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25 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

103 εμφανίσεις

By :

Prof.Dr.
\
Nabil Mahmoud


Content

1
-
Introduction

2
-
Parts of steel Bridge

3
-
Loads on bridge

4
-
Allowable stresses

5
-
Fatigue

6
-
Plate girder

7
-
Length of flange plate girder

8
-
Connection of flange plate with web

9
-
Web stiffnner

10
-
Web splice

11
-
Splice of flange plate

12
-
Maximum defleciton in Bridge

13
-
Bearing

14
-
Road way bridge

1
-
Introdution


1.1
Introduction



1.2
Railway Bridge


1.3
Highway Bridge


1.1
Introduction



Most

bridges

are

built

for

the

transportation

of

highway

or

railway

traffic

across

natural

or

artificial

obstacles
.

A

deck

bridge

supports

the

roadway

or

railway

on

its

top

chords

(truss

bridge)

or

flanges

(plate

girder

bridge),

while

a

through

bridge

supports

the

floor

system

at

or

near

the

lower

chords

or

flanges,

so

that

traffic

passes

through

the

supporting

structure

(main

girder)
.


The

rolled
-
beam

bridge

supports

its

roadway

directly

on

the

top

flanges

of

a

series

of

rolled

beams

placed

parallel

to

the

direction

of

traffic

and

extending

from

abutment

to

abutment
.

It

is

simple

and

economical
.

It

may

also

be

used

for

multiple

spans

where

piers

or

intermediate

bents

can

be

built

economically
.

Beam

bridges

may

be

economical

for

spans

up

to

15

m
.

a

typical

beam

bridge

for

highway

traffic

is

illustrated

in

Fig
.

(
1
.
1
)
.



For

crossings

greater

than

those

which

can

be

spanned

economically

by

a

rolled
-
beam

bridge,

(deck

or

through)

plate
-
girder

bridges

may

be

used
.

In

this

simplest

form,

a

plate

girder

consists

of

three

plates

(two

flanges

and

web)

welded

together

in

the

form

of

an

I
.

Ties

and

rails

for

railway

bridges

may

rest

directly

on

the

top

flanges

of

the

deck

plate
-
girder

bridge
.

When

clearance

below

the

structure

is

limited,

a

through

plate

girder

bridge

is

used
.

The

floor

system

may

consist

of

a

single

line

of

stringers

under

each

rail,

supported

by

floor

beams

(cross

girders)

forming

into

the

main

girders

just

above

their

lower

flanges
.


If

an

open

floor

is

objectionable,

ballast

may

be

laid

on

concrete

or

steel
-
plate

decking

supported

by

closely

spaced

floor

beams

(cross

girders)

without

stringers
.

Knee

braces

(U

frames)

are

used

to

support

the

top

flanges

of

through

bridges,

as

illustrated

in

Fig
.

(
1
.
2
)

.

Highway

plate
-
girder

bridges

are

usually

of

the

deck

type
.

The

floor

slab

is

usually

supported

directly

on

the

main

girder,

as

in

the

beam

bridge

Fig
.

(
1
.
1
)
.


In

orthotropic

steel
-
deck

plate

construction

the

floor

consists

of

a

steel

deck

plate

stiffened

in

two

mutually

perpendicular

directions

by

a

system

of

longitudinal

and

transverse

ribs

welded

to

it

(Fig
.

(
1
.
3
))
.

The

deck

structure

functions

as

the

top

flange

of

the

main

girder

and

floor

beams
.

This

system

makes

efficient

and

economical

use

of

materials,

particularly

for

long
-
span

construction
.


When

the

crossing

is

too

long

to

be

spanned

economically

by

plate

girders,

a

through

or

deck

truss

bridge

may

be

used
.

Deck

bridges

are

more

economical

than

through

bridges

because

the

trusses

can

be

placed

closer

together,

so

that

the

span

of

the

floor

beam

is

shortened
.

For

multiple

spans

there

is

also

a

saving

in

the

height

of

the

piers
.


back

1.2
Railway Bridge



The

stringers,

cross

girders

and

the

main

girders

are

the

main

load

carrying

members
.

The

design

of

various

elements

is

done

in

the

sequence

in

which

the

load

is

transmitted
.

In

railway

bridge,

there

will

be

either

an

open

timber

floor

or

a

ballasted

floor
.


STRINGERS



CROSS
-
GIRDERS



MAIN

GIRDERS




STRINGERS


The

stringers

are

placed

parallel

to

the

main

girders,

and

the

stringers

span

between

adjacent

cross
-
girders

(floor

beams)
.

The

stringers

have

spans

from

3

m

to

5

m
.

the

stringers

are

assumed

to

be

simply

supported

or

continuous

according

to

their

connection

to

the

cross

girder
.

The

stringers

are

placed

about

10

to

15

cm

outside

the

main

stock

rails

(standard
-
gauge

=

1
.
435
m),

so

that

the

effect

of

impact

is

less
.



The stingers carry the weight of stock rails,
guard rails (=
250
kg/m of track) (p
149
),
fastenings, weight of sleepers (=
350
kg/m of track)
and the self
-
weight. The self weight of stringers
may be assumed. The stringers are subjected to
maximum vertical live load, lateral shock and
impact load, when the one complete span of
stringer, (i.e. the distance between adjacent cross
-
girder) is fully loaded.

The

dead

load,

live

load,

lateral

shock

and

impact

load

is

computed

per

track
.

Then,

the

total

load

is

found

per

stringer
.

The

simply

supported

stringers

are

designed

for

the

maximum

Mx

and

the

corresponding

My

and

checked

for

maximum

shear

force
.

In

case

the

rolled

steel

beam

sections

may

furnish

the

required

modulus

of

section

for

the

stringers,

then

the

rolled

steel

beams

are

provided,

otherwise

a

plate

girder

sections

are

adopted

for

the

stringers
.

The

stringers

are

connected

at

their

ends

to

the

cross
-
girders

with

suitable

connections
.



The

stringers

transmit

the

load

to

the

cross
-
girders
.

The

stringers

are

also

braced

similar

to

the

main

plate

girders

in

the

deck

type

bridges
.

In

the

case

of

rolled

steel

sections

the

depth

of

stringers

shall

preferably

be

not

less

than

1
/
12

of

their

span

(p
145
)
.

However,

the

maximum

deflection

of

stringers

should

be

less

than

1
/
800

of

their

span

(p
132
)
.

In

the

calculation

of

continuous

stringers,

unless

otherwise

obtained

by

a

structural

analysis,

the

following

bending

moments

may

be

assumed

(p
145
)
:

Positive

moment

in

end

span
.............................................
0
.
9

M


Positive

moment

in

intermediate

span
................................
0
.
8

M


Negative

moment

at

support
.............................................
0
.
75

M



Where
M


is the maximum bending moment for a
simply supported stringer. The same value of
bending moment shall be assumed for stringer fitted
between cross girders and provided with top and
bottom plates resisting the full negative moment at
the support. In all other cases, stringers shall be
calculated as simply supported beams


back

CROSS
-
GIRDERS


The

cross
-
girders

(floor
-
beams)

span

right

angles

to

the

main

girders

and

shall

be

rigidly

connected

thereto
.

The

span

of

cross
-
girder

is

equal

to

the

distance

between

center

to

center

of

the

main

girders
.


The cross
-
girders carry the weight of stock
rails, guard rails, fastening, and weight of
sleepers, weight of stingers and the self
weight. The self weight of cross
-
girder acts
as uniformly distributed load.


The cross
-
girders are subjected to maximum live
load and impact load when both the adjacent
stringers are loaded. These live load and impact
load, along with dead load (weight of stock rails,
guard rails, fastenings and sleepers) excluding self
-
weight act as two concentrated loads at the points
at which the stringers are connected to the cross
-
girder. The maximum bending moment and shear
force are found for corresponding loading. The
rolled steel beam sections or plate girder sections
are provided.


The

cross
-
girders

are

connected

as

near

the

bottom

or

top

flange

of

the

main

girders

as

possible
.

These

points

of

connections

are

known

as

panel

points
.

The

cross
-
girders

transmit

the

load

to

the

main

girders

at

the

panel

points
.

The

depth

of

cross

girders

shall

preferably

be

not

less

than

1
/
10

of

their

span

(p
145
)
.

However,

the

maximum

deflection

of

the

cross

girder

should

be

less

than

1
/
800

of

their

span

(p
132
)
.

Sidewalk

brackets

shall

be

connected

in

such

a

way

that

the

bending

stresses

will

be

transferred

directly

to

the

cross

girder

(p
145
)
.


Back

MAIN GIRDERS


The

main

girder

may

be

plate

girders

or

trusses

and

the

bridge

may

be

through

or

deck

bridge

type
.

These

girders

in

through

type

railway

bridges

are

spaced

with

sufficient

width

to

suit

the

clearance

requirement
.

The

spacing

of

main

girders

necessary

for

the

clearance

requirements

is

sufficient

to

develop

lateral

strength

and

rigidity

and

to

resist

the

overturning

with

the

specified

wind

pressure

and

load

conditions
.


Back


The

plate

girder

carry

the

weight

of

stock

rails,

guard

rails,

fastenings,

sleepers,

weight

of

stringers,

weight

of

cross
-
girders

and

self
-
weight
.

In

addition

to

this

dead

load,

the

plate

girders

also

carry

the

live

load

and

impact

load
.

When

the

spacing

of

cross
-
girders

is

up

to

4

m,

then,

the

load

transmitted

by

the

cross
-
girder

is

treated

as

uniformly

distributed

load
.



1.3
Highway Bridge


The

floor

is

a

part

of

bridge

which

carries

the

load

directly
.

The

floor

system

in

case

of

Highway

Bridges

generally

consists

of

reinforced

concrete

slab

or

steel

deck

plate

and

wearing

surface
.

In

case

of

deck

type

plate

girder

Highway

Bridges,

the

slab

is

supported

directly

by

the

plate

girders
.

In

case

of

through

type

Highway

Bridges,

the

reinforced

concrete

slab

is

supported

on

stringers,

and

cross
-
girders,

or

by

the

cross
-
girders

alone
.

Many

times,

the

reinforced

concrete

slab

provides

its

own

traffic

surface
.

In

addition

to

this,

the

bituminous,

asphalt

or

carpet

surface

is

also

furnished
.

This

acts

as

a

wearing

surface
.

The

design

of

reinforced

concrete

slab

has

not

been

discussed

in

the

text
.


STRINGERS



CROSS
-
GIRDERS



MAIN

GIRDERS


STRINGERS


The stringers support the reinforced concrete slab in case
of through type Highway Bridges. The stringers are
supported by the cross
-
girder. The stringers may be
supported on the top of cross
-
girders or may be framed
into the cross
-
girders by the use of suitable connections.
When the reinforced concrete slabs are used, then either
the stringers should be supported on the top of the cross
-
girders or in case the stringers are framed into the cross
-
girders,


then the top of stringers should be on the same
level as the cross
-
girders. The stringers carry the
dead load, which consists of the weight of wearing
coat, the weight of reinforced concrete slab and the
self
-
weight. In addition to this, the stringers also
support the live load and the impact load due to
highway standard vehicles or trains. The preferable
depth of the stringers, the maximum deflection and
the calculation of bending moment are as given for
railway bridge


Back

CROSS
-
GIRDERS



The

load

from

floor

system

is

carried

to

the

cross

girders

by

means

of

the

stringers

or

the

loads

may

be

carried

to

the

cross
-
girders

directly

by

the

reinforced

concrete

slab
.

The

cross
-
girders

carry

dead

load,

which

consists

of

the

weight

of

wearing

coat,

the

weight

of

reinforced

concrete

slab,

the

reaction

from

the

stringers

and

the

self
-
weight
.

In

addition

to

this,

the

cross
-
girders

carry

live

load

and

impact

load

due

to

highway

standard

vehicles

or

trains
.

The

preferable

depth

of

the

cross

girder,

the

maximum

deflection

and

the

arrangement

of

sidewalk

are

as

given

for

railway

bridge
.

back

MAIN GIRDERS



The main girder may be plate girders or
trusses and the bridge may be through or
deck bridge type. In the deck type Highway
Bridges, the spacing between the main
girders is kept sufficient to develop lateral
strength and rigidity, and to resist the
overturning with the specified



wind

pressure

and

the

load

conditions
.

In

the

through

type

Highway

Bridges

the

spacing

between

plate

girders

is

kept

sufficient

to

suit

the

clearance

requirement
.

The

spacing

of

plate

girders

required

for

the

clearance

requirement

is

sufficient

to

resist

the

overturning

with

the

specified

wind

pressure

and

load

conditions,

and

to

develop

lateral

strength

and

rigidity
.


In

the

deck

type

Highway

Bridges,

the

two

plate

girders

are

used

for

single

lane

carriageway

width

and

three

or

four

plate

girders

depending

upon

the

design,

as

used

for

two

lane

carriageway

Highway

Bridge
.

The

reinforced

concrete

slabs

inclusive

of

wearing

coat

is

supported

directly

by

the

plate

girders
.

The

plate

girders

carry

dead

load
.

The

dead

load

consists

of

the

wearing

coat,

the

weight

of

reinforced

concrete

slab

and

self
-
weight

of

plate

girders
.

In

addition

to

the

dead

load,

the

plate

girders

carry

the

live

and

impact

load

due

to

the

highway

standard

vehicles
.

In

case

of

through

type

highway

bridges,

the

plate

girders

carry

the

dead

load
.

The

dead

load

consists

of

the

weight

of

wearing

coat,

the

weight

of

reinforced

concrete

slab,

the

weight

of

stringers,

the

weight

of

the

cross
-
girders,

and

self
-
weight
.

In

addition

to

this,

the

plate

girders

carry

the

live

load

and

the

impact

load

due

to

the

highway

standard

vehicles
.





Figure (
1.4
)

shows the common types of simple
-
span bridge trusses. By varying the depth of a truss
throughout its length
(Fig.
1.4
c)

forces in the chord
members can be more nearly equalized and the
forces in the web reduced. Trusses of economical
proportions usually result if the angle between
diagonals and verticals ranges from
45
to
60

.
However, if long
-
span trusses are made deep
enough for adequate rigidity as well as for economy

,

a

suitable

slope

of

the

diagonals

may

produce

panels

too

long

for

an

economical

floor

system
.

Using

the

subdivided

panels

(Figure

1
.
4
(f

and

g))

solve

this

problem
.

Certain

objections

to

subdivided

panels

overcome

with

the

invention

of

the

K

truss

(Fig
.

1
.
4
h)
.

Cantilever

bridges(Fig
.

2
.
2
)

,

continuous

bridges

(Fig
.

2
.
3
),

arch

bridges

(Fig
.

2
.
4
),

suspension

bridges

(Fig
.

2
.
5
)

and

three

Chord

Bridge

(Fig
.

2
.
6
)

are

common

types

of

structures

suitable

for

long

spans
.


A

cantilever

bridge

consists

of

two

shore,

or

anchor,

spans

flanked

by

cantilever

arms

supporting

a

suspended

simple

span
.

Positive

bending

moments

are

decreased

because

of

the

shorter

simple

beam,

while

the

cantilever

and

anchor

arms

subjected

to

negative

bending

moments
.

Positive

bending

moments

in

continuous

bridges

are

reduced

because

of

the

negative

moments

at

the

piers
.

Arch

bridges

may

be

fixed,

single
-
hinged,

two
-
hinged,

or

three
-
hinged
.

The

principal

supporting

elements

of

the

suspension
-
bridge

superstructure

are

the

cables

which

pass

over

the

towers

to

be

anchored

in

foundations

at

each

end
.

Back

Figure
1
-
1


Figure
1
-
2

Figure
1
-
3

Back

Figure
1
-
4

Back