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STEEL BRIDGE - : PREPARED BY :-

NAME: HUZAIF BIN MOHMAD.

CLASS: 2nd year. SECTION: B (G1).

BRANCH: CIVIL

ROLL NO.: 120107099

SYSTEM ID: 2012018204

EMAIL ID: (bhathuzi99@gmail.com)

Department of Civil Engineering And Technology

SUBMITTED TO:Ms. CHAVVI GUPTAAssistant Professor, Department of Civil EngineeringSharda University.

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CONTENT

S.NO. TOPIC PAGE NO.

1 Abstract 03

2 Introduction 04

3 History of Bridge 05

4 Types of Bridges 06-08

5 Basic Concepts of Bridges 09

6 Material Properties Required For Design 10

7 Steel Used In Bridges 11

8 Loads On Bridges 12-13

9

10

Summary

References

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15

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01 ABSTRACT

The primary function of a bridge deck is to support the vehicular vertical loads and distribute these loads to the steel superstructure. This module provides practical information regarding the decking options and design considerations for steel bridges, presenting deck types such as concrete deck slabs, metal grid decks, orthotropic steel decks, wood decks, and several others. The choice of the particular deck type to use can depend on several factors, which may include the specific application, initial cost, life cycle cost, durability, weight, or owner requirements. For the deck types discussed herein, a brief description of the particular deck type is given, in addition to general design and detail considerations.

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02 INTRODUCTION

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. There are many different designs that all serve unique purposes and apply to different situations. Designs of bridges vary depending on the function of the bridge, the nature of the terrain where the bridge is constructed and anchored, the material used to make it, and the funds available to build it. The main advantages of structural steel over other construction materials are its strength and ductility. It has a higher strength to cost ratio in tension and a slightly lower strength to cost ratio in compression when compared with concrete. The stiffness to weight ratio of steel is much higher than that of concrete. Thus, structural steel is an efficient and economic material in bridges. Structural steel has been the natural solution for long span bridges since 1890, when the Firth of Forth cantilever bridge, the world's major steel bridge at that time was completed. Steel is indeed suitable for most span ranges, but particularly for longer spans. Howrah Bridge, also known as Rabindra Setu, is to be looked at as an early classical steel bridge in India. This cantilever bridge was built in 1943. It is 97 m high and 705 m long. This engineering marvel is stillserving the nation, deriding all the myths that people have about steel.

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03 History of Bridge

The first bridges were made by nature itself — as simple as a log fallen across a stream or stones in the river. The first bridges made by humans were probably spans of cut wooden logs or planks and eventually stones, using a simple support and crossbeam arrangement. Some early Americans used trees or bamboo poles to cross small caverns or wells to get from one place to another. The greatest bridge builders of antiquity were the ancient Romans.The Romans built arch bridges and aqueducts that could stand in conditions that would damage or destroy earlier designs. Some stand today.An example is the Alcántara Bridge, built over the river Tagus, in Spain. The Romans also used cement, which reduced the variation of strength found in natural stone.One type of cement, called pozzolana, consisted of water, lime, sand, and volcanic rock. Brick and mortar bridges were built after the Roman era, as the technology for cement was lost then later rediscovered. The use of stronger bridges using plaited bamboo and iron chain was visible in India by about the 4th century.A number of bridges, both for military and commercial purposes, were constructed by the Mughal administration in India. Although large Chinese bridges of wooden construction existed at the time of the Warring States, the oldest surviving stone bridge in China is the Zhaozhou Bridge, built from 595 to 605 AD during the Sui Dynasty. This bridge is also historically significant as it is the world's oldest open-spandrel stone segmental arch bridge. Rope bridges, a simple type of suspension bridge, were used by the Inca civilization in the Andes mountains of South America, just prior to European colonization in the 16th century. During the 18th century there were many innovations in the design of timber bridges by Hans Ulrich, Johannes Grubenmann, and others. The first book on bridge engineering was written by Hubert Gautier in 1716. A major breakthrough in bridge technology came with the erection of the Iron Bridge in Coalbrookdale, England in 1779. It used cast iron for the first time as arches to cross the river Severn.

With the Industrial Revolution in the 19th century, truss systems of wrought iron were developed for larger bridges, but iron did not have the tensile strength to support large loads. With the advent of steel, which has a high tensile strength, much larger bridges were built, many using the ideas of Gustave Eiffel.

In 1927 welding pioneer Stefan Bryła designed the first welded road bridge in the world, the Maurzyce Bridge which was later built across the river Słudwia at Maurzyce near Łowicz, Poland in 1929. In 1995, the American Welding Society presented the Historic Welded Structure Award for the bridge to Poland.

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04 Types of Bridges

Bridges can be categorized in several different ways. Bridges may be classified by how the forces of tension, compression, bending, torsion and shear are distributed through their structure. Most bridges will employ all of the principal forces to some degree, but only a few will predominate. The separation of forces may be quite clear. In a suspension or cable-stayed span, the elements in tension are distinct in shape and placement.

Beam Bridge

Beam bridges are horizontal beams supported at each end by substructure units and can be either simply supported when the beams only connect across a single span, or continuous when the beams are connected across two or more spans. When there are multiple spans, 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 can range from small, wooden beams to large, steel boxes. The vertical force on the bridge becomes a shear and flexural load on the beam which is transferred down its length to the substructures on either side[12] They are typically made of steel, concrete or wood. Beam bridge spans rarely exceed 250 feet (76 m) long.

Truss Bridge

A truss bridge is a bridge whose load-bearing superstructure is composed of a truss. This truss is a structure of connected elements forming triangular units. The connected elements (typically straight) 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. 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 weight of the bridge is thrust into the abutments at either side. The earliest known arch bridges were built by the Greeks.The arch has great natural strength. Thousands of years ago, Romans built arches out of stone. Today, most arch bridges are made of steel or concrete, and they can span up to 800 feet. The arch is squeezed together, and this squeezing force is carried outward along the curve to the supports at each end. The supports, called abutments, push back on the arch and prevent the ends of the arch from spreading apart.

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. Sub-types include the simple suspension bridge, the stressed ribbon bridge, the underspanned suspension bridge, the suspended-deck suspension bridge, and the self-anchored suspension bridge.The longest suspension bridge in the world is the 3,909 m (12,825 ft) Akashi Kaikyō Bridge in Japan.

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Cable-Stayed Bridge

The cable-stayed bridge, like the suspension bridge, supports the roadway with massive steel cables, but in a different way. The cables run directly from the roadway up to a tower, forming a unique "A" shape.

Cable-stayed bridges are becoming the most popular bridges for medium-length spans (between 500 and 3,000 feet).

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05 Basic Concepts of Bridges

How Bridges Work?

Every passing vehicle shakes the bridge up and down, making waves that can travel at hundreds of kilometers per hour.  Luckily the bridge is designed to damp them out, just as it is designed to ignore the efforts of the wind to turn it into a giant harp.   A bridge is not a dead mass of metal and concrete: it has a life of its own, and understanding its movements is as important as understanding the static forces.

Span: The distance between two bridge supports, whether they are columns, towers or the wall of a canyon.

Force: Any action that tends to maintain or alter the position of a structure. Compression: A force which acts to compress or shorten the thing it is acting on. Tension: A force which acts to expand or lengthen the thing it is acting on.

Beam: A rigid, usually horizontal, structural element.

Pier: A vertical supporting structure, such as a pillar Cantilever: A projecting structure supported only at one end, like a shelf bracket or a diving

board. Load: Weight distribution throughout a structure. Truss: A rigid frame composed of short, straight pieces joined to form a series of triangles or

other stable shapes. Stable: Ability to resist collapse and deformation; stability (n.) characteristic of a structure

that is able to carry a realistic load without collapsing or deforming significantly. Buckling: It is what happens when the force of compression overcomes an object's ability to

handle compression. A mode of failure characterized generally by an unstable lateral deflection due to compressive action on the structural element involved.

Snapping: It is what happens when tension overcomes an object's ability to handle tension.

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06 Material Properties Required For Design

The properties that need to be considered by designers when specifying steel construction products are:

Yield strength

Yield strength is the most common property that the designer will need as it is the basis used for most of the rules given in design codes . In European Standards for structural carbon steels (including weathering steel ), the primary designation relates to the yield strength, e.g. S275 steel is a structural steel with a specified minimum yield strength of 275 N/mm².The product standards also specify the permitted range of values for the ultimate tensile strength (UTS). The minimum UTS is relevant to some aspects of design.

Toughness

It is in the nature of all materials to contain some imperfections. In steel these imperfections take the form of very small cracks. If the steel is insufficiently tough, the 'crack' can propagate rapidly, without plastic deformation and result in a 'brittle fracture'. The risk of brittle fracture increases with thickness, tensile stress, stress raisers and at colder temperatures. The toughness of steel and its ability to resist brittle fracture are dependent on a number of factors that should be considered at the specification stage. A convenient measure of toughness is the Chirpy V-notch impact test. This test measures the impact energy required to break a small notched specimen, at a specified temperature, by a single impact blow from a pendulum.

Ductility

Ductility is a measure of the degree to which a material can strain or elongate between the onset of yield and eventual fracture under tensile loading as. The designer relies on ductility for a number of aspects of design, including redistribution of stress at the ultimate limit state, bolt group design, reduced risk of fatigue crack propagation and in the fabrication processes of welding, bending and straightening.

Weldability

All structural steels are essentially wieldable. However, welding involves locally melting the steel, which subsequently cools. The cooling can be quite fast because the surrounding material, e.g. the beam, offers a large 'heat sink' and the weld (and the heat introduced) is usually relatively small. This can lead to hardening of the 'heat affected zone' (HAZ) and to reduced toughness. The greater the thickness of material, the greater the reduction of toughness.

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07 Steel Used In Bridges

Steel used for bridges may be grouped into the following three categories:

Carbon Steel: This is the cheapest steel available for structural users where stiffness is more important than the strength. Indian steels have yield stress values up to 250 N/mm2 and can be easily welded. The steel conforming to IS: 2062 -1969, the American ASTM A36, the British grades 40 and Euronorm 25 grades 235 and 275 steels belong to this category.

High strength steels: They derive their higher strength and other required properties from the addition of alloying elements. The steel conforming to IS: 961- 1975, British grade 50, American ASTM A572 and Euronorm 155 grade 360 steels belong to this category. Another variety of steel in this category is produced with enhanced resistance to atmospheric corrosion. These are called 'weathering' steels in Europe, in America they conform to ASTM A588 and have various trade names like ' cor-ten'.

Heat-treated carbon steels: These are steels with the highest strength. They derive their enhanced strength from some form of heat-treatment after rolling namely normalisation or quenching and tempering.

The physical properties of structural steel such as strength, ductility, brittle fracture, weldability, weather resistance etc., are important factors for its use in bridge construction. These properties depend on the alloying elements, the amount of carbon, cooling rate of the steel and the mechanical deformation of the steel.

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08 Loads On Bridges

Dead load The dead load is the weight of the structure and any permanent load fixed thereon. The dead load is initially assumed and checked after design is completed.

Live load Bridge design standards specify the design loads, which are meant to reflect the worst loading that can be caused on the bridge by traffic, permitted and expected to pass over it. In India, the Railway Board specifies the standard design loadings for railway bridges in bridge rules. For the highway bridges, the Indian Road Congress has specified standard design loadings in IRC section II.

Impact load The dynamic effect caused due to vertical oscillation and periodical shifting of the live load from one wheel to another when the locomotive is moving is known as impact load. The impact load is determined as a product of impact factor, I, and the live load. The impact factors are specified by different authorities for different types of bridges.

Longitudinal Forces Longitudinal forces are set up between vehicles and bridge deck when the former accelerate or brake.This loading is taken to act at a level 1.20 m above the road surface. No increase in vertical force for dynamic effect should be made along with longitudinal forces. The possibility of more than one vehicle braking at the same time on a multi-lane bridge should also be considered.

Thermal forces The free expansion or contraction of a structure due to changes in temperature may be restrained by its form of construction. Where any portion of the structure is not free to expand or contract under the variation of temperature, allowance should be made for the stresses resulting from this condition. The coefficient of thermal expansion or contraction for steel is 11.7 x 10-6 /0 C.

Wind loadWind load on a bridge may act

Horizontally, transverse to the direction of span Horizontally, along the direction of span Vertically upwards, causing uplift Wind load on vehicles

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Wind load effect is not generally significant in short-span bridges; for medium spans, the design of sub-structure is affected by wind loading; the super structure design is affected by wind only in long spans. For the purpose of the design, wind loadings are adopted from the maps and tables given in IS: 875 (Part III). A wind load of 2.40 kN/m2 is adopted for the unloaded span of the railway, highway and footbridges. In case of structures with opening the effect of drag around edges of members has to be considered.

Seismic load If a bridge is situated in an earthquake prone region, the earthquake or seismic forces are given due consideration in structural design. Earthquakes cause vertical and horizontal forces in the structure that will be proportional to the weight of the structure. Both horizontal and vertical components have to be taken into account for design of bridge structures. IS: 1893 – 1984 may be referred to for the actual design loads.

Erection forces There are different techniques that are used for construction of railway bridges, such as launching, pushing, cantilever method, lift and place. In composite construction the composite action is mobilized only after concrete hardens and prior to that steel section has to carry dead and construction live loads. Depending upon the technique adopted the stresses in the members of the bridge structure would vary. Such erection stresses should be accounted for in design. This may be critical, especially in the case of erection technologies used in large span bridges.

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09 Summary

After brief introduction, the steel used in bridges and its properties were discussed. The broad classification of bridges was mentioned and various loads to be considered in designing railway and highway bridges in India were discussed.

To design a bridge like you need to take into account all the forces acting on it:

1. The friction of the earth on every part2. The strength of the ground pushing up the supports 3. The resistance of the ground to the pull of the cables4. The dead weight and all vehicle loads5. Then there is the drag and lift produced by wind and water6. The turbulence as fluids pass the towers

Need to use appropriate materials and structural shapes in the cheapest way, yet maintaining a certain degree of safety. To account for natural disasters, engineers design bridges with a factor of safety: usually around 3 or 4.

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10 References

1. Owens. G.W., Knowles. P.R., Dowling. P.J. (1994): Steel Designers' Manual, Fifth edition,

2. Chatterjee. S. (1991): The Design of Modern Steel Bridges, First edition, BSP

3. Demetrios. E.T. (1994): Design, Rehabilitation and Maintenance of Modern Highway

4. Victor. D.J. (1973): Essentials of Bridge Engineering

5. IRC: 6 - 1966 – Section II, Indian Standard for loads and stresses on Highway Bridges.

6. Bridge rules - 1982, Specifications for Indian Railway loading.