Prestressed Concrete Structures MCQ Set 1
1. The design values of the resistance must equal or exceed the sum of:
a) Design deflection
b) Design loads
c) Design bars
d) Design cross section
Answer: b [Reason:] In the design of prestressed concrete member, the minimum required resistance is predetermined for certain limit states such as collapse, deflection and cracking for each of these, the design values of the resistance must equal or exceed the sum of the design loads obtained by multiplying the specified characteristic loads by the appropriate partial safety factors.
2. The design strength of the material being known, the problem generally reduces to the determination of:
Answer: a [Reason:] The design strength of the material being known, the problem generally reduces to the determination of suitable dimensions for the member, that is the cross sectional details followed by the design of prestress required and the corresponding eccentricity and area of reinforcement for the section.
3. The trial and error method of assuming a certain section and checking its resistance is often:
a) Easy method
b) Time consuming
c) Reverse method
d) Direct method
Answer: b [Reason:] The trial and error method of assuming a certain section and checking its resistance using the appropriate design formula is often time consuming since a section satisfying the requirements at the serviceability limits may be deficient at the limit state of collapse.
4. A direct method for computing the leading dimensions of a section is often feasible as in the case of:
a) Pure flexure
b) Partial flexure
c) Total flexure
d) Unpure flexure
Answer: a [Reason:] The direct method for computing the leading dimensions of a section is feasible in case of pure flexure where the necessary effective depth and breadth of the compression face are controlled mainly by the collapse limit states.
5. In the case of flanged member on the basis of collapse the width and depth of the compression flange is:
Answer: c [Reason:] In the case of flanged member on the basis of collapse the width and depth of the compression flange is, while the thickness of the web is based on ultimate shear or an practical considerations of having curved cables with minimum cover requirements.
6. The minimum prestressing force required and the corresponding eccentricity are controlled by the serviceability limit states at which the stresses are not to exceed the:
a) Permissible values
d) Limited values
Answer: a [Reason:] The minimum prestressing force required and the corresponding eccentricity are controlled by the serviceability limit states at which the stresses are not to exceed the Permissible values are these values are permitted or limited to certain extent.
7. The limit states of deflection rarely influence the design of prestressed members:
a) Class 4
b) Class 3
c) Class 1 and 2
d) Class 5
Answer: c [Reason:] The limit states of deflection rarely influence the design of prestressed members Class 1 and 2 since the members will be normally uncracked at service loads and in addition a pre camber will be provided by the initial upward deflection due to the prestress.
8. In case of member subjected to axial tension, the concrete section and the minimum prestress are mainly controlled by:
a) Permissible stress
b) Transverse stress
d) Principle stress
Answer: a [Reason:] In case of member subjected to axial tension, the concrete section and the minimum prestress are mainly controlled by Permissible stress at the service loads and in some cases (walls of tanks) by practical considerations.
9. The dimensioning of prestressed members subjected to axial load and bending is governed by:
a) Permissible stresses
b) Neglected stresses
c) Allowable stresses
d) Ranged stresses
Answer: c [Reason:] The dimensioning of prestressed members subjected to axial load and bending is governed by stress condition equations formulated for the opposite extreme faces of the section or by the aid of design charts for the different cases of members with uniform or non uniform prestress.
10. The required cross sectional dimensions and the prestress may be determined by solving:
a) Stress conditions equations
b) Multiple equations
c) Single equations
d) Unique equations
Answer: a [Reason:] Stress condition equations formulated for the opposite extreme faces of the section or by the aid of design uniform or non uniform prestress are solved for determining required cross sectional dimensions and the prestress.
Prestressed Concrete Structures MCQ Set 2
1. The primary aim of structural optimization is to determine the:
a) Design variables
b) Design parameters
c) Design constants
d) Design limits
Answer: a [Reason:] The primary aim of structural optimization is to determine the most suitable combination of design variables, so as to achieve satisfactory performance of the structures subjected to the behavior and geometric constraints imposed with the goal of optimality being defined by the conditions and the three basic features of the structural optimization problem are:
The design variables, the objective function, the constraints.
2. The process of optimum design of prestressed concrete structures may be looked as:
a) Computer programming problem
b) Mathematical programming problem
Answer: b [Reason:] Basically the process of optimum design of prestressed concrete structures may be looked upon as a mathematical programming problem in which the total cost or consumption of materials is minimized, subject to certain functional constrains such at serviceability limit states and flexural and shear strength requirements at the limit state of collapse.
3. The optimization problem involves:
a) Short computations
b) Zero computations
c) Long computations
d) Span computations
Answer: c [Reason:] Generally optimization problems involve long and tedious computations and as such manual computations are limited to simple problems comprising a few design variables and however the development of high speed electronic digital computer has revived the interest in optimization problems and significant advances have been made in the field of structural optimization.
4. The design variables are generally grouped under which parameters:
a) Dimensional variables
b) Span variables
c) Foundation variables
d) Constant variables
Answer: a [Reason:] The design variables are generally grouped under which parameters dimensional variables represented by the member sizes such as the thickness of a plate, cross sectional area of a member and moment of inertia of a flexural members, configuration or geometric variables represented by the coordinates of element joints, variables involving the mechanical or physical properties of the material, such as the variable modulus of elasticity.
5. In the sequential unconstrained minimization techniques, which problems are converted?
a) Un constrained
Answer: b [Reason:] In the sequential unconstrained minimization technique, the constrained minimization problem is converted into an unconstrained one by introducing an interior or exterior penalty function and this method introduced by Carroll and amplified by Fiacco and Mc cormick has proved to be highly advantageous in practical structural design problems.
6. In sequential linear programming, the non-linear objective functions and constrains are:
Answer: a [Reason:] In sequential linear programming, the non-linear objective function and constrains are linearized in the vicinity of the starting point and a new design point is obtained by solving the linear programming problem and the sequence of line arising in the neighborhood and solving by linear programming is continued from the new point till the optimum is reached.
7. The further improvement method of sequential linear programming is:
a) Beam limit method
b) Rise limit method
c) Move limit method
d) Fall limit method
Answer: c [Reason:] Further improvements in these methods are due to pope, who suggested the move limit method and more recently Ramakrishna and Bhavikati has improved and used this method for the optimum design of mechanical components under stress.
8. Dynamic programming developed in optimization techniques are widely applied in:
Answer: a [Reason:] Dynamic programming developed by Bellman in the early 1950s and widely applied in operations research and economics is basically a mathematical approach for multi stage decision problems and this approach is well suited to the optimal design of certain kinds of structure, in general those in which the interaction between different parts is rather simple.
9. The limitation of dynamic programming is that it does not lend itself for:
a) Construction general purpose computer programmes
b) Machine design
c) Graphic design
d) Architectural design
Answer: b [Reason:] The limitation of dynamic programming is that it does not lend itself to the construction of general purpose computer programmes suitable for a wide range of distinct problems and dynamic programming has been used for optimizing the shape of pin jointed structures and for the optimal design of transmission towers by palmer and Sheppard.
10. In geometric programming, the emphasis is on:
a) Optimal distribution
b) Single distribution
c) Variable distribution
d) Linear distribution
Answer: c [Reason:] Reliability of prestressed concrete structural systems like beams and frames has been examined by Ranganathan while the reliability design of prestressed concrete beams has been reported by chandrashekhar and dayaratnam and application of geometric programming to structures optimization problems has been attempted by temple man and of the total cost among the various terms in the objective function instead of on the values of the variables.
Prestressed Concrete Structures MCQ Set 3
1. The prestressed concrete structures pressure vessels can be triaxially prestressed resulting in:
b) High load factors
c) Tensile factors
d) Ductile factors
Answer: b [Reason:] Reinforced concrete are widely used for energy structures like dams, surge shafts in hydroelectric power stations and the use of prestressed concrete biological shields for nuclear reactor and containment vessels of few several advantages and prestressed concrete pressure vessels can be triaxially prestressed resulting in higher load factors against limit states of service and ultimate failure and the structural form normally used comprises a cylindrical concrete vessel capped with a shallow dome and cylindrical and spherical shapes have been used for the oldbury and wylfa pressure vessels.
2. One of the nuclear power station located in Tamilnadu shielded by a double containment system is:
a) Lankesh nuclear power station
b) Gauri nuclear power station
c) Kalpakkam nuclear power station
d) Radant nuclear power station
Answer: c [Reason:] In the case of kalpakam nuclear power station located in Tamilnadu, India shielding is provided by a double containment system with an inner cylinder of 600mm thick prestressed concrete surrounded by an outer wall of rubble masonry 711mm thick and the two walls are separated by an annular air space 1m wide and in general prestressed concrete reactor and containment vessels and cylinder in shape facilitating slip form method of construction and circumferential prestressing resulting in considerable economy coupled with speedy construction.
3. The maximum credible accident (MCA) is a:
a) Nuclear containment structures
b) Explosive container
c) Hydrogen container
d) Mica container
Answer: a [Reason:] The nuclear containment structure of an atomic reactor is a physical barrier which is designed to contain the total fluid energy and the radioactive products in the event of which is termed as the maximum credible accident (MCA) and the MCA corresponds to the rupture of pipes carrying the primary or secondary coolants and the associated rise of pressure and temperature within the containment structures.
4. The atomic power reactor at Rajasthan was built in:
Answer: c [Reason:] In the latter part of the 20 century, India has developed and built several atomic power stations at Tarapur, Rajasthan, Kalpakkam, Narora, Kakrapur and kaigo located in several stages of the country as reported by tendon and the dimensional details of the Rajasthan atomic power reactors at kota built in 1965 and at the time, the prestressed concrete in the world, with the first two having been built in France between 1960 and 1965 and the dome is anchored to a 1.22 thick reinforced concrete cylindrical wall of the reactor vessel by 127mm diameter prestressing cables.
5. One of the prestressed power reactor vessels in the following is:
Answer: a [Reason:] The salient feature of the basic reactor vessel of madras atomic power project and the prestressed vessel consists of an inner containment monolithic structure made up of prestressed concrete wall and dome designed for maximum pressure and practically complete leak tightness is ensured by the introduction of an outer reinforced masonry wall separated by an annular air space and is kept under small positive pressure intensity so that the effective leakage into the atmosphere is almost zero.
6. The prestressing system of the dome in madras power atomic reactor vessel comprises of how many brands?
Answer: b [Reason:] The prestressing system of the dome in madras power atomic reactor vessel comprises of how many brands three banded layers housed within the dome thickness of 250mm and this structure is also notable for being the most economical and cheapest in the world by comparison with 27 similar containment vessels which were designed and built around the world in 1967.
7. The Narora atomic power plant consists of a:
a) Single containment vessel
b) Triple containment
c) Prestressed containment vessel
d) Double containment vessel
Answer: d [Reason:] The Narora atomic plant consists of a double containment vessel and the inner unit is a prestressed concrete cylindrical wall capped by a prestressed concrete cellular slab and the outer wall is rigidly connected to the foundation raft at base while the inner prestressed wall is made monolithic with the raft after stressing.
8. The prestressed concrete silos are generally preferred for storage of:
Answer: c [Reason:] Prestressed concrete silos are generally preferred in place of vertical reinforced concrete silos for the storage of fertilizers and the shell concrete precast structural elements are combined by cast insitu joints and prestressed cables in the longitudinal.
9. The thickness of concrete in the shell is in the range:
Answer: b [Reason:] The thickness of concrete in the shell is in range of 50-75mm and the curved shell segments are connected by cast insitu joints which are prestressed by suitable high tensile cables and transverse directions at modular intervals to achieve integrity of joints resulting in large interrupted space inside the shell.
10. The economical concrete silos shape is:
a) Paraboloid shell shape
b) Ellipse shell shape
c) Circle shell shape
d) Dome shell shape
Answer: a [Reason:] The paraboloid shell shape results in significant economy with minimum quantities of materials like concrete and steel and yet providing the maximum covered space for the storage and packing of fertilizers and typical examples of such silos can be found in the Mangalore fertilizers and chemicals LTD factory located near the harbor at panambur near Mangalore and another notable example is the silo at nangal having a width of 32m and 312m long and the height of crown of shell is 20m from the floor and this shell built by m/s gammon India ltd for the fertilizer corporation of India.
Prestressed Concrete Structures MCQ Set 4
1. The resultant stresses in concrete at any section are obtained by the effect of:
a) Prestress and flexural stresses
b) Prestress and bending stresses
c) Prestress and shear stresses
d) Prestress and torsion stresses
Answer: a [Reason:] Resultant stresses in concrete at any section are obtained by superimposing the effect of prestress and flexural stresses developed due to the loads, other common types of corrosion frequently encountered in prestressed concrete construction are pitting corrosion and chloride corrosion, a critical review of the different types of corrosion of high tensile steel in structural concrete is reported.
2. The resultant stress distribution due to eccentric prestressing, dead and live loads at any given section are obtained as:
a) Fsup = (p/a-pe/zt)+(mg/zt)+(mq/zt)
b) Fsup = (p/a-pe/zt)+(mg/zt)+(mq/zt)
c) Fsup = (p/a-pe/zt)+(mg/zt)+(mq/zt)
d) Fsup = (p/a-pe/zt)+(mg/zt)+(mq/zt)
Answer: a [Reason:] If Mq
are live loads and dead load moments at the central span section;
3. A concrete beam of rectangular section, 250mm wide and 600mm deep. Calculate the bending moment that can be applied without applying tension at the soffit of the beam with given m/z value as 5.74?
Answer: d [Reason:] m/z = 5.74, b = 250mm, d = 600mm
Z = (250×6002/6) = 15×106mm3,
M = (5.74×15×106) = 86.1×106nmm = 86.1knm.
4. A prestressed concrete beam of section 200mm wide by 300mm deep of imposed load 4kn/m at a span of 6m, density of concrete is 24kn/m3. Find the concentric prestressing force necessary for zero fiber stress at the soffit?
Answer: a [Reason:] b = 200mm, d = 300mm, A = (200×300) = 6×104mm2, g = (0.2×0.3×24),
Mg = (0.125×1.44×62) = 6.48knm, Mq = (0.125×4×62) = 18knm, Zb=Zt = (200×3002/6) = 3×106mm3 P/A = 8.16, P = (8.16×6×104) = 489.6kn.
5. The locus of the points of application of resultant force in any structure is termed as:
a) Pressure line
b) Hollow line
c) Beam line
d) Tendon line
Answer: a [Reason:] The combined effect of prestressing force and the externally applied load will result in a distribution of concrete stresses that can be resolved into a single force and the locus of the points of application of this resultant force in any structure is termed as “pressure or thrust line”.
6. The concept of pressure line is very useful in understanding the concept of:
a) Load carrying mechanism
b) Bending mechanism
c) Shear mechanism
d) Torsion mechanism
Answer: a [Reason:] The concept of pressure line is very useful in understanding the load carrying mechanism of a prestressed concrete section, if a prestressed concrete member is cracked, it behaves similar to that of a reinforced concrete section, in contrast to the direct method of analysis of resultant stresses at a section of a prestressed concrete beam outlined the pressure or thrust line concept can also be used to evaluate stresses.
7. The location of the pressure line depends upon:
a) Breakage and Bondage
b) Magnitude and direction
c) Shear and Torsion
d) Pressure and equilibrium
Answer: b [Reason:] In the case of prestressed concrete members, the location of the pressure line depends upon the magnitude and direction of the moments applied at the cross section and the magnitude and distribution of stresses due to the prestressing force, the increase in resultant forces are due to a more or less constant lever arm between the forces, characterized by the properties of the composite section.
8. The eccentricity e in the pressure line diagram is:
Answer: a [Reason:] At the support section, since there are no flexural stresses resulting from the external loads, the pressure line coincides with that of the centroid of steel, located at an eccentricity of h/6, at the centre of the span section the external loading is such that the resultant stress developed in maximum at the top fiber and zero at the bottom fibers and it can be easily be seen that for this section the pressure line has shifted towards the top fiber by an amount equal to h/3 from its initial position.
9. The change in the external moments in the elastic range of prestressed concrete beam results in:
a) Bending moment in pressure line
b) Torsion in pressure line
c) Flexure in pressure line
d) Shift of the pressure line
Answer: d [Reason:] “A change in the external moments in the elastic range of a prestress concrete beam results in a shift of the pressure line rather than in an increase in the resultant force in the beam, this is in contrast to a reinforced concrete beam section where an increase in the external moment results in a corresponding increase in the tensile force and the compressive force.
10. The shift of pressure line measured from centroidal axis is obtained as:
Answer: a [Reason:] The shift of pressure line is measured from the centroidal axis is obtained as
E’= (a-e) = (m/p)-e, basically the load carrying mechanism is comprised of a constant force with a changing lever arm as in the case of prestressed concrete sections, and a changing force with a constant lever arm prevailing in reinforced concrete sections.
Prestressed Concrete Structures MCQ Set 5
1. The computation of ultimate flexural strength of under and over reinforced sections, as well as of sections is provided by
a) Indian code
b) British code
c) American code
d) France code
Answer: c [Reason:] The Indian and British code methods are limited to under reinforced sections in flexure based on the effective reinforcement ratio, the American code method provides empirical relations to compute the ultimate flexural strength of under and over reinforced sections as well as of sections with compression reinforcement.
2. The strain compatibility method of analysis, involves the use of:
a) Tension compression curves
b) Stress strain curves
c) Bending bondage
d) Elasticity curve
Answer: b [Reason:] The rigorous strain compatibility method of analysis, which involves the use of idealized stress strain curves of steel and concrete, can also be used for an accurate assessment of the flexural strength of sections with reinforcements in the tension and compression zones.
3. The current Indian, British and American codes have more or less similar provisions for the computation of:
a) Shear strength
b) Shear stress
c) Shear strain
d) Shear principle
Answer: a [Reason:] The current Indian, British and American codes have more or less similar provisions for the computation of the shear strength of prestressed members that fail in web – shear or flexure – shear cracking modes.
4. The primary serviceability limit state corresponds to excessive:
a) Compression and tension
b) Deflection and cracking
c) Shear and Friction
d) Torsion and mass
Answer: b [Reason:] Serviceability limit state corresponds to excessive deflection and cracking and it is customary in most codes to safeguard against excessive deflection under serviceability limit state, either indirectly by prescribing minimum span/depth ratio for the member or directly specifying a maximum permissible deflection expressed as a fraction of the span.
5. The permissible deflections vary from a maximum of:
Answer: a [Reason:] According to the American code ACI: 318-1989, the permissible deflection vary from a maximum of span/180 to a minimum of span/480 depending upon the type of member and the seriousness of damage to the adjoining structural element.
6. The short term deflections of prestressed members of class-1 and class-2 types under service loads are influenced by:
a) Length of prestressing force
b) Depth of prestressing force
c) Magnitude of prestressing force
d) Eccentricity of prestressing force
Answer: c [Reason:] Short term deflections of prestressed members of class-1 and class-2 types under service loads are influenced by: magnitude of the prestressing force and its profile, applied load and self weight of the member and flexural rigidity of the Un cracked concrete sections.
7. The limit state of cracking is important in the case of:
a) Partially prestressed members
b) Fully prestressed members
c) Tangential prestressed members
d) Hollow prestressed members
Answer: a [Reason:] The limit state of cracking is particularly important in the case of partially prestressed members according to Abeles, who has contributed much information about members with limited prestress.
8. The Class 1-type members are preferred for:
a) Block structures
b) Containment structures
c) Cracked structures
d) Aged structures
Answer: b [Reason:] No tensile stresses are permitted under service loads and hence the structure is crack-free at the working load stage and the members are often referred to as fully prestressed, requiring higher quantity of prestressing steel associated with higher cost, generally class 1 type members are preferred for containment structures housing atomic reactors, pressure pipes and in important structures where cracking at service loads is not acceptable.
9. In class 2 structures limited tensile stresses of magnitude not exceeding the modulus of rupture of concrete are permitted under:
a) Tensile loads
b) Compressive loads
c) Principle loads
d) Working loads
Answer: d [Reason:] Class 2 structures limited tensile stresses of magnitude not exceeding the modulus of rupture of concrete are permitted under working loads members are often referred to as moderately prestressed visible cracks are not permitted in this type abeles has used such structures in British railways with very satisfactory results.
10. Which type of class structure is considered as econimal?
Answer: c [Reason:] Tensile stresses of magnitude exceeding both the modulus of rupture of concrete and the visible cracking of limited width are permitted under service loads as compiled and members are referred to as partially prestressed class-3 type constitute the most economical of prestressed concrete structures due to limited prestressing forces and high tensile steel requirements.