Cable-Stayed Bridge Project Overview

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Kafr El Sheikh University
Faculty of Engineering
Civil Engineering Department
Suez-Canal
Cable-Stayed Bridge Project
(The Graduation Project)
Prepared By /
Mohamed Ahmed Elfeky
Mohammed Abdelkawy
Ahmed Bahgat Zamil
4th
Year Civil

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The Cable-Stayed Bridge
Basics
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 suspension bridges 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 deck with 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 compression forces 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 compression and 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
winds.
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.

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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 support conditions 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 compression forces 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
construction;
- Arch bridges with large spans are not stable during erection until
The arch is closed and the horizontal support forces are anchored.
- Self-anchored suspension bridges, which may be required when
Their horizontal cable component cannot economically be anchored
Due to bad soil conditions, need temporary supports of their beams
until the main cables are installed.

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- 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
Bridge:
1-Deck:
The deck or road bed is the roadway surface of a cable-stayed bridge.
The deck can be made of different materials such as steel, concrete or
composite steel-concrete. The choice of material for the bridge deck
determines the overall cost of the construction of cable stayed bridges.
The weight of the deck has significant impact on the required stay cables,
pylons, and foundation.

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2-Pylon:
Pylons of cable stayed bridges are aimed to support the weight and live
load acting on the structure. There are several different shapes of pylons
for cable stayed bridges such as 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, concrete towers 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
today.

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3-Cables:
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.

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1- Locked coil ropes: Traditionally used in Germany, completely
shop fabricated, permit construction by geometry.
Advantages: good corrosion protection, 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 corrosion protection comprises galvanizing of all
wires, filling the interstices with a corrosion inhibitor and painting the
outside in several layers.
The different wire layers rotate in opposite directions in order to achieve
twist-free ropes, Fig. 3.3.

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When stressing the cables, the Z-shaped outer wires are pressed against
one another by lateral contraction and which ‘locks’ the rope surface
against intrusion of water, hence the name ‘locked coil ropes’.

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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
completely shop-fabricated.
Advantages: high stiffness, no creep, high tensile and fatigue strength
with Hiam-anchorage
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-out inside a conical anchor head.

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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.

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Main Types of Cable Stayed Bridges:

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Bridge Layout
1) Bridge Structural Type: Concrete Box Girder
Cable-Stayed Bridge
2) Span Arrangement: 165+400+165=730m
3) Stay Cable Arrangement: Semi Fan
4) Stay Cable: Strand Cables
5) Pylon Type: Reinforced Concrete H-Shaped Column
6) Pylon Height: 150m
7) Navigation Clearances: 70m Above H.H.W.L
8) Bridge Width: 20m

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Bridge Components
Cable-Stayed bridges have 3 main components:-
1) Pylon
2) Deck
3) Cables
3D Model

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The Pylon
The Pylon is the main support of cable-stayed bridges.
Cables link the deck to the pylon, so it can carry the deck
safely.
Our pylon is a Reinforced Concrete H-Shaped Column.
The section of the pylon is a nonprismatic section
Pylon Bottom Pylon Top

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The Deck
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

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Material Properties for Pylon and Deck:
concrete has a specified compressive strength equals
400 kg/cm^2, Considering Creep and Shrinkage.

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Cables
In this bridge we have 16 cables in each side of the
pylon
The distance between cables in the deck plan equals
to 10.00 meters In the Side Spans and Equal To
12 meters Between the Pylons
The distance between them at its links to the pylon
equals to 2.00 meters
Material Properties:
Fu = 17.7 T/Cm^2
Fy= .89* 17.7 = 15.7 T/Cm^2
E = 1950 T/Cm^2
Diameter = 15.7 mm

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Modeling Steps
(Using CSI Bridge Program)
1) Drawing the layout line of the bridge.
The layout has 2 stations the 1st
at 0.0 and the 2nd
at
730.00.
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 zero.
9) Defining the design vehicle and vehicle class.
10) Defining All Cases Of Moving Load.
11) Solving due to moving load and getting
deformation.

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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 forces.
16) Defining the wind loads.
17) Solving.
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 effects

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The Program Outputs:
Deformation due to Dead Load only (Without Cables)
Joints Labels
These joints are at the center of the deck.

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From the table:
The max deflection is at p54 and p56 which are at
the mid span, and equals to 54.41 m.

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We will use 3 groups of cables
The 1st
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 called
Target.
After Using Cables With Pretension Force:

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The 2nd
group consists of the next 5 cables.
The 3rd
group consists of the next 6 cables.

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Deformed Shape:
Almost no deformation …
The output values are due to the combination
between Target and Dead Load.

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The uplift at P34 equals to 3 cm, and the max
Settlement equals to 1.5 cm at P71.

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The Pylon Sway due to Dead Load:
The Max Sway from D.L. equals to17.6 cm.
The Moment Diagram:
Max Moment = 7272 t.m

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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

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Moving Loads:
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 width equals to 3.50 meters.

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Moving Load Model (1):
Consists Of concentrated and distributed load.
Truck 60ton.
Truck40ton.

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Truck 20ton.
Uniform 0.25t/m^2 for The rest of road width
Uniform 0.5t/m^2 for Pavements and Median

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The max deflection equals to 29 cm

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Bending Moment Diagram:
Max Moment = 3956 t.m
Shear Force Diagram:
Max Shear = 243 ton

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Normal Force Diagram
Max Torsion = 1882 t.m
Moving Load Model (2):
consists of uniform 0.5t/m^2 for bridge width

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the max deflection equals to 28.9 cm
allowable Deflection (50-80) cm Safe

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Load Case for torsion
(2 lanes occupy other 2lanes are empty)
Max Torsion Moment = 2606 t.m

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Earthquake Analysis
Dynamic Time History linear Analysis
1) Define Mass Source:

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2) Define Time History Function:
(time &acceleration)
We Will Use (ELCENTRO) General EQ
in X&Y Direction

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3) Define Time History Load Case:
- Damping Ratio: Take (2%)
- Response Modification Factor (R): Take = 3

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If we Want to increase the damping ratio
we can use cable anchorage with Hydraulic Damper
For great values up to 5%.
This is reducing the response of the super structure.

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- Scale Factor: I*g/R= (1.3*9.81)/ (3) =4.25

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Max Lateral Displacement = 28.7 cm

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Seismic Analysis Using (Simplified Response Spectrum)
>> (Seismic Coefficient Method) <<

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Max Lateral Displacement = 29.6 cm

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Wind Loads
Wind load which affect on the deck of the bridge
and on the trucks can be calculated from the
EGYPTIAN code of loads as following:

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Wind Load on Deck (With Live Load)
Wind load (deck) = 0.15 * 6 = 0.9 ton /m.
The wind applied in Y – Direction.

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Load Combinations
1) Characteristic Load Combinations
According To Egyptian Code:
1.35 Dead+1.35 Live (1)
1.35 Dead+1.35 Live (2)
1.35 Dead+1.35 Live (1) +0.9 Winds
1 Dead+0.2 Live (1) +EQ
1 Dead+0.2 Live (2) +EQ

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Final Design
Design of cable: Subjected to Tension with
Small Compression Values:

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Design of pylon: pylons designed as
Columns subjected to Axial Force and Biaxial
Moments.
Max Straining Action:
p m3 m2
23817.09 -3748 -5006.61
17244.32 -2914.12 -35635.8
17913.68 9806.453 -12637
17358.85 3167.38 31823.26

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Design by SCI COLUMN Program:
Using 254 bar ᶲ 22
Total area Steel=966 Cm^2 Steel ratio = 0.4%

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Design of the Deck:
Max Straining Action:
Max Compression= 18171 ton
Max positive Mx=9972.35 t.m
Max negative Mx= -9605 t.m
Max Positive My= 26560 t.m
Max Negative My= 27280 t.m
Max Torsion = 2845 t.m
Max Shear = 1272 ton

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Flexure Design
For Exterior Girder (right, left)
Using upper and lower
R.F.T = 50 ᶲ 25
(Upper & Lower)
Achieve Moment of
Resistance = 2512t.m

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For Exterior Girder (right, left)
Using upper and lower
R.F.T = 60 ᶲ 25
Achieve Moment of Resistance =
3330t.m

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Design of Sec Using CSI COLUMN as Column:

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Comparison for Better Results:
1- We can use prestressed concrete to achieve the
tensile stresses and get Small effective cross section
or using Steel deck.
2- We can do camber for Pylon and the deck to
prevent high deflections for the deck And lateral
Displacements For the pylon
3- high damping rubber bearings (HRB) were used
as seismic isolators (supports) for the steel girder,
With allowable movable length (seismic) = ± 450
mm.
4- To limit the horizontal movements, lateral rubber
bearings were installed between the bridge deck and
the tower with a gap of 10 mm.

Cable-Stayed Bridge Project Overview

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