Bridge Construction.ppt

Bridge Construction

‫بسم هللا الرحمن الرحيم‬

BRIDGE CONSTRUCTION

BY Dr. Ahmed Abdel-Atty Gab-Allah (Zagazig University) 1

Bridge Construction

OUTLINE 1. INTRODUCTION. 2. BRIDGE CONSTRUCTION SYSTEMS.

3. BRIDGE CONSTRUCTION IN EGYPT.

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Bridge Construction

1. INTRODUCTION 

Importance of bridges.



Objective:  Review



latest bridge construction systems.

Scope:  Highway

bridges (90%).  Prestressed concrete (most recent developments).  Superstructures.

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2. BRIDGE CONSTRUCTION SYSTEMS 

Classification of Bridges: 

Purpose of Bridge: Highway bridges, railway bridges, foot bridges, viaducts, elevated roads, etc.



Material of Construction: Timber, masonry, steel, reinforced concrete, prestressed concrete, etc.



Type of Superstructure: Slab, girder, arch, truss, rigid frame, etc.



Type of Support: Simply supported, continuous, balanced cantilever, cable-stayed, and suspension bridges.

  

Life of Bridge: Permanent and temporary bridges. Navigation Requirements: Fixed, movable, and overhead bridges. Span Length: Minor bridges (spans of 8 to 30 m), major bridges (spans of 30 to 120 m), and long span bridges (spans above 120 m). 4

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2. BRIDGE CONSTRUCTION SYSTEMS 

Selection of Bridge Construction Systems:  Phases

of Bridge Construction Projects: Surveying

works, Soil investigation, Bridge layout planning, Selection of construction system, Design, and Construction (Construction-Oriented Design).  Alternative

Bridge Designs: (Based on broad

requirements specified by the owner).  Evaluation

Criteria: Economy, Functional

Requirements, Long-Term Performance, Construction and Design Requirements.

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Classification of Prestressed Concrete Bridges: Category Pre-tensioned Girder Bridges (I- or T- Beam)

Method of Construction  Erected with Cranes  Erected with Launching Girders

Cast in-situ:

Post-tensioned Bridges

 On Falsework  Cantilever Segmental  Span by Span

Precast:  Incremental Launching  Cantilever Segmental  Span by Span

Cable-Stayed Bridges Suspension Bridges

 Incremental Launching  Free Cantilever  Balanced Cantilever

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Bridge Construction

Latest Bridge Construction Systems:

System Code

Description

A

Precast, Prestressed Concrete Girders

B C D E F G

Incremental Launching Construction (Deck Pushing System) Cast-in-place, Balanced Cantilever Construction Precast Segmental, Balanced Cantilever Construction Flying Shuttering System Cable-Stayed Bridges Suspension Bridges 7

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Suitability of Bridge Construction Systems: Structure Span Lengths Structure Depth Level

Sys.

Site Cond.

Other Aspects

A

Inaccess.

High

Short (40 - 80 m)

Variable

Sharp curvatures & superelevations.

B

Inaccess.

High

Short (40 - 80 m)

Constant

Straight or slightly-curved superstructures.

C

Inaccess.

High

Long (up to 250 m)

Variable

Crossing navigable waterways.

D

Inaccess.

High

Long (up to 200 m)

Variable

Crossing navigable waterways.

E

Inaccess.

High

Short (40 – 70 m)

Variable

Long viaducts with short spans.

F

Inaccess.

Very High

Long (200 to 1,000 m)

Variable

Crossing deep rivers, deep valleys, and mountains.

G

Inaccess.

Very High

Very Long (500 to 2,000 m)

Variable

Crossing deep rivers, deep valleys, and mountains. 8

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(A) Precast, Prestressed Concrete Girders 

System Concept:



Utilization of precast, prestressed I- of T- girders, on top of which a deck slab is cast.  Girders are usually erected by means of mobile cranes.  However, in case of inaccessible sites, a launching truss may be used for this purpose.

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(A) Precast, Prestressed Concrete Girders

Launching Truss – Schematic Diagram

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(A) Precast, Prestressed Concrete Girders 

Main System Components: 

Formwork: Forms for precast girders and formwork for deck slab. (In case of T- girders, the flanges provide support for deck slab).



Gantry Cranes: Required at fabrication area (to carry girders to storage area and load them to trolleys, as well as to carry reinforcing cage to the form).



Trolleys: Two trolleys are usually required to transport girders to their spans. Specially designed rubber-tired vehicles may also be used for this purpose.



Launching Truss: A steel launching truss, equipped with two hoists, is required for erecting precast girders into their final positions.

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(A) Precast, Prestressed Concrete Girders 

Construction Sequence:



Casting of girders in a casting yard.  Transporting girders to their spans by means of trolleys.  Carrying girders by launching truss which is positioned over respective span.  Erecting girders into their final positions.  Casting of deck slab.  Moving launching truss forward to next span.

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(A) Precast, Prestressed Concrete Girders Advantages: 

Economy, speed, and improved quality of mass production.  Sharp curvatures & superelevations.  Inaccessible sites.  No interference with traffic.

Disadvantages: 

Casting yard, transport and erection equipment.  Unsuitability for complex roadway geometry.

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(A) Precast, Prestressed Concrete Girders

Post-Tensioning of Girders

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(B) Incremental Launching (Deck Pushing) 

System Concept:



Superstructure segments are cast in stationary formwork in a casting yard located at one end of the bridge.  After each segment is completed, the superstructure is pushed forward to the other end of the bridge.  In case of long superstructures, two casting yards (one at each abutment) may be provided.  In this case, the superstructure is pushed forward from both abutments towards the center of the bridge.

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(B) Incremental Launching (Deck Pushing)

Incremental Launching Construction – Schematic

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(B) Incremental Launching (Deck Pushing) 

Main System Components: 

Formwork: Rear half consists of forms for bottom slab and lower part of webs, whereas front half of forms for the rest of box section.



Lifting and Pushing Equipment: Vertical hydraulic jacks are used to lift the bridge slightly at the abutment before each advance. Then, horizontal jacks are used to push the superstructure forward.



Temporary Bearing Blocks: Concrete blocks covered with thin stainless-steel sheets, constructed on top of all supports to reduce friction during launching operation. (Friction forces can be reduced to about 2% of vertical loading by feeding Teflon sheets between the bridge soffit and the top of stainless-steel sheets).



Launching Nose: Lightweight-steel girder, tied to front end of bridge girder to reduce cantilever moment during launching operations.



Intermediate Supports: Temporary supports may be provided between final piers to reduce bending moments during launching of superstructure. (Used when span-to-depth ratio > 17:1).

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(B) Incremental Launching (Deck Pushing)

Temporary Bearing Blocks

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(B) Incremental Launching (Deck Pushing) 

Construction Sequence:



Construction of casting yard(s), including formwork and launching nose.  Installation of pushing and/or pulling systems, and temporary bearing blocks.  Construction of superstructure.  Disassembling of formwork, pushing and pulling systems, and launching nose.  Demolition of casting yard(s).  Erection and stressing of post-tensioning cables in longitudinal girders (webs).  Replacement of temporary bearings by permanent bearings. 19

Bridge Construction

(B) Incremental Launching (Deck Pushing) Advantages: 

Inaccessible sites.  Riding learning curve (Repetitive operations).  No interference with traffic.

Disadvantages: 

Casting yard and pushing equipment.  Increase in longitudinal prestressing (cantilever moments).  Large labor force during launching.  Unsuitability for complex roadway geometry.

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(B) Incremental Launching (Deck Pushing)

Construction Sequence

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(B) Incremental Launching (Deck Pushing)

Inc. Launching Construction

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(C) Cast-in-Place, Balanced Cantilever (Cantilever Carriage System) 

Bridge Construction

System Concept:



Superstructure is cast in segments in traveling forms.  These forms are supported from one end on completed part of superstructure, while the other end is a free cantilever.  After concrete reaches required strength, forms are moved forward and prepared for next segments.

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(C) Cast-in-Place, Balanced Cantilever 

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Main System Components: 

Form Travelers: Consist of main frames, guide rails, and suspended platforms. Main frames run on upper guide rails and both frames and rails are attached to finished portion of superstructure by means of tie-down anchors. Forms are suspended from main frames; they can be stripped in a single operation by lowering main frames.



Pier Brackets: Used to provide support for the formwork of pier tables. If a pier is low, pier brackets may be supported on pier footing or directly on the ground. But if a pier is high, pier brackets are usually built out from the pier cap and pier shafts.



Local Bracings: Required for closure pours.

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(C) Cast-in-Place, Balanced Cantilever

Form Travelers - Schematic Diagram

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(C) Cast-in-Place, Balanced Cantilever 

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Construction Sequence:

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(C) Cast-in-Place, Balanced Cantilever 

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Construction Sequence (Contd.):

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(C) Cast-in-Place, Balanced Cantilever

Cantilever Carriage System – Closure Pour

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(C) Cast-in-Place, Balanced Cantilever

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Advantages: 

Inaccessible sites.  Long navigation channels.  No interference with traffic or navigation.  High labor efficiency.

Disadvantages: 

Special equipment and skilled labor.  High precision required.  Increase in reinforcement (cantilever moments).  Limited length of segments.  Low construction rate. 29

(C) Cast-in-Place, Balanced Cantilever

Construction Sequence

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(C) Cast-in-Place, Balanced Cantilever

Cantilever Carriage Construction

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(D) Precast Segmental, Balanced Cantilever 

System Concept:



Superstructure is precast and prestressed in segments in a fabrication area.  Segments are then transported to bridge site, where they are erected into their final positions.

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(D) Precast Segmental, Balanced Cantilever

Erection Procedure 33

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(D) Precast Segmental, Balanced Cantilever

Erection Procedure (Contd.)

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(D) Precast Segmental, Balanced Cantilever 

Main System Components: 

Formwork: Consists of a rigid outer shuttering and a hydraulically operated collapsible inner shuttering. Inner shuttering can be completely removed during demoulding.



Transport Equipment: Precast segments are normally transported to the site by trailers. Segments should be of transportable size and weight.



Erection Equipment: A variety of erection equipment types can be used (such as truck cranes, crawler cranes, floating cranes, launching girders, cableways, etc.). However, a launching truss equipped with hoists is commonly used.

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(D) Precast Segmental, Balanced Cantilever 

Fabrication of Precast Segments:



To achieve a perfect fit between the ends of adjacent segments, each segment is cast against the end face of the preceding one. (This is called “Match-Casting” of segments).  Segments are then erected in the same order in which they were cast.  An epoxy resin (about 0.8 mm thick) is normally applied to the match-cast contact surface. It serves as a bonding and leveling agent that transfers the shear and bending stresses to the adjacent segment.  Shear keys are usually provided in each web of the segments to handle erection stresses prior to the epoxy achieving final strength. 36

Bridge Construction

(D) Precast Segmental, Balanced Cantilever  

Erection of Precast Segments:

Precast segments are picked from transport trailer and launched to their spans by means of launching truss.  They are then lowered to their level where epoxy resin is applied to the contact surface with the previously erected segments.  They are finally tied to previously erected segments by posttensioning cables.  Segments are erected on either sides of the pier alternatively (to maintain balanced cantilevers, which will minimize the out-of-balance moment at the pier).  After the two cantilevers reach mid-span, the launching truss is moved forward to next span, where it will be ready for erecting another pair of balanced cantilevers. 37

Bridge Construction

(D) Precast Segmental, Balanced Cantilever Advantages: 

Economy, speed, and improved quality of mass production.  No interference with traffic or navigation.  Low labor requirement for both fabrication and erection operations.  Adaptability to curvatures and superelevation.

Disadvantages: 

Casting yard, transport and erection equipment.  High precision required.  Increase in reinforcement (cantilever moments). 38

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(D) Precast Segmental, Balanced Cantilever

Construction Sequence

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(D) Precast Segmental, Balanced Cantilever

Precast Segmental Construction

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(E) Spanwise Construction Using Stepping Formwork (Flying Shuttering System) 

System Concept:



Entire span is cast in place in stepping formwork (flying shuttering), supported on specially designed and fabricated steel trusses extending over the piers.  After completion of the span, form trusses carrying the formwork are moved forward to next span.

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(E) Flying Shuttering System

Bridge Construction

Stepping Shuttering Construction – Schematic Diagram

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(E) Flying Shuttering System 

Bridge Construction

Main System Components: 

Stepping Formwork: Made of steel panels. Outer formwork is supported by steel trusses, whereas inner formwork rolls forward on rails within the box section.



Form Trusses: Two longitudinal steel trusses are erected beneath the two side cantilevers of the box girder. They are designed to carry the forms of entire span.



Support Frames (or Pier Brackets): Erected on top of piers to support form trusses. Steel rollers are usually used at support frames to facilitate launching of trusses.



Hydraulic Jacks: Used for advancing form trusses. They may be installed at end of trusses, at next pier, or at finished portion of the bridge.



Intermediate Supports: In case of long spans, intermediate supports for the trusses may be used. 43

(E) Flying Shuttering System 

Bridge Construction

Construction Sequence:



Erection of support frames.  Erection of form trusses and outer formwork.  Concreting of the box girder floor.  Erection of inner formwork.  Concreting of webs and top slab at one pour.  Partial prestressing of longitudinal cables.  Opening the stepping shuttering, and advancing form trusses and stepping shuttering to next span using hydraulic jacks.  Preparation of stepping shuttering to cast the next span.  Final prestressing of cables after concreting of all spans, to make the whole bridge continuous. 44

(E) Flying Shuttering System

Bridge Construction

Advantages: 

Long viaducts with short spans.  No interference with traffic.  High construction progress rate.

Disadvantages: 

Special equipment.  Unsuitability for long spans.

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(E) Flying Shuttering System

Construction Sequence: Concreting Phase and Advancing Phase

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(E) Flying Shuttering System

Flying Shuttering Details

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(F) Cable-Stayed Bridges  

Bridge Construction

System Concept: The superstructure is supported at one or more points by high-tensile steel cables, extending from support towers and connected directly to the deck.

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(F) Cable-Stayed Bridges 

Bridge Construction

Cable Arrangements:

Transverse: (a) (b) (c) (d)

Single Plane – Vertical Single Plane - Vertical/Lateral Double Plane – Vertical Double Plane - Sloping

Longitudinal: (a) (b) (c) (d)

Radiating Harp Fan Star

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(F) Cable-Stayed Bridges 

Bridge Construction

Construction Methods:



The selection of appropriate construction method depends on many factors (stiffness of pylon, cable anchorage system, possibility of installing temporary supports, maximum length of unsupported spans permitted by design, and ease of transporting materials).  Balanced cantilever construction is probably the most favorable construction method for modern cable-stayed bridges.  However, other construction methods can also be used [e.g, Incremental Launching (Deck Pushing) and Free Cantilever Construction]. 50

Bridge Construction

(F) Cable-Stayed Bridges 

Stay Technology: Cables

(a)

(c)

(b)

(d)

Types of Stay Cables: (a) Parallel-Bar; (b) Parallel-Wire; (c) Stranded; (d) Locked-Coil

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(F) Cable-Stayed Bridges 

Bridge Construction

Stay Technology: Anchorages

Anchorage System for Parallel-Wire Cables

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(F) Cable-Stayed Bridges 

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Stay Technology:

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(F) Cable-Stayed Bridges

Bridge Construction

Advantages: 

High clearance for traffic or navigation.  Suitability for long spans.  Less material quantities (smaller depths).

Disadvantages: 

High risks involved in bridge construction.  High tech. required (very long span lengths).  High degree of control required on quality, time and budget.

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(F) Cable-Stayed Bridges

Bridge Construction

Construction Systems:

• • •

Balanced Cantilever. Free Cantilever. Deck pushing.

Balanced Cantilever (Cast-in-Place)

Free Cantilever

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(G) Suspension Bridges  

Bridge Construction

System Concept: The superstructure is supported by steel suspenders (vertical hangers) attached to main cables that are stung over the support towers in the form of a catenary.

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(G) Suspension Bridges 

Bridge Construction

Construction Methods:



Most construction methods for cable-stayed bridges are still applicable for suspension bridges.  However, the suspension cable technology is different from the stay cable technology, particularly the anchorage of main cables, and the connections of vertical hangers to the main cables.

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(G) Suspension Bridges 

Bridge Construction

Construction Sequence:

1. 2.

3. 4. 5.

Construction of towers and precasting of superstructure segments. Erection of main cables. Strands are pulled by winches and erected individually using specialized equipment. Installation of cable clamps and hanger rods using cranes. Transporting superstructure segments below their final position on barges. Erection of segments using erection equipment (erection girders, for example).

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(G) Suspension Bridges 

Bridge Construction

Construction Sequence: (Contd.)

6. 7.

8. 9. 10.

Jacking-up of each segment prior to erection of hanger bars. Erection of hanger bars and their adjustment to predetermined lengths to bring the segments into alignment. Interconnection of superstructure segments. Cambering the superstructure upwards by controlled adjustment of hangers before casting the deck. Bringing the deck to its final level through a final set of hanger adjustments.

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(G) Suspension Bridges

Bridge Construction

Advantages: 

High clearance for traffic or navigation.  Suitability for very long spans.  Less material quantities (smaller depths).

Disadvantages: 

High risks involved in bridge construction.  High tech. required (very long span lengths).  High degree of control required on quality, time and budget.

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3. BRIDGE CONSTRUCTION IN EGYPT 

Major Bridge Projects in Egypt

Sys.

Major Applications

Span Lengths (m)

Comp. Date

A

 6th of October Bridge (Ramsis/Ghamra).  Ring Road 9-D Bridge.

B

 Zamalek Elevated Road.  Dessouk Overhead Bridge.

C

 Al-Giza New Bridge.  6th of October Bridge.  Abou El-Ela Bridge.  Rod El-Farag Bridge.  New Benha Bridge.  Al-Warrak Bridge

33 – 40 40 31@25, [email protected] 34.2, [email protected], 5@40, 34 104, 2@69 110, 2@100, 2@70 115, 2@69 130, 2@75 120, 2@69 120, 2@60

1988 1998 1986 1987 1969 1976 1986 1990 1990 2000

D E

Has Not Been Applied  6th of October Br. (Ghamra/ Autostrad).  Suez Canal Bridge, Approach Spans.  6th of October Br.(Ghamra/Autostrad).  Suez Canal Bridge, Main Spans. Has Not Been Applied

42 40 133 (66.5 in each side) 404, 2@163

1998 2001 1998 2001

F G

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Bridge Construction Systems Applicable forBridge Construction Different Site Conditions in Egypt

System # Site Conditions Code A Under Running I B Traffic E C Across Navigable II D Waterways F Deep Waterways and F III Mountains G A* IV At Accessible Sites* B* E*

System Description Precast concrete girders. Incremental launching. Flying shuttering. Cantilever carriage. Precast segmental construction. Cable-stayed bridges. Cable-stayed br. (up to 1000 m). Suspension bridges (> 1,000 m). Precast concrete girders. Incremental launching. Flying shuttering.

* May be feasible for accessible sites, particularly for very high superstructures (high approach spans and viaducts).

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Thank you for listening

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