Understanding Batten Thickness in Steel Structures as per IS:800-2007

Battens are structural elements used in built-up compression members, like columns, which consist of two or more components connected together. They serve to tie the individual components together and ensure they act as a single unit, transferring shear forces and preventing buckling of the individual parts between connections.

The design of these battens, including their minimum thickness, is governed by specific clauses in relevant standards such as the Indian Standard IS:800-2007, which is the code of practice for general construction in steel.

Minimum Thickness Requirement for Battens (IS:800-2007)

According to Clause 7.7.2.1 of IS:800-2007, which deals with the design of battens, there are specific requirements regarding the dimensions of the batten plates to ensure adequate stiffness and strength.

One crucial requirement is the minimum thickness of the batten plate. The clause states that the thickness of the batten plate, denoted as 't', shall not be less than one-fiftieth of the distance between the innermost connecting lines of rivets or welds perpendicular to the main member.

The question defines this distance as \(I_b\). Therefore, as per IS:800-2007, the minimum thickness 't' must satisfy the condition:

$$t \ge \frac{I_b}{50}$$

This means the thickness 't' cannot be less than \(I_b/50\).

Analyzing the Given Options

Let's compare the derived minimum thickness requirement with the options provided:

1. \(I_b/20\)
2. \(I_b/30\)
3. \(3( I_b/20)\)
4. \(I_b/50\)

The requirement from IS:800-2007 is that 't' shall not be less than \(I_b/50\). Option 4 directly matches this condition.

Options 1, 2, and 3 represent values that are greater than \(I_b/50\) (since \(1/20 > 1/50\), \(1/30 > 1/50\), and \(3/20 > 1/50\)). While a greater thickness would satisfy the 'not less than' condition, the question asks for the minimum value specified by the code.

Thus, the minimum thickness specified by the code is \(I_b/50\).

Conclusion on Minimum Batten Thickness

Based on the provisions of IS:800-2007 for the design of battens, the thickness of the batten plate ('t') must not be less than the distance between the innermost connecting lines of rivets or welds perpendicular to the main member ('\(I_b\)') divided by 50.

Therefore, the minimum thickness allowed for the batten 't' is \(I_b/50\).

Revision Table: Batten Thickness IS:800-2007

Additional Information on Batten Design in Steel Structures

Beyond minimum thickness, IS:800-2007 provides other essential requirements for batten design to ensure the stability and strength of built-up members:

• Batten System Design: Battens must be designed to resist the transverse shear force and longitudinal force arising from moments between the battens.
• Length of Batten: The effective depth of battens parallel to the main member (longitudinally) must be not less than twice the width of the narrower main member or not less than three-fourths of the distance between the centroids of the main members, whichever is greater.
• Spacing of Battens: The spacing of battens depends on the slenderness ratio requirements of the individual components between the battens and the overall slenderness ratio of the built-up column. The slenderness ratio of the unsubdivided member between two adjacent battens must be less than 50 and also less than 0.7 times the slenderness ratio of the overall built-up member.
• Connections: Connections of battens to the main members must be designed to transfer the calculated shear and moment.
• Transverse Shear: The batten system must be designed for a transverse shear equal to 2.5% of the total axial force in the member.

Adhering to all these requirements is crucial for the safe and efficient design of built-up steel compression members using battens.