JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech III STRUCTURAL ENGINEERING - II (STEEL) Previous Question Paper (August/September - 2021 - R18)

In the limit state method, a structure is designed to ensure it remains fit for its intended use throughout its design life. This is achieved by satisfying two primary categories of limit states:

1. Limit State of Strength (Ultimate Limit State): This relates to the safety of the structure against collapse or failure. It involves ensuring the structure can withstand the maximum design loads without reaching a state of instability. Key considerations include:

• Loss of equilibrium of the structure or any part of it.
• Failure by excessive deformation (plastic collapse).
• Rupture or fracture of members or connections.
• Instability due to buckling (local or global).
• Fatigue failure under cyclic loading.

2. Limit State of Serviceability: This ensures the structure remains functional and comfortable for users under normal working loads. It focuses on the aesthetic and operational performance of the structure, including:

• Deflection limits to prevent damage to finishes or partitions.
• Vibration control to ensure occupant comfort.
• Corrosion and durability requirements.
• Crack control in reinforced concrete elements (where applicable).

Bolted connections fail due to the interaction between the bolt and the connected plates. The primary modes of failure are:

1. Shear Failure of Bolts: Occurs when the bolt shank is sheared off across its cross-section due to the applied load exceeding the shear capacity of the bolt material.
2. Bearing Failure of Plates or Bolts: Occurs when the bearing stress between the bolt and the plate exceeds the allowable limit, leading to localized crushing of the plate or deformation of the bolt hole.
3. Tension Failure of Plates: The plate fails in tension across the net section (the section containing the bolt holes). This is often referred to as tearing of the plate.
4. Shear Block Failure: A combination of shear failure along the longitudinal plane and tension failure along the transverse plane, causing a block of material to tear out from the end of the plate.
5. Splitting or Tearing Failure: Occurs when the edge distance is insufficient, causing the plate to split or tear along the line of bolts towards the edge.

Sketches would typically illustrate a plate with a bolt hole showing: (i) the bolt shearing in half, (ii) the bolt hole elongating (bearing), (iii) the plate snapping across the hole (tension), and (iv) a rectangular block of the plate being pulled out (block shear).