When considering the design and construction of steel structures, adherence to specific codes of practice is essential to ensure safety and durability. The question refers to the 'Indian Standard General Construction in Steel- Code of practice', which governs various aspects of steel fabrication, including welding.

Deep Penetration Welds in Steel Construction

Deep penetration welds are a type of fillet weld where the fusion extends significantly into the base metal beyond the visible root of the weld. This deeper fusion effectively increases the load-carrying capacity of the weld. The Indian Standards, such as IS 800 (Code of Practice for General Construction in Steel), provide guidelines on how to account for this increased penetration when determining the effective size of the fillet weld.

The primary benefit of deep penetration welds is that for a given nominal leg size, they achieve a greater effective throat thickness. This means they can either carry more load or allow for a smaller nominal leg size to achieve the same strength as a conventional fillet weld.

Fillet Weld Sizing with Deep Penetration

The question specifies that the depth of penetration beyond the root run is a minimum of 2.4 mm. According to the provisions outlined in the Indian Standard for deep penetration welds, this additional depth directly contributes to the effective size of the fillet weld. To calculate the effective size of such a fillet weld, this penetration depth is added to the minimum leg size.

The formula for calculating the effective fillet weld size for deep penetration welds, as per the relevant Indian Standard, is:

\( \text{Effective Fillet Weld Size} = \text{Minimum Leg Size} + \text{Depth of Penetration Beyond Root Run} \)

Given the depth of penetration beyond the root run is 2.4 mm, the formula becomes:

\( \text{Effective Fillet Weld Size} = \text{Minimum Leg Size} + 2.4 \text{ mm} \)

Let's evaluate the provided options based on this standard practice:

• Option 1: Minimum leg size – 2.4 mm. This option suggests subtracting the penetration depth. This is incorrect because deep penetration enhances the weld's effective size and strength, rather than reducing it.
• Option 2: Minimum leg size + 2.4 mm. This option correctly reflects the provision in the Indian Standard. The additional 2.4 mm of penetration directly contributes to the effective size of the fillet weld, increasing its capacity.
• Option 3: Maximum leg size + 2.4 mm. While leg size is important, the calculation for effective weld size with deep penetration typically starts from the 'minimum' required leg size for design purposes, not a 'maximum' leg size. This option is not aligned with standard design practices for accounting for penetration.
• Option 4: Minimum leg size + (2*2.4) mm. This option implies multiplying the penetration depth by two. The Indian Standard specifies that the actual measured or guaranteed depth of penetration is added, not a multiple of it.

Therefore, the correct way to determine the size of the fillet for deep penetration welds, where the depth of penetration beyond the root run is a minimum of 2.4 mm, is by adding this penetration depth to the minimum leg size.