Superstructure Concrete Bridges

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

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Bridge Engineering (6)


Superstructure


Concrete Bridges

1.
*Determination of concrete bridge superstructure:

1.1 the geometry of the bridge;

1.2 the span length; and

1.3 the method of construction

2.
*Bridge types and suitability

2.1 Non pre
-
stressed concrete slab bridges

2
.
1
.
1

The

simplest

type

in

which

the

deck

slab

also

serves

as

the

principal

load

carrying

element
.


2
.
1
.
2

The

solid,

cored,

or

ribbed

concrete

slab

is

supported

directly

on

the

substructure
.

2
.
1
.
3

For

spans

below

about

12
m,

a

cast
-
in
-
place

simple

spans

or

continuous

span

solid

slab

may

be

used
;

and

for

spans

over

12
m,

voided

slabs

become

more

economical
.

2
.
1
.
4

Pre
-
cast

slab

decks

usu
.

consist

of

a

number

of

pre
-
cast

voided

slab

sections

placed

side

by

side
.



1

Monday,

November

25
,

2013

Bridge Engineering (6)


Superstructure


Concrete Bridges

2.
Bridge types and suitability

2.1 Non pre
-
stressed concrete slab bridges

2
.
1
.
5

The

individual

slab

units

are

made

to

act

integrally,

either

by

the

use

of

longitudinal

shear

key

or

by

casting

a

concrete

slab

on

top
.


2
.
1
.
6

For

simple

spans

of

less

than

15
m,

pre
-
cast

slabs

are

usu
.

used
;

for

longer

spans,

box

sections

are

preferable
.


2
.
2

Non

pre
-
stressed

concrete

girder

bridges


2
.
2
.
1

This

type

consists

of

a

deck

slab

supported

by

non

pre
-
stressed

concrete

longitudinal

girders
.


2
.
2
.
2

The

two

most

common

forms

are

cast
-
in
-
place

T
-
beams

and

box

girders
.


2
.
2
.
3

The

spans

may

be

simply

supported

or

continuous
.



__

simple

spans

are

generally

prismatic

(of

constant

cross
-
section)
;



__

continuous

spans

may

be

haunched
;




2

Monday,

November

25
,

2013

Bridge Engineering (6)


Superstructure


Concrete Bridges


__ diaphragms are normally provided at piers and
abutments;


__

intermediate

diaphragms

may

be

used

to

improve

load

distribution

particularly

at

mid
-
span
.


2
.
2
.
4

The

analysis

should

take

into

consideration

the

interaction

of

the

axial,

flexural

and

torsional

stiffness

of

the

longitudinal

girders

and

transverse

components

(deck

slab,

floor

beams

and/or

diaphragms)

2
.
3

Pre
-
stressed

concrete

slab

bridges

2
.
3
.
1

For

expressway

interchanges
:


____

because

the

inherent

torsional

stiffness

of

slabs

bridges

suitable

for

curved

continuous

structures,

and

structures

with

single

column

intermediate

supports
;



3

Monday,

November

25
,

2013

Bridge Engineering (6)


Superstructure


Concrete Bridges




__

solid

slabs

for

the

short

spans
;

round

voided

slabs

for

the

intermediate

range
;

and

rectangular

voided

slabs

for

the

longer

range
.

2
.
3
.
2

For

simple

spans,

but

more

commonly

for

continuous

spans

2
.
3
.
3

Other

issues

in

design

and

construction


__

For

post
-
tensioned

voided

slabs,

the

section

should

be

solid

over

the

piers

and

the

abutment

bearings
.



__

At

fixed

piers

the

slabs

are

generally

cast

integral

with

the

piers
.



__

At

expansion

piers

sliding

pot

bearings

are

used
.





4

Monday,

November

25
,

2013

Bridge Engineering (6)


Superstructure


Concrete Bridges


__ Continuous multi
-
span decks used to reduce the
number of deck expansion joints, and thereby
minimize maintenance problems.


__

Structures

on

horizontal

curves

or

single

column

supports

require

particular

attention

to

torsional

stresses
.


2
.
3
.
4

Pre
-
cast

pre
-
tensioned

concrete

slabs,

like

pre
-
cast

non

pre
-
stressed

concrete

slabs

are

usually

limited

to

straight

square

spans

and

are

not

adaptable

to

varied

deck

geometries
;


2
.
3
.
5

Simple

spans

may

be

made

partially

continuous

for

live

load

in

the

same

way

as

pre
-
cast

beams

or

box

girders
.




5

Monday,

November

25
,

2013

Bridge Engineering (6)


Superstructure


Concrete Bridges


2
.
4

*Prestressed

concrete

girder

bridges

2
.
4
.
1

In

the

short

span

range,

pre
-
cast

AASHTO

beams

with

a

composite

cast
-
in
-
place

non
-
pre
-
stressed

concrete

slab

or

closed

box

girders

with

pre
-
cast

top

slabs

are

frequently

used

for

simple

spans
;


2
.
4
.
2

In

the

medium

span

range,

I
-
girders

and

closed

box

girders

with

pre
-
cast

top

slabs

are

used

for

partially

continuous

spans
;

2
.
4
.
3

In

the

medium

to

long

span

range,

continuous

pre
-
cast

segmental

trapezoidal

open

box

girders

with

the

deck

cast
-
in
-
place

are

common
;

2
.
4
.
4

The

longest

spans

are

generally

cast
-
in
-
place

segmental

box

girders
.




6

Monday,

November

25
,

2013

Bridge Engineering (6)


Superstructure


Concrete Bridges

3. Design and Construction Techniques


__ For cast
-
in
-
place construction, the girders (T
-
beams and box girders) and slab are formed
together and cast before the removal of formwork
and supports.


__

the

usage

of

continuous

spans,

and

thinner

transverse

post
-
tensioned

slabs

and

a

reduced

number

of

longitudinal

girders

at

a

larger

spacing
;


__

the

importance

of

temperature

effects

for

box

girders

due

to

the

possibility

of

large

differential

temperatures

between

the

top

and

bottom

slabs
;



__

the

necessity

of

knowing

exact

construction

loads

for

cast
-
in
-
place

segmental

construction

built

by

the

balanced

cantilever

method,

in

order

to

calculate

stresses

and

deformations

at

each

stage
.




7

Monday,

November

25
,

2013

Bridge Engineering (6)


Superstructure


Concrete Bridges


__ the essentiality of knowing the creep
characteristics of the concrete for calculating
deformations after the addition of each segment,
and for calculating the redistribution of moments
after completion and final stressing;


__

the

usage

of

intermediate

diaphragms
;


__

the

same

design

and

analysis

items

as

given

for

reinforced

concrete

girder

bridges
;


__

construction

procedures

for

composite

beams

and

slabs
:

erecting

beams
;

placing

forms

for

the

slabs

between

beams
;

casting

a

reinforced

concrete

slab


__

The

slab

and

beams

act

compositely

for

superimposed

dead

load

and

live

load
.





8

Monday,

November

25
,

2013

Bridge Engineering (6)


Superstructure


Concrete Bridges



__

the

advantage

of

reducing

the

number

of

deck

joints

by

using

partially

continuous

pre
-
cast

pre
-
stressed

beams

for

multi
-
span

bridges
;



__

the

development

of

support

moments

due

to

superimposed

dead

load,

live

load,

differential

temperature,

shrinkage

and

creep
.



__

the

achievement

of

continuity

for

superimposed

dead

load

and

for

live

load

by

casting

diaphragms

at

the

time

the

deck

concrete

is

placed
.



__

the

placement

of

longitudinal

reinforced

steel

in

the

deck

slab

across

the

intermediate

pier

in

order

to

resist

the

tension

from

negative

moments

at

the

supports
.




9

Monday,

November

25
,

2013

Bridge Engineering (6)


Superstructure


Concrete Bridges


__

the

connecting

of

the

bottom

flanges

of

adjacent

beams

at

the

diaphragms

to

resist

the

tensile

stress

due

to

positive

moments

generated

by

differential

temperature,

shrinkage

and

creep
;


__

the

application

of

segmental

pre
-
cast

pre
-
tensioned

girders

to

achieve

continuous

spans,

beyond

the

range

of

pre
-
cast

girders
;


__

the

employment

of

single

or

multiple

cell

boxes

with

transverse

segments

post
-
tensioned

together

longitudinally
;



__

the

use

of

pre
-
cast

segmental

construction

for

medium

spans


__

the

use

of

the

balanced

cantilever

method

for

longer

spans

where

each

segment

is

successively

stressed

after

erection
;



10

Monday,

November

25
,

2013

Bridge Engineering (6)


Superstructure


Concrete Bridges


__

being

aware

of

the

time

difference

between

segment

pre
-
casting

and

erecting

against

the

deformation

of

the

structure
;


__

the

application

of

elastic

analysis

and

beam

theory

in

the

design

of

segmental

box

girder

structures
.






11

Monday,

November

25
,

2013