7.4Column Bases

IS 800:2007, General Construction in Steel — Code of Practice

Last Updated 29 Oct 2026

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7.4.1 General

Column bases should have sufficient stiffness and strength to transmit axial force, bending moments and shear forces at the base of the columns to their foundation without exceeding the load carrying capacity of the supports. Anchor bolts and shear keys should be provided wherever necessary. Shear resistance at the proper contact surface between steel base and concrete/grout may be calculated using a friction coefficient of 0.45.

The nominal bearing pressure between the base plate and the support below may be determined on the basis of linearly varying distribution of pressure. The maximum bearing pressure should not exceed the bearing strength equal to $0.6 f_{\mathrm{ck}}$ , where $f_{\mathrm{ck}}$ is the smaller of characteristic cube strength of concrete or bedding material.

7.4.1.1

If the size of the base plate is larger than that required to limit the bearing pressure on the base support, an equal projection $c$ of the base plate beyond the face of the column and gusset may be taken as effective in transferring the column load as given in Fig. 9, such that bearing pressure on the effective area does not exceed bearing capacity of concrete base.

7.4.2 Gusseted Bases

For stanchion with gusseted bases, the gusset plates, angle cleats, stiffeners, fastenings, etc, in combination with the bearing area of the shaft, shall be sufficient to take the loads, bending moments and reactions to the base plate without exceeding specified strength. All the bearing surfaces shall be machined to ensure perfect contact.

7.4.2.1

Where the ends of the column shaft and the gusset plates are not faced for complete bearing, the weldings, fastenings connecting them to the base plate shall be sufficient to transmit all the forces to which the base is subjected.

7.4.2.2 Column and base plate connections

Where the end of the column is connected directly to the base plate by means of full penetration butt welds, the connection shall be deemed to transmit to the base all the forces and moments to which the column is subjected.

7.4.3 Slab Bases

Columns with slab bases need not be provided with gussets, but sufficient fastenings shall be provided to retain the parts securely in place and to resist all moments and forces, other than direct compression, including those arising during transit, unloading and erection.

7.4.3.1

The minimum thickness, $t_{\mathrm{s}}$ , of rectangular slab bases, supporting columns under axial compression shall be

$t_{\mathrm{s}}=\sqrt{2.5 w\left(a^{2}-0.3 b^{2}\right) \gamma_{\mathrm{m} 0} / f_{\mathrm{y}}} \quad>t_{\mathrm{f}}$

where

$\begin{aligned} w & =\text { uniform pressure from below on the slab } \\ & \text { base under the factored load axial } \\ & \text { compression; }\end{aligned}$
$a, b=$ larger and smaller projection, respectively of the slab base beyond the rectangular circumscribing the column; and
$\begin{aligned} t_{\mathrm{f}} & =\text { flange thickness of compression member }\end{aligned}$

When only the effective area of the base plate is used as in 7.4.1.1, $c^{2}$ may be used in the above equation (see Fig. 9) instead of $\left(a^{2}-0.3 b^{2}\right)$ .

7.4.3.2

When the slab does not distribute the column load uniformly, due to eccentricity of the load etc., special calculation shall be made to show that the base is adequate to resist the moment due to the non-uniform pressure from below.

7.4.3.3

Bases for bearing upon concrete or masonry need not be machined on the underside.

7.4.3.4

In cases where the cap or base is fillet welded directly to the end of the column without boring and shouldering, the contact surfaces shall be machined to give a perfect bearing and the welding shall be sufficient to transmit the forces as required in 7.4.3. Where full strength butt welds are provided, machining of contact surfaces is not required.