This set of Prestressed Concrete Structures online test focuses on “Application to Prestressed Structures”.
1. In the design of prestressed concrete structural elements the objective is:
a) Total cost of member
b) Design of the member
c) Economy of the member
d) Foundation of the member
Explanation: The objective or merit function is generally the total cost of the member per unit length comprising the individual costs of concrete, high tensile steel and supplementary reinforcement and in a typical flexural member, the objective function can be expressed as: F(x) = CcA+CsAs+CpAp, F(x) = cost of the member unit length, CcCsCp = unit costs of concrete supplementary and high tensile steel respectively, ApAsAp = areas of concrete supplementary of high tensile steel and respectively.
2. The stresses developed at the top and bottom fibres of the critical section developed at:
a) Stages of stresses
b) Stages of deflection
c) Stages of transfer
d) Limits of transfer
Explanation: Stresses are developed at the top and bottom fibres of the critical section at the stages of transfer of prestress and under service loads these conditions yield four inequalities expressed as:
(p/a –pe/zt + Mg/zl) > fu, (p/a+pe/zb-Mg/zb) < fct
(p/a-pe/zt+mg+mq/zt) < fcw, (p/a+pe/zb-mg+mq/zb) > ftw.
3. The deflection constraint at the limit state of serviceability is taken as:
a) a < ap
b) a > ap
c) a > ae
d) a < ae
Explanation: Where a and ap are the actual and permissible deflection, which is usually a small fraction of the span code requirements for the limit state of collapse to ensure desirable load factors against flexural failure which can be written as Mu > (δf1Mg+δf2Mq).
4. The limitation on the minimum and maximum ratios of reinforcements is expressed as:
a) ρmin < ρ < ρmax
b) ρmin < ρ
c) ρ < ρmax
d) ρmin > ρ > ρmax
Explanation: ρmin < ρ < ρmax where ρ is the ratio of reinforcement provided ρmin is the minimum ratio required to prevent to prevent failure by fracture of steel in tension, ρmax is the maximum permissible ratio to ensure failure of the section by yielding of steel.
5. In case of partially prestressed members cracks of limited width are permissible under:
a) Deflection loads
b) Working loads
c) Tensile loads
Explanation: In the design of fully prestressed (class 2) members, all the constraints as given in a < ap, ρmin < ρ < ρmax are not valid, however in this case of partially prestressed members where cracks of limited width of permissible under working loads an additional constraint to impose limitations on the width of crack is required and this can be expressed as: w < wp, w = actual widt, wp = permissible crack width.
6. The additional constraints are imposed on the geometrical dimensions of:
a) Cross section
Explanation: The additional constraints are imposed on the geometrical dimensions of the cross section such as the minimum thickness of the web and bottom flange, based on practical requirements of housing the cables with due regard to cover requirements and the constraints being non linear the optimal solution is obtained by the non linear programming techniques.
7. The complete definition of the optimum design of prestressed beams for class 1:
a) 24 constraints
b) 27 constraints
c) 23 constraints
d) 20 constraints
Explanation: The complete definition of the optimum design of prestressed beams for class 1 is 24 and
the complete definition of the optimum design of prestressed beams involves 27 constraints for class 2, 26 constraints for class 2 and 40 constraints for class 3 structure and further, they have reported a saving of 60 percent in high tensile steel in class 3 structure design when compared with a fully prestressed class1 structure design and however their studies on a 40m long higway bridge has also revealed that the cost wise savings in class 2 and 3 structure designs are nearly 14.3 and 9.4 percent in comparison with class 1 structure design.
8. Which elements were standardized and tabulated for design office use:
a) Bridge girders
b) Span Girders
c) Foundation girders
d) Transverse girders
Explanation: Optimization studies as applied to prestressed concrete structures have been pursued during the last decade and some organizations have developed practical programmes for the analysis and design of simple structures like highway bridge girders comparative cost studies have been standardized and tabulated for design office use by using computer programmes developed at the structural engineering research centre.
9. Optimization studies were conducted for slabs of type:
b) Post tensioning
c) Partially prestressed slabs
d) Limited slabs
Explanation: Bond has reported optimization studies on partially prestressed in which several parameters, such as span, volume of the prestressing wire and steel bar reinforcements, cube strength, thickness of the slab and permissible tensile stress are examined in relation to the total cost of the slab per unit area.
10. The structural shapes, unit costs are assumed without considering:
a) Machines used
b) Site conditions
Explanation: Many of the studies have included only a few variables and invariably the structure and shapes, unit costs of labour and materials are assumed without considering the specific site conditions and constructional techniques which can have a greater influence on the overall costs of the structural scheme and further studies in this field should include cost estimates of alternative schemes, formwork design, probabilistic design considering the variability of load applications and materials properties.
Sanfoundry Global Education & Learning Series – Prestressed Concrete Structures.
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