ENGINEERING They vary depending on the materials and

 

ENGINEERING STUDIES

FAIRFIELD HIGH SCHOOL

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CIVIL STRUCTURE

ELIKSAN SOMO

DUE DATE: 31/01/18

 

 

 

Executive summary:

This report will discuss various bridge
designs used overtime and the materials used for different structures. This
report will discuss the advantages and disadvantages of different bridge
designs. It will also explain why various materials are used during the
construction processes. It will state the material’s advantages and
disadvantages and why they are used or no longer in use. This report may help
engineers decide what bridge must be built relying on the materials available
and what it is used for.

 

Table of Content:

 

 

 

Title page
………………………………………………………………………………………………………………………………………… 1

Executive Summary ………………………………………………………………………………………………………………………….
2

Table of Content
……………………………………………………………………………………………………………………………… 3

Introduction
……………………………………………………………………………………………………………………………………. 4

Arch bridge
…………………………………………………………………………………………………………………………………… 4-7

Truss bridge
…………………………………………………………………………………………………………………………………. 7-8

Suspension bridge
…………………………………………………………………………………………………………………………… 8

Method of
construction of all bridges ………………………………………………………………………………………… 9-10

Materials used
…………………………………………………………………………………………………………………………. 11-12

Conclusion  
………………………………………………………………………………………………………………………………….. 12

Reference
…………………………………………………………………………………………………………………………………….. 13

 

Introduction

Civil engineering is one type of engineering
that deals with constructed environment such as, designing constructing and innovating
new methods in construction and maintenance of civil structures. Bridges are
essential in our life. They
connect two separated lands and make transport quicker. Ancient engineers faced
problems that modern engineers will try to solve. Engineers have been studying varied
materials and calculating to build a safer civil structure. The purpose of this report is to discuss the different types of
bridges and stating their advantages and disadvantages. The report will discuss the materials used in
constructing different types of bridges and discussing the advantages in
disadvantages of each material. There are several types of bridge designs. They vary
depending on the materials and shapes used in constructing a bridge. Some
bridges have been used centuries ago. Some are still being used nowadays.

Types of bridges:

·       
Arch bridge:

 Arch bridges are one of the oldest bridge
structures and have been around for thousands of years. Arch bridges were first built by
ancient Romans. The load on an arch bridge is carried outwards along the curve
of the bridge to the supports at each end (http://www.design-technology.org/archbridges.htm). The supports are also called
abutments. In the old days stone was used in constructing arch bridge. If a
load was placed on the bridge, the load is distributed and each stone pushes on
the one next to it until the load is applied to the abutments at each end.
Materials used in construction of arch bridges compact closer and closer
together during time and use giving it a solid foundation. On the other hand,
they take a long time and large amount of labor to build an arch bridge.
Regular maintenance is required to ensure that the bridge is safe and stiff.
This includes repairing damages caused by any types of storms and painting the
bridge to prevent rusting when steel is used. Less amounts of materials are
required compared to a truss bridge. and how load is distributed, this keeps it
in use until now.

 

The
materials used in constructing an arch bridge, has changed over time. In the
Roman age, arch bridges were built of stone or bricks. After the production of
steel, arch bridges are built of reinforced concrete and steel. Steel has
properties that makes it suitable for bridge construction. Steel has a yield
strength of maximum 550MPa which means that it can withstand high amount of
stress without causing plastic deformation. It is affordable. Concrete has
compressive strength of 20-40 MPa. Difference between steel arch bridge and
stone arch bridge is that steel is stronger under tension whereas stone bridges
are stronger under compression. Their resistance to bending moment changes the
position of the curve on an arch bridge. A steel bridge has the curve on top of
the deck because steel wires will hold it better without failure. A stone
bridge will have the curve bellow the deck because stone is stronger under
compression. In modern days steel is used more in constructing an arch bridge
because it is cheaper to manufacture and can be spanned over longer distances
than a stone bridges. Arch bridges attract tourists due to their attractive
view. This can benefit the country’s economy. An example of an arch bridge that
attracts tourists is “The Sydney Harbour Bridge” in Sydney, Australia.

·       Beam bridge:

Beam
bridges are the simplest and oldest structural forms of bridge designs. The
earliest beam bridge was built in 7th
century by the ancient Romans. A beam bridge is a beam supported by an
abutment at each end. There are three different types supports;

·       
Fixed support: they
resist vertical and horizontal loads as well as moment. They are designed to securely
hold a structure.

 

 

 

·       
Pinned support also resist vertical and
horizontal loads but does not resist moment.

 

 

·       
Roller support can only provide reactions normal
to surface as they allow side movement for expansion.

 

 

 

The
idea of beam bridges came from nature. Ancient people saw a tree fallen across
a stream and they imitated the idea and started building bridges classified as
beam bridges. Original beam bridges were made of timber in its natural state
where a tree is placed across a stream. After centuries of making beam bridges,
wooden beams were replaced with steel and reinforced concrete beams that have
higher yield strength and can with stand higher loads without failure. Since
concrete is weak in tension, reinforced concrete gives concrete the ability to
stretch and when steel is being compressed, more compressing force is applied
on the concrete that makes it ideal for bridge designs. Reinforced concrete was
achieved in two methods:

·       
Pre-stressed
concrete occurs when concrete is casted over a series of steel mesh that have
been tensioned before pouring. Once the concrete sets the cables are released.
Then steel cables try to return to their original stat, they build up
compressive stress in the concrete.

·       
Post-stressed concrete is formed when concrete
is cast with tubes running through the piece of concrete. After setting, wires
are pulled through the piece of concrete and attached to plates at one end and
tensioned at the other. The tensioning tends to compress the concrete and place
it into a state of compressive stress. When the required tension is gained, the
wires are attached to the end where tension occurred.

 Constructing a beam bridge using timber faced
a few issues such as availability and cost. It required regular maintenance as
it rots and attacked by termites. Engineers started painting timber with chemicals
to prevent termites form eating the beam. These chemicals were harmful for
people’s health as it caused lung cancer. beam bridges are helpful for short
spans and have a reasonable cost. Requires shorter time to build a beam bridge as
to build any other bridge type. It is difficult and risky to build a long span
over long stream to reach the other end of the stream in a case where there is
one support only, then a cantilever bridge can solve this issue. Cantilever is
a bridge that is supported at one end and the span in the centre is supported
by the cantilever arms at each end. They are also suitable for rail road on
long distances over a stream of water because it is cheaper and the modern
materials are developed to withstand heavy loads. Also engineers have invented
beams in such shapes that can resist bending moment very effectively.

Engineers
came up with beam shapes that suit different cases. The shapes are I,
T and rectangular beams. 

¾    T-shaped
beams have a cross section of T shape, it acts as a compression member in
resisting compressive stress. It offers great resistance as it reduces amount
of steel required.

¾    T
shape beam saves reinforcement as compared to other beam types.

¾    T
beam lacks the bottom flange making it have less tensile strength.

¾    An I beam
is heavier than a T beam and lighter than a rectangular beam.

¾    The
additional flange in an I beam helps it to resist tensile strength and bending
moment.

¾    A
rectangular beam requires less calculations to construct.

¾    T
beams are used more often because they are lighter and cost effective. They are
attached to the deck to act as a flange and obtain tensile strength.

 

 

 

 

 

·       
Truss bridge

Truss bridge is
one kind of bridge designs that was invented in the 1840s. They are based on
Newton’s law of motion. It is similar to beam bridge but it has trusses that
would help spread compression and tension forces so that the bridge does not
collapse. Tension is a force that is directed along a cable and pulls equally
on the object on both opposite sides of the cable. Compression is the opposite
to tension where the forces are pushed towards to compact a material. Truss
bridges are based on connected materials in a triangular shape. They are very
rigid structure as load is transferred from a single point to a wider area (http://www.historyofbridges.com/facts-about-bridges/truss-bridge/). After the development of machines, timber was cut
into pieces and shaped
into trusses and placed over a beam. Wood was used at the
start of the invention of truss bridges. Wood is good in tension and
compression which made it a good option to use in the construction of the
bridge as wood was the easiest material to extract.

 

Advantages:

·       
Truss brides are quickly
installed with very cost efficiency. The trusses are manufactured and delivered
into the site as a complete set to be built.

·       
The triangular shape
provides support to the entire bridge making it suitable for heavy loads.

·       
The unique properties of
triangles allow truss bridges to span across longer distances. This feature
makes it the option for long spans.

·       
Maths involved in truss
bridges is simple and it helps determine force in each member of the truss
bridge to help build a safer and cost-effective bridge.

 

Disadvantages:

·       
Requires regular
maintenance, many parts which means more parts to look at which is expensive.
As well as, it is very time consuming.

·       
Any mistake during the construction
practice, can lead to a damage of the whole bridge and waste of materials.

 

Suspension bridges:

Suspension bridges are
one type of bridges that have the deck slung by steel cables. The first suspension
bridge was built in the early 19th century. The load on a suspension
bridge transfers into tension in cables and compression in the pillars.
One problem happened in 1940 where a bridge collapsed. “Tacoma Narrows Bridge”
in
United States lost the government a lot of money to build the narrowest
suspension bridge to collapse in four months because of wind at 68km/h. This
was a lesson for engineers to do more calculations and to never build a narrow
bridge and it has to be stiff because it will carry wind easily and result in
damaging the bridge and wasting money and materials.

Advantages:

·       
Long spans are achieved with suspension bridges.

·       
Less materials are required to build it, leading to reduce in
construction cost.

·       
Does not impede the flow of water traffic during construction

·       
May withstand earthquake better than heavier bridges.

Disadvantages:

·       
Flexibility and light deck cause deck vibrations under high winds that
can cause the bridge to collapse.

·       
Difficult to carry heavy rail traffic because of its deck’s low
stiffness as it is resisting gravitational force that is acting on the
materials used.

·       
Major foundation work is required to build a suspension bridge over
stream of water where the ground is soft.

 

 

 

o  
Method of constructing an Arch bridge:

 

o  
Method of constructing a suspension
bridge:

o    

o  
Method of constructing a beam bridge:

          

o  
Construction method of a truss bridge:

 

1-    
The process starts the same for all different types of bridges. Each
bridge must be designed individually before building. Designers must think
about all the factors that can impact their bridge design such as, earthquakes,
wind, etc.

2-    
Then a sample soil is taken to do calculation to find the soil
conditions and the load that the ground can withstand to figure out the
foundation required.

3-    
Abutments are built on each end.

4-    
For an arch bridge, the arch is built first and then the deck is built
over or beneath the arch depending on the design.

5-    
For a suspension bridge, the towers are built after the abutments. Then
the cables are attached between towers and suspender cables are attached. After
that, the deck is built and delivered to the work place and attached to the
suspender cables.

6-    
For a truss and a beam bridge, the deck is delivered and placed over the
supports built.

 

 

Materials involved
in the construction of bridges:

Rope:

Rope was used in the early suspension bridges and it rotted and could
only carry small loads. They are built for footbridges only because they will
collapse when loaded with heavy loads. It is an inexpensive material. On the
other hand, ropes used in early suspension bridges were made of nylon. Nylon is
a polymer that is derived from petroleum and the production of nylon produces
greenhouse gases and requires a lot of energy. Instead of wasting energy on
producing nylon ropes, it can be used to manufacture a better material.

Stone:

Stone has a unique appearance which makes it requested in designing a civil structure. Stone is strong in compression but weak in tension
which made it only a good option for arch bridges only, and failed in other
bridges such as suspension bridges where the bridge is slung with material that
must have high elasticity like steel. Stone is low in toughness and does not
have the ability to withstand forces without failure. It is brittle which means
it is hard but liable to break easily. It does not resist chemicals and stains.
It does not come in the shapes needed. Ancient cultures had to mine
stone by digging large quarries which impacted the surrounding flora and fauna.

Cast iron:

Cast iron properties are similar to stone it
is strong in compression but weak in tension. Thus, it was used in bridge
construction such as arch bridges because of its low cost corrode resistance
that requires less maintenance. Cast iron provided strength equal to stone but
greatly reduced the weight of the bridge.

Wrought iron:

Wrought iron was used in the early suspension bridges in the chains from
which the deck was suspended. This alloy can withstand major environmental
disasters such as earthquakes and hurricanes and it is cheap to manufacture.
Iron is a ferromagnetic material. Wrought iron is an alloy that consist iron
with very low amount of carbon (less than 0.08%). When the alloy is made, the
structure is fibrous that weakens the material and makes it unreliable. This
property limited the length of the bridges until the production of steel.

Wrought and cast iron have to be mined and smelted. It requires
combustion of fuel that affect the amount of fossil fuels for future generation
as it causes greenhouse gas.  

Concrete:

Concrete is a material that consists of cement, sand and aggregate. The
sand fills the gaps of aggregate while the cement acts as a mould that holds
the sand and aggregate together. cement can come in two forms hydraulic that
hardens under water and non-hydraulic that does not harden under water.
Hydraulic cement is mixed with sand and aggregate to enable concrete to harden
under water. It is useful when bridge supports are made in a soft ground or
under water. This property helps engineers to span bridges over longer
distances. The other type of cement is mixed to make concrete that is used for
the beam or the deck of the bridge.

It is cheap and offers great strength. Concrete behave in a very similar
way to stone. It resists corrosion. Tension causes cracks to form and cracks
can lead to damage in the bridge. Concrete is reinforced with steel mesh that
takes the tensile load and then concrete resists failure.

Timber:

Timber is a strong and light weight material that makes it desirable for
bridge constructions. It does not require high maintenance because it does not
necessarily need to be painted to prevent corrosion. It is highly available and
will not delay the process of construction but it deforests the surrounding
area as it impacts the environment.

Steel:

Steel is the most favourable material for civil engineers. It allows the
bridges to span over longer distances. It is very elastic material that helps
build a safer and stronger suspension bridge. It is strong is compression and
tension and resists bending moments making it suitable for all types of
bridges. On the other hand, steel falls into the same category of cast and
wrought iron requiring combustion of fuel and mining that causes erosion and
other environmental impacts.

In
conclusion, bridges are essential and have been around for thousands of years. There
are four different types of bridges and they are used for different
circumstances depending on the conditions and the materials provided. Materials
have been changing overtime trying to use the best material that can be safe
and easy to use during construction process.  All bridges are strong and can withstand
different loads and I personally think that truss arch bridge is the best
bridge design. It consists the materials and shapes used for a truss and an
arch bridge. they both can withstand very heavy load and that load is spread
between all members with makes it ideal for heavy road uses.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

http://www.warwickallen.com/bridges/ArchBridges.htm

What Is a Beam Bridge – Advantages & Disadvantages – Beam Bridge Types

Bridge Types

http://web.mit.edu/4.441/1_lectures/1_lecture13/1_lecture13.html

https://www.quora.com/What-is-the-difference-between-a-rectangular-beam-and-a-T-beam

http://www.design-technology.org/archbridges.htm

http://www.madehow.com/Volume-4/Concrete-Beam-Bridge.html

http://bridgebuilders.com/timber-bridge-construction/why-use-timber