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Construction of prestressed concrete structures


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This presentation defines the construction of prestressed concrete structures

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Construction of prestressed concrete structures

  1. 1. Title : Presented by: Major Adviser: HARPREET KAUR Dr. Jaspal Singh L-2015- AE- 187 M -Tech Prof. cum Head
  2. 2.  Management functions of construction comprises of some following activities 1. Tendering and winning the contract 2. Contract negotiations 3. Mobilizing the financial resources for the work 4. Maintaining proper accounts 5. Work planning 6. Work supervision 7. Project control and monitoring 8. Maintenance of good labour relation 9. Completion of the work
  3. 3. Mainly following two methods are widely used in ‘ PROJECT MANAGEMENT’ 1.CPM- (Critical Path Method) 2.PERT-(Project Evaluation And Review Technique)
  4. 4.  This method of const. first developed in western Europe particularly in France & Germany during 1950’s.  Over 70 bridges of this type under const. during 1971-75 in France.  In India during 1960-61,@ 250m long Barak bridge was constructed.
  5. 5.  There are the two basic materials for the construction of prestressed concrete structures 1. High-strength concrete 2. High-tensile steel
  6. 6. According to Indian standard code IS:1343 1. The minimum grade for post tensioning is M-30. 2. The minimum grade for pretensioning is M-40. Recent advances in concrete technology include the development of 1.Rheodynamic concrete 2.High performance concrete 3.Nano concrete 4.Ultra high strength concrete ….are suitable for prestressed concrete structures.
  7. 7. These joints are necessary due to following reasons …. 1. Thermal contraction and expansion in structure 2. Shrinkage of concrete 3. Creep or inelastic deformation of structure 4. Elastic shortening under prestress 5. Displacement of the structure under load or any other action
  8. 8. Construction techniques includes the following…. 1.General aspects 2.Cantilever construction 3.Choice of spans and the method of construction 4.Prestressing cables 5.Epoxy bonding of precast segmental box girders 6.Innovative construction techniques
  9. 9. 1. Rapid developments in construction techniques. 2. Advances in materials of construction. 3. Prestressed concrete is ideally suited for large spans, its application is much less for substructures than for superstructures.
  10. 10. This method … 1. Eliminates the use of expensive formwork 2. Scaffolding Especially for bridges in deep valleys and rivers with large depth of water. It is mainly includes following two methods 1. Cast insitu construction. 2. Construction using precast segment.
  11. 11.  In this method bridge is cast in situ with section 3 to 6 m long, cantilevering on both sides of pier.  Formwork is cast by steel frame work  The operations of this method are as follows 1. Fabrication and shuttering 2. Placing of reinforcement and duct tubes for high tensile cables 3. Concentering 4. Curing of concrete
  12. 12. 1. Threading ,anchoring and grounting of the cables. 2. Releasing the formwork and moving on to next section. Prestress can be applied only after the concrete developed the desired strength after one week. For e.g. the Bessein creek bridge by Gammon India company at Bombay
  13. 13.  This method is used for the long bridges. It is economical when there is large no of span. This method involves the following steps.  Casting of Precast segments in casting yard.  Transporting the precast segments at the site.  Erection of the precast segment using launcher or crane.  External Prestressing.  Grouting.
  14. 14.  A Segmental Bridge is a bridge built in short sections (called segments), that is one piece at a time. And then segments are erected to make the bridge. The bridge is either cast-in- place or precast.
  15. 15.  It is economical for large project, due to investment req. for casting, handling & erection of precast segments.  The construction of a flyover in an urban environment is not always welcomed by the society because of traffic disturbance & construction delays, nuisance caused during concreting & erecting the formwork at site and noise & visual pollution.
  16. 16. Selection of method of construction is mainly based on following 1. Size of the bridge 2. Length of the span 3. Precasting facilities available at site 4. Equipments available  Cantilever method is used in range of 50 to 200 m .  For small spans of less than 50 m ,precast segmental method is preferred
  17. 17.  The following points are important for cantilever construction technique 1. After erection of each modular section cables should be threaded into the ducts. 2. The voids must be enough large for proper grouting. 3. The commonly used cables comprise 12 wires of 13 dia. And 12wires of 8mm diameter cables (Freyssient system).
  18. 18.  Following re the techniques used for the construction of prestressed concrete bridges are listed below…… 1. The staging method 2. Incremental launching or push out technique 3. Progressive placement construction method 4. Cantilever construction method
  19. 19.  This technique is adopted when 1. Low clearance is required below the deck 2. Supporting formwork does not interface with the traffic This method facilitates rapid construction by maintaining correct geometry of the structure with low cost. This technique has been used in the construction of Rhine river at Maxau,Japan
  20. 20. 1. Segments of the Bridge superstructure are cast at site in length of 10 to 30 m in stationary forms located behind the abutment. 2. Each unit is cast directly against the previous unit. 3. After the concrete attains the desired strength, the new unit is joined to the previous unit by post tensioning. 4. The assembly of units is pushed forward in stepwise for casting and succeeding segments
  21. 21.  In this case construction starts at one end of the structure and proceeds continuously to the other end (cantilever end) 1. This method have found to be practicable and economical in range of 30 to 90 m. 2. This method has been used for ‘Linn cove viaduct in north Carolina’ USA .
  22. 22. Basic information related to ‘ Linn cove viaduct in north Carolina’USA. 1. Total length1,243 feet (379 m) 2. Width39.5 feet (12.0 m) 3. Construction begin1979 4. Construction end1987
  23. 23.  During the last decades, construction techniques developed have shown major progress towards simplification.  The collective experience and knowledge gained through research and practice during the last fifty years will help in involving innovative applications in the construction of prestressed concrete structures
  24. 24. 1. N Krishna raju Prestressed concrete ,Tata McGraw –Hill publishing Co. Ltd, New Delhi,2007,pp 715-729 2. Internet