Prestressed Concrete Structures Questions and Answers – Methods of Optimisation

This set of Prestressed Concrete Structures Multiple Choice Questions & Answers (MCQs) focuses on “Methods of Optimisation”.

1. What is the first approach in optimization methods?
a) Theory of bending
b) Theory of layout
c) Theory of elongation
d) Theory of stress

Explanation: The first approach is the theory of layout in which the uniaxial structural members are arranged to yield a minimum volume structure for specified loads and materials based on the theorems established by Maxwell in 1854 and later developed and used by michell, cox and hemp.

2. During which period the simultaneous mode of failure approach was persued?
a) 1940 to 1950
b) 1930 to 1940
c) 1920 to 1930
d) 1910 to 1920

Explanation: During the period from 1940 to 1950, the simultaneous mode of failure approach was persued in which each component of the complete structure is at its limit of strength as the complete structure reaches the limit state of collapse and based on the classical ideas of function minimization, this approach was used to solve simple structural forms having a limited applicability to practical design.

3. The third major approach of structural optimization is based on the concept?
a) Criterion of design
b) Criterion of optimality
c) Criterion of texture
d) Criterion of span

Explanation: The third major approach of structural optimization is based on the concept developed by Prager and Taylor and this approach derived from the extremum principles of structural mechanics and after the advent of the finite element techniques, large scale computer programmes have been developed to demonstrate the practical utility of the optimality criterion approach to the design of minimum weight structures.

4. The structural optimization problem is generally expressed as __________
a) Maximize Z = F(x)
b) Minimize Z = F(x)
c) Z = F(x)
d) Z = F(t)

Explanation: The structural optimization problem is generally expressed in the mathematical form, involving the design variables, objective function and constraints accordingly the problem is expressed as:
Minimize Z = F(x), subject to Gj(x) < 0, j = 1,2….m
Where x is the design variable, represented by the column vector of dimensions n and each design represented by x is a point in hyper-space defined by the design variables, F(x) = the objective or merit function, Gj(x) = constraints, m = number of constraints.

5. What is the fourth major area of development?
a) Mathematical programming
b) Computer
c) Planning
d) Machine design

Explanation: The fourth major area of developed is the mathematical programming formulations, first applied to structural optimization problems by livesley and pearson an excellent survey of optimum structural design using mathematical programming procedure has been reported by schmit and the excellent example which users this method is the twenty five bar transmission tower reported by marcel and venkayya.
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6. What is a constraint?
a) Response
b) Parameter
c) Limitation
d) Principle

Explanation: A constraint is a limitation or restriction imposed directly on a variable or group of variables in order that the design is acceptable and they are expressed in the equality or inequality from and are divided into two groups and they are side constraints and behavior constraints.

7. The behavior constraints are those imposed on the __________
a) Cross sectional response
b) Structural response
c) Sequential response
d) Durability response

Explanation: Behavior constraints are those imposed on the structural response typical explicit behavior constraints are given by formulae presented in design specifications are generally non linear function of design variables are implicitly related to design variables.

8. In structural designs, behavior constraints are imposed on __________
a) Stresses
b) Strain
c) Reactions
d) Bending

Explanation: In structural designs, behavior constraints are usually imposed on stresses and displacements constraints prescribe the global rigidity of the structure side constraints are specified limitations (minimum or maximum) imposed on a design variable are usually explicit in form.

9. What is the objective function of a structural design problem?
a) Bending
c) Bondage
d) Costs

Explanation: In a structural design problem, there should be a well defined criterion by which the performance or cost of the structure can be judged under different combinations of the design variables and the index is generally referred to as the objective cost or merit function.

10. In the design of prestressed concrete structural elements, the objective function comprises cost of __________
a) Steel and concrete
b) Aggregates
c) Cement
d) Machines

Explanation: In the design of prestressed concrete structural element the objective function may comprise the cost of steel and concrete in the member and a general guide for selecting an objective function is that the design should be optimized with respect to the most important design property that can be meaningfully quantified and which is not constrained in advance.

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