Traditional methods for calculating welded joints are based on approximate methods for determining the forces that occur in the joint. This leads to inaccuracies in the definition of stress. In addition, this approach does not allow obtaining a complete picture of the stress-strain state of the joint. All this leads to the need to increase the coefficient of safety margin and, as a result, to increase the cost of construction. The proposed method of calculating the connection using the finite element method allows us to determine the stresses in all the elements of the connection very accurately. This makes it possible to obtain a reliable picture of the stress-strain state of all elements of the connection. As a result, it is possible to reduce the complexity of creating a compound and its mass. The finite element method should be used for calculating critical connections with complex operating conditions. An example of calculating such a connection is considered. A comparative analysis of the results of calculating the t-joint using the arm Joint module Of the WinMachine arm system and the Abaqus finite element package is performed.