ISHB 250 Buckling Class Determination (Y-Y Axis)

To determine the buckling class of a compression member as per IS 800:2007, we need to consider the type of cross-section, its dimensions, and the axis of buckling. The relevant information for classifying the buckling class of steel sections is provided in Table 10 of IS 800:2007.

Section Properties and Axis of Buckling

The given section is a rolled ISHB 250. The provided dimensions are:

• Depth of section (h) = 250 mm
• Width of flange (b_f) = 250 mm
• Thickness of web (t_w) = 8.8 mm
• Thickness of flange (t_f) = 9.7 mm

The buckling is considered about the Y-Y axis, which is the major axis for ISHB sections.

IS 800:2007 Criteria for Buckling Class

According to Table 10 of IS 800:2007, for rolled I-sections buckling about the y-y axis (major axis), the buckling class depends on the ratio of depth to flange width (h/b_f) and the thickness of the flange (t_f). The criteria are typically:

• If h/b_f > 1.2 and t_f <= 40 mm, the buckling class is 'b'.
• If h/b_f > 1.2 and t_f > 40 mm, the buckling class is 'c'.
• If h/b_f <= 1.2, the buckling class is 'c'.

Calculation of h/b_f Ratio

Let's calculate the ratio of the depth of the section (h) to the width of the flange (b_f) for the given ISHB 250 section:

\(\frac{h}{b_f} = \frac{250 \text{ mm}}{250 \text{ mm}} = 1.0\)

The thickness of the flange is t_f = 9.7 mm.

Applying the Criteria

We have h/b_f = 1.0 and t_f = 9.7 mm. We are considering buckling about the Y-Y axis (major axis).

Checking the criteria from IS 800:2007 Table 10 for buckling about the y-y axis:

• Is h/b_f > 1.2? No, \(1.0 \not> 1.2\).
• Is h/b_f <= 1.2? Yes, \(1.0 \le 1.2\).

According to the criteria, if h/b_f <= 1.2, the buckling class for a rolled I-section buckling about the y-y axis is 'c'.

Buckling Class Conclusion

Based on the dimensions of the ISHB 250 section and the criteria specified in IS 800:2007 for buckling about the Y-Y axis, the ratio h/b_f is 1.0, which is less than or equal to 1.2. Therefore, the corresponding buckling class for this compression member is 'c'.