Prestressed Concrete Structures MCQ Set 1
1. The initial prestress in concrete with ongoing time undergoes?
Answer: a [Reason:] The initial prestress in concrete undergoes a gradual reduction with time from the stage of transfer due to various causes and this is generally referred to as “loss of prestress” since there is no bending moment at the span the stress in the tendon changes only at the midspan but not at the end, since concrete and steel are considered as one section after bonding the change in stresses due to the bending of this section can be calculated by using transformed section method.
2. The loss in prestress is necessary to make an estimate of:
Answer: a [Reason:] A reasonably good estimate of the magnitude of lines of prestress is necessary from the point of view of design, if the prestress present in the steel is considered as the force applied on the concrete at the ends and the change is stress along with length of entire beam is not concluded as change in prestress.
3. How many types of losses in prestress are observed in pretensioned member?
Answer: c [Reason:] The losses in prestress in pretensioned member are four types: Losses due to elastic deformation of concrete, Loss due to relaxation of stress in steel, Loss due to creep of concrete, Loss due to shrinkage of concrete, in pretensioned members, due to prestress present at the ends of the members the tendon bends upwards due to bending action and the tendon becomes shortened, this is not considered as loss in prestress.
4. How many types of loss in prestress are observed in post tensioned members?
Answer: d [Reason:] The loss of prestress in post tensioned members is of 6 types: Elastic deformation of concrete, relaxation of stress in steel, creep of concrete, shrinkage of concrete, slip of anchorages, friction, if the tendon is not the particular line from centre of gravity of concrete section the calculation of the change in length of the beam due to bending moment will be complicated and this is considered as ordinary loss or gain 2 to 3%.
5. The frictional and anchorage slip losses are observed in:
a) Post tensioned members
b) Pretensioned members
c) Ruptured members
d) Tensile members
Answer: a [Reason:] The frictional losses and loss due to anchorage slip are observed in post tensioned members only because pretensioned members do not require anchorages for prestressing and in post tensioned beams which are unbounded the loss and gain of prestress depends upon the upward bending movement of the beam and the beam when loaded fully respectively.
6. The concrete members which are prestressed by providing the tensioned tendons are termed as:
a) Pre tensioning members
b) Internally prestressed members
c) Linear prestressed members
d) Circular prestressed members
Answer: b [Reason:] The concrete members which are prestressed by providing the tensioned tendons are termed as internally prestressed members due to bending moment in the beam is developed and the bending in the beam results in change of unit stresses, unit strains in the tendons.
7. Which of the following is a loss of prestress in post tensioned members?
a) Loss due to slip of anchorages
b) Loss due to deformations
c) Loss due to tensioning
d) Loss due to pumped concrete
Answer: a [Reason:] The loss of prestress in post tensioned members in the following is the loss of slip due to anchorages and friction, in post tensioned beams which are bounded, before grouting action the prestress in the steel is affected by the bending action of the member.
8. The sudden changes in loss of prestress may be due to:
Answer: b [Reason:] In addition to loss of prestress in post and pre tensioning members, there may be losses of prestress due to sudden changes in temperature, especially in steam curing of pretensioned units before the bonding of tendon to the concrete, the prestress in the tendon will be influenced by the bending of the member.
9. The rise in temperature in loss of prestress causes:
a) Partial transfer
b) Shifting of prestress
c) Full transfer of prestress
d) Prestress elongation
Answer: a [Reason:] The rise in temperature causes a partial transfer of prestress due to elongation of the tendons between adjacent units in the long line process which may cause a large amount of creep if the concrete is not properly cured.
10. The loss of change of temperature is between:
a) Tension and transfer
b) Compression and prestress
c) Bending and shear
d) Principle stress and loading
Answer: a [Reason:] If there is a possibility of a change of temperature between the times of tensioning and transfer the corresponding loss should be allowed for design, due to bending of a member the prestress may vary depending upon the line of bending, position of tendons(high strength steel cables which are flexible) number of tendons which are kept at different stages and also the type of prestressing whether it is a post tensioned or pretensioned the effect of bending may be either a positive or negative in prestress.
Prestressed Concrete Structures MCQ Set 2
1. The significant observations which resulted from the pioneering research on prestressed concrete were:
a) High strength steel and losses of prestress
b) High strength tendon and losses of creep
c) High strength bars and losses of strain
d) High strength rings and losses of shrinkage
Answer: a [Reason:] The necessity of using high strength steel, concrete and recognisation of losses of prestress due to various causes were the observations which resulted in research on prestressed concrete while high strength tendons, bars, rings are used for transmitting prestress and losses of creep, strain and shrinkage are types of loss considered in post and pretensioned members.
2. The necessity of high strength concrete in prestressed concrete is due to:
a) Shear and Bonding
b) Loading and Unloading
Answer: a [Reason:] High strength concrete is necessary in prestressed concrete, as the material offers high resistance in tension, shear, bond and bearing while loading and unloading, cracking, bending actions are actions occurring at the time of transfer of concrete.
3. In the zone of anchorages the material preferred to minimize costs is:
a) High strength steel
b) High strength bars
c) High strength tendons
d) High strength concrete
Answer: d [Reason:] In the zone of anchorages, the bearing stresses being higher, high strength concrete is invariably preferred to minimize costs and it is less liable to shrinkage cracks, and has a higher modulus of elasticity.
4. The length of the prestressing tendon between the end of the member and the point where the steel attains its stress is called as:
b) De bonding
c) Cracking load
d) Transmission length
Answer: d [Reason:] The length of the prestressing tendon between the end of the member and the point where the steel attains its full stress and adequate transmission length is necessary to reduce the radial forces acting on the concrete.
5. In cab cable, the curved portion of the tendon and anchors lie in:
a) Compression and Tension zone
b) Cracking zone
c) Tension and Compression zone
d) Loading zone
Answer: c [Reason:] A short curved tendon arranged at the interior support of a continuous beam where the anchors are in compression zone and the curved portion is in the tensile zone is called as a cab cable and it is small in size and consists of anchorages and its sides.
6. The load at which the prestressed member develops its first crack is called as:
a) Transfer load
b) Creep load
c) Bending load
d) Cracking load
Answer: d [Reason:] The load on the structural element corresponding to the first visible crack is called as cracking load and transfer refers to the phase in which the prestress is transferred to the concrete, transfer load occurs at pretensioned members when prestress is released from bulk heads while in post tensioned members, transfer occurs after the tensioning of tendons.
7. In circular prestressing members, the tendons are supplied in form of:
Answer: d [Reason:] The term circular prestressing refers to prestressing in round members, such as tanks and pipes and the members are prestressed in a circular way while the use of bar tendons with threaded anchorages reduces the possibility of pull and are used in post tensioning system, wire tendons are mainly used in post tensioning system, cables are formed by arrangement of wires or strands.
8. In case of continuous prestressed concrete members to gain continuity, splicing is done by:
Answer: d [Reason:] A stretched element used in a prestressed concrete member which serves the purpose of transmitting the prestress to concrete and it may be in the form of high tensile steel wires, cables or strands.
9. The phenomena of drying process of contraction concrete refer to:
a) Moisture loss
b) Shrinkage of concrete
c) Drying process
d) Weight loss
Answer: b [Reason:] Shrinkage of concrete is due to moisture loss resulting in difference in volume results in contraction of concrete on drying and it is based on relative humidity, exposure time, quantity and type of aggregate, water cement ratio in the mix.
10. The ratio between the creep strain and elastic strain of concrete is defined as:
a) Creep ratio
b) Creep elasticity
c) Creep coefficient
d) Creep factor
Answer: c [Reason:] Creep coefficient is progressive increase in the inelastic deformation of concrete under sustained stress components and the estimation of loss of prestress due to creep of concrete is carried out by creep coefficient method.
11. The phenomena of reduction of stress in steel at a constant strain are known as:
a) Reduction of stress
b) Relaxation of stress
c) De bonding
d) Proof stress
Answer: b [Reason:] Relaxation of stress refers to decrease of stress in steel at constant strain, at a certain level reduction of stress in steel occurs at a constant strain in concrete member and this phenomena occurs as a result of creep in steel while the relaxation of stress in steel changes according to the variation of percentage of creep.
12. A device which helps the tendons to transmit prestress to the member and maintain it for the design period is?
a) Cab cable
Answer: b [Reason:] Anchorage is the term used to denote a device which helps the tendons to transmit prestress to the member and maintain it for the design period, generally used to enable the tendon to impart and maintain prestress in concrete and the commonly used anchorages are Freyssinet, Magnel, Balton, Gifford-udall, Leon hardt etc.
13. Which of the following type of prestress applied to concrete in which tensile stresses to a limited degree are permitted is known as:
a) Moderate prestressing
b) Partial prestressing
c) Full prestressing
d) Axial prestressing
Answer: b [Reason:] Partial prestressing refers to the prestressing of concrete members in which some flexural cracking is allowed at full service load and an additional tensile reinforcement is also provided to achieve adequate bending strength.
14. Prevention of bond between the steel and concrete is known as:
a) Bond prestressed concrete
b) Axial prestressing
c) De bonding
d) Proof stress
Answer: c [Reason:] Prevention of bond between the steel wire and the surrounding concrete is known as de bonding, the concrete in which prestress is imparted to concrete through bond between tendons and surrounding concrete, members in which the entire cross section of concrete has a uniform compressive prestressing is termed as axial prestressing, the tensile stress in steel which produces a strain of 0.2 percent of the original gauge length on unloading is proof stress.
Prestressed Concrete Structures MCQ Set 3
1. The ultimate load capacity is higher in case of:
a) Statically indeterminate structures
b) Statically determinate structures
c) Prestressed structures
d) Reinforced structures
Answer: a [Reason:] The ultimate load carrying capacity is higher than in statically indeterminate structures than in determinate structure due to the phenomenon of redistribution of moments, reduction in the size of member’s results in lighter structures.
2. The bending moments are more evenly distributed between:
a) Ends and supports
b) Centre and supports
c) Edge and supports
d) Surface and supports
Answer: b [Reason:] The bending moments are more evenly distributed between the centre of span and the supports of member’s leads to increased stability and in continuous prestresssed structures, the deflections are comparatively small as compared to simply supported span.
3. In continuous post tensioned girders the curved cables can be positioned to resist:
a) Edge and supports
b) Beam and supports
c) Span and supports
d) Columns and supports
Answer: c [Reason:] In continuous post tensioned girders, the curved cables can be suitably positioned to resist the span and support moments, continuity of the members in framed structures leads to increase stability, in framed structures leads to increase stability continuous girders are formed by segmental construction using precast units connected by prestressed cables.
4. There is a reduction of anchorage in case of:
a) Precast prestressed beam
b) Pre tensioned prestressed beam
c) Continuous prestressed
d) Partially prestressed
Answer: d [Reason:] A reduction in the number of anchorages in a continuous prestressed beam in comparison with a series of simply supported beam only one pair of post tensioning anchorages and a single stressing operation can serve several members.
5. When an indeterminate structure is prestressed which reactions develop?
Answer: b [Reason:] When an indeterminate structure is prestressed, reductant reactions will develop due to the redundancies exercising a restraint at the supports and the redundant reactions which develop as a consequence of prestressing an indeterminate structure result in secondary moments.
6. Which type of structure is free to deform?
a) Statically determinate
b) Continuous structure
c) Statically indeterminate
d) Partially prestressed structure
Answer: c [Reason:] While a statically determinate structure is free to deform when prestressed a continuous structure cannot deform freely and however the deflections should conform to the law of consistent deformation.
7. The formation of redundant reactions is examined with reference to:
a) One span continuous beam
b) Two span continuous beam
c) Three span continuous beam
d) Four span continuous beam
Answer: b [Reason:] The formation of redundant reactions and secondary moments are examined with reference to a two span continuous beam, prestressed by a straight cable local at a uniform eccentricity throughout the span.
8. The problem of excessive frictional losses can be tackled by reducing:
b) Prestressing force
Answer: c [Reason:] The problem of excessive frictional losses can be tackles by reducing the curvature of the cables housed in members of variable depth and also by temporarily overstressing the tendons from both ends.
9. The stresses due to secondary moments can be eliminated by selecting suitable:
a) Cable profile
b) Tendon profile
c) Anchorage profile
d) Wedge profile
Answer: b [Reason:] Stresses due to secondary moments can be eliminated by selecting suitable tendon profile which do not induce secondary moments and it is also possible to provide for secondary stresses in the design and if under reinforced sections are used, the redistribution of moments will be more or less complete resulting in higher collapse loads and these loads could be estimated by suing the well established plastic theory as applied to structural steel members.
10. The computation of collapse or ultimate load is influenced by:
a) Degree of compression
b) Degree of bending
c) Degree of redistribution
d) Degree of strain
Answer: c [Reason:] The computation of collapse or ultimate load is influenced by the degree of redistribution of moments in the continuous structure cables positioned to cater for secondary moments are not generally suitable to provide the required ultimate moment under a given system of loads.
Prestressed Concrete Structures MCQ Set 4
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
Answer: a [Reason:] 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
Answer: c [Reason:] 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
Answer: a [Reason:] 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
Answer: a [Reason:] 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
Answer: b [Reason:] 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
Answer: a [Reason:] 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
Answer: b [Reason:] 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
Answer: a [Reason:] 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
Answer: c [Reason:] 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
Answer: b [Reason:] 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.
Prestressed Concrete Structures MCQ Set 5
1. The technique for selecting a new point depends upon:
a) Scope of the problem
b) Nature of the problem
c) Range of the problem
d) Analysis of the problem
Answer: b [Reason:] In using the mathematical programming methods the process of optimization begins with an acceptable design point and new point is selected suitability so as to minimize the objective function and the search for another new point is continued is continued from the previous point until the optimum point is reached and there are several well established techniques for selecting a new point and to proceed towards the optimum point, depending upon the nature of the problem, such as linear and non linear programming.
2. In linear programming, the solution is based on:
a) Tensile properties
b) Strain properties
c) Elementary properties
d) None of the mentioned
Answer: c [Reason:] In a linear programming problem, the objective function and constraints are linear functions of the design variables and the solution is based on the elementary properties of systems of linear equations and the properties of systems proportionally, additivity, divisibility and deterministic features are utilized in the mathematical formulation of the linear programming problem.
3. A linear function in three-dimensional space is a:
Answer: b [Reason:] A linear function in tree-dimensional space is a plane representing the locus of all design points in n-dimensional space, the surface so defined is a hyper plane and in these cases, the intersections of the constraints give solutions which are the simultaneous solutions of the constraint equations meeting at that point.
4. Linear programming problems can be solved by:
a) Revised simplex method
b) Termed method
c) Moment derivation method
d) Hollow method
Answer: a [Reason:] Linear programming problems can be conveniently solved by the revised simplex method and the simplex algorithm for solving the general linear programming problem is an iterative procedure which yields an exact optima solution in a finite number of steps.
5. One of the most powerful techniques for solving non linear programming is to transform the:
Answer: b [Reason:] One of the most powerful techniques for solving non linear programming is to transform the problem by some means into a form which permits the application of the simplex algorithm and thus, the simple method turns out to be one of the most powerful computational devices for solving linear as well as non linear programming problems.
6. In non linear programming the boundaries of the contours of the function are:
a) Parallel line
b) Zig Zag lines
c) Straight lines
d) Trapezoidal lines
Answer: c [Reason:] In non linear programming problems, the objective function and or the constraints are non linear function of the design variables and since the boundaries of the feasible region or the contours of equal values of the merit function are straight lines the optimum solution need not necessarily be at an intersection of the constraints.
7. One of the techniques developed for solution of non linear programming is:
a) Single programming
b) Multilinear propramming
c) Reverse programming
d) Dynamic programming
Answer: d [Reason:] Over the years, several techniques have been developed for the solution of non linear programming problems and some of the prominent techniques are: method of feasible directions, sequential unconstrained minimization technique, sequential linear programming and dynamic programming.
8. The method of feasible direction can be grouped under the:
a) Direct methods of approach
b) Sequential method of approach
c) Terminate method of approach
d) Laminar method of approach
Answer: a [Reason:] In non linear programming the method of feasible direction can be grouped under the direct methods of approach on general non linear inequality constrained optimization problems and two well known procedures which embody the philosophy of the method of feasible directions are Rosens gradient projection algorithum and Zountendijks procedure.
9. The first non linear programming procedure to be used in:
Answer: c [Reason:] This method (method of feasible direction) was probably the first non linear programming procedure to be used in structural optimization problems by schmist in 1960 and this method starting from an initial feasible point, the nearest boundary is reached and a new feasible direction is found and an appropriate step is taken along this feasible direction to get the new design point and the procedure is repeated until the optimum design point is reached.
10. One of the element considered in the economy of prestressed concrete structural system:
a) Structural optimization
b) Beam optimization
c) Slab optimization
d) Transverse optimization
Answer: a [Reason:] Structural optimization together with the efficient management of labour, materials and the use of new construction techniques, development and use of indigenous and new materials of construction would result in considerable economy in the overall cost of prestressed concrete structural systems.