Design of Steel Structures MCQs on “General Requirements for Plastic Design and Plastic Hinge”.
1. Which of the following assumptions is correct for plastic design?
a) material obeys Hooke’s law before the stress reaches fy
b) yield stress and modulus of elasticity does not have same value in compression and tension
c) material is homogenous and isotropic in both elastic and plastic states.
d) material is not sufficiently ductile to permit large rotations
Answer: c
Clarification: The material obeys Hooke’s law till the stress reaches fy. The yield stress and modulus of elasticity have the same value in compression and tension. The material is homogeneous and isotropic in both elastic and plastic states. The material is assumed to be sufficiently ductile to permit large rotations of section to take place.
2. Which of the following assumptions is not correct for plastic design?
a) plastic hinge rotations are small compared with elastic deformations so all the rotations are concentrated at plastic hinges
b) segments between plastic hinges are rigid
c) influence of normal and shear forces on plastic moments is not considered
d) plane section remains plane after bending and the effect of shear is neglected
Answer: a
Clarification: The plastic hinge rotations are large compared with elastic deformations so all the rotations are concentrated at plastic hinges. The segments between plastic hinges are rigid. The influence of normal and shear forces on plastic moments is not considered. The plane section remains plane even after bending and the effect of shear is neglected.
3. Which of the following are the conditions that stress strain characteristics of steel should obey to ensure plastic moment redistribution?
a) yield plateau should be less than 6 times the yield strain
b) ratio of ultimate tensile stress to yield stress should be less than 1.2
c) steel should not exhibit strain-hardening capacity
d) elongation on standard gauge length should be more than 15%
Answer: d
Clarification: The conditions that stress strain characteristics of steel should obey to ensure plastic moment redistribution are: (i) yield plateau(horizontal portion of stress strain curve) should be greater than 6 times the yield strain, (ii) ratio of ultimate tensile stress to yield stress should be more than 1.2, (iii) elongation on standard gauge length should be more than 15%, (iv) steel should exhibit strain-hardening capacity.
4. Which of the following conditions are true for using plastic method of analysis as per IS 800?
a) members shall not be hot-rolled or fabricated using hot-plates
b) yield stress of steel should not be greater than 450MPa
c) cross section should be unsymmetrical about its axis perpendicular to axis of plastic hinge rotation
d) cross section of members not containing plastic hinges should be ‘plastic’ and those members containing plastic hinges should be ‘compact’
Answer: b
Clarification: The following are conditions for using plastic method of analysis as per IS 800: (i) yield stress of steel should not be greater than 450MPa, (ii) members shall be hot-rolled or fabricated using hot-plates, (iii) cross section should be symmetrical about its axis perpendicular to the axis of plastic hinge rotation, (iv) cross section of members not containing plastic hinges should be ‘compact’ and those members containing plastic hinges should be ‘plastic’.
5. Which of the following is true regarding plastic design methods?
a) design needs to satisfy elastic strain compatibility conditions
b) different factor of safety for all parts of the structure
c) saving of material over elastic methods resulting in lighter structures
d) design is effected by temperature changes, settlement of support, etc