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Faculty of Engineering
Civil Engineering Department
Cable-Stayed Bridge Project
(The Graduation Project)
Prepared By /
Mohamed Ahmed Elfeky
Ahmed Bahgat Zamil
The Cable-Stayed Bridge
The position of cable-stayed bridges within all bridge systems their spans
range between continuous girders and arch bridges with shorter spans at
one end, and suspensionbridges with longer spans at the other. The
economic main span range of cable-stayed bridges thus lies between
100m with one tower and 1100m with two towers.
A typical cable stayed bridge is a deckwith one or two pylons erected
above the piers in the middle of the span. The cables are attached
diagonally to the girder to provide additional supports. Large amounts
of compressionforces are transferred from the deck to the cables to the
pylons and into the foundation.
Cable stayed-bridges have a low center of gravity, which makes them
efficient in resisting earthquakes. Cables are extremely well suited for
axial tension, however are weak against compressionand bending forces.
As a result, long span cable stayed bridges, though strong under normal
traffic loads, are vulnerable to the forces of winds. Special measures are
taken to assure that the bridge does not vibrate or sway under heavy
Because the only part of the structure that extends above the road is the
towers and cables, cable stayed bridges have a simple and elegant look.
Advantages of cable-stayed bridges:
First of all the bending moments are greatly reduced by the load transfer
of the stay cables, By installing the stay cables with their predetermined
precise lengths the supportconditions for a beam rigidly supported at the
cable anchor points can be achieved and thus the moments from
permanent loads are minimized, Even for live loads the bending moments
of the beam elastically supported by the stay cables remain small.
Large compressionforces in the beam are caused by the horizontal
components of the inclined stay cables. The normal forces in the main
and side span equal one another so that only uplift forces have to be
anchored in the abutments which act as hold-down piers.
A second important advantage of cable-stayed bridges is their ease of
- Arch bridges with large spans are not stable during erection until
The arch is closed and the horizontal supportforces are anchored.
- Self-anchored suspension bridges, which may be required when
Their horizontal cable componentcannot economically be anchored
Due to bad soil conditions, need temporary supports of their beams
until the main cables are installed.
- In cable-stayed bridges, however, the same flow of forces is
Present during free-cantilever construction stages as after completion.
This is true for free cantilevering to both sides of the tower
As well as for free cantilevering the main span only.
The Main Components OF Cable Stayed
The deck or road bed is the roadway surface of a cable-stayed bridge.
The deck can be made of different materials suchas steel, concrete or
compositesteel-concrete. The choice of material for the bridge deck
determines the overall costof the construction of cable stayed bridges.
The weight of the deck has significant impact on the required stay cables,
Pylons of cable stayed bridges are aimed to supportthe weight and live
load acting on the structure. There are several different shapes of pylons
for cable stayed bridges suchas Trapezoidal pylon, Twin pylon, A-frame
pylon, and Single pylon. They are chosen based on the structure of the
cable stayed bridge (for different cable arrangements), aesthetics, length,
and other environmental parameters.
The first cable-stayed bridges used steel towers. Since towers are mainly
loaded by compression, concretetowers are more economical and,
therefore, mainly used today. Only if extremely bad foundation
conditions would require very long piles, are the lighter steel towers used
Cables are one of the main parts of a cable-stayed bridge. They transfer
the dead weight of the deck to the pylons. These cables are usually post-
tensioned based on the weight of the deck. The cables post-tensioned
forces are selected in a way to minimize both the vertical deflection of the
deck and lateral deflection of the pylons. There are four major types of
stay cables including, parallel-bar, parallel-wire, standard, and locked-
coil cables. The choice of these cables depends mainly on the mechanical
Properties, structural properties and economic criteria.
1- Locked coil ropes: Traditionally used in Germany, completely
shop fabricated, permit construction by geometry.
Advantages: good corrosionprotection, simple maintenance
Disadvantages: reduced stiffness, subject to creep, reduced tensile
strength and fatigue strength.
Locked coil ropes consist of internal round wires with a diameter of
5 mm and outer layers of Z-shaped wires with a depth of 6 – 7 mm,
Fig. 3.2. Their modern corrosionprotection comprises galvanizing of all
wires, filling the interstices with a corrosioninhibitor and painting the
outside in several layers.
The different wire layers rotate in oppositedirections in order to achieve
twist-free ropes, Fig. 3.3.
When stressing the cables, the Z-shaped outer wires are pressed against
one another by lateral contraction and which ‘locks’ the ropesurface
against intrusion of water, hence the name ‘locked coil ropes’.
2- Parallel wire cables: Developed by LAP in the 1960s from
BBR post-tensioning system in order to overcome the disadvantages of
Locked coil ropes, almost exclusively used in Germany since then, also
Advantages: high stiffness, no creep, high tensile and fatigue strength
Disadvantage: complex corrosion protection with several components
Parallel wire cables comprise a bundle of straight wires with 7 mm or 1⁄4
inch diameter which are anchored with button heads in a retainer plate.
In order to further improve the fatigue strength, the so-called ‘HiAm’
anchorage was developed and investigated in many tests.
The basic design idea is to anchor the individual wires gradually by
lateral pressure exerted by small steel balls into which the wires are
broomed-outinside a conical anchor head.
3- Parallel strand cables: Developed from strand tendons in
order to exploit higher tensile strength and better availability of strands
Advantages: cost-effective, fabrication on site from components,
exchange of individual strands
Disadvantage: slightly reduced stiffness.
Cable-Stayed bridges have 3 main
The Pylon is the main support of cable-stayed
Cableslink the deck to the pylon, so it can carry the
Our pylon is a Reinforced Concrete H-Shaped
The section of the pylon is a nonprismatic section
Pylon Bottom Pylon Top
The Deck View
The Deck Properties:-
The Deck Width = 20.00 meter
(Consists of 4 lanes - 2 lanes in each direction ,
2 sidewalks of width equals 2.0 m , and an
island of width equals 2.0 meters)
t1 = t2 = t3 = t4 = 0.30 m t5 = t6 = 0.25m
L1 = L2 = 2.00 m
The Depth = 3.00 m
Material Properties for Pylon and Deck:
concrete has a specified compressive strength
equals 400 kg/cm^2, ConsideringCreepand
In this bridge we have 16 cables in each side of
The distance between cables in the deck plan
equals to 10.00 meters In the Side Spans and
12 meters Between the Pylons
The distance between them at its links to the
pylon equals to 2.00 meters
Fu = 17.7 T/Cm^2
Fy= .89* 17.7 = 15.7 T/Cm^2
E = 1950 T/Cm^2
Diameter = 15.7 mm
(Using CSI Bridge Program)
1) Drawing the layout line of the bridge.
at 0.0 and thest
The layout has 2 stations the 1
2) Defining the deck sec. which is box girder
has 3 vents.
3) Defining Lanes.
4) Defining and drawing the pylon.
5) Defining and drawing the rigid links to link
the deck sec. to cables as one unit.
6) Defining springs.
7) Solving the model to get the deformation
due to dead load.
8) Defining the cables (Diameter & Pretension
Force) which achieve deformation equals to
9) Defining the design vehicle and vehicle
10) Defining All Cases Of Moving Load.
11) Solving due to moving load and getting
12) Defining the Earthquake loads Using Static
Analysis (Seismic Coefficient Method) and
Safety Was Checked by Dynamic Analysis
(Time History Method).
15) Solving the model due to earthquake
16) Defining the wind loads.
18) Defining load combinations.
19) Design the bridge.
Philosophy of Analysis:
1-Find the value of cable tension that will give
optimum deck profile for final model.
2- Stage construction analysis to find cable
force during erection.
3- Final checks with seismic, Wind and other
The Program Outputs:
Deformation due to Dead Load only (Without
These joints are at the center of the deck.
From the table:
The max deflection is at p54 and p56 which are
at the mid span, and equals to 54.41 m.
We will use 3 groups of cables
one consists of 5 cables (the nearest
cables to the pylon)
This group has cables of diameter equals to
7.00 cm, and a tension force of 340 ton of its
end I which linked to the pylon.
The Force in cables is put in a load pattern
After Using Cables With Pretension
The Pylon Swaydue to Dead Load:
The Max Sway from D.L. equals to17.6 cm.
The Moment Diagram:
Max Moment = 7272 t.m
The Shear Force Diagram:
Max Shear = 840 ton.
The Normal Force Diagram:
Max axil compression force in deck =12064 ton
Reaction for pylon Column = 16574 ton
The Bridge consists of 4 lanes, 2 lanes in each
direction, and 2 sidewalks of 2.00 m width in
each one and central median 2m Width.
The lane widthequals to 3.50 meters.
Design of pylon: pylons designed as
Columns subjected to Axial Force and Biaxial
Max Straining Action:
p M3 m2
24096.5 -2889.78 2566.837
17554.56 3248.732 31692.79
17453.64 1929.603 -35305.0983
18088.44 10097.54 10378.07