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CHAPTER I
INTRODUCTION
1.1
Introduction
The guyed bridges or known as suspension bridges are recognized for
spanning the longest distances and for their superior aesthetics. The suspension
bridge suspends the roadway from huge main cables, which extend from one end of
the bridge to the other. These cables rest on top of the high towers and are secured at
each end by anchorages. Figure 1 shows the guyed monorail steel bridge in
Putrajaya.
Figure 1.1: Guyed monorail steel bridge.
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The principle of a suspension bridge consists four essential parts, which are
the towers, the anchorages, the cables, and the deck. The deck, usually supported on
stiffening trusses, is hung from the suspension cables. It consists of a central main
span and is flanked on each side by a side span that is separated from the main span
by towers. The ends of the suspension cables are secured at the anchorages, which
are usually built of masonry or concrete.
1.2
Problem Statements
Notwithstanding the collapse of several 19th century suspension bridges in
high winds, a vast development of the suspension bridge took place in the United
States, following the development by Roebling of a wire-by-wire spinning technique,
which made possible the construction of parallel wire cables of very long span.
However, the failure of the Tacoma Narrows Bridge in 1940, due to torsional
oscillation caused by aerodynamic flutter came as a severe shock to the engineering
community. The failure reopened the eyes of engineers to the necessity for greater
consideration of wind behaviour and adequate stiffening of decks.
The deflection by the wind load is a serious problem because the suspension
bridges are light and flexible. The windy weather poses variety of problems to the
suspension bridge structure. Therefore, wind tunnel testing of bridge design is
mandatory. Furthermore, with the development computers, it is possible to carry out
a structure analysis to predict the deflection profile of the suspension bridge to
supplement the wind tunnel testing.
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1.3
Objectives of Study
The objectives of the study are as follows:
1)
To analyse and predict the deflection profile of the guyed monorail steel
bridge at serviceability limit states.
2)
To define the stresses in the pylon structure of the guyed monorail steel
bridge at ultimate limit states for checking the safety of the guyed bridge.
3)
To seek justification of the guyed bridge model to expect the behaviour of
bridge structure.
1.4
Scope of Study
The structural geometry of guyed bridge under study is a steel bridge
supported at the ends by two reinforced concrete pylons. It is used for the monorail
track crossing the lake, which located in Putrajaya, Selangor Darul Ehsan. Modelling
and guyed monorail steel bridge is analysed using the structure analysis software,
STAAD Pro 2003.
From the study, the oscillation and deformation shape of the suspension
bridge using frame analysis will be focussed. Meanwhile, the load carrying capacity
for the suspension bridge in serviceability limit state and ultimate limit state were
carried out with the limitation in BS 5400: Part 2 Specification for Loads: 1978.
Furthermore, the study considering the possibility of predicting deflection profile and
stresses of pylons for the guyed monorail steel bridge by computer modelling
method.