Design of Prestressed Concrete for Fire Resistance

Unbonded post tensioned concrete in fire: A review of data from furnace tests and real fires

“…The prescribed covers are based largely on results of standard furnace tests conducted on isolated UPT slabs and beams during the 1950s and 1960s [4][5][6][7][8], although some codes have been revised based on more recent furnace testing [9,23]. As described below, in some cases these tests used concrete which had been pre-conditioned before fire testing, or used a light steel mesh within the concrete cover to prevent or arrest spalling during fire.…”

“…In 1964, as part of a larger study on the fire performance of various types of concrete beams, the Fire Research Laboratory of the Portland Cement Association (PCA), Illinois, conducted two standard furnace tests of UPT beams with T-shaped cross sections [8,41,42]. The beams' cross-sections are shown in Figures 1c and 1d; they were essentially rectangular, with a depth of 635 mm, a web width of 356 mm, and small flanges of 150 mm × 100 mm.…”

“…It is noteworthy that while details of the mild steel reinforcement are not shown in the summaries of these tests published in PCI's Post-Tensioning Manual [41], the original PCA research report [8] clearly shows that both of these beams included a light steel mesh (welded wire fabric of orthogonal 2 mm diameter wires, 51 mm on centre in both directions) placed at a depth of 25 mm (mid-depth of the concrete cover) over the entire fire-exposed perimeter of the beams. This is significant, since the presence of this mesh may have mitigated cover spalling [43] and would have arrested it if it occurred.…”

“…Available experimental data on the fire performance of UPT structures come from relatively few unrealistic and outdated large-scale furnace tests on isolated UPT beams and slabs [3][4][5][6][7][8][9][10][11]. It appears that no realistic fire tests of multiple bay continuous UPT elements have ever been performed.…”

“…While available standard furnace test data are instructive, they are neither representative nor necessarily conservative with respect to the performance of real UPT buildings in real fires [12]. Indeed, available case studies of real fires in UPT buildings [13][14][15][16][17][18] suggest that when UPT beams or slabs fail in fire it is rarely for the reasons that would be expected on the basis of available testing [3][4][5][6][7][8][9][10][11] or design guidance. This paper focuses on the structural fire performance of modern flat-plate UPT concrete slabs.…”