This set of Prestressed Concrete Structures Multiple Choice Questions & Answers (MCQs) focuses on “Maintenance of Structures”.
1. In prestressed concrete structures the primary problem is damaged caused to:
a) Bridge decks
Explanation: In prestressed concrete structures the primary problem is damage caused to anchorages and unbounded tendons due to rusting under exposure to humid weather conditions and good maintenance practice requires periodical surveillance identification of local damage, deterioration and loss of durability of the structure due to environmental and other load effects and in such cases local repairs are needed.
2. Rehabilitation of structures may be required due to several reasons one reason is:
a) Environmental effects
b) Tensile effects
c) Compressive effects
d) Range effects
Explanation: Rehabilitation of structures may be required due to several reasons one reason is:
Environmental effects some common causes are constructional deficiency, environmental effects, deficiency in design, overloading of structures either due to un anticipated loading or due to accidents and user made changes in the structures during the service life of the structure.
3. The problem of rehabilitation is:
Explanation: The problem of rehabilitation is Unique, For the particular structure and hence the use of common techniques for rehabilitation of various structures is limited and as far as maintenance is concerned, several new cementations materials and epoxy resigns and compounds have been developed which are highly effective in protecting the basic structure from the destructive effects of severe exposure conditions in the environment.
4. Maintaining prestressed concrete structures of various types in a fit and serviceable condition is primary function of:
a) Maintenance engineer
b) Design engineer
c) Surface engineer
d) Structural engineer
Explanation: Maintaining prestressed concrete structures of various types in a fit and serviceable condition is primary function of Maintenance engineer investment towards effective periodical maintenance forms only a fraction of the cost to be incurred due to major repairs to rehabilitate the structures and hence it is always advisable to establish a programmed preventive maintenance system to detect any signs of distress in the initial stages itself through inspection procedures and appropriate repairs.
5. The structural concrete slab panels can be repaired by:
a) Internal bonding
b) External bonding
c) Stress bonding
d) Layered bonding
Explanation: The structural concrete slab panels and beams exhibiting distress can be repaired by external bonding of steel plates to the soffit by using epoxy adhesives and hollows, honey combs and cavities in concrete can be repaired by the process of guniting and shortcreting applied pneumatically with impact force.
6. The impression of structure is of:
Explanation: Routine inspection under this category, general inspections are carried out quickly and frequently by highway maintenance engineers having reasonably practical knowledge of highway structures through not necessarily experts in design,
Detailed inspection: This type of inspection can be further divided as general and major depending upon the frequency and extent of inspection,
Special inspection: Special inspection is resorted to under extraordinary situations such as earthquakes, high intensity/ abnormal loading, floods etc.
7. Which type of inspection is more intensive involving examination of structural elements?
a) Minor inspection
b) General inspection
c) Major inspection
d) Reverse inspection
Explanation: Major inspection is generally more intensive involving detail examination of all structural elements and even requiring setting up of special access facilitates (like soffits of long span beams and articulation locations, bearing etc) where required depending upon the importance of the structure, this type of inspection is spaced between 2 and 3 years or may be at smaller intervals for sensitive structures which are exposed to aggressive environments.
8. Prestressed concrete structures showing visible signs of distress in the form of:
a) Surface cracks
d) None of the mentioned
Explanation: Prestressed concrete structures showing visible signs of distress in the form of surface cracks, spalling of concrete should be special inspection using instruments to users the extent of damage to the structure.
9. One of the testing equipments used for inspection is:
a) Strain gauges
b) Measuring jar
c) Test tubes
d) None of the mentioned
Explanation: Modern testing equipments which could be of use to the specialized inspection team are listed below:
Rebound hammer compressive strength (Schmidt hammer), ultrasonic pulse velocity detection of cracks, snooper-crawler and adjustable ladders, magnetic decor for measuring thickness of concrete cover and for locating reinforcement bars, mechanical extensometer, transparent templates and microscope for reading of crack widths on the surface of the concrete hydraulic jacks, pressure transducers or load cells for measurement of forces etc, electronic strain gauges for measurement of strain in concrete and steel, vibration measuring equipment, electrical resistance meter(for rust pockets).
10. The pachometer is used to locate the:
a) Steel reinforcement
b) Aluminium reinforcement
c) Tensile reinforcement
d) Surface reinforcement
Explanation: A wide variety of electronic equipment is presently available in the market in many countries for monitoring and inspection of distress in different types of structures and ultrasonic meters are used to determine the degree of deterioration and distress and / or material imperfections that are relevant to the structural integrity of the structure to be inspected and pachometer is used to locate the steel reinforcements and measures the sizes of the bars embedded in concrete to an accuracy of 3m.
11. In case of bridge greater than 10.7m in height and which cannot be inspected from beneath due to watery situation the instrument suited for inspection work is:
a) Electrical resistance meter
b) Strain gauges
c) Barins snooper vehicle
d) Rain guages
Explanation: In the case of bridges greater than 10.7m in height and in those bridges which cannot be inspected from beneath due to rugged terrain or watery situations, a mechanical contraction widely known as Barins snooper vehicle is ideally suited for inspection work and the snooper is mounted on a heavy duty truck with a swiveling platform and the underside of the bridge deck can be inspected by using the hydraulically operated platform.
12. In the case of dormant cracks wider than about 1m, it is more economical to use:
a) Epoxy resin
Explanation: In the case of dormant cracks wider than about 1mm, it is more economical to use the grouting and sealing technique and this method involves enlarging the crack along its exposed face and then the crack is cleaned and grouted and the surface is then sealed with a suitable joint sealant and various other techniques widely used for repair of dormant or dead cracks include dry packing, polymer impregnation over lays and surface treatments and autogenous handling.
13. How many sealants are there used depending upon their suitability in a given situation:
Explanation: The following three types of sealants are generally used depending upon their suitability in given situation: Mastics are asphalts with a low melting point with added fillers or fibers and they are recommended where the total movements will not exceed 15 percent of the width of groove, Thermoplastics comprising of asphalts, pitches and coal tar become liquid or semi viscous when heated and the groove depth to width ratio should 1:1 and the total design movement is of order of 25 percent of groove width and Elastomers include a wide range of materials such as poly sulphides, epoxy poly sulphides, poly urethane, silicones and acrylics and these materials advantages since they can be used without heating.
14. How many types of damages are present in classification of damage?
Explanation: Minor damage requires superficial patching by using epoxy grout or guniting using Shortcrete and the damages and delaminated concrete is removed by hand tools and the surface is cleaned before the application of epoxy grout, moderate damage involves extensive spalling and cracking of concrete is generally applicable as in minor repairs and in Several damage Prestressed concrete girders requires a detailed structural analysis of a design check based on the conditions of the damage and the best engineering assumptions and judgments.
15. If the loss of prestress is excessive resulting in tensile cracks, which method should be used:
a) Preloading method
b) Hollow method
c) Transparent method
d) Layered method
Explanation: If the loss of prestress is excessive resulting in tensile cracks, preloading methods should be seriously considered in making concrete repairs in order to restore the equivalent full or partial prestress effect, as per original designs.
Sanfoundry Global Education & Learning Series – Prestressed Concrete Structures.
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