Design of Steel Structures Multiple Choice Questions on “Cross Sectional classification”.
1. Which of the following factor is considered for classification of cross section?
a) location where member is used
b) width-to-thickness ratio
c) length of member
d) seismic force
Answer: b
Clarification: Cross section are classified into four behavioural groups depending upon the material yield strength, width-to-thickness ratio of individual components (e.g. webs and flanges) within the cross section, and the loading arrangement.
2. What is a plastic section?
a) cross section which can develop plastic moment
b) cross section which can resist seismic force
c) cross section in which buckling can occur
d) cross section which can develop plastic hinges
Answer: d
Clarification: Plastic or class I sections are cross sections which can develop plastic hinges and have a rotation capacity required for failure of structure by formation of plastic mechanism.
3. What is a compact section?
a) cross section which can develop plastic moment resistance
b) cross section which can resist seismic force
c) cross section in which buckling can occur
d) cross section which can develop plastic hinges
Answer: a
Clarification: Compact or class II sections are cross sections which can develop plastic moment resistance, but have inadequate plastic hinge rotation capacity because of local buckling.
4. What is a semi-compact section?
a) cross section which can develop plastic moment resistance
b) cross section which can resist seismic force
c) cross section in which elastically calculated stress in extreme compression fibre can reach yield strength
d) cross section which can develop plastic hinges
Answer: c
Clarification: Semi-compact or class III sections are cross sections in which elastically calculated stress in extreme compression fibre of steel can reach yield strength.
5. What is a slender section?
a) cross section which can develop plastic moment resistance
b) cross section which can resist seismic force
c) cross section in which elastically calculated stress in extreme compression fibre can reach yield strength
d) cross section in which local buckling will occur before yield stress
Answer: d
Clarification: Slender or class IV sections are cross section in which local buckling occurs even before the yield stress is attained in one or more parts of the cross section.
6. Which of the following is correct regarding class I section?
a) They are not fully effective under pure compression
b) They are capable of reaching and maintaining full plastic moment in bending
c) They are not capable of reaching and maintaining full plastic moment in bending
d) They does not exhibit sufficient ductility
Answer: b
Clarification: Class I sections are fully effective under pure compression, and capable of reaching and maintaining full plastic moment in bending and hence used in plastic design. These sections will exhibit sufficient ductility.
7. Match the following design moment capacity with the classes of cross section
Cross section Design moment capacity
i) Compact A) Md = Zpfy
ii) Semi-Compact B) Md < Zefy
iii) Plastic C) Md = Zefy
iv) Slender
a) i – B, ii – C, iii – A, iv – B
b) i – A, ii – B, iii – C, iv – B
c) i – A, ii – C, iii – A, iv – B
d) i – C, ii – C, iii – A, iv – B
Answer: c
Clarification: The design moment capacity Md of each of the four classes of cross sectioncan be calculated as i) Plastic – Md = Zpfy, ii) Compact – Md = Zpfy, iii) Semi-Compact – Md = Zefy, iv) Slender – Md < Zefy, where Zp = plastic modulus, Ze = elastic modulus.
8. Which of the following statement is correct?
a) Internal elements are elements attached along both longitudinal edges to other elements
b) Outstanding elements are elements attached along both longitudinal edges to other elements
c) Outstanding elements are elements which are free along both the edges
d) Internal elements are elements which are free along both the edges
Answer: a
Clarification: Internal elements are elements attached along both longitudinal edges to other elements or to longitudinal stiffeners connected at suitable intervals to transverse stiffeners connected at suitable intervals to transverse stiffeners (e.g. web of I-sections and flange and web of box sections). Outstanding elements are attached along only one of the longitudinal edges to an adjacent element, the other edge being free to displace out of plan (e.g. flange overhang of an I-section, stem of T-section, leg of angle section).