Base plate for ISHB 350, 1200 kN

Data: ISHB 350 @ 72.4 kg/m: $h=350$, $b_f=250$, $t_f=11.6$, $t_w=10.1$ mm. Factored load $P=1200$ kN; steel E250; concrete M20.

1. Bearing strength of concrete (IS 800:2007 cl. 7.4.1)

$0.45f_{ck}=0.45\times20=9.00$ N/mm²

2. Plate size

$$A_{req}=\frac{P}{0.45f_{ck}}=\frac{1200\times10^3}{9.00}=133333\ \text{mm}^2$$

Projection of about 50 mm all round the column (not less than 50 mm): $L=350+2\times50=450$ mm, $B=250+2\times50=350$ mm. Area provided $=157500$ mm² $>A_{req}$ ✓

$$w=\frac{P}{BL}=\frac{1200\times10^3}{450\times350}=7.62\ \text{N/mm}^2<9.00\ \text{N/mm}^2$$

3. Thickness (cl. 7.4.3.1)

Projections $a=50$ mm and $b=50$ mm (larger and smaller):

$$t_s=\sqrt{\frac{2.5w(a^2-0.3b^2)\gamma_{m0}}{f_y}}=\sqrt{\frac{2.5\times7.62\times(50^2-0.3\times50^2)\times1.10}{250}}=12.11\ \text{mm}$$

It must also be not less than the flange thickness $t_f=11.6$ mm. Provide $t_s=14$ mm.

4. Connections

• The column end is machined to bear on the plate; connect with a nominal 6 mm fillet weld all round (load is transferred mainly by contact).
• Anchor bolts: 4 nos. M20, embedded about 450 mm with a washer plate (for erection and to resist any uplift).

Answer: base plate 450 × 350 × 14 mm, 4 anchor bolts M20, 6 mm weld, pedestal of M20 concrete.