Derivation of new, optimized strength criteria for steel components

  Testing machine for wide-plate tests at IEHK. Copyright: IEHK/Brixius Testing machine for wide-plate tests at IEHK.

The design concepts in the technical rules for steel structures were developed in order to cover the real bearing capacities of components. In general, the related design functions in such codes have been validated against experimental tests and were derived on a pure phenomenological basis. As these engineering models predict the limit loads by the yield strength or the tensile strength of the steel material, two consequences arise for the application of these resistance criteria:

  • The prediction accuracy of the current resistance functions has shortcomings due to the related model concepts that do not consider the real failure behavior of the material.
  • In addition, the application of high strength steels is - without justification - significantly restricted due to the fact that the steel standards specify minimum values of the uniform elongation or the yield strength ratio.

Yet, high strength steels offer economic and ecological benefits for the use in steel structures, for example by cost savings and energy conversation combined with a reduced amount of material or the opening of new markets for the local quality-oriented steel industry. Hence, the improvement of the strength criteria is desirable.

Within the framework of the research project the ultimate limit state will be investigated by an innovative damage mechanics approach to derive optimized strength criteria for steel components particular with regard to high strength steel. The damage mechanics model to be used for the numerical simulation of ductile crack initiation and damage evolution considers the toughness properties of the material and the complete stress state in terms of stress-triaxiality and Lode-angle-parameter. The damage mechanics models are validated by numerical simulations of large sets of experimental tests representing typical structural details. Within this project, a damage mechanic based procedure will be developed to derive more efficient assessment rules.