Abstract :
Suspension bridge is
most commonly built to span across water body. It is
built by suspending the roadway from cables attached to a master cable which
runs above the length of the bridge. In addition to being strong and
lightweight, suspension bridges are also beautiful. The design of a suspension
bridge is simple and straightforward, and takes advantage of several techniques
to distribute the weight of the bridge safely and evenly.
The main
forces in a suspension bridge are tension in the main cables and compression in
the pillars. Since almost all the force on the pillars is vertically downwards
and they are also stabilized by the main cables, they can be made quite
slender.
In a
suspended deck bridge, cables suspended via towers hold up the road deck. The
weight is transferred by the cables to the towers, which in turn transfer the
weight to the ground.
Most of the
weight or load of the bridge is transferred by the cables to the anchorage
systems. These are imbedded in either solid rock or huge concrete blocks.
Inside the anchorages, the cables are spread over a large area to evenly
distribute the load and to prevent the cables from breaking free.
Advantages
of suspension bridge:-
1. The
center span may be made very long in proportion to the amount of materials
required, allowing the bridge to economically span a very wide canyon or
waterway.
2. It can
be built high over water to allow the passage of very tall ships.
3. Neither
temporary central supports nor access from beneath is required for construction,
allowing it to span a deep rift or busy or turbulent waterway.
4. being
relatively flexible it can flex under severe wind and seismic conditions, where
a more rigid bridge would have to be made much stronger and so also heavier.
Precautions
while constructing suspension bridge:
1. The
foundation type and depth must be the major attention that needs to be taken
care of, since the entire load of bridge is being transferred into ground by
means of towers. The towers must be designed such that it becomes easy for the
maintainers to climb the tower for purpose of painting etc. In case of seismic
prone regions steel towers are advisable, since they have allowable swing on
either side the towers don’t collapse during a sustainable earthquake. Also
huge pendulums can be fixed within towers which help in maintaining tranquility
of the bridge, whenever there is earthquake, by swaying in opposite direction
to that of towers by means of hydraulics.
3. It must
be accounted that the anchorages are strong enough to with stand the stress and
strain imposed on them by the master and suspended cables. Another major issue
regarding anchorages would be addressing the impact of weather conditions which
often results in rusting of the cables within anchorages. So it is evitable to
make the entire anchorage air tight.
4. After
hoisting pilot cable utter issue needs to be addressed is the safety of
catwalks, which will used by workers to put in place the suspension cables.
Using large no of wire strands make the cable strong enough to carry the heavy
load deck. Hence the wire strands must be closely spanned so that it can with
stand heavy load of deck without crossing the allowable tensile limit. Also it
is advisable to paint the support cables to prevent it from rusting.
5. Once the
master and suspended cables are in place the deck must be placed in position.. The
hydraulics which moves the deck should be sufficiently lubricated so that they
will not fail in between, as it consumes huge amount of time to repair them. As
a precautionary measure the navigation of ships must be stopped when the decks
are being placed. Major issue that needs to be addressed during placing of
decks would be safety of workers.
6. Three
kinds of forces operate on any bridge: the dead load, the live load, and the
dynamic load. Dead load refers to the weight of the bridge itself. Like any
other structure, a bridge has a tendency to collapse simply because of the
gravitational forces acting on the materials of which the bridge is made. Live
load refers to traffic that moves across the bridge as well as normal
environmental factors such as changes in temperature, precipitation, and winds.
Dynamic load refers to environmental factors that go beyond normal weather
conditions, factors such as sudden gusts of wind and earthquakes. All three
factors must be taken into consideration when building a bridge.
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