(SEM VII) THEORY EXAMINATION 2017-18 DESIGN OF STEEL STRUCTURES

SECTION A

(Short questions – explained clearly)

1. What is meant by buckling of a column?

Buckling of a column is a failure mode in which a compression member suddenly bends sideways when the applied load exceeds a critical value. This failure occurs even when the stress in the column is less than the yield stress of steel. Buckling mainly depends on the length of the column, end conditions, and slenderness ratio. It is a dangerous type of failure because it happens suddenly without warning.

2. What do you mean by laterally restrained beam?

A laterally restrained beam is a beam whose compression flange is prevented from moving sideways by adequate supports or bracing. Lateral restraint helps in preventing lateral torsional buckling of the beam. When a beam is properly restrained, it can carry higher bending moments safely and behaves more efficiently under load.

SECTION B

(Medium questions – conceptual explanation)

3. Distinguish between Working Stress Method, Ultimate Strength Method, and Limit State Design.

The Working Stress Method is based on elastic behavior of materials and uses permissible stresses by applying a factor of safety. It does not consider ultimate strength and is considered conservative.
The Ultimate Strength Method is based on the ultimate load-carrying capacity of the structure and applies load factors to reach failure conditions. However, it ignores serviceability aspects.
Limit State Design is the modern method adopted in IS 800:2007. It considers both safety and serviceability by checking structures against different limit states such as strength and deflection, providing a more realistic and economical design.

4. What is prying action in bolted connections?

Prying action occurs in bolted joints when the connected plates bend under tension and produce additional forces in the bolts. This increases the tensile force in bolts beyond the applied load. Prying action is common in flexible connections and must be considered in design to avoid bolt failure. Proper plate thickness and stiffening help reduce prying action.

SECTION C

(Long questions – detailed explanation)

5. What are the main objectives of a structural engineer while designing steel structures?

The main objective of a structural engineer is to design a steel structure that is safe, economical, and functional. Safety ensures that the structure can resist all expected loads without failure. Economy ensures optimal use of material without unnecessary cost. Serviceability ensures acceptable deflection and vibration limits. Durability, ease of construction, and compliance with codes such as IS 800:2007 are also important objectives.

6. Explain local buckling and lateral buckling of beam members.

Local buckling occurs when individual elements of a beam such as flange or web buckle without overall bending of the member. It usually happens in thin plates under compression.
Lateral buckling, also called lateral torsional buckling, occurs when a beam bends and twists sideways due to lack of lateral restraint on the compression flange. It reduces the load-carrying capacity of the beam and can be prevented by providing proper bracing.