Faculty of Engineering: Suspension Bridge Report - 1018EXQ Resit

This report provides a comprehensive overview of suspension bridges, detailing their structural components such as decks, steel cables, suspenders, towers, and anchorage blocks. It explores the different types of suspension bridges, including simple, modern, under spanned, post-stressed ribbon, and self-anchored designs. The report also examines the construction process, from tower foundation and anchorage construction to cable and deck construction, and finishing. Furthermore, it analyzes the loads acting on suspension bridges, including compression and tension forces, and explains how these forces are managed within the structure. References to relevant literature are provided to support the analysis.

Suspension bridge
Introduction
Bridge could be classified and structural elements that would allow easier passage of either
people or vehicles over obstacles like, water bodies, rough terrains and valleys by crossing the
obstacles using manmade or natural materials. Bridges have been used since the time
immemorial from the basic structures which could be accessed naturally to bridge construction
revolution that started from Ancient Rome and spread through other continents.
Suspension bridge
Suspension bridge is a type of bridge that comprises of deck that flexibly hung below cables that
suspends on suspenders that are vertical. The simple bridges of this type would be found in areas
that are mountainous where their vertical suspended cables that are mandated to carry deck’s
weight would be attached between towers. The arrangement would allow leveling of the deck.
The anchorage of the suspension cables would be done at the bridge’s end, since any applied
load on the bridge would be transformed to tension of the main cables. These main cables would
extend past the pillars to level supports of the deck, and continues further to connect with ground
anchors. Hangers which are vertical suspenders would support the roadways. In certain
conditions towers may be situated on canyon edge or bluff to allow road to directly proceed to
major span, or else there would be existence of two spans that would be running between the
highway and pair of pillars that would either be supported by truss bridge or suspender cables.
Types of suspension bridges
The deck of suspension bridges would be held in position by vertical hanging suspension cables.
Different techniques used and materials applied would make their design different as follows
(Çavda, 2012);
a. Simple suspension bridge
Type of suspension bridges that have neither piers nor towers their suspended cables are only
anchored at their own ends. Their decks are arched upward and downward and they have
additional handrail at their higher levels. The bridge only accommodates pedestrians and no
railroads and modern roads could be carried.
b. Suspension bridge
The bridge comprises of modern suspension designed. The bridge has towers where cables that
would hold the road deck originate. The deck’s weight would be transferred by the tensions on
cables to both the towers and ground through anchored cables. The bridge are designed to carry
both the light rail and heavy vehicle.

c. Under spanned
The deck of this type of suspension bridge is raised above the anchored of the main cables on
post
d. Stressed ribbon
The bridge is a variant improved simple suspension having rigid deck that lies on the cables that
are suspended that are fixed on the deck. The bridges are made up of concrete and are reinforced
by tensioned cables steel that are capable to carry traffic of vehicles.
e. Self-anchored
The main cables of this type of bridges are fixed at the deck’s end and not ground like other
suspended bridges that are constructed on unstable soils and elevated piers. Suspended cables
would be anchored at the complete designed deck.
Components of suspension bridges
Figure 1: components of suspension bridge (Serap et al., 2012)
The bridge would comprise basically of the following components, as shown in the figure above;
a. Deck
Decks are also known as roadways that would allow traffic rail, pedestrian and motorists to pass
over them. They deck are normally constructed out of concrete reinforced steel.
b. Steel cables

A steel cable suspends the roadway or decking, they are preferred over iron because steel is an
alloy that makes it stronger in compression and tension.
c. Suspenders
The suspenders are mandated on shaping the bridge and connecting the deck to cables of steel.
The absence suspenders would sway the roadways and would not be controlled, their used in in
reinforcing the deck more.
d. Towers
The steel weight of the cables normally would be transferred onto towers to help stand the
swaying of the bridge. The weight that tower would be supporting would be transferred to the
ground and this would reinforce more the feet of the tower and ensuring that the bridge would be
upright.
e. Anchorage block
The weight of the block are more than the weight of the cables that hold the deck because they
are design in a way that they need to withstand the roadway portion and also they are meant to
endure the weight of the traffic of vehicles that crosses the bridge throughout.
f. The tower’s foundation
The foundation would be expected to be secure since all the weight on the bridge is transferred
by the tower at its foundation. The depth of the foundation would always be considered to ensure
that the tower would not tilt and ensure that towers are vertical and able to withstand weight
transferred to them by the cables.
g. Truss
Trusses would found below the deck or roadways in order to support them. They also stiffen the
deck and reduce the chances of deck swaying vertically.

Major suspension bridge components
a. Tower construction
The foundation of towers would be dig to sufficient firm rock depth. Caissons would first be
lowered to the grounds that are under the water, the caissons would help remove water easily as
workers excavate the foundation without workers operating in water to ensure towers standing in
water are stable. At the end of excavation a prepared concrete would be poured to ensure that the
tower foundations are formed.
Figure 2: Construction of tower foundation (Diana et al., 2013)
Attached concrete massive blocks on strong rock are used in anchorages to support the cables of
the bridge. Pilot line would be strung on the cables path attaching one anchorage to another
across the tower.
b. Anchorage construction
The end of the cable of the bridge would be secured at the anchorages. The anchorages
comprises of concrete block that are attached on a strong formed rocks. The strong steel bars
having circular hole at its end during construction would be fixed on the concrete. The spray
saddles would be mounted on the anchorage front would be used to support the cable at
individual point of the wire bundles (ZHANG et al., 2012).
c. Cable construction
The free wire end would be looped around the shoe of the strand. Between the strand shoe and
spool of wire, looping of the wire would be done on the spinning wheel mounted along the pilot

line. At the path of the bridge the wire would be carried by the wheel and would be looped on the
anchorage strand shoes, another strand would be laid by the wheel when it returns back on the
first anchorage (Lonetti and Pascuzzo, 2014).
The structure of the deck would be built once the main cables supports are attached by the
vertical cables and this would be from the direction of the tower’s support in order to ensure that
the forces are balance on the towers throughout. The decks sections would be lifted by a crane
that moves and thereafter workers would attach it to the vertical cables hanging from major
suspension cables and sections that they were previously placed
Figure 3: Deck construction (Gimsing and Georgakis, 2011)
d. Deck construction
The deck structures be built from both the towers support direction at a constant rate that would
ensure all the forces are throughout balanced. Other techniques would involve crane that would
roll the main suspension top cables to lift into place the deck section, where workers would
attach it to the vertical cables hanging from major suspension cables and sections that they were
previously placed (Gunaydin et al 2014).
e. Finishing
A base layer that comprise of steel plate would be used to cover a complete structure of deck and
surfaced. The surface of the steel would be painted and electric line installed in order to provide
light.

Figure 4: Component and forces acting on suspension bridges (Su and Wang, 2012)
LOADS ON SUSPENSION BRIDGES
The figure blow shows suspension cables withstanding tension but they would have no
compression resistance (Thai and Choi, 2013)
a. Compression
The compression forces would push down the deck of the suspension bridge, but due to the
roadway being suspended, the compression forces would be transferred with the cables to the
towers, the towers would distribute directly the compression forces to the soil where are
anchored firmly.
b. Tension
The support cables that are attached between two anchorages would receive the tension forces.
The cables are stretched from the bridge weight that includes the traffic at runs between the
anchorages that supports them. The anchorages would also be under tension, but the experienced
tension would be distributed since they are held firmly on the earth.
Apart from the cables found in suspension bridges, they will also have trusses that support the
bridge deck beneath. The trusses would help in stiffening the deck in order to reduce rippling and
swaying of the roadways.

Figure 5: Forces acting on suspension bridge (Thai and Choi, 2013)
The cables tensions would carry the weight of the whole bridge deck and the weight of the traffic
over it. The anchorages found at each end would resist the tension since it is attached at its cables
end. But since the towers held up the main cables, then the whole weight of the bridge would be
transferred from this elements through the tower and would end at the ground.

References
Çavdar, Ö.Z.L.E.M., 2012. Probabilistic sensitivity analysis of two suspension bridges in
Istanbul, Turkey to near-and far-fault ground motion. Natural Hazards and Earth System
Sciences, 12(2), p.459.
Diana, G., Yamasaki, Y., Larsen, A., Rocchi, D., Giappino, S., Argentini, T., Pagani, A., Villani,
M., Somaschini, C. and Portentoso, M., 2013. Construction stages of the long span suspension
Izmit Bay Bridge: Wind tunnel test assessment. Journal of Wind Engineering and Industrial
Aerodynamics, 123, pp.300-310.
Gimsing, N.J. and Georgakis, C.T., 2011. Cable supported bridges: Concept and design. John
Wiley & Sons.
Gunaydin, M., Adanur, S., Altunisik, A.C., Sevim, B. and Turker, E., 2014. Determination of
structural behavior of Bosporus suspension bridge considering construction stages and different
soil conditions. Steel and Composite Structures, 17(4), pp.405-429.
Lonetti, P. and Pascuzzo, A., 2014. Design analysis of the optimum configuration of self-
anchored cable-stayed suspension bridges. Structural Engineering and Mechanics, 51(5),
pp.847-866.
Serap, A., Kubilay, K. and Semih S, T., 2012. Dynamic analysis of suspension bridges and full
scale testing. Open Journal of Civil Engineering, 2012.
Su, Q.T. and Wang, D.F., 2012. Mechanical analysis for anchorage zone connecting main cable
and main girger of self-anchored suspension bridge. In Applied Mechanics and Materials (Vol.
178, pp. 2281-2284). Trans Tech Publications Ltd.
Thai, H.T. and Choi, D.H., 2013. Advanced analysis of multi-span suspension bridges. Journal
of Constructional Steel Research, 90, pp.29-41.
ZHANG, Q.H., Jian-hua, H.U. and Guo-ping, C.H.E.N., 2012. Study of rock foundation stability
of Aizhai bridge. Chinese Journal of Rock Mechanics and Engineering, 31(12), pp.2420-2430.