CENG 426(Steel and Concrete Bridges)

Presented by: Osama Mahmoud 900080661

Ramy Ghowiba 900071976

Presented to: Dr. Mohamed Abdel Mooty

Eng. Ayman Thabit

Date: 6-3-2011

The American University in Cairo

Department of Construction & Architectural Engineering.

Research One (Imbaba Bridge)

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ContentsList of Figures...............................................................................................................................................3

Introduction.................................................................................................................................................4

History.........................................................................................................................................................5

Structural System........................................................................................................................................6

1)Supports:..............................................................................................................................................6

2) Train Structural System:......................................................................................................................7

3)Bracing.................................................................................................................................................8

4)Vehicles Structural System...................................................................................................................9

5)Pedestrian Structural System.............................................................................................................10

6) Movable Span....................................................................................................................................11

Conclusion.................................................................................................................................................13

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List of FiguresFigure 1(Sheikh Zayed Bridge).....................................................................................................................4Figure 2(Imbaba Bridge)..............................................................................................................................6Figure 3(The adjacent hinges that support the different spans with the complete structural separation). 6Figure 4(A Hinge Support)...........................................................................................................................7Figure 5(Another Hinge Support)................................................................................................................7Figure 6(Railway Supports)..........................................................................................................................8Figure 7( A rough Sketch of the 70 meters Typical Arch Truss for Imbaba Bridge)......................................8Figure 8(The arched trusses that feature the Imbaba bridge).....................................................................8Figure 9: The different bracings occurring to add stability to the main structural system..........................9Figure 10: The structural system of the Vehicles from below...................................................................10Figure 11: Structural System of the pedestrian part of Imbaba bridge......................................................11Figure 12(Movable Span)...........................................................................................................................11Figure 13(Circular Spacing between the movable span and the neighboring span)..................................12Figure 14(Circular Spacing between the movable span and the neighboring span)..................................12

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Introduction

Nowadays, as the demand for making transportation and moving from one place to

another in one city increased, the demand for bridges increased. Although in the past the main

purpose of a bridge was to allow cross from one side of a river to the other side of the river,

recently bridges are considered a prestige symbol and landmark for any country and that is why

nowadays architectural engineers are keen on giving the bridge a beautiful and attractive design,

and large spans. For example, Zaha Hadid’s Sheikh Zayed bridge shown in the picture below

which is no doubt a magnificent architectural engineered bridge. No doubt, such bridges

introduced new structural challenges

for structure and construction

engineers, so as to keep up with that

change in the design of the bridges.

Structural engineers and construction

engineers and other engineers began to

define new structural systems and construction techniques for building

bridges using modern technology. This research paper is about Imbaba bridge in Cairo, which Is

the an old bridge connecting Imbaba to the other side of the Nile which is Shobra, and the span

of the bridge is about 490 meters. Although Egypt has a great deal of bridges crossing the Nile,

Imbaba Bridge is no doubt a unique bridge, since the quality of the design and construction of

this bridge is amazing, and this is obviously seen by just looking on the amount of rivets, and

how they were assembled in this Arch Truss Bridge. So, the design of such a bridge is going to

be the main Focus of this research.

Figure 1(Sheikh Zayed Bridge)

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History

Imbaba Bridge was built between 1913 and 1925, and is was mainly built as to connect

Imbaba with the other side of the Nile which is Shobra, and doing so blocked the Nile, because

the height of the bridge from the water surface was not to height by which it can pass huge ships,

as a result, the second span of the bridge from the side of Imbaba was designed to be movable as

to allow the ships to cross to the other side of the bridge. It is said that this bridge was designed

by Gustave Eiffel who designed Eiffel Tower in France, although such information is not

verified, looking at the design of Imbaba Bridge can no doubt make the people believe that

Gustave Eiffel is the designer of Imbaba Bridge, due to the amazing structural design of this

Bridge. Also, what makes Imbaba Bridge unique is that it is considered one of bridges which was

designed for as a railway, roadway, and pedestrian bridge.

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Structural System

Figure 2(Imbaba Bridge)

- Imbaba Bridge consists of 7 spans each 70 meters, resulting in a bridge 490 meters long

1)Supports: Imbaba Bridge is divided into seven simply supported structures (Each having a hinge at each

side of the span). The seven structures are totally separated from each other as structural

components; however, they are joined with a thin layer of asphalt to allow the continuity needed

for the movement of the different kinds of transportation from vehicles to pedestrians to trains.

Figure 3(The adjacent hinges that support the different spans with the complete structural separation)

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Figure 4(A Hinge Support)

Figure 5(Another Hinge Support)

2) Train Structural System:As the train is a major load on the bridge that causes high vibration during the movement, the

main structural system was used to support it directly. This system is the two huge arched trusses

that feature Imbaba Bridge. This truss is composed of a long horizontal member with 14 joints

and 13 spans at the bottom. At each joint there is a vertical member joining the arched member at

the top to the straight member at the bottom. The diagonal members change their direction at the

mid-span so that these members would have tension forces to have more economic section

avoiding the buckling phenomena as much as possible.

The Hinge at the beginning of the first span of the bridge from the side of imbaba

The Hinge at the beginning of the last span of the bridge from the side of shobra

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Figure 6(Railway Supports)

Figure 7( A rough Sketch of the 70 meters Typical Arch Truss for Imbaba Bridge)

Figure 8(The arched trusses that feature the Imbaba bridge)

3)BracingTo ensure the strength of the system, a lot of bracings were added increasing the stability of the

structure. These bracings occur between the top arched chords of the truss, between the vertical

members and the bottom five main girders. Two of the five main girders are the bottom chords of

the truss

Cross-Girders supporting the rail-way

Main-Girders

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Figure 9: The different bracings occurring to add stability to the main structural system

4)Vehicles Structural SystemThe deck that support the vehicular load is stiffened by adding longitudinal hollow steel

sections(orthotropic sections) to the bottom increasing the moment of inertia of the section; thus

stiffening the deck. This deck is supported by cantilever girders stretching transversely from the

two main girders which are the bottom truss chord. To resist buckling of these cantilevers,

vertical stiffeners were added. Moreover, to decrease the load as well as the critical deflection of

the cantilever, two approaches were implemented: first decreasing the cross section of the

cantilever at the free end as the bending moment is zero, second decreasing the spacing between

the cantilevers so that each cantilever would resist small loads. Furthermore, to ensure that the

girders would act as one unified unit and the stiffness of these girders at the intersection with the

cantilevers, cross girders were attached to these girders joining the external cantilevers together

(allowing continuity). These cross girders vary from beams to trusses.

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Figure 10: The structural system of the Vehicles from below

5)Pedestrian Structural SystemTransversely, the deck is supported by a framed truss. This truss is supported by the cantilever

girders at the bottom of the vehicular deck and the vertical members of the truss. The connection

between the vertical members and the framed truss is located at the middle of the members. To

avoid the great bending moment accumulated at the member the vertical bracing between the

members was extended to this point stiffening the member to resist this moment. The deck of

this part is supported by four girders: three beams and one arched truss. Due to the accumulated

deflection that would reach the cantilever at the bottom, this deck was stiffened greatly by four

strategies. First, the frame supporting the deck was truss with small spacing rather than solid

section to increase stiffness with lower own weight. This solution is also an economic one.

Second, the deck was supported by main and secondary girders with small spacing although the

loads does not need this small grid. Third, bracings were added to the girders increasing the

stiffness of these girders. Forth, the outer girder was an arched truss because this truss is closer to

the cantilevers as well as the low deflection and high stiffness provided.

Cross Girder

Cantllivers carrying the road way

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Figure 11: Structural System of the pedestrian part of Imbaba bridge

6) Movable Span

Figure 12(Movable Span)

A ring beam supported on the mechanical system that moves this span of the bridge, and the bridge is supported on a group of 4 hinges connected to the ring beam as it is shown in the sketch below, and two ends of the span has an intermediate hinge as those also shown on the sketch below.

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Figure 13(Circular Spacing between the movable span and the neighboring span)

Figure 14(Circular Spacing between the movable span and the neighboring span)

The Circular spacing between the movable span and the neighboring span to prevent them from hitting each other when the bridge moves

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Conclusion

In conclusion, Imbaba Bridge has a very challenging and interesting structural system,

and what makes it more and more challenging is the fact that the designer of this bridge did not

use any software or technology in the building of the bridge, and all the bridge is consisting of

rivets, which are not used nowadays a lot. Also, The designer of the bridge integrated a group of

steel structures like the Arch Truss supported on the main girders, and the main girder is

connected to a group of cantilevers supporting the roadway, and from these cantilever a group of

members are used to support the pedestrian and at the same time the pedestrian road is connected

to the truss. No doubt, the technology and software found nowadays can facilitate the design and

construction of such a bridge, but still the structural design of such a bridge is amazing.

Unfortunately, while our visit to the bridge we noticed that a huge deflection is taking place in

that bridge, and some steel members are rusting, and no doubt, such a bridge requires regular

maintenance, and no doubt leaving it to rust in this way would destroy one of the structural

landmarks in Egypt.