This set of Prestressed Concrete Structures Multiple Choice Questions & Answers (MCQs) focuses on “Design Loads and Strengths”.
1. The design loads for various limit states are obtained as product of the:
a) Characteristic loads
b) Seismic loads
c) Ultimate loads
d) Wind loads
Explanation: The design loads for various limit states are obtained as products of the characteristic loads and partial safety factor and are expressed as:
Fd = γf Fk, where Fd = appropriate design load, γf = partial safety factor for loads, Fk = characteristic load.
2. The characteristic load is expressed as:
a) Mean load – K x standard deviation
b) Mean load + K x standard deviation
c) Load – standard deviation
d) Load + standard deviation
Explanation: The characteristic load Fk which is independent of the limit state considered and is seldom exceeded in service is defined as: Characteristic load = Mean load + K x standard deviation, K is a factor so chosen as to ensure that the probability of the characteristic load being exceeded is small and a value of 1.64 for K ensures the probability that the characteristic load is exceeded by only 5 percent during the intended life of the structure.
3. The statistical data required to define the characteristic loads, need recording of data and:
Explanation: The statistical data required to define the characteristic loads for different types of occupancy is not readily available, since loading statistics are invariably difficult to compile as they need a systematic observations and recording of data on loading and the nominal imposed loads provided in various national codes, such as IS: 875-1987, BS: 6399 may be treated as characteristic loads.
4. The characteristic values of the loads take account of expected variations but do not allow for:
a) Variations in stress
b) Variations in dimensional accuracy
c) Variation in strain
d) Variation in loads
Explanation: The characteristic values of the loads take account of expected variations but do not allow possible unusual increases in load beyond those considered in deriving the characteristic load, in accurate assessment of effects of loading and unforeseen stress distribution within the structure and variations in dimensional accuracy achieved in construction.
5. The values of partial safety factors are recommended for:
Explanation: Partial safety factor γf are therefore used for each limit state being reached and the values of partial safety factors for loads recommended in the British, Indian and American codes and FIP recommendations.
6. The design strength of materials is expressed as:
a) Fd = Fe / γk
b) Fd = Fc / γk
c) Fd = Fk / γm
d) Fd = Fd / γm
Explanation: FIP recommendations regarding partial safety factors are comprehensive, as they provide for a combination coefficients for basic variable actions as well as for other variable factors depending upon different types of structures, such as dwellings, offices, parking area and highway bridges and the design strength of materials are expressed as: Fd = Fk / γm.
7. The term WL is termed as:
a) Wind load
c) Live load
d) Wall load
Explanation: DL is the dead load, LL is the live load and WL is the wind load while considering earthquake effects substitute EL for WL and these loads are considered while calculation of loads and deflections of the beam.
8. In characteristic strength of the material, the tensile strength of tendons below which the failure are not more than:
Explanation: Fk is the characteristic strength of the material which corresponds to the 28 days cube strength compressive strength of concrete or the tensile strength of tendons below which the failures are not more than 5 percent.
9. The characteristic strengths of concrete and steel may be taken as the works cube strength and:
a) Yield strength
d) Principle strength
Explanation: In the absence of statistical data, the characteristic strengths of concrete and steel may be taken as the works cube strength and the specified proof or yield strength respectively as provided for in the codes.
10. The partial safety factor (γm) for materials has a value which depends upon the importance of the:
a) Principal sates
b) Limit states
c) Strain states
d) Stress states
Explanation: The partial safety factor (γm) for materials has a value depends upon the importance of limit states being considered, materials when tested and when incorporated in construction during service life of the structure.
Sanfoundry Global Education & Learning Series – Prestressed Concrete Structures.
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