PSI - Issue 64

Patrick Covi et al. / Procedia Structural Integrity 64 (2024) 1774–1781 Patrick Covi and Nicola Tondini./ Structural Integrity Procedia 00 (2019) 000 – 000

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3.2. Example of one FFE simulation For brevity, one simulation is selected as an example to demonstrate the methodology used for the FFE analyses. The same seismic action selected in the previous chapter is reported in this example (Northridge earthquake). The probabilistic FFE framework was used to automatically determine the compartment damages, fire ignition, and fire spread. The results of the seismic simulation are depicted in Fig. 6. Fig. 6b the IDR and PFA exceed the ignition threshold on all the floors. Therefore, the fire starts in a compartment on each floor. The flashover time is set as the threshold for the vertical spread between two exterior compartments. The fire spread rate between adjacent compartments is influenced by the status of partitions (damaged or intact) after the earthquake. In the horizontal direction, the delay times for fire spread are 30 minutes for intact partitions and 15 minutes for damaged partitions. Fig. 7a shows a qualitative representation of the fire spread after 72 min from the ignition in the compartments for the selected simulation. The time-temperature curve and fire behaviour characteristics in the compartments were obtained using the zone model software Ozone. The heat transfer analysis was automatically performed to obtain the steel temperatures for each element in the compartment subjected to fire using the probabilistic FFE framework. The FFE structural analysis followed the heat transfer analysis for the selected scenario. The partial structural collapse occurred 72 minutes after the start of the fire due to the excessive vertical deflection rate in the beams located on the 1 st and 2 nd floors and in the 4 th bay, as illustrated in Fig 7b-c. a b

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Fig. 7. (a) Fire spread within the building after 72 min ˆ”‘ ‹‹–‹ƒŽ ‹‰‹–‹‘• ƒˆ–‡” ‡ƒ”–Š“—ƒ‡ ; (b) Beam failure criteria deflection; (c) Deformed shape and element surface temperatures after 72 min from initial ignitions after earthquake. 3.3. Results of the FFE analyses As listed in Table 2, 189 simulations were performed for 7 accelerograms scaled at 3 different intensity values, 3 different window width values, and 3 different fire load densities.

Table 2. FFE Analysis parameters. Parameter Values Accelerograms

7 accelerograms

Acceleration scale factor

1.00 1.25 1.50

Window width (m)

3.0 4.5 6.0

Window width (m)

3.0 4.5 6.0