Material choice for seismic resistant structures (MATCH) : final report

Large alternating plastic amplitudes during seismic events frequently result in catastrophic fractures. Instable brittle failures are the result of insufficient deformation capacity in combination with non-appropriate toughness properties of the steel. Eurocode 3 provides a procedure for the choice of steel material in the lower part of the toughness-temperature-diagram to avoid brittle fracture. Concerning plastic design, there are some empirical rules in EC 3 and EC 8 for monotonic and cyclic loading, but these rules are not justified by toughness considerations. Hence, mechanically justified upper shelf toughness requirements for structures subjected to seismic action should be investigated. First promising attempts by means of innovative damage mechanics on how to ensure a sufficient ductile behaviour related to toughness demands have been developed in the RFCS Project PLASTOTOUGH. The approach has successfully been applied to welded beam-column-connections in combination with the effective plastic strain concept acc. to OHATA and TOYODA. However, recent research has shown that the damage model needs extension in case of dominant shear stress by considering the third invariant of the stress deviator. This has successfully been realised by a further extension of the damage mechanics model. To validate this extended approach its application to components with a high portion of shear stress has been investigated. The damage prediction in case of increasing amplitudes led to highly satisfying results, whereat a premature estimation for constant amplitudes has been noticed. Within a subsequent parametric study upper shelf toughness requirements could be derived and transferred to a simplified steel selection procedure.