Question

A slab base for a column ISHB 350@710.2 N/m is subjected to a factored axial compressive load of 2000 kN. Load is transferred to the base plate by direct bearing of column flanges. The depth of the section and width of the flange are 350 mm and 250 mm respectively . The minimum thickness of slab base is _______mm. [Assume square base plate of 500 mm size and concrete of M20 grade,
$f_y=250N/m{m}^2$]

• A. 36

Answer 1

The correct option is A 36
Bearing strength of concrete
$=0.45f_{ck}$

$=0.45\times 20=9.0N/m{m}^2$

Given, a base plate of 500 mm x 500 mm in size.

The bearing pressure of concrete,

$w=\frac{p}{A_1}=\frac{2000\times {10}^3}{500\times 500}=8N/m{m}^2<9.0N/m{m}^2$

Which is all right

The greater projection,
$a=\frac{500-250}{2}=125mm$

The smaller projection,
$b=\frac{500-350}{2}=75mm$

Thickness of slab base ,

$t=\sqrt{2.5w(a^2-0.3b^2)\frac{Y_{m0}}{f_y}}$

$=\sqrt{2.5\times 8\times ({125}^2-0.3\times {75}^2)\frac{1.1}{250}}=35.02mm\simeq 36mm$

Hence minimum thickness of base plate is 36 mm.