Gusseted base for ISHB 350, 2000 kN

Data and assumptions: ISHB 350 @ 710 N/m ($h=350$, $b_f=250$, $t_f=11.6$ mm) with two 450 × 20 mm plates (one on each flange) forming the column shaft: overall shaft size $D=350+2\times20=390$ mm by $B_s=450$ mm. Factored load $P=2000$ kN; pedestal M20; E250 steel. Gusset angles (ISA 100×100×10) are used on the long sides.

        |==450x20 plate==|
        |    ISHB 350    |      shaft 390 x 450
        |==450x20 plate==|
     ISA cleats ---> |_|   |_| <--- ISA cleats
    ===================================
         base plate  L x B x t

1. Bearing and plate area

$0.45f_{ck}=9.0$ N/mm²; $A_{req}=\dfrac{2000\times10^3}{9.0}=222222$ mm². Provide base plate $L\times B=500\times520$ mm (area $260000$ mm² $>A_{req}$):

$$w=\frac{2000\times10^3}{500\times520}=7.69\ \text{N/mm}^2<9.0\ \text{N/mm}^2\ \checkmark$$

2. Thickness of base plate

Projections beyond the shaft: $a=\dfrac{500-390}{2}=55$ mm, $b=\dfrac{520-450}{2}=35$ mm.

$$t_s=\sqrt{\frac{2.5w(a^2-0.3b^2)\gamma_{m0}}{f_y}}=\sqrt{\frac{2.5\times7.69\times(55^2-0.3\times35^2)\times1.10}{250}}=15.0\ \text{mm}$$

Because the plate is also loaded between the gusset angles, provide $t_s=16$ mm (minimum 16 mm for a gusseted base).

3. Transfer of load from the shaft to the base plate

The column end is not machined, so the full 2000 kN is carried by fillet welds (shop welds, $s=10$ mm):

$$q=\frac{f_u}{\sqrt3\gamma_{mw}}\times0.7s=189.4\times0.7\times10=1326\ \text{N/mm},\qquad L_w=\frac{2000\times10^3}{1326}=1509\ \text{mm}$$

Weld all round the shaft and the cover plates: perimeter $2(390+450)=1680$ mm $\ge$ required; in addition provide the two gusset angles ISA 100×100×10, 450 mm long, welded to the cover plates and to the base plate with 8 mm fillets, which carry the balance. If the column is milled to bear, the welds need carry only a part.

4. Anchor bolts

4 nos. M24 (or more) near the corners, embedded 600 mm with plate washers.

Answer: base plate 500 × 520 × 16 mm; shaft ISHB 350 + 2 PL 450×20; ISA 100×100×10 gusset angles; 10 mm fillet weld; 4 M24 anchor bolts.