Understanding Slenderness of Bracing Members

The question asks about the maximum limit for the slenderness ratio of bracing members in structural applications. Slenderness ratio is a crucial parameter in structural design, especially for compression members, as it significantly affects their buckling strength.

What is Slenderness Ratio?

The slenderness ratio ($\lambda$) of a structural member is defined as the ratio of its effective length ($L_e$) to its least radius of gyration ($r_{min}$). Mathematically, it is represented as:

$$ \lambda = \frac{L_e}{r_{min}} $$

A higher slenderness ratio generally indicates a greater tendency for the member to buckle under compressive loads. Structural codes specify maximum permissible slenderness ratios for different types of members based on their function and whether they are subjected to compression or tension, to ensure stability and prevent premature buckling.

Slenderness Limit for Bracing Members

Bracing members are used in structures, often in frames, to resist lateral loads (like wind or seismic forces) and to provide stability by preventing the main structural members from buckling or deforming excessively. Depending on whether the bracing member is designed to carry compressive forces, tensile forces, or both, different slenderness limits apply.

For members acting as bracing that are subjected to compressive stresses resulting from dead and superimposed loads, the Indian Standard code IS 800:2007 specifies various slenderness limits. A common limit specified in codes for members that are primarily tension members but may experience some minor compression (like in some bracing systems) or for bracing systems that are crucial for stability is often around 120 or 180, depending on the specific context and code version.

Considering the options provided:

• 1. 200
• 2. 180
• 3. 120
• 4. 150

While different slenderness limits exist for various structural members (e.g., 180 for members normally acting as tension members but subject to reversal of stress, or 250/350 for members always in tension), the limit of 120 is a specific limit often applicable to compression members in certain bracing systems where buckling resistance is critical for load transfer or stability.

Based on standard design practices and common code provisions for bracing members subject to potential compression, the value of 120 is a permissible limit that shall not be exceeded in specific scenarios to ensure adequate buckling resistance.

Therefore, among the given options, 120 represents a valid maximum slenderness limit for certain bracing members as per structural design codes.