Steel connection capacity design

Capacity design is a part of a joint check-in seismic design. When relying on the ductility of a structure, the capacity design must be performed. 

The objective of capacity design is to confirm a building undergoes controlled ductile behavior to avoid a collapse in a design-level earthquake.

A dissipative item is selected with increased strength and a modified material diagram. An overstrength factor \(\gamma_{ov}\) is defined in Materials, and a strain-hardening factor \(\gamma_{sh}\) at the dissipative item operation. Note that the nomenclature differs between the codes. A dissipative item is excluded from the strain check of plates. 

Modified material diagram for dissipative item

IDEA StatiCa Connection checks the connection on applied design load, which should create a plastic hinge in the selected dissipative item, usually the beam. The plastic strain in the dissipative item should be around 5%. This can serve as a confirmation that the magnitude and position of loads were determined properly. 

Plastic hinge created at the intended place of the dissipative item – the beam

The supports of the continuous member are automatically defined as supported at one end and with restrained moments at the other end. This way, the continuous column may be loaded by the normal force and shear forces, and also one side may move sideways so that the failure of the column web in shear is revealed.

Note, that detailing is very important for seismic resistant joints but is not checked in IDEA StatiCa.