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Authors: Do Viet Hai – Phan Hoang Nam Unit 1: BRIDGE TYPES A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providin

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Authors: Do Viet Hai – Phan Hoang Nam

Unit 1: BRIDGE TYPES

A bridge is a structure built to span physical obstacles such as a body of water, valley, or road, for the purpose of providing passage over the obstacle Designs of bridges vary depending on the function of the bridge, the nature of the terrain where the bridge is constructed, the material used to make it and the funds available to build it

There are six main types of bridges: beam bridges, truss bridges, arch bridges, cantilever bridges, suspension bridges and cable-stayed bridges

Beam bridges

Beam bridges are horizontal beams supported at

each end by abutments, hence their structural name

of simply supported When there is more than one

span the intermediate supports are known as piers The earliest beam bridges were simple logs that sat across streams and similar simple structures In modern times, beam bridges are large box steel girder bridges Weight on top of the beam pushes straight down on the abutments at either end of the bridge They are made up mostly

of wood or metal Beam bridges typically do not exceed 76 m long The world's longest beam bridge is Lake Pontchartrain Causeway in southern Louisiana in the United States, at 38.35 km, with individual spans of 17 m

Truss bridges

A truss bridge is a bridge composed of connected

elements (typically straight) which may be stressed

from tension, compression, or sometimes both in

response to dynamic loads Truss bridges are one of the oldest types of modern bridges The basic types of truss bridges shown in this article have simple designs which could be easily analyzed by nineteenth and early twentieth century engineers

A truss bridge is economical to construct owing to its efficient use of materials

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Arch bridges

Arch bridges have abutments at each end The

earliest known arch bridges were built by the

Greeks, and include the Arkadiko Bridge The

weight of the bridge is thrust into the abutments at either side Dubai in the United Arab Emirates is currently building the Sheikh Rashid bin Saeed Crossing, which is scheduled for completion in 2012 When completed, it will be the largest arch bridge in the world

Cantilever bridges

Cantilever bridges are built using cantilevers—

horizontal beams supported on only one end Most

cantilever bridges use a pair of continuous spans that

extend from opposite sides of the supporting piers to meet at the center of the obstacle the bridge crosses Cantilever bridges are constructed using much the same materials & techniques as beam bridges The difference comes in the action of the forces through the bridge The largest cantilever bridge is the 549 m Quebec Bridge

in Quebec, Canada

Suspension bridges

Suspension bridges are suspended from cables The

earliest suspension bridges were made of ropes or

vines covered with pieces of bamboo In modern

bridges, the cables hang from towers that are attached to caissons or cofferdams The caissons or cofferdams are implanted deep into the floor of a lake or river The longest suspension bridge in the world is the 3,909 m Akashi Kaikyo Bridge in Japan

Cable-stayed bridges

Cable-stayed bridges, like suspension bridges, are

held up by cables However, in a cable-stayed

bridge, less cable is required and the towers holding

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the cables are proportionately shorter The first known cable-stayed bridge was designed in 1784 by C.T Loescher The longest cable-stayed bridge is the Sutong Bridge over the Yangtze River in China

By use

A bridge is designed for trains, pedestrian or road traffic, a pipeline or waterway for water transport or barge traffic An aqueduct is a bridge that carries water, resembling a viaduct, which is a bridge that connects points of equal height A road-rail bridge carries both road and rail traffic

Bridges are subject to unplanned uses as well The areas underneath some bridges have become makeshift shelters and homes to homeless people, and the undersides

of bridges all around the world are spots of prevalent graffiti Some bridges attract people attempting suicide, and become known as suicide bridges

To create a beautiful image, some bridges are built much taller than necessary This type, often found in east-Asian style gardens, is called a Moon bridge, evoking a rising full moon Other garden bridges may cross only a dry bed of stream washed pebbles, intended only to convey an impression of a stream Often in palaces a bridge will be built over an artificial waterway as symbolic of a passage to an important place or state of mind A set of five bridges cross a sinuous waterway in

an important courtyard of the Forbidden City in Beijing, the People's Republic of China The central bridge was reserved exclusively for the use of the Emperor, Empress, and their attendants

(Source: Wikipedia)

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Match the words in column A with their meanings in column B

1 Beam bridge a In theory, the individual parts of this structure only

subject to tension and compression forces but not bending forces

2 Truss bridge b The second oldest bridge type This structure doesn’t

require piers in the center and uses a curved structure

3 Arch bridge c The support is in the middle of a span, not the end

4 Cantilever bridge d This structure is a continuous girder with one or more

towers erected above piers in the middle of the span

5 Suspension bridge e This structure often uses I-beams or box girders in their

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Vocabulary

span spæn the part of a bridge or an arch between one

vertical support and another

obstacle ˈɒbstəkl an object that is in your way and that makes it

difficult for you to move forward

terrain təˈreɪn used to refer to an area of land when you are

mentioning its natural features

material məˈtɪəriəl a substance that things can be made from

fund fʌnd money that is available to be spent

abutment əˈbʌtmənt a masonry mass supporting and receiving the

thrust of part of an arch or vault

stream striːm a continuous flow of liquid or gas

box steel girder bɒks stiːl ˈɡɜːrdər

element ˈelɪmənt a necessary or typical part of something

tension ˈtenʃn the state of being stretched tight

compression kəmˈpreʃn an increase in pressure of the charge in an

engine or compressor obtained by reducing its volume

dynamic load daɪˈnæmɪk ləʊd a force exerted by a moving body on a

resisting member, usually in a relatively short time interval

thrust θrʌst to push something/somebody suddenly or

violently in a particular direction

schedule ˈʃedjuːl a plan that lists all the work that you have to

do and when you must do each thing

continuous span kənˈtɪnjuəs spæn a span which is formed of a series of

consecutive spans (over three or more supports) that are continuously or rigidly connected so that bending moment may be transmitted from one span to the adjacent ones

pier pɪə(r) a large strong piece of wood, metal or stone

that is used to support a roof, wall, bridge, etc

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suspend səˈspend to hang something from something else

cable ˈkeɪbl a set of wires, covered in plastic or rubber,

that carries electricity, telephone signals, etc

caisson kəˈsuːn a watertight chamber open at the bottom and

containing air under pressure, used to carry out construction work under water

cofferdam ˈkɒfəˌdæm a watertight structure, usually of sheet piling,

that encloses an area under water, pumped dry

to enable construction work to be carried out

tower ˈtaʊə(r) a tall narrow building or part of a building,

especially of a church or castle

train treɪn a railway/railroad engine pulling a number of

coaches/cars or trucks, taking people and goods from one place to another

pedestrian pəˈdestriən a person walking in the street and not

travelling in a vehicle

road traffic rəʊd ˈtræfɪk a hard surface built for vehicles to travel on

pipeline ˈpaɪplaɪn a series of pipes that are usually underground

and are used for carrying oil, gas, etc over long distances

waterway ˈwɔːtəweɪ a river, canal, etc along which boats can

travel

water transport ˈwɔːtə(r) ˈtrænspɔːt

barge bɑːdʒ a large boat with a flat bottom, used for

carrying goods and people on canals and rivers

aqueduct ˈækwɪdʌkt a structure for carrying water, usually one

built like a bridge across a valley or low ground

road-rail bridge rəʊd-reɪl brɪdʒ

makeshift shelter ˈmeɪkʃɪft ˈʃeltə(r) used temporarily for a particular purpose

because the real thing is not available

prevalent graffiti ˈprevələnt ɡrəˈfiːti

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suicide ˈsuːɪsaɪd the act of killing yourself deliberately

dry bed draɪ bed

convey kənˈveɪ to make ideas, feelings, etc known to

exclusively ɪkˈskluːsɪvli only given to one particular person or group

attendant əˈtendənt a person whose job is to serve or help people

in a public place

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Further reading

Golden Gate Bridge

The Golden Gate Bridge is a

suspension bridge spanning the

Golden Gate, the opening of the San

Francisco Bay into the Pacific

Ocean As part of both U.S Route

101 and California State Route 1, the

structure links the city of San

Francisco on the northern tip of the

San Francisco Peninsula to Marin

County The Golden Gate Bridge was the longest suspension bridge span in the world when it was completed in 1937, and has become one of the most internationally recognized symbols of San Francisco, California, and of the United States Despite its span length being surpassed by eight other bridges since its completion, it still has the second longest suspension bridge main span in the United States, after the Verrazano-Narrows Bridge in New York City It has been declared one of the modern Wonders of the World by the American Society of Civil Engineers The Frommers travel guide considers the Golden Gate Bridge "possibly the most beautiful, certainly the most photographed, bridge in the world"

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Sutong Yangtze River Bridge

The Sutong Yangtze River Bridge

is a cable-stayed bridge that spans

the Yangtze River in China between

Nantong and Changshu, a satellite

city of Suzhou, in Jiangsu province

With a span of 1,088 metres

(3,570 ft), it is the cable-stayed

bridge with the longest main span in

the world as of 2011 Its two side

spans are 300 metres (980 ft) each, and there are also four small cable spans The bridge received the 2010 Outstanding Civil Engineering Achievement award (OCEA) from the American Society of Civil Engineers

Two towers of the bridge are 306 metres (1,004 ft) high and thus the second tallest

in the world The total bridge length is 8,206 metres (26,923 ft) Construction began in June 2003, and the bridge was linked up in June 2007 The bridge was opened to traffic on 25 May 2008 and was officially opened on 30 June 2008 Construction has been estimated to cost about US$1.7 billion

The completion of the bridge makes the commute between Shanghai and Nantong, previously a four-hour ferry ride, shorten to about an hour It brings Nantong one step closer to becoming an important part of the Yangtze River Delta economic zone, and has further attracted foreign investors into the city The bridge is also pivotal in the development of poorer northern Jiangsu regions

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Unit 2: BASIC BRIDGE TERMS

An important first step in understanding the principles and processes of bridge construction is learning basic bridge terminology Although bridges vary widely in material and design, there are many components that are common to all bridges In general, these components may be classified either as parts of a bridge superstructure or as parts of a bridge substructure

Bridge decks are required to conform to the grade of the approach roadway so that there is no bump or dip as a vehicle crosses onto or off of the bridge The most common causes of premature deck failure are:

1 Insufficient concrete strength from an improper mix design, too much water, improper amounts of air entraining admixtures, segregation, or improper curing

2 Improper concrete placement, such as failure to consolidate the mix as the concrete is placed, pouring the concrete so slowly that the concrete begins the initial set, or not maintaining a placement rate

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3 Insufficient concrete cover due to improper screed settings or incorrect installation of the deck forms and/or reinforcement

A bridge deck is usually supported by structural members The most common types are:

1 Steel I-beams and girders

2 Precast, prestressed, reinforced concrete bulb T beams

3 Precast, prestressed, reinforced concrete I beams

4 Precast, prestressed, concrete box beams

5 Reinforced concrete slabs

Secondary members called diaphragms are used as cross-braces between the main structural members and are also part of the superstructure Parapets (bridge railings), handrails, sidewalks, lighting, and drainage features have little to do with the structural strength of a bridge, but are important aesthetic and safety items The materials and workmanship that go into the construction of these features require the same inspection effort as any other phase of the work

SUBSTRUCTURE

The substructure consists of all of the parts that support the superstructure The main components are abutments or end-bents, piers or interior bents, footings, and piling

Abutments support the extreme ends of the bridge and confine the approach embankment, allowing the embankment to be built up to grade with the planned bridge deck Three typical abutment designs are illustrated in Figure 1

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Figure 1 Abutments

When a bridge is too long to be supported by abutments alone, piers or interior bents are built to provide intermediate support Although the terms may be used interchangeably, a pier generally is built as a solid wall, while bents are usually built with columns Figure 1-2 illustrates several types of piers

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Figure 2 Piers

The top part of abutments, piers, and bents is called the cap The structural members rest on raised, pedestal-like areas on top of the cap called the bridge seats The devices that are used to connect the structural members to the bridge seats are called shoes or bearings

Abutments, bents, and piers are typically built on spread footings Spread footings are large blocks of reinforced concrete that provide a solid base for the substructure and anchor the substructure against lateral movements Footings also serve to transmit loads borne by the substructure to the underlying foundation material When the soils beneath a footing are not capable of supporting the weight of the structure above the soil, bearing failure occurs The foundation shifts or sinks under the load, causing structure movement and damage (Figure 3)

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Figure 3 Soil Failure

In areas where bearing failure is likely, footings are built on foundation piling (Figure 4) These load-bearing members are driven deep into the ground at footing locations to stabilize the footing foundation Piling transmits loads from the substructure units down to underlying layers of soil or rock

Figure 4 Structure Pilings

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Fill in the blanks with proper terms in the box

wing walls pier flexibility solid abutments vehicle parapet pier foundation bridge bearings open abutment bearing movements

1 for narrow bridges should only be adopted where the open abutment solution is not possible In the case of wide bridges the

solution is to be preferred, but there are many cases where economy must be the overriding consideration

2 are devices for transferring loads and movements from the deck to the substructure and foundations In highway bridge are accommodated by the basic mechanisms of internal deformation (elastomeric), sliding (PTFE), or rolling

3 as a safety barrier that is installed on the edge of a bridge or on

a retaining wall or similar structure where there is a vertical drop, and which may contain additional protection and restraint for pedestrians and other road users

4 If the has a bearing at its top, corresponding to a structural pin joint, then the horizontal movements will impose moments at the base, their magnitude will depend on the

5 Design the to transfer and distribute the loads from the structure to the ground Ensure that the factor of safety against shear failure in the soil is not reached and settlement is within the allowable limits

6 are essentially retaining walls adjacent to the abutment The walls can be independent or integral with the abutment wall

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drainage feature ˈdreɪnɪdʒ ˈfiːtʃə

roadway portion ˈrəʊdˌweɪ

reinforced concrete ˌriːɪnˈfɔːs ˈkɒnkriːt

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Further reading

Quality Control

The design and construction of a bridge must meet standards developed by several agencies including the American Association of State Highway and Transportation Officials, the American Society for Testing and Materials, and the American Concrete Institute Various materials (e.g., concrete batches) and structural components (e.g., beams and connections) are tested as construction proceeds As a further example, on the Albuquerque bridge project, static and dynamic strength tests were conducted on a sample column foundation that was constructed at the site, and on two of the production shafts

The Future

Numerous government agencies and industry associations sponsor and conduct research to improve materials and construction techniques A major goal is the development of lighter, stronger, more durable materials such as reformulated, high-performance concrete; fiber-reinforced, polymer composite materials to replace concrete for some components; epoxy coatings and electro-chemical protection systems to prevent corrosion of steel rebar; alternative synthetic reinforcing fibers; and faster, more accurate testing techniques

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Unit 4: STRUCTURAL ANALYSIS

Structural analysis is the determination of the effects of loads on physical structures and their components Structures subject to this type of analysis include all that must withstand loads, such as buildings, bridges, vehicles, machinery, furniture, attire, soil strata, prostheses and biological tissue Structural analysis incorporates the fields of applied mechanics, materials science and applied mathematics to compute a structure's deformations, internal forces, stresses, support reactions, accelerations, and stability The results of the analysis are used to verify a structure's fitness for use, often saving physical tests Structural analysis is thus a key part of the engineering design of structures

Structures and Loads

A structure refers to a body or system of connected parts used to support a load Important examples related to Civil Engineering include buildings, bridges, and towers; and in other branches of engineering, ship and aircraft frames, tanks, pressure vessels, mechanical systems, and electrical supporting structures are important In order to design a structure, one must serve a specified function for public use, the engineer must account for its safety, aesthetics, and serviceability, while taking into consideration economic and environmental constraints Other branches of engineering work on a wide variety of nonbuilding structures

Classification of Structures

It is important for a structural engineer to recognize the various types of elements composing a structure and to be able to classify structures as to their form and function Some of the structural elements are tie rods, rod, bar, angle, channel, beams, and columns Combination of structural elements and the materials from which they are composed is referred to as a structural system Each system is constructed of one or more basic types of structures such as Trusses, Cables and Arches, Frames, and Surface Structures

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Loads

Once the dimensional requirement for a structure have been defined, it becomes necessary to determine the loads the structure must support In order to design a structure, it is therefore necessary to first specify the loads that act on it The design loading for a structure is often specified in building codes There are two types of codes: general building codes and design codes, engineer must satisfy all the codes requirements for a reliable structure There are two types of loads that structure engineering must encounter in the design First type of load is called Dead loads that consist of the weights of the various structural members and the weights of any objects that are permanently attached to the structure For example, columns, beams, girders, the floor slab, roofing, walls, windows, plumbing, electrical fixtures, and other miscellaneous attachments Second type of load is Live Loads which vary in their magnitude and location There are many different types of live loads like building loads, highway bridge Loads, railroad bridge Loads, impact loads, wind loads, snow loads, earthquake loads, and other natural loads

Analytical methods

To perform an accurate analysis a structural engineer must determine such information as structural loads, geometry, support conditions, and materials properties The results of such an analysis typically include support reactions, stresses and displacements This information is then compared to criteria that indicate the conditions of failure Advanced structural analysis may examine dynamic response, stability and non-linear behavior

There are three approaches to the analysis: the mechanics of materials approach (also known as strength of materials), the elasticity theory approach (which is actually a special case of the more general field of continuum mechanics), and the finite element approach The first two make use of analytical formulations which apply mostly to simple linear elastic models, lead to closed-form solutions, and can often be solved by hand The finite element approach is actually a numerical method for solving differential equations generated by theories of mechanics such

as elasticity theory and strength of materials However, the finite-element method

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depends heavily on the processing power of computers and is more applicable to structures of arbitrary size and complexity

Regardless of approach, the formulation is based on the same three fundamental relations: equilibrium, constitutive, and compatibility The solutions are approximate when any of these relations are only approximately satisfied, or only

an approximation of reality

Limitations

Each method has noteworthy limitations The method of mechanics of materials is limited to very simple structural elements under relatively simple loading conditions The structural elements and loading conditions allowed, however, are sufficient to solve many useful engineering problems The theory of elasticity allows the solution of structural elements of general geometry under general loading conditions, in principle Analytical solution, however, is limited to relatively simple cases The solution of elasticity problems also requires the solution of a system of partial differential equations, which is considerably more mathematically demanding than the solution of mechanics of materials problems, which require at most the solution of an ordinary differential equation The finite element method is perhaps the most restrictive and most useful at the same time This method itself relies upon other structural theories (such as the other two discussed here) for equations to solve It does, however, make it generally possible to solve these equations, even with highly complex geometry and loading conditions, with the restriction that there is always some numerical error Effective and reliable use of this method requires a solid understanding of its limitations

Strength of materials methods (classical methods)

The simplest of the three methods here discussed, the mechanics of materials method is available for simple structural members subject to specific loadings such

as axially loaded bars, prismatic beams in a state of pure bending, and circular shafts subject to torsion The solutions can under certain conditions be superimposed using the superposition principle to analyze a member undergoing

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combined loading Solutions for special cases exist for common structures such as thin-walled pressure vessels

For the analysis of entire systems, this approach can be used in conjunction with statics, giving rise to the method of sections and method of joints for truss analysis, moment distribution method for small rigid frames, and portal frame and cantilever method for large rigid frames Except for moment distribution, which came into use

in the 1930s, these methods were developed in their current forms in the second half

of the nineteenth century They are still used for small structures and for preliminary design of large structures

The solutions are based on linear isotropic infinitesimal elasticity and Bernoulli beam theory In other words, they contain the assumptions (among others) that the materials in question are elastic, that stress is related linearly to strain, that the material (but not the structure) behaves identically regardless of direction of the applied load, that all deformations are small, and that beams are long relative to their depth As with any simplifying assumption in engineering, the more the model strays from reality, the less useful (and more dangerous) the result

Euler-Elasticity methods

Elasticity methods are available generally for an elastic solid of any shape Individual members such as beams, columns, shafts, plates and shells may be modeled The solutions are derived from the equations of linear elasticity The equations of elasticity are a system of 15 partial differential equations Due to the nature of the mathematics involved, analytical solutions may only be produced for relatively simple geometries For complex geometries, a numerical solution method such as the finite element method is necessary

Many of the developments in the mechanics of materials and elasticity approaches have been expounded or initiated by Stephen Timoshenko

Methods Using Numerical Approximation

It is common practice to use approximate solutions of differential equations as the basis for structural analysis This is usually done using numerical approximation

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techniques The most commonly used numerical approximation in structural analysis is the Finite Element Method

The finite element method approximates a structure as an assembly of elements or components with various forms of connection between them Thus, a continuous system such as a plate or shell is modeled as a discrete system with a finite number

of elements interconnected at finite number of nodes The behaviour of individual elements is characterised by the element's stiffness or flexibility relation, which altogether leads to the system's stiffness or flexibility relation To establish the element's stiffness or flexibility relation, we can use the mechanics of materials approach for simple one-dimensional bar elements, and the elasticity approach for more complex two- and three-dimensional elements The analytical and computational development are best effected throughout by means of matrix algebra

Early applications of matrix methods were for articulated frameworks with truss, beam and column elements; later and more advanced matrix methods, referred to as

"finite element analysis," model an entire structure with one-, two-, and dimensional elements and can be used for articulated systems together with continuous systems such as a pressure vessel, plates, shells, and three-dimensional solids Commercial computer software for structural analysis typically uses matrix finite-element analysis, which can be further classified into two main approaches: the displacement or stiffness method and the force or flexibility method The stiffness method is the most popular by far thanks to its ease of implementation as well as of formulation for advanced applications The finite-element technology is now sophisticated enough to handle just about any system as long as sufficient computing power is available Its applicability includes, but is not limited to, linear and non-linear analysis, solid and fluid interactions, materials that are isotropic, orthotropic, or anisotropic, and external effects that are static, dynamic, and environmental factors This, however, does not imply that the computed solution will automatically be reliable because much depends on the model and the reliability of the data input

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