Imbaba Bridge Report
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Transcript of Imbaba Bridge Report
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)
2
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
3
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
4
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)
5
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.
6
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)
7
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
8
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
9
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.
10
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
11
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.
12
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
13
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.