## Fire resistance

a) Check adequacy of section for R120 to Method A. Axis distance available = 43 mm + (/) / 2

Required axis distance to main bars, a for 350 mm square column For /ufi = 0.5, a = 45 mm; and for pf = 0.7, a = 57 mm, providing:

■ e < emax = 0.15h = 0.15 x 350 = 52 mm but e = 146.1 x 106 / 1722.7 x 103

b) Check adequacy of section for R120 to Method B.

Determine parameters n, m, e and check Afi.

<BS 8500-1 Table

<BS EN 1991-1-2: 5.3.1(1) & NA 5.3.2, Table 5.2a>

Try Method B.

Assume 4 no. H32 + 4 no. H25 = (5180 mm2 : 4.2%) (say 4.2% OK - integrity OK)

= 0.7 x 1722.7 x 103 / 0.7 (350 x 350 x acc x fck / yc + 5180 x 500 / y) = 1205.9 x 103 / 0.7 (350 x 350 x 0.85 x 30 / 1.5 + 5180 x 500 / 1.15) = 1205.9 x 103 / 0.7 (2082.5 + 2252.0)

But say within acceptable engineering tolerance .'. use m = 1.0 OK

<9.5.2(3)> <BS EN 1992-1-2: Exp. (5.8a)>

: 0.7/ = 0.7 x 4000 = 2800 mm : radius of gyration : h / 3.46 for a rectangular section

where /

■- clear height between restraints : 4000 - 300 / 2 = 3850 mm

: relative flexibilities of rotational restraints at ends 1 and 2 respectively

: E'col / 'col / [2E'beam1 / 'beam1 + 2EIbeam2 / 'beam2] — 0.1

Treating beams as rectangular and cancelling E throughout: 'col / Pool = 3504 / (12 x 3850) = 3.25 x 105 'beam1 / 'beam1 = 8500 x 3003 / 12 x 6000 = 31.8 x 105

<BS EN 1992-1-2: Exp. (5.8b)> <BS EN 1992-1-2: 2.4.2(3)>

Table 5.2b valid for use in this case Interpolating from BS EN 1992-1-2 Table 5.2b for n = 0.40 and m = 1.0, column width = 350 mm and axis distance = 48 mm

c)_ As additional check, check adequacy of section to Annex B3 and Annex C. Using BS EN 1992-1-2 Table C.8

For m = 1.0, e = 0.25b, R120, 1 = 30 and interpolating between n = 0.3 and n = 0.5, bmin = 350 mm, amin = 48 mm.

.'. Axis distance = 43 mm + (/) / 2 is OK .'. 4 no. H32 + 4 no. H25 with 35 mm cover to 8 mm links

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