Understanding IS 800:2007 Web Slenderness Limits

The question concerns the limits specified by the Indian Standard IS 800:2007 for the web slenderness ratio (d/t_w) of steel members, particularly when the web does not have transverse stiffeners, focusing on serviceability conditions.

Defining the Web Slenderness Ratio

The web slenderness ratio is defined as the relationship between the clear depth of the web (d) and its thickness (t_w). A higher ratio implies a relatively thinner web, which increases susceptibility to buckling under load.

IS 800:2007 Guidelines for Webs

IS 800:2007, the primary standard for steel structure design in India, sets criteria to ensure the stability and safety of structural members. For webs that lack transverse stiffeners, specific limits on the d/t_w ratio are essential to prevent instability issues, especially concerning serviceability, which relates to the structure's performance under normal usage conditions.

The standard utilizes a factor known as the yield stress ratio, represented by $ \epsilon_w $, calculated using the formula:

$$ \epsilon_w = \sqrt{\frac{250}{f_y}} $$

Here, f_y represents the characteristic yield strength of the steel material in N/mm².

Limit for Unstiffened Webs

As per IS 800:2007 provisions for members where the web is not provided with transverse stiffeners, the serviceability requirement dictates that the web slenderness ratio must not exceed a specified limit. This limit is given by:

$$ \frac{d}{t_w} \le 200 \epsilon_w $$

This condition ensures the web's stability against buckling modes under typical service loads, contributing to the overall serviceability of the structure.

Evaluating the Options

The calculated limit based on the standard is $ 200 \epsilon_w $. Let's compare this to the provided options:

• $ 400 \epsilon_w $
• $ 250 \epsilon_w $
• $ 200 \epsilon_w $
• $ 150 \epsilon_w $

The limit stated in IS 800:2007 for unstiffened webs under serviceability conditions corresponds to $ 200 \epsilon_w $. Therefore, the correct option is the one matching this value.