PSI - Issue 60

Sarmili Swain et al. / Procedia Structural Integrity 60 (2024) 553–563

561

Sarmili Swain / Structural Integrity Procedia 00 (2024) 000 – 000 9 deterioration under 60 minutes of fire exposure resulting in exceedance of collapse threshold value. Further, the adjacent load bearing column members to the lost column experience DCR values of 1.864 at ambient temperature state and is found to experience global failure in 30 minutes of its exposure to fire (temperature of around 800 o C to 850 o C). This clearly pronounces the vulnerability of building structure in resisting the structural loads under fire.

Table 6. Moment Carrying Capacities of typical floor beams under various Fire Load durations for Case 3: Progressive collapse

Demand (KN-m)

Beam no.

Capacity (KN-m)

Ambient Temperature

30 minutes

60 minutes

B1 B2 B3 B4 B5 B6 B7 B8 B9

19.8 19.8 19.8 19.8 19.8 19.8 19.8 19.8 19.8 19.8 19.8 19.8

10.79 10.79 10.79 10.79 10.79 10.79 10.79 10.79 22.09 22.09 22.09 22.09

22.603 22.659 22.661 22.664 22.663 22.662 22.664 22.663 27.287 27.283 27.282 27.292

37.904 37.852 37.883 37.866 37.994 37.722 37.946 37.912 35.461 35.525 34.495 35.624

B10 B11 B12

a

b

Case-3: Instantaneous removal of Center Column

2.5

2

1.5

1

B11

B10

0.5

0

Demand capacity ratio(DCR)

B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 B12

Typical Floor Beam

Ambient Temp.

30 min

60 min

Fig. 8. (a) DCR value of typical floor beams for Case 3 (b) DCR values of adjacent components for ambient temp. of Case 3

Considering the results obtained, it is evident that in all three cases of progressive collapse initiation, the structural components have experienced significant deterioration leading to collapse of the structure. In addition, it can be noted that the building structure has significantly lost in its ability to resist the structural loads under fire exposure resulting as a potential secondary event. Further, Case 2 appears to be the worst-case scenario for the building as global failure or loss of structural integrity is indicated even before exposure to fire and vulnerability of the local structural components are clearly pronounced for its exposure to 30 minutes of fire duration. Moreover, the structural components are exposed to temperatures of around 800°C to 950°C during 30 minutes to 60 minutes of fire exposure, respectively (depicted in Fig. 9). Therefore, when the building structural components experience these high temperatures, deterioration in terms of spalling of concrete takes place after exceeding 800 o C for a certain duration of time. This results in tremendous decrease in structural cross section as depicted in Fig.9. Therefore, this feature leads to exposure of steel rebars to fire, resulting in increased vulnerability of the structure in resisting the structural loads. These can be envisaged as leading to loss of structural integrity as well as functionality for which the structure is designed for. Therefore, it can be concluded that exposure of structural components for at-least 30 minutes duration of fire as a consequential event to progressive collapse have pronounced severe deterioration of the structure, which