BÀI GIẢNG THIẾT KẾ CẦU THÉP ENG VER

Nguyễn Ngọc Tuyển – Trường đại học Xây dựng – Website: http://nguyenngoctuyen.tk/ 9/15/2016 – NUCE Structural types of steel bridges cont.. Nguyễn Ngọc Tuyển – Trường đại học Xây dựng –

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Class website: https://sites.google.com/site/tuyennguyenngoc/courses-in-english-nuce/be05-design-and-construction-of-steel-bridges-s1

BE05: Design and Construction

of Steel Bridges S1

DR TUYEN NGUYENNGOC DEPARTMENT OF BRIDGE AND TUNNEL ENGINEERING

Hanoi, 08‐2016

CHAPTER 1

OUTLINE FOR CHAPTER 1:

1 INTRODUCTION

2 MATERIALS USED IN STEEL BRIDGES

3 STRUCTURAL TYPES OF STEEL BRIDGES

4 BRIEF HISTORY AND GROWTH TREND OF STEEL BRIDGES

GENERAL CONCEPT ABOUT STEEL BRIDGES

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• Emphasis in this course is on short (15 m) to medium (60m) simple span

girder bridges These girder bridges are readily adapted to different terrain

and alignment and can be erected in a relatively short time with minimum

• Steel is an alloy of iron and other elements, primarily carbon, that is widely

used in construction and other applications because of its high tensile

strength and low cost.

• Steel contains less than 2% carbon and 1% manganese and small amounts

of silicon, phosphorus, Sulphur and oxygen.

• When compared with iron,

Steel has greater strength characteristics

Steel is more elastic and can withstand the effects of impact and vibration better

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TS. Nguyễn Ngọc Tuyển – Trường đại học Xây dựng – Website: http://nguyenngoctuyen.tk/

9/15/2016 – NUCE

Materials used for steel bridges (cont.)

 STRUCTURAL STEELS FOR BRIDGES

• Structural steels for use in bridges generally have more stringent

performance requirements compared to steels used in buildings and many

other structural applications

• Bridge steels have to perform in an outdoor environment with relatively large

temperature changes, are subjected to millions of cycles of live loading, and

are often exposed to corrosive environments containing chlorides

• Steels are required to meet strength and ductility requirements for all

structural applications However, bridge steels have to provide adequate

service with respect to the additional Fatigue and Fracture limit state

• They also have to provide enhanced atmospheric corrosion resistance in

many applications where they are used without expensive protective

coatings

• For these reasons, structural steels for bridges are required to have fracture

toughness and often corrosion resistance that exceed general structural

requirements.

 TYPICAL STEEL TYPES

(Fy=250MPa) Carbon steels have well

defined points and generous yield plateau,

high ductility Carbon steels are weldable

and available as plates, bars, and structural

shapes Mostly used as connection plates

(Fy=345MPa); hot rolled steel with a

well-defined yield point and excellent ductility

They are weldable and available as plates,

bars, and structural shapes Mostly used for

main member in small and medium span

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removes the well-defined yield point (determined by 0.2% offset), increases

the strength, hardness, and toughness Heat treated low alloy steels are

weldable and available only in plates

With higher chemical composition to develop higher strength, greater

toughness and good corrosion resistance.

comparison to High strength low alloy steel The goal of HPS is to provide a

steel that is forgiving enough to be welded under a variety of conditions

without requiring excessive weldprocess.

deformations without fracture and can be expressed as a ratio of elongation

at fracture to the elongation at first yield.

indenter

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under the action of repeated stresses Fatigue failure suddenly occurs at a

stress level below the yield stress

is most commonly caused by the wet-dry cycles of exposed steel

component without any applied external forces.

The processes of rolling steel products naturally introduce

internal residual stresses due to plastic deformation and

differential cooling effects during their production

The resulting residual stress distribution has both tensile(+)

and compressive(-) stresses that are always in static

equilibrium

Welding, flame cutting, and hole drilling will alter the

residual stress pattern for fabricated members

Determining the exact distribution and magnitude of

residual stress in fabricated members is a very complicated

subject that depends on the shape geometry, processing,

and the sequence of fabrication operations

It is possible to measure residual stresses through

destructive sectioning and hole drilling techniques and

through non-destructive X-ray diffraction and neutron

diffraction techniques However, these techniques are

impractical except in a research environment (a) Hot-rolled shape, (b) welded box section, (c) plate

with rolled edges, (d) plate with flame-cut edges, and (e) beam fabricated from flame-cut plates

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1.3 Structural types of steel bridges

 GIRDER STEEL BRIDGES

• Girder bridge is the most common type of steel bridges In girder system,

load from the superstructure are transmitted vertically to the substructure.

• Simple design, simple fabrication and build.

• Steel girder bridges can be simple span bridges or continuous span bridges

The girder cross-section could be either I-Section or Box girder

• Span length could be up to 200 - 300m

Pontecosta E Silva Bridge in Brazil built in 1974 with span length of 300m,

Neckartalbruecke-1 bridge in German, 1978 with span of 263m

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Structural types of steel bridges (cont.)

• Truss members including chords, verticals and

diagonals primary carry axial tension and

compression loads

• Truss members are only subjected to tension

and/or compression forces and not bending

forces.

• In most cases the design, fabrication, and erection

of trusses are relatively simple.

• Common types: simple span truss or continuous

Forth Bridge (1890) in Scotland L = 521m, Quebec (1917) in

Canada L = 549m, Minato Bridge - Ohashi in Japan L = 510m

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 STEEL ARCH BRIDGES

• Arch bridge is a vertically curved and axially compressed structural member

spanning an opening and providing a support for the moving loads above the

opening.

• Reactions at supports always have two components: (1) Vertical force and

(2) Horizontal force even if the arch bridge is only subjected to vertical loads

Slide # 17

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• To be used with large span

• Because of horizontal forces

occur in the bearings, it should be

used where the ground or

foundation is solid and stable.

• The roadway can pass over the

arch or though the arch or both

• Common types: hinge-less arch,

two-hinge arch and three-hinge

arch.

• The tied-arch can be used if the

ground is too soft to deal with the

horizontal forces

• Span length: over 500m

(Sydney Bridge in Australia L = 503m,

Bayonne (1931) in US L = 508m,

Fayetterille (1977) in US L = 518m)

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 STEEL RIGID FRAME BRIDGES

• A rigid frame bridge is one in which the piers and girder are one solid

structure.

• Design calculations for rigid frame bridges are more difficult than those of

simple girder bridges The junction of the pier and the girder can be difficult

to fabricate and requires accuracy and attention to detail.

 SUSPENSION BRIDGES

• A suspension bridge has a deck-girder system, which is supported by vertical

suspender cables that are in turn supported by main suspension cables The

suspension cables are supported by saddles atop towers and are anchored

at their ends

• Suspension bridges usually use large anchors or counter weights for

anchoring suspension cables.

• Suspension bridges are normally constructed when intermediate piers are

not feasible because of long span requirements

• Golden Gate Bridge (1937) in US, L = 1280m; Great Belt Bridge (1997) in

Denmark, L = 1624m; AkashiKaikyo Bridge (1998) in Japan, L = 1991m

Thuận Phước Bridge in Đà Nẵng (2008) L = 405m.

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Golden Gate Bridge (1937) in US, L = 1280m Akashi Kaikyo Bridge (1998) in Japan, L = 1991m

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 CABLE STAYED BRIDGES

• A cable-stayed bridge is another long span cable supported bridge where the

superstructure is supported by cables passing over or anchored to towers

located at the main piers

• Cable-stayed bridges are the more modern version of cable-supported

bridges.

• Span lengths of cable stayed bridges are up to 1000m.

Tatara Bridge (1999) in Japan L = 890m; Normandie Bridge (1995) in France L = 856m ; Stonecutter

Bridge in Hong Kong L = 1018m; Suton Bridge in China L = 1088m

Bãi Cháy Bridge L = 435m, is recorded as the longest span in the world for cable stayed bridges

having only one-plane of cables

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Stonecutter Bridge in Hong Kong L = 1018m Tatara Bridge (1999) in Japan L = 890m

1.4 Brief history and growth trend of steel bridges

 BRIEF HISTORY OF STEEL BRIDGES

• (1) The first bridges with a structure of load-bearing iron elements were

suspension bridges

The idea of a suspended bridge is extremely old; the first known footbridge, using suspension chains,

was constructed in China around 65 A.D

Until the end of the 18th century, very few bridges were constructed from metal

The weight of the chains limited spans to around 20 m, and only the invention of chains made of

articulated iron bars, known as eye bars and patented in England in 1817, allowed spans to

substantially increase

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Brief history and growth trend of steel bridges (cont.)

The first important suspension bridge by the Englishman, Telford, was constructed over the Menai

Straits in 1826

•Menai Straits bridge

is noteworthy for achieving a record span of 176 m.

•This bridge is still in service, the original iron chains having been replaced by articulated steel bars in 1938.

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• (2) Towards the end of the 18th century, in 1779 to be precise, the first cast

iron bridge appeared over the Severn at Coalbrookdale in England

Conceived and constructed by a blacksmith named Abraham Darby, the bridge comprises five arches

of 30 m span

Other cast iron arch bridges were constructed at the end of the 18th century and the beginning of the

19th century, such as the bridge at Sunderland (Great Britain) with a span of 72 m (1796)

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• (3) Parallel with the development of cast iron bridges, suspension bridges

progressed with the adoption of cables to replace chains

This solution is credited to a Frenchman, Seguin

The first use of cables dates back to 1816, by an Englishman, Rees, while the Swiss, Dufour,

undertook systematic testing of cables between 1823 and 1824 In 1823 he completed the first

suspension bridge in continental Europe, the St-Antoine-Geneva footbridge for pedestrians,

comprising two 40 m spans

A record for the longest single span, indeed a record that stood for many years, was established in

Europe by the suspension bridge at Fribourg (CH) with a span of 265 m This was constructed by a

Frenchman, Joseph Chaley, in 1834 and demolished in 1930

Only one suspension bridge of this era is still in existence in continental Europe: the Pont de la Caille

over the ravine des Usses in Savoy, credited to Belin in 1839, spanning 192 m

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Engineer Joseph Chaley

Slide # 29

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• (4) Cast iron, a relatively brittle material, did not lend itself to the

construction of beam bridges It was only towards the middle of the 19th

century that the first examples of such bridges appeared, with the

development of wrought iron (which is notably better in tension) for use on an

industrial scale

One of the first great beam bridges was the Britannia in Wales, which entered service in 1850 With

two main spans of 146 m, this beam bridge had a closed cross section in the form of a rectangular

box inside which passed a railway line It was replaced in 1971 by a bridge with a structure of steel

truss arches

Wrought iron had thereby replaced cast iron for large span arches The most spectacular example of

this form of construction was the Viaduc de Garabit, constructed by the team of Gustav Eiffel in 1884

The total length of 564 m includes a triangulated arch of 165 m span and rise of 52 m It was erected

using the cantilever method, spanning out from the supports

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• (5) Development of the industrial fabrication of steel followed the invention of

the Bessemer converter in 1856 and the Siemens-Martin process in 1864

Due to its mechanical properties, and in particular its improved tensile

behaviour, steel went on to entirely replace both cast iron and wrought iron

The era of steel bridges in Europe began with the Firth of Forth (Fig 3.7), which adopts truss beams,

of variable depth and extremely rigid Constructed between 1881 and 1890, this bridge comprises

two central spans of 521 m and two side spans of 207 m each The central spans comprise two

cantilevers, each of 207 m, supporting between them a beam of 107 m span This system, know

simply as "cantilever", was subsequently adopted for a large number of similar bridges

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• (6) The first developments of long span bridges in the United States are

credited to John A Roebling

One of the most notable is the first suspension bridge crossing the deep gorge downstream of the

Niagara Falls

• Completed in 1855 this bridge had a span of 250 m and was constructed in two stages - firstly for a

railway and secondly for horse drawn carriages

• It was demolished in 1896 During this period (1877) electric arc welding was discovered Alongside

the ever increasing ability to produce thicker steel plates, this new joining method allowed, later on

in the second half of the twentieth century, the fabrication of the solid web beams (plate girders)

widely used today

John A Roebling was also the father of the Brooklyn suspension bridge across the East river in New

York, which entered service in 1883 Its span of 487 m set a world record at the time, and was

achieved thanks to the first use of steel cables This bridge was also original in the form of the

cables, which combined suspension cables and cable stays in a form known as "hybrid"

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• (7) For a long time the United States was known as the country of long span

suspension bridges.

This is particularly due to the works of the Swiss engineer, Othmar H Ammann

• He was the first to achieve a span exceeding 1000 m, with the George Washington Bridge, which

crosses the Hudson River in New York

• This bridge was inaugurated in 1932 with a span of 1067 m and had a second deck added in 1962

The magnificent Golden Gate Bridge was inaugurated five years later with a span of 1280m

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• (8) Specific studies of the aerodynamic performance of suspension bridges

were undertaken following the collapse of the Tacoma Bridge, which was

destroyed in 1940 due to the resonance of its deck in adverse wind

conditions

These studies led to the adoption of decks comprising large truss box girders

In addition to their aerodynamic advantages, the use of such boxes facilitated the construction of twin

deck bridges using beams between 10 m to 12 m deep, and carrying traffic on the upper and lower

flanges of the box girders

The Verrazano-Narrows Bridge at the entrance to New York, also the work of Ammann, was

conceived in this way and inaugurated in 1964 This suspension bridge held the world record until

1981 at a span of 1298 m

That record for longest span was finally beaten in 1981 by the Humber Suspension Bridge in Great

Britain This bridge has a span of 1410 m, and its deck adopted a new form, comprising a box girder

with an aerodynamic shape to significantly reduce the effects of wind

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Humber Bridge (UK). Engineers

Gilbert Roberts and Bill Harvey

However, this modern form of deck has not been used in Japan where large suspension bridges are

still constructed using box girder trusses (mainly due to the need to separate railway and road traffic

on double decks)

Most of the long span suspension bridges in Japan link the islands of Honshu and Shikoku One of

them, the Akashi Kaikyo Bridge, has held the world record for longest span since its inauguration in

1998, with a central span of 1991m

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• (9) In the world of arch bridges, it is worth considering some notable

examples, such as:

New River Gorge Bridge in the United States, constructed in 1977 with a span of 518 m;

The bridge at Bayonne in the United States (1931 and 504 m); and

Sydney Harbour Bridge in Australia (1932 and 503 m)

Since 2003 the Lupu Bridge in China spanning 550 m has held the record for a steel arch bridge

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• (10) The spectacular growth in the use of cable stayed bridges since the

middle of the 20th century

Developments in materials (high strength steels), methods of calculation by computer, and the

capacity of lifting equipment used for erection have all contributed to this trend

In 1957 the longest span for a cable stayed bridge was 260 m for the Theodor Heuss Bridge in

Düsseldorf, Germany

By the end of the 1980s, the longest spans were between 400 and 500 m, which included numerous

bridges in Thailand (Rama IX, 450m, 1987), Japan (Yokohama Bay, 460 m, 1989) and Canada

(Annacis Island, 465 m, 1986)

During the final years of the millennium, the record for longest span was toppled with increasing

frequency: reaching 856 m in 1995 with the Pont de Normandie in France, then 890m in 1999 with

the Tatara Bridge in Japan

Now cable stayed bridges are competing in the span range that was previously the exclusive domain

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• (11) Another evolution is the use of multiple span cable stayed bridges

The most notable example of this type of structure is the Viaduc de Millau in France, which was

opened in 2004 Conceived by Michel Virlogeux, it comprises eight cable stayed spans, of which six

spans reach 342m

In Switzerland a number of noteworthy steel and composite bridges were constructed as part of the

development of the freeway network Examples include the composite bridge over the Veveyse near

Vevey (1968), which comprises a 5m deep steel box girder with spans of 58m, 129m and 111m

Additionally, there are the bridges over the Rhone at St Maurice (1986), which are cable stayed

composite bridges spanning 100 m

More recently, two important and innovative bridges have been constructed on the Yverdon-Berne

section of freeway Al The Viaduc des Vaux (1999) is a box girder composite bridge with spans of

130 m It was launched despite its complex S shape geometry plan

The Viaduc de Lully (1995) is a composite bridge that adopts space frame steel trusses A

particularity of this bridge is that the trusses are formed from thick walled tubes welded to each other

without the use of gusset plates

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• New world records for span are no longer possible for box girder bridges,

truss bridges and arch bridges because cable stayed and suspension

bridges are significantly more economic for spans over 400m or so.

Suspension bridges have always dominated the world of long spans (more than 500m) It is

interesting to note that recent years have seen a spectacular jump in spanning ability, passing from

1410m in 1981 to nearly 2000m today

All the indications are that this trend will continue For example, plans to cross the Messina straits to

link Sicily to mainland Italy include the provision of a 3300 m span hybrid cable stayed suspension

bridge

Since around 1980, cable stayed bridges are the type that has seen the most spectacular

development A cable stayed bridge in China that was opened to traffic in 2008 has a span of 1088m

and forms part of the Sutong Bridge, that has a total length of 8206m

Evolution of record spans from 1800 to the present day for different types of bridge

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Class website: https://sites.google.com/site/tuyennguyenngoc/courses-in-english-nuce/be05-design-and-construction-of-steel-bridges-s1

BE05: Design and Construction

of Steel Bridges S1

DR TUYEN NGUYENNGOC DEPARTMENT OF BRIDGE AND TUNNEL ENGINEERING

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2.1 General concepts

 ADVANTAGES OF GIRDER STEEL BRIDGES

• Compared to truss and other type of bridges, girder steel bridges have:

Simpler composition,

Simpler design and construction

Economical for short and medium spans (and upto 50-80m)

• Superstructure could use welded connections

On site

In factory

• Easy to provide composite action between deck slab and steel girders to

form a stable girder system

General concepts (cont.)

 SPAN LAYOUT AND BASIC DIMENTIONS

• Span layout:

Simple span

Continuous span

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• For simple spans

Apply for span lengths from 30-40m (maximum is 60m)

I – girder, depth of girder is unchanged

Ratio of span length over girder depth

Non‐composite Section Composite Section

• For continuous spans

Apply for span lengths greater than 50-60m

Negative moments at supports help to reduce the

positive moments at spans and thus help to reduce the

girder depth

Only need one row of bearings on top of pier caps

This helps to reduce the pier size since the eccentricity

of the vertical load is zero

Increase the stiffness of girders, deflection and rotation

profiles are smooth

The expansion joints required will be less

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However, undesired force effects may appear if there is

uneven settlement of girder supports since the

superstructure is statically indeterminate

The placing of concrete and removal of formwork are to

be executed carefully in proper sequence

The external span lengths are about 0.75-0.8 time the

length of intermediate spans:

Girder depth at intermediate supports is greater than

girder depth at mid-spans 1.3-1.5 times

For medium spans, the depth over span length ratio is:

For large spans using box cross-section, the ratio is:

2.2 Components of girder system

 SOME TYPES OF BRIDGE CROSS-SECTIONS

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Haunching is the increasing of the web depth for a specified portion of the girder

To haunch a rolled beam, the bottom flange is separated from the web and an

insert plate of the required depth is welded in place

A fabricated variable depth girder is the method used today The web plate is fabricated to the

required depth The top and bottom flange plates are then welded to the web plate

Components of girder system (cont.)

 SOME TYPES OF DECK SLAB

• Deck slabs in steel bridges

could be concrete decks (like in

concrete bridges), steel decks,

metal decks, or timber decks.

• Steel deck slabs could be used

when the weight is a critical

factor.

Precast concrete deck slab – Nhật Tân Bridge

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An orthotropic deck consists of a flat, thin steel plate stiffened by a series of closely spaced

longitudinal ribs at right angles to the floor beams

The deck acts integrally with the steel superstructure An orthotropic deck becomes the top

flange of the entire floor system

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Non‐composite I‐girder

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• Thickness of webs tw≥ 12mm and

For carbon steel:

h wshould be in (cm)

For high strength low carbon steel:

Thickness of webs also need to satisfy the following requirement:

• For web having no longitudinal stiffeners:

• For web having longitudinal stiffeners:

where: E = Elastic modulus of steel; fc= Compressive stress at extreme edges

w

f

E t

h

77 6



c w

w

f

E t

h

63.11

• In the case the flexural resistance of the girder

need to vary to satisfy the moment envelop

profile:

The width and thickness of tension flanges can be varied as

shown in the figure or

Cover plates may be applied

• Minimum length of cover plates are twice times greater

than the girder height plus 90cm and they should extend

over the designed section at least 1.5 times the width of

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• Vertical stiffeners

Vertical stiffeners (so called transverse stiffeners) increase the resistance to shear

Vertical stiffeners can be placed at the locations of concentrated forces, location of diaphragms or

cross frames, and along the length of the girder

Vertical stiffeners can be placed on one or both sides of the webs

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Longitudinal stiffeners increase the resistance to flexural buckling of the web.

Longitudinal stiffeners can be placed at the compression region of the web, at a distance of 0.2hw

below the compression flanges

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• To ensure a full composite action, shear connectors must be provided at the

interface between the concrete slab and the steel girders to resist the

interface shear.

• To resist the horizontal shear at the interface, connectors are welded to the

top flange of the steel girders that are embedded in the deck slab when the

concrete is placed

• These shear connectors come in various types: headed studs, channels ,

spirals, inclined stirrups, and bent bars Headed studs is commonly used

today.

Rigid Shear Connectors

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Diaphragms are secondary members that do not resist primary loads

Diaphragms are provided to stabilize the girders during construction and to help distribute live load

more evenly to beams or girders

In the case of a curved bridge, the diaphragms are designed to withstand the torsional loading

attributed to curved structures and therefore, they are considered as primary members

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Diaphragms may or may not be present on a multi-beam girder Diaphragms can be rolled shapes

(i.e I beam and channels) or they can be cross frames fabricated from angles, tee shapes, and

plates

Diaphragms are usually attached to transverse web stiffeners which are normally referred to as

connection plates

Current design specifications discourage the use of lateral bracing This is due to connections for

lateral bracing being fatigue-prone

Lateral bracing

2.3 Connections

 BOLT CONNECTIONS

• There are two types of bolt connections:

Riveted connection & Standard bolt connection

High strength bolt connection

• Failure modes

Shear failure of bolts

Shear failure of base metal

Bearing failure of bolt

Bearing failure of base metal

Tension failure of high strength bolt

Bending failure of bolt

Tension failure of base metal

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Connections (cont.)

• Design of Riveted connections & Bolt connections

(1) Nominal shear strength resistance of a bolt or rivet:

• If threads are excluded from the shear plane:

• If threads are included in the shear plane:

• where:

◦ Ab= area of the bolt corresponding to the nominal diameter (mm2)

◦ Fub= specified minimum tensile strength of the bolt specified in Article 6.4.3 (MPa)

◦ Ns= number of shear planes per bolt or rivet

• Note: The nominal shear resistance of a bolt in connections greater than 1270 mm in length shall

be taken as 0.80 times the values given above

• The nominal slip resistance of a

bolt in a slip-critical connection:

• Where:

◦ Ns= number of slip planes per

bolt

◦ Pt= minimum required bolt

tension specified in Table 1 (N)

◦ Kh= hole size factor specified

N = T b

N =T b

P F=N

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◦ with bolts spaced at a clear distance between holes not less

than 2.0d and with a clear end distance not less than 2.0d:

Rn= 2.4d (t) Fu

◦ if either the clear distance between holes is less than 2.0d, or

the clear end distance is less than 2.0d:

Rn= 1.2Lc(t) Fu

• For long-slotted holes perpendicular to the applied bearing force:

◦ with bolts spaced at a clear distance between holes not less

than 2.0d and with a clear end distance not less than 2.0d:

Rn= 2.0d (t) Fu (Article 6.13.2.9-3)

◦ if either the clear distance between holes is less than 2.0d, or

the clear end distance is less than 2.0d:

F u = tensile strength of the connected material , Table 6.4.1-1 (MPa);

L c = clear distance between holes or between the hole and the end of the member

in the direction of the applied bearing force (mm).

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• High-strength bolts subjected to axial tension shall be tensioned

to the force specified in Table 6.13.2.8-1 The nominal tensile

resistance of a bolt:

Tn= 0.76AbFub (6.13.2.10.2-1)

where:

A b = area of bolt corresponding to the nominal diameter (mm 2 )

F ub = specified minimum tensile strength of the bolt specified in Article 6.4.3 (MPa)

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Connections (cont.)

(5) Combined Tension and Shear Resistance

• The nominal tensile resistance of a bolt subjected to combined

P u = shear force on the bolt due to the factored loads (N)

R n = nominal shear resistance of a bolt specified in Article 6.13.2.7 (N)

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