This paper presents a linear global-to-local procedure for the seismic low-cycle fatigue assessment of steel details affected by stress concentration. The method is intended to complement conventional Eurocode-based seismic analysis when the global structural response does not directly describe the local cyclic plasticity developing at critical details. A global beam model is first analysed by linear transient analysis under spectrum-compatible accelerograms. The resulting displacement histories are then transferred to a refined local model, from which the nominal stress history is extracted outside the notch field. After rainflow counting, each nominal cycle is converted into a local elasto-plastic response through a representative fatigue notch factor, Neuber's rule and cyclic Ramberg-Osgood relationships. Crack-initiation life is estimated by means of the Smith-Watson-Topper strain-life formulation within the ISO 19902 framework, and cumulative damage is evaluated through Palmgren-Miner linear summation. The procedure is also discussed against the LS2 cyclic plasticity criterion of EN 1993-1-6, interpreted as a smooth-reference benchmark for the assessment of the safety margin. The proposed procedure is applied to the case study of a two-storey steel portal frame subjected to three spectrum-compatible accelerograms. The derived cumulative damage values varies in a range between 0.85% and 2.08%, confirming that different spectrum-compatible records may still produce different local fatigue demand. If only the most damaging record is considered, the fatigue full failure (i.e. cumulative damage equal to 100%) is reached for a PGA scaling factor equal to 4.5. The obtained results indicate that the proposed workflow provides a practical and computationally efficient way to relate global seismic response and local fatigue damage in steel structures.
Linear evaluation of low-cycle fatigue damage in steel structures under seismic loading
Gastaldello, Marco
;
In corso di stampa
Abstract
This paper presents a linear global-to-local procedure for the seismic low-cycle fatigue assessment of steel details affected by stress concentration. The method is intended to complement conventional Eurocode-based seismic analysis when the global structural response does not directly describe the local cyclic plasticity developing at critical details. A global beam model is first analysed by linear transient analysis under spectrum-compatible accelerograms. The resulting displacement histories are then transferred to a refined local model, from which the nominal stress history is extracted outside the notch field. After rainflow counting, each nominal cycle is converted into a local elasto-plastic response through a representative fatigue notch factor, Neuber's rule and cyclic Ramberg-Osgood relationships. Crack-initiation life is estimated by means of the Smith-Watson-Topper strain-life formulation within the ISO 19902 framework, and cumulative damage is evaluated through Palmgren-Miner linear summation. The procedure is also discussed against the LS2 cyclic plasticity criterion of EN 1993-1-6, interpreted as a smooth-reference benchmark for the assessment of the safety margin. The proposed procedure is applied to the case study of a two-storey steel portal frame subjected to three spectrum-compatible accelerograms. The derived cumulative damage values varies in a range between 0.85% and 2.08%, confirming that different spectrum-compatible records may still produce different local fatigue demand. If only the most damaging record is considered, the fatigue full failure (i.e. cumulative damage equal to 100%) is reached for a PGA scaling factor equal to 4.5. The obtained results indicate that the proposed workflow provides a practical and computationally efficient way to relate global seismic response and local fatigue damage in steel structures.
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
