**Introduction:** The slenderness effect is a crucial consideration in structural engineering, particularly in the design of walls. It involves evaluating the impact of the ratio between the effective height and thickness of a wall on its structural behavior. In this context, the slenderness effect becomes significant when the effective height of the wall exceeds its thickness. This case study explores the implications of the slenderness effect and its application in structural design.

**Step 1: Definition of Slenderness Effect:** The slenderness effect refers to the change in the structural behavior of a wall when its effective height becomes relatively large compared to its thickness. It is a phenomenon that becomes particularly notable in slender elements, where stability considerations become critical.

**Step 2: Determination of Effective Height:** The effective height of a wall is a key parameter in assessing the slenderness effect. It is not merely the physical height of the wall but accounts for the end conditions and support conditions. Effective height is influenced by factors such as boundary conditions, fixity, and lateral restraints, and it is crucial to accurately determine this parameter for a comprehensive analysis.

**Step 3: Significance of Slenderness Effect:** The slenderness effect has significant implications for the design of walls. When the effective height exceeds the thickness, the wall becomes more prone to buckling or instability. This can result in reduced load-carrying capacity and may necessitate additional structural measures, such as the introduction of bracing or reinforcement, to address the slenderness-induced challenges.

**Step 4: Design Considerations:** In structural design, considering the slenderness effect involves evaluating the critical slenderness ratio (effective height to thickness ratio) of a wall. Design codes often provide guidelines and limits for this ratio to ensure the stability and safety of the structure. Engineers must carefully assess the slenderness effect during the design phase to prevent unexpected failures and ensure the structural integrity of the wall.

**Objective Type Question:** When is the slenderness effect of a wall considered significant in structural design?

A. When the thickness of the wall exceeds its effective height.

B. When the effective height of the wall exceeds its thickness.

C. When both the effective height and thickness are equal.

D. When the wall has lateral restraints.

Please choose the correct option and provide a brief explanation for your choice based on the information provided in the case study.