UNIT V PART A

Transcription

1 1. Why concrete bridges are used? [N/D 14] UNIT V PART A a. Reinforced concrete and prestressed concrete have been found most suited for the construction of high way bridges the former for small and medium spans and latter for long spans. Reinforcement concrete has been used on the railways upto 10m span and prestress concrete upto 24m in India but upto 35m in other countries. 2. What are the general aspects of prestressed concrete? a. Prestressed concrete is ideally suited for the construction of medium and long-span bridges. It has been widely used throught the world for simply-supported, continuous, balanced cantilever, suspension, hammer-head and bridle-chord-type bridge in the span range of 20 to 500 m. 3. Mention the advantages of prestressed concrete bridges? a. The advantages of prestressed concrete bridges are: b. High-strength concrete and high-tensile steel

2 c. Crack free structures d. Little maintenance e. Minimum disruption of traffic. 4. Where are the pretensioned prestressed concrete bridges deck used? (M/J 16) The pretensionedprestressed concrete bridges deck are used in conjunction with cast in situ concrete, resulting in composite bridge decks which are ideally suited for small and medium spans in the range of 20 to 30 m. 5. Where are the post tensioned prestressed concrete bridges deck used? a. The post tensioned prestresses concrete bridges is ideally suited for prestressing longspan girders at the site of construction, without the need for costly factory type installations like pretensioning beds. Segmental construction is ideally suited for posttensioning work. 6. What are the basic parts of a bridge?. [N/D 16] a. The basic parts of a bridge are: b. The substructure and c. The superstructure. 7. How do the structural systems of a bridge may be classified? a. The structural systems of a bridge are classified as: b. Beam bridges c. Frame bridges d. Arch bridges e. Cable stayed bridges f. Suspension bridges. 8. What are the two basic types for the deck systems? [A/M 14] a. The two basic type for the deck systems are: b. A reinforced concrete or partially prestressed concrete slab. c. An orthotropic steel plate. 9. Define plate girder (M/J 16) a. Plate girder bridges can provide a very competitive solution for short and medium span bridges. They are almost always designed to act compositely with the concrete slab.the plate girders are fabricated with two flanges welded to a thin web which usually has transverse stiffening and may have longitudinal stiffening. 10. Explain the uses of pigeaud s curve. a. M.Pigeaud developed these curves which help to analyze and design RCC bridge deck. But these curves are cumbersome to use since involve lot of minute graphical works and interpolations. To use these curves in computer we need the equations which could make the engineer s a lot easier. 11. What are the codes referred to design the concrete bridges elements? [A/M 14] a. The codes referred to design the concrete bridges elements are: b. IRC codes for concrete and prestressed composite bridges on railways. c. IRC , standard specification and code of practice for road bridges section III cement concrete. d. IS , Indian standard specification and code of practice for plain and reinforced

3 i. concrete. e. IS , Indian standard specification for mild steel and medium tensile bars and hard drawn wires for concrete mix for concrete. f. IRC , Design criteria for prestressed concrete road bridges. g. ID , Indian standard specification for cold twisted steel bars for concrete reinforcement tensile steel deformed bars concrete reinforcement. 12. What are the types of bridges usually used in PSC construction? a. The types of bridges that are used in PSC construction are: b. Arch bridges c. Slab bridges d. Beam and plate girder bridges e. Open web girder bridges f. Suspension bridges g. Cable stayed bridges 13. What are the methods used for design of deck slab? a. The following are the methods for design of deck slab: b. Determination of effective width of slab for a single concentrated load over a slab simply supported at two ends. c. Determination of effective width of slab for a single concentrated load placed on a cantilever slab. d. Determination of effective width of slab area over which the concentrated load is dispersed and coefficients to be used direction when slab is supported on four sides. e. Based on Pigeaud s method. 14. Mention the components for design of composite girders. a. The components for design of composite girders are: b. Steel beam which may be a rolled joist or a built up section c. Cast in situ reinforced concrete slab d. Shear connections 15. What are the specifications for the design of intermediate beams and edge beams? [A/M 14] 16. Specifications for the design of intermediate beams: a. One-fourth of the span of the beam b. Web thickness plus twelve time the least thickness of the slab c. Centre of centre distance between beams Specifications for the design of edge beams: d. One twelfth of the span of the beam e. Half web thickness plus six times the least thickness of the slab f. Half the distance to the adjoining beam. Part B (16marks) 1. A cylindrical PSC water tank of internal diameter 30m is required to store water over a depth of 7.5m. The permissible compressive stress in concrete at transfer is 13 N/mm2 and the minimum compressive stress under working pressure is 1 N/mm 2. The loss ratio is Wires of 5mm diameter with an initial stress of 1000 N/mm2 are available for circumferential winding and Freyssinet cables made up of 12 wires of 8mm diameter stressed to 1200 N/mm2 are to be used for vertical prestressing. Design the tank walls assuming the base as fixed. The cube strength of concrete is 40 N/mm2 [A/M 14]

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6 2. A prestressed cylindrical pipe is to be designed using a steel cylinder of 1000mm diameter and thickness 1.6mm. The circumferential wire winding consist of a 4mm high tensile wire initially tensioned to a stress of 1000 N/mm2. The ultimate tensile strength of wire is 1600 N/mm2. The yield stress of the steel cylinder is 280 N/mm2. fct=14 N/mm2, Ww =0.8 N/mm2. Determine the thickness of concrete lining required. Fmin = 0; modular ratio = 6 3. Design a free edge water tank of diameter 36m to store water for a depth of 5m. Assume ultimate stress in steel = 1500N/mm2. Stress in steel at transfer = 70% of ultimate stress. Safe stress in concrete = 0.5fck. Compressive stress in concrete at service condition= 0.1fck. Final stress in steel = 0.8 x stress in steel at transfer. Take modular ratio=5.5 fck = 45N/mm2 [N\D14] [A\M 16]

7 3. Write the design criteria of PSC pipes in detail

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10 4. Explain the step by step design procedure of circular tanks. [A/M 14]

11 5. Explain the types of PSC pipes with neat sketch [A/M 14]

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14 6. A non cylindrical PSC pipe of 1000mm diameter and thickness of concrete shell is 75mm is required to convey water at a working pressure of 1.5 N/mm2. The length of the pipe is 6m. The loss ratio is 0.8. Determine the circumferential wire winding of using 5mm diameter wires stretched to 1000 N/mm2. The maximum permissible tensile stress is 11.2 N/mm2[A/M 14]

15 7. Design a non cylindrical PSC pipe of 600mm internal diameter to withstand a working hydrostatic pressure of 1.05 N/mm2 using 2.5mm HYSD stressed to 1000N/mm2 at transfer.

16 Permissible maximum and minimum stresses in concrete at transfer and service load are 14 N/mm2 and 0.7 N/mm2. The loss ratio is Es = 210kN/mm2 and Ec = 35kN/mm2 [N/D 15]