PUNJAB AGRICULTURAL UNIVERSITYLUDHIANA

Title :

Presented by: Major Adviser:HARPREET KAUR Dr. Jaspal SinghL-2015- AE- 187 M -Tech Prof. cum Head

CONSTRUCTION OF PRESTRESSED

CONCRETE STRUCTURES

CONSTRUCTION OF PRESTRESSED

CONCRETE STRUCTURES

Management functions of construction comprises of some following activities

1. Tendering and winning the contract2. Contract negotiations3. Mobilizing the financial resources for the work4. Maintaining proper accounts5. Work planning6. Work supervision7. Project control and monitoring8. Maintenance of good labour relation9. Completion of the work

CONSTRUCTION MANAGEMENT

Mainly following two methods are widely used in ‘ PROJECT MANAGEMENT’

1.CPM- (Critical Path Method)

2.PERT-(Project Evaluation And Review Technique)

METHODS FOR PROJECT MANAGEMENT

History

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.

There are the two basic materials for the construction of prestressed concrete structures

1. High-strength concrete

2. High-tensile steel

CONSTRUCTION MATERIALS

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.

HIGH STRENGTH CONCRETE

These joints are necessary due to following reasons ….

1. Thermal contraction and expansion in structure2. Shrinkage of concrete3. Creep or inelastic deformation of structure4. Elastic shortening under prestress5. Displacement of the structure under load or any

other action

CONSTRUCTION AND EXPANSION JOINTS

Construction techniques includes the following….1.General aspects2.Cantilever construction cast insitu using precast segments

3.Choice of spans and the method of construction 4.Prestressing cables5.Epoxy bonding of precast segmental box girders6.Innovative construction techniquesStaging method push out technique Progressive placement construction method

CONSTRUCTION TECHNIQUES

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.

1.General aspects

This method …1. Eliminates the use of expensive formwork2. Scaffolding Especially for bridges in deep valleys and

rivers with large depth of water.It is mainly includes following two methods3. Cast insitu construction.4. Construction using precast segment.

CANTILEVER CONSTRUCTION

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 follows1. Fabrication and shuttering2. Placing of reinforcement and duct tubes

for high tensile cables3. Concentering4. Curing of concrete

CAST IN SITU METHOD

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

CONT…

 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.

 Precast Segmental Method

Segmental Construction Method Span-by-span

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.

SEGMENTAL BRIDGE CONSTRUCTION

PRECAST SEGMENTAL BRIDGE CONSTRUCTION USING LAUNCHING TRUSS

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.

Selection of method of construction is mainly based on following

1. Size of the bridge 2. Length of the span3. Precasting facilities available at site4. 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

CHOICE OF SPANS AND METHOD OF CONSTRUCTION

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).

PRESTRESSING CABLES

EPOXY BONDING OF PRECAST SEGMENTAL BOX GIRDER

Following re the techniques used for the construction of prestressed concrete bridges are listed below……

1. The staging method2. Incremental launching or push out technique3. Progressive placement construction method4. Cantilever construction method

INNOVATIVE CONSTRUCTION TECHNIQUES

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

THE STAGING METHOD

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

INCREMENTAL LAUNCHING OR PUSH OUT TECHNIQUE

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 .

PROGRESSIVE PLACEMENT CONSTRUCTION METHOD

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 begin19794. Construction end1987

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

Conclusion

1. N Krishna raju Prestressed concrete ,Tata McGraw –Hill publishing Co. Ltd, New Delhi,2007,pp 715-729

2. Internet

REFERENCES….