**Problem Statement**

It is required to specify the appropriate thickness of a base plate to support a UC 203 x 203 x 60 subjected to the following loads. The connection is assumed to be pinned with four bolts outside the column profile.

The supporting concrete is to have a grade f

_{ck}= 25 N/mm

^{2}

Characteristic force from permanent action G

_{k}= 620 kN

Characteristic force from leading variable action Q

_{k}= 132 kN

**Partial Factor for loads (BS EN 1990 NA 2.2.3.2 Table NA.A1.2(B))**

Permanent action Î³

_{G}= 1.35 (unfavourable)

Variable action Î³

_{G}= 1.5

Reduction factor Î¾ = 0.925

At ultimate limit state;

N

_{Ed}= 1.35G

_{k}+ 1.5Q

_{k}

N

_{Ed}= 1.35(620)

_{}+ 1.5(132) = 1035 kN

**Column Dimensions and Properties**

Depth (d) = 209.6mm

Width (b) = 205.8mm

Thickness of web (t

_{w}) = 9.4mm

Thickness of flange = (t

_{f}) = 14.2mm

Root radius (r) = 10.2mm

Perimeter of section = 1206.4mm

Area of section = 76.4 cm

^{2}

**Partial factor for resistance**

Î³

_{m0}= 1.0

Î³

_{m1}= 1.25

**Base Plate Details**

Strength of concrete = 25 N/mm

^{2}

Foundation bearing strength f

_{cd}= Î±

_{cc}f

_{ck}/Î³

_{c}

Take Î±

_{cc}= 0.85 (for axial compression)

Î³

_{c}= 1.5

Therefore;

f

_{cd}= (0.85 × 25)/1.5 = 14.167 N/mm

^{2}

Area of base plate required A

_{c0}= N

_{Ed}/ f

_{cd}= (1035 × 1000)/14.167 = 73057.104 mm

^{2}

Effective Area = 4c

^{2}+ (Section Perimeter × c) + Section Area

Where c is the cantilever outstand of the effective area. This is shown below;

73057.104

^{ }= 4c^{2}+ 1206.4c + 7640
On solving;

c = 46.924 mmCheck;

(h - 2t

_{f})/2 = (209.6 - 2 × 14.2) / 2 = 90.6mm

Since 90.6mm > 46.924 mm, there is no overlap between the flanges.

**Thickness of base plate (t**

_{p})t

_{p}= c[3f

_{cd}/ (f

_{y}Î³

_{m0})]

^{0.5}

_{p}= 46.924 × [(3 × 14.167) / (275 × 1.0)]

^{0.5}= 18.447 mm

Therefore provide a base plate of thickness t

_{p}= 20 mm in S275 material (since t

_{p}is less than 40mm).

**Connection of base plate to column**

It is assumed that the axial force is transferred by direct bearing, which is achieved by normal fabrication processes. Only nominal welds are required to connect the base plate to the column, though in practice full profile 6mm fillet welds are often used.

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