Progressive collapse induced by fire and blast

Tipo di pubblicazione: Tesi di dottorato
Tipologia MIUR: Tesi di dottorato > Tesi di dottorato - Polito
Titolo: Progressive collapse induced by fire and blast
Autori: Forni, Daniele
Autori di ateneo:
Tutor: Bernardino Chiaia, Ezio Cadoni.
Dottorato di ricerca: XXIX Ciclo > INGEGNERIA DELLE STRUTTURE
Istituzione: Politecnico di Torino
Numero di pagine: 168
Abstract: Comprehensive finite element modelling of key elements is essential to improve the robustness assessment of structures subjected to a coupled effect of fire and blast. Focusing the attention on steel structures, a method for a realistic multi-hazard approach is presented. The problem has been investigated at the material level first and then at the structural level. The material level was studied performing a detailed experimental investigation in a wide range of strain rates and temperatures. A typical structural steel, namely S355, has been studied. A Split Hopkinson Tensile Bar equipped with a water-cooled induction heating system was used for the mechanical characterisation at high strain rates (300 1/s, 500 1/s and 850 1/s) and in a wide range of temperatures (20C, 200C, 400C, 550C, 700C and 900C). A Hydro-Pneumatic machine and a universal electromechanical testing machine were used for intermediate (5 1/s and 25 1/s) and quasi-static (0.001 1/s) strain rate tests at room temperature, respectively. Results showed that the S355 structural steel is strain rate sensitive, keeping its strain hardening capacity with increasing strain rates. The temperature effect was studied by means of the reduction factors for the main mechanical properties. Results at high strain rates highlighted also the blue brittleness phenomenon between 400C and 550C. The link between the material and the structural level is a material constitutive law able to take into account the strain rate sensitivity and the thermal softening. The widely used constitutive law proposed by Johnson and Cook was calibrated using the experimental results. A critical review of this material model highlighted a perceptible variation of the thermal softening parameter at different temperatures. Following a fitting approach, a modification of the dimensionless temperature (T*) has been proposed.The structural level was numerically investigated adopting the calibrated material model. Explicit non-linear dynamic analyses of a steel column under fire conditions and followed by an explosion were performed. The commercial code LS-DYNA was used. A method for a realistic multi-hazard approach has been proposed by studying the residual load bearing capacity. The results can be also of great interest to establish the initial conditions that could potentially lead to the onset of progressive collapse in steel framed structures under a combined effect of fire and blast. As expected, the results indicated that the load bearing capacity is influenced by the stand-off distance, the charge size as well as the column boundary conditions. The time of fire loading at which an explosion is triggered is a critical parameter as well.
Data: 2017
Status: Pubblicato
Lingua della pubblicazione: Inglese
Parole chiave: high strain-rates tests, blast loads, fire, multi-hazard approach., progressive collapse, robustness, s355 mild steel, non-linear dynamic analyses
Dipartimenti (originale): DISEG - Dipartimento di Ingegneria Strutturale, Edile e Geotecnica
URL correlate:
    Area disciplinare: Area 08 - Ingegneria civile e Architettura > TECNICA DELLE COSTRUZIONI
    Area 08 - Ingegneria civile e Architettura > SCIENZA DELLE COSTRUZIONI
    Data di deposito: 09 Giu 2017 13:33
    Data ultima modifica (IRIS): 09 Giu 2017 14:06:42
    Data inserimento (PORTO): 13 Giu 2017 12:25
    Numero Identificativo (DOI): 10.6092/polito/porto/2674396


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