means that civil engineering is a science that has been studied more than 5000 years. Even so, nowadays there are many fields to investigate and study. Not everything is known. This thesis was thought to study a topic that nowadays is not reflected on the regulations. This theme is the connection between steel beams and composite columns. This thesis starts with theoretical concepts, the review and analysis of the composite structures and steel and composite joints. This first part was made with the basis of Eurocode and Design Guide. After this first theoretical part the practical part starts; this part is based on the comparison of two types of connections, two connections that are equal CHS column joint with an I-Beam, but one of the connection the CHS is filled of concrete. The analysis of the connections was done by hand, all the calculation than could made with Eurocode, and following with a finite elements study, with the support of the ANSYS program. To sum up, the thesis was finished with the comparison of both types of joints to solve questions like: which are the benefits of infill concrete on behaviour of joint? How much load can support?