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This set of Design of Steel Structures Multiple Choice Questions & Answers (MCQs) focuses on “Plastic-Collapse Load”.

a) load at which sufficient number of elastic hinges are formed
b) load at which sufficient number of plastic hinges are not formed
c) load at which sufficient number of plastic hinges are formed
d) load at which structure fails

Explanation: The load at which sufficient number of plastic hinges are formed in a structure such that a collapse mechanism is created is called plastic-collapse load or plastic-limit load.

2. What is difference between plastic design and elastic design?
a) In plastic design, redistribution of bending moment is considered
b) In plastic design, redistribution of bending moment is not considered
c) In elastic design, redistribution of bending moment is considered
d) Both in plastic and elastic design, redistribution of bending moment is considered

Explanation: The difference between plastic design and elastic design is that plastic design takes into account the favourable redistribution of bending moment which takes place in indeterminate structure after first hinge forms at the point of maximum bending moment.

3. Which of the following is true in a fixed beam having concentrated load at one-third point?
a) first hinge is formed at centre of beam
b) after first hinge, moment at that point increases
c) after first hinge, moment at that point decreases
d) after first hinge, moment at that hinge remains constant

Explanation: In a fixed beam having concentrated load at one-third point, first hinge forms at one of the end supports. As load is increased further, moment at this hinge remains constant at Mp, while the moments at the other support and load point increase until second hinge is formed. When load is further increased, the moment at these two hinges remain constant at Mp, until third and final hinge is formed to make the beam a mechanism. The final ultimate load will be 33% higher than first hinge load.
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4. In a fixed beam having concentrated load at one-third point, final ultimate load will be ____ than first hinge load.
a) 33% lower
b) 33% higher
c) 50% higher
d) 50% lower

Explanation: In a fixed beam having concentrated load at one-third point, final ultimate load will be 33% higher than first hinge load.

5. Which of the following statement is correct?

Explanation: Plastic limit load is obtained by multiplying working load with load factor. Depending on combination of loads and their probability of acting at same time, different load factors are used.

6. Cantilevers and over hanging beams collapse as _____
a) single-bar mechanism
b) double-bar mechanism
c) three-bar mechanism
d) does not collapse

Explanation: Cantilevers and over hanging beams generally collapse as single-bar mechanisms with a single plastic hinge at one of the supports.

7. Single-span beams collapse as ________
a) single-bar mechanism
b) two-bar mechanism
c) three-bar mechanism
d) does not collapse

Explanation: Single-span beams generally collapse as two-bar mechanisms with a hinge at each support and plastic hinge within the span.

8. Multi-span beams collapse in one span as ___________
a) does not collapse
b) single-bar mechanism
c) two-bar mechanism
d) three-bar mechanism

Explanation: Multi-span beams generally collapse in one span as a local two-bar mechanism, within the span and a hinge at each support. It is possible to have a three-bar mechanism, where two adjacent spans combine to form a mechanism.

9. Among which of the following is the location of plastic hinge?
a) at supports
b) at centre of beam
c) at points away from concentrated load
d) at centre for uniformly distributed load

Explanation: Plastic hinges normally occur at supports, points of concentrated load, and points where cross section change. The location of plastic hinge in a beam with uniformly distributed load is not well defined.