Prestressed Concrete Structures MCQ Set 1
1. The stresses developed in the prestressed structures are computed using:
a) Simple bending equations
b) Stress strain theory
c) Strain analysis
d) Stress curves
Answer: a [Reason:] The stresses developed in prestressed and cast insitu concrete are computed using the simple bending equations until the stage of cracking and if the precast prestressed unit is unpropped during the placing of insitu concrete, the stresses that develop in the precast unit are sum of stresses due to self weight of members.
2. Once the insitu concrete hardens, we assume the section to be:
Answer: b [Reason:] After the insitu concrete has hardened the whole section is assumed to be monolithic and the stresses that develop due to subsequent live loads are computed using the properties of the composite sections.
3. If the precast unit is propped during the placing of insitu concrete, the stresses due to self weight are computed using:
a) Section modulus
d) Principle stress
Answer: a [Reason:] The stresses developed due to self weight of the insitu concrete are computed using the section modulus of the composite section and in all cases the live loads stresses are based on the composite section.
4. In most composite constructions which involve prestressed units and insitu cast concrete the latter is of:
a) High strength concrete
b) Medium strength concrete
c) Colored concrete
d) Reinforced concrete
Answer: b [Reason:] In most composite constructions which involve precast prestressed units and insitu cast concrete the latter is invariably of low or medium strength concrete while the former are generally made of high strength concrete of grade exceeding M35.
5. For computing the live load stresses, the effect of different moduli between the cast in situ and precast unit is considerable by:
b) Modular ratio
c) Tensile stresses
Answer: b [Reason:] For computing the live load stresses, the effect of different moduli between the cast in situ and precast unit is considerable by using the modular ratio of precast insitu concrete for calculating the area, centroid, second moment of area and second modulus of the equivalent composite sections.
6. In modulus of elasticity of insitu concrete of grade M20 will be about:
Answer: a [Reason:] In most practical instances, the modulus of elasticity of insitu concrete of grade M 20 will be about 25kn/mm2, while the modulus of concrete in precast prestressed units could vary from 28 to 36kn/mm2 for concrete grades of M30 toM60.
7. The modular ratio of precast prestressed unit is:
a) 2.0 to 1.6
b) 1.1 to 1.5
c) 2.4 to 1.4
d) 2.2 to 1.7
Answer: b [Reason:] The modular ratio of precast prestressed unit varies in the range of 1.1 to 1.5 however this value could be larger if light weight concrete with a modulus in the range of 5 to 12kn/mm2 is used in conjunction with precast units made of normal weight aggregates.
8. A precast pretensioned beam of rectangular section has a breadth of 100mm and depth of 200mm and the beam with an effective span of 5mm is prestressed by tendon with their centroidal coinciding with the bottom kern and the initial force in the tendons is 150kn. Find prestressing force?
Answer: c [Reason:] A = (100×200) = 20000mm2, p = 150kn = 150×103 Stresses due to prestressing force = (2P/A) = (2x150x103/20000) = 15n/mm2.
9. Calculate stresses due to slab weight in precast sections given moment due to slab weight is 1200nm of section modulus 667×103?
Answer: a [Reason:] Section modulus Z = 667×103, moment due to slab weight is 1200nm
Stresses due to slab weight in the precast sections = (1200000/667×103) = 1.8n/mm2.
10. Calculate the stress of pretensioned beams assuming as propped during the casting of the slab if Zt is 225×10, Zb is 128x104mm3 and moment due to self weight is 1200nmm?
a) 12.3 and 4.5
b) 0.53 and 0.94
c) 0.23 and 0.45
d) 1.23 and 0.67
Answer: b [Reason:] Zt = 225×10, Zb = 128×104mm3, moment due to self weight =1200nmm
Stresses due to this moment in the composite section:
At top = (1200000/225×104) = 0.53n/mm2 (compression), At bottom = (1200000/128×104) = 0.94n/mm2 (tension).
Prestressed Concrete Structures MCQ Set 2
1. Based on experimental investigations, the members of truss are analyzed on assumption that the joints are:
Answer: d [Reason:] Based on theoretical and experimental investigations, it well established that the forces in the various members of the truss are analyzed on the assumption that the joint are hinged in the case os steel, reinforced concrete and prestressed concrete trusses.
2. Which action of joint does not affect the forces developed in the members?
Answer: b [Reason:] The rigidity of the joint does not significantly affect the forces developed in the members and hence the analysis is generally carried out on the assumption of hinged joints and the action of rigidity joint is flexible and tough enough towards the deflection.
3. The trusses are analyzed for dead, wind and:
a) Wave loads
b) Fire actions
c) Snow loads
d) Tensile loads
Answer: c [Reason:] The trusses are analyzed for dead, wind and snow loads applied to the joints of the top chord and the load of suspend mechanical handling facilities is applied at the panel points of bottom chord and these loads are analyzed against check for deflection for safety of structure.
4. When loads are applied to the chords the bending moment developed are determined by assuming chord as a:
Answer: b [Reason:] When loads are applied to the chords of a truss between the panel points and the bending moment developed are determined by assuming the chord as a continuous beam with spans equal to the distance between the joints.
5. Trusses must be analyzed for forces developed during:
a) Fabrication and erection
b) Twisting and lining
Answer: a [Reason:] Trusses must also be analyzed for forces developed during fabrication and erection and initial stresses developed due to the prestressing of the bottom chord members should also be considered in the design of trusses.
6. One of the functions involved in construction management is:
a) House owners
b) Tax planners
d) Area of site
Answer: b [Reason:] Construction of any structure forms only a small part of the whole gamut of construction management and the modern approach in construction management involves several diverse functions like designers, estimators, constructors, supervisors, accountants, financial managers, corporate secretaries, tax planners working under professional managers.
7. Which methods are widely used in project works?
Answer: a [Reason:] Critical path method of project evaluation review techniques (PERT) are widely used in the management of project work and with the advent of computers, data processing, preparation of working drawings, work scheduling, materials management, controlling the various activities of the project and upgrading the various tasks have become more simpler and they can be efficiently handled with less paper works.
8. The grade of concrete used for construction of prestressed concrete structures is:
a) Heavy mix concrete
b) Design mix concrete
c) Partially mix concrete
d) Fully mix concrete
Answer: b [Reason:] The most important consideration in the construction of prestressed concrete structures is the design, production and control of high strength concrete with desirable properties the minimum grade specified in the Indian standard code IS: 1343: 2005 for post tensioned concrete is M30 and for prestressed concrete work it is M40, the code also specifies the only Design mix concrete should be used to ensure the desired strength and durability.
9. The cement content limit which is not permitted unless special consideration has been considered in design:
Answer: d [Reason:] The cement content exceeding 475kg/m3 is not permitted unless special consideration has been considered in design to the increased risk if cracking due to drying shrinkage in thin sections or to early thermal stresses in thick sections and the Indian standard code also prescribes the minimum cement content together with the corresponding maximum free water cement ratio for different types of cements when prestressed concrete likely to be exposed to sulphate attack.
10. The aim of workability is to use the lower percentage of:
a) Coarse aggregates
b) Fine aggregates
Answer: b [Reason:] The aim should be to use the lowest percentage of fine aggregates which is consistent with the job conditions and which will permit placing of the concrete without honey combs and finishing it to a satisfactory surface and for high strength concrete used for prestressed concrete structures, the degree of workability as categorized in Indian standard code IS: 456-2000.
Prestressed Concrete Structures MCQ Set 3
1. The Zielinski and Rowe conducted experiments on concrete prismatic specimens using the technique?
a) Surface stress
b) Surface strain
c) Surface tension
d) Surface edge
Answer: b [Reason:] Experimental investigation on concrete prismatic specimen was conducted by Zielinski and Rowe using the technique of surface strain measurements, if groups of anchorages are encountered the end block is divided into a series of symmetrically loaded prisms and each prism is analyzed for bursting tensile forces using the recommended Indian code provision expressions.
2. The parameters considered for concrete prisms are:
c) Cross sectional area
d) End block
Answer: c [Reason:] The concrete prisms act as end blocks and the investigations were carried out on parameters like cable duct or hole, the ratio of loaded to cross sectional area, the cracking, type of anchorages and ultimate loads.
3. The distribution of transverse stress and ultimate load of the end block is not effected by:
a) Anchorage material
b) Curing concrete
c) Tendons applied
d) Jacking provided
Answer: a [Reason:] The studies revealed that the distribution of transverse stress and ultimate load of the end block is not affected by: the anchorage being either embedded or external, the material of the anchorage, the method of anchoring the wires.
4. The Zielinski and Rowe developed empirical relations for computation of:
a) Maximum transverse tensile stress
b) Minimum transverse tensile stress
Answer: a [Reason:] Zienlinski and Rowe developed empirical relations to compute the maximum transverse tensile stress and the bursting tension and when an end block is subjected to a concentrated load at the end face and at equal distances to 0.5ẙ the distribution of transverse stress is found to be maximum.
5. The equation for maximum tensile stress, fmax is given as:
Answer: a [Reason:] The maximum tensile stress, fvmax = fc(0.98-0.825(ypo/yo) which is valid for ypo/yo = 0.3 to 0.7 bursting tension, Fbst = pk(0.48-0.4(ypo/yo), (ypo/yo) = ratio of sides of loaded area to bearing area of the prism, fv = transverse tensile stress, fc = average compressive stress in the prism, pk = applied compressive force on the end block.
6. The creating bursting tension is given by:
Answer: c [Reason:] When allowance is provided for tension taken by concrete, the creating bursting tension is given by Fbst, corred = Fbst(3-(fv/fv,max)2), ft = permissible tensile strength of concrete.
To resist bursting tension, the reinforcement should be arranged between 0.2y0 and 2y0 providing the maximum intensity of stress.
7. Estimate the position and magnitude of the maximum transverse tensile stress and bursting tension for the end block with a concentric anchor force of 100kn using Rowe’s method?
Answer: d [Reason:] pk = 100kn, 2ypo = 50mm, 2ypo = 100mm, ypo/yo =0.5, fc = (100×103/100×100) = 10n/mm2, fv(max) = fc(0.98-0.825(ypo/y0)) = 10(0.98-0.825(0.5)) = 5.68n/mm2.
8. The end block and a prestressed beam, 200mm wide and 300mm deep, has two Freyssinet anchorages (100mm diameter) with their centre at 75mm from the top and bottom of the beam. The force transmitted by each anchorage being 200kn, estimate the maximum tensile and bursting tension?
Answer: b [Reason:] Anchorage diameter = 100mm, equivalent side of square 2ypo = (π/4×1002) = 89mm, side of the surrounding prism 2yo = 150mm, ypo /yo = 0.593, average compressive stress fc = (200×103/150×150) = 8.9n/mm2, Tensile stress fv(max) = 8.9(0.98-0.825(0.593)) = 4.45n/mm2, Transverse tension Fbst = 200×103(0.48-0.4(0.593)) = 50000n = 50kn.
9. In case of large bridge girders with massive end block, for computation of bursting tension end block is divided into:
Answer: c [Reason:] In the case of large bridge girders with massive end block supporting multiple anchorages, the end block is divided into a series of symmetrically loaded prisms for the computation of the bursting tension.
10. The design strength assumed to act to sustain bursting tension is:
Answer: c [Reason:] The reinforcement is designed to sustain this bursting tension and it is assumed to act at its design strength of 0.87fy and the stress however is limited to value corresponding to a strain of 0.1% when the concrete cover is less than 50mm.
Prestressed Concrete Structures MCQ Set 4
1. The limit state design philosophy recognizes the need to provide:
a) Safe structures
b) Designed structures
c) Stressed structures
d) Curved structures
Answer: a [Reason:] The limit state design philosophy recognizes the need to provide safe and serveciable structures at on economic price and at the same time presents a clearer idea of margins of safely actually employed to cover uncertainity and ignorance of the function as well as the performance of structure in actual practice.
2. The limit state design proposals have been evolved from the provisions of various:
Answer: b [Reason:] It is important to note that the limit state design proposals have been evolved from the provisions of various earlier codes and the resulting changes in design, being minimal, provides the designer a greater freedom of choice.
3. A successful design should not only satisfy requirements but also ensure:
b) Total cost
c) Critical period
Answer: a [Reason:] A successful design should not only satisfy the requirements of safety against total collapse of the structure due to various causes, but also ensures that the serviceability of the structure is not impaired while resisting normal working loads.
4. The primary object of structural design is to obtain:
a) Structural plan
b) Structural solution
c) Structural design
d) Structural lane
Answer: b [Reason:] The primary object of structural design is to obtain a structural solution which can result in the result greater overall economy by providing the maximum assistance in satisfying all the other requirements of the structure.
5. The permissible or working stress method of design, by Morsh is also referred as:
a) Limit theory
b) State theory
c) Elastic theory
d) Stress theory
Answer: c [Reason:] In this method the permissible stresses in a concrete and steel are assumed to be a fraction of the specified strength of individual material and a constant modular ratio is assumed for all loading conditions with the elastic behavior of concrete and steel, the permissible or working stress method of design pioneered by the German professor Morsch is also sometimes referred as elastic theory of design.
6. The inadequacy of the working load design in predicting ultimate loads of structure was recognized after:
a) Second world war
b) Cold war
c) Red war
d) First world war
Answer: d [Reason:] The inadequacy of the working load design in predicting ultimate loads of a structure was recognized after the first world war the factor of safety applied to the consistent materials does not present a realistic picture of the degree of safety against the collapse of the composite materials such as reinforced concrete used in the structural component.
7. The structure designed by ultimate load method, although having a desirable margin of safety may not be safe at:
Answer: a [Reason:] A structure designed solely by the ultimate load method, although having a desirable margin of safety against collapse, may not be serviceable due to excessive deflections or development of objectionable cracks at service loads, this type of distress is particularly notecable in structures designed by ultimate load methods using high strength materials.
8. The ultimate load design concepts extended to the design of continuous beams and frames is referred as:
a) Working stress design
b) Permissible stress design
c) Limit state design
d) Collapse state design
Answer: c [Reason:] The ultimate load design have been extended to the design of continuous beams and frames where it is referred to as limit state design and this involves a redistribution of moments due to development of plastic hinges and an eventual collapse when the last critical hinge formed.
9. The philosophy of limit states is adopted and elaborated by:
a) European concrete committee(CEB)
b) European concrete committee(CEB)
c) European concrete committee(CEB)
d) European concrete committee(CEB)
Answer: a [Reason:] The philosophy of limit states was adopted and elaborated by the European concrete committee (CEB) to form the basis of the committee’s original publication in 1964and later in conjuction with the international federation for prestressing issued a complimentary report dealing with prestressed concrete in 1996.
10. The new philosophy of design termed the limit state approach was incorporated in which country code:
Answer: b [Reason:] A new philosophy of design, termed the limit state approach, which was incorporated in Russian code in 1954 basically the limit state design is a method of designing structures based on statistical concept of safety and the associated statistical probability of failure.
Prestressed Concrete Structures MCQ Set 5
1. The analysis of stresses developed in prestressed concrete structural elements is based on how many assumptions?
Answer: c [Reason:] The analysis of stresses developed in a prestressed concrete structural elements is based on the following assumptions: Concrete is a homogeneous elastic material, Within the range of working stresses, both concrete and steel behave elastically, notwithstanding the small amount of creep which occurs in both the materials under sustained loading, a plan section remains plain even after bending.
2. The tensile stresses when do not exceed the limit of modulus then change in loading of member results in:
a) Change of bending moment
b) Change of stress
c) Change in shear
d) Change in rupture
Answer: b [Reason:] As long as tensile stresses do not exceed the limit of modulus of rupture of concrete (corresponding to the stage of visible cracking of concrete), any change in loading of the member results in a change of stress in the concrete only, the sole function of the prestressing tendon being to impart and maintain the prestress in the concrete.
3. Which conditions are negligible at the stage of visible cracking on concrete?
a) Bending conditions
b) Joint conditions
c) Zone conditions
d) Loading conditions
Answer: d [Reason:] Up to the stage of visible cracking on concrete, the changes in the stress of steel, the loading being negligibly small, are generally not considered in the computations, the phenomenon of stress corrosion in steel is particularly dangerous, as it results in sudden brittle fractures.
4. The stresses due to prestressing are referred as:
a) Combined stresses
b) Bending stresses
c) Anchoring stresses
d) Tensioning stresses
Answer: a [Reason:] The stresses due to prestressing alone are generally combined stresses due to the action of direct load and bending resulting from an eccentricity applied load, the stresses in concrete are evaluated by using the well known relationship for combined stresses, this type of attack in alloys is due to the internal metallurgical structure, which is influenced by composition, heat treatment and mechanical processing.
5. Which of the following notations are used for evaluating the relationship for combined stresses?
a) P, E, M, A, I
b) P, σ, M, g, I
c) P, W, M, π, L
d) P, θ, M, Z, L
Answer: a [Reason:] The notations and sign conservations used for the analysis of prestress are
P-Prestressing force, e-eccentricity of prestressing force, m – p × e – moment
A – Cross sectional area of the concrete member, I – second moment of area of section about its centroid.
6. The uniform prestress in a concrete member subjected to concentric prestressing is:
Answer: d [Reason:] Uniform prestress in concrete p/a, which is compressive across the depth of the beam and the applied loads, dead loads of the beam include tensile stress towards the soffit and are counterbalanced more effectively by eccentric tendons.
7. In case of eccentric prestressing force the support force Fsup is:
a) Fsup = p/a(1+eyb/i2)
b) Fsup = p/a(1+eyb/i2)
c) Fsup = p/a
d) Fsup = p/a-eb
Answer: b [Reason:] The stresses developed at the top and bottom fibers of the beam are obtained by the two relations:
Finf = (p/a+pe/zb) = p/a(1+eyb/i2), Fsup = (p/a-pe/zb) = p/a(1-ybt/i2).
8. The diagram indicating the direct stress of the beam is:
Answer: a [Reason:]
9. The diagram indicating the bending stress of the cross section the beam is:
Answer: a [Reason:]
10. The cross section of beam is combination of:
a) Direct stresses and Bending stresses
b) Principal stresses and Shear stresses
c) Anchorage and Tension stresses
d) Flexural and Rigidity stresses
Answer: a [Reason:]