Stress / Strain
Clicking on the "Stress / Strain" button starts the stress analysis and checks. The first time the analysis is run, the implemented version of OpenSees© will be installed automatically.
Clicking on the "Rotational stiffness" button will start the force analysis and checks. This analysis option allows users to obtain the resistant moment, the initial stiffness, the secant stiffness and the classification of the connection (rigid, semi-rigid or pinned) of the steel sections.
The results are displayed on the right-hand side of the "Analysis" tab. In the drop-down menu at the top, you can select the type of results to be displayed, "Stress/Strain" or "Rotational stiffness". When choosing "Rotational stiffness", the program displays two tables and the "Moment - Rotation" graph.
To obtain the "Moment - Rotation" graph, the program runs an iterative process analysing the rotation in different load steps. The resistant moment is obtained when any element of the connection (plates, sections, welds or bolts) does not comply, i.e. when its demand capacity ratio is greater than 100%.
The first table shows all bars analysed with the secant stiffness and the classification of the connection in each plan. The second table displays the analysed load cases for the selected bar. Each load case indicates the acting moment, the resisting moment, the secant stiffness and the initial stiffness.
The graph shows the curves for "Moment - Rotation", "Acting moment of the selected load case", "Resistant moment", "Ultimate stiffness for rigid connections (Sj,1)" and "Ultimate stiffness for pinned connections (Sj,2)".
Classifying the connection
To classify the connection as rigid, semi-rigid or pinned, the limit stiffnesses of rigid and pinned connections must first be established. Depending on the selected steel codes, the initial stiffness or the secant stiffness will be compared with these limits.
Clicking on the "Buckling" button will start the analysis. The local buckling of a connection component occurs due to compression forces and mostly depends on the stiffness of the component and the distribution of the applied loads. The buckling analysis helps to detect unstable connection design configurations under the load of a particular load case.
There are several ways to evaluate the buckling phenomenon using Finite Elements. The one implemented in the connection analysis is the "Linear buckling analysis" which allows users to obtain the critical load factors of the different local buckling modes of the connection for a given load case.
Once the analysis is completed, we obtain the critical load factors for each of the buckling modes as well as their deformed shape. The smaller the first critical load factor, the closer we are to an unstable connection configuration.