Deformation limit for the ultimate strength of hollow section joints

In order to determine the ultimate load capacity of hollow section joints with CHS or RHS chords, in cases the load - deformation diagrams or moment - rotation diagrams do not show a pronounced peak load, a deformation criterion has been discussed and evaluated. For this aim, various research activities have been carried out for the following types of connections: plate or I-beams to CHS connections, plate or I-beams to RHS connections, X-joints in CHS, X- and T-joints in RHS. From the previous research, it has been shown that the behaviour of hollow section joints is mainly dependent on the local plastification of the chord if the connection is designed in such way that the failure of the brace does not occur before connection failure. Therefore, the deformation limit criteria should be based on the local deformation of the chord face at the intersection between brace and chord. For the design of connections, it must be ensured that conditions with regard to the ultimate strength, deformation capacity and serviceability are satisfied. For this reason, the given deformation limit has been verified by checking the numerical results for the above mentioned types of connections loaded by axial compression or in-plane bending moment. Finally, the ultimate strengths at the deformation limit for connections with RHS chord have been compared with available design formulae from several references.