2. WHAT IS A BRIDGE ?
Bridge is a structure which covers any gap or any obstacle to
give a passage through it.
Generally bridges carry a road or railway across a natural
or artificial obstacle such as, a river, canal or another
railway or another road.
Approach slab
Deck slab
PARAPET
ABUTMENT
PIER
BEARING
PILE CAP
LONG GIRDER
CROSS GIRDER
3. WHAT IS FOUNDATION ?
A foundation is the part constructed under the pier/abutment and
over the underlying soil or rock.
The loads transmitted by the foundation to the underling soil
must not cause soil shear failure or damaging settlement of the
superstructure.
The foundations of a bridge are particularly critical because
they must support the entire weight of the bridge and the traffic
loads that it will carry.
4. PURPOSE OF FOUNDATION
Purpose of foundation is to distribute the load of bridge
over a large bearing area and provide stability of bridge
against settlement and tilting.
It is provided sufficiently deep so that it is not affected
by the scouring.
FORCES ACTING ON A BRIDGE
5. HOW THE LOAD TRANSFER FROM
BRIDGE TO THE FOUNDATION?
Beam
Pier
FIG3. WORKING OF FORCES
6. IN ORDER TO DESIGN THE FOUNDATION MUST
DETERMINE THE FOLLOWING REASONABLY AND
ACCURATELY :
The maximum grip length
required,
The maximum likely scour
depth,
The soil pressures at the
base, and
The stresses in the structure
constituting the foundation.
The foundation should be taken to a depth which is safe from
scour, and is adequate from considerations of bearing
capacity, settlement stability of suitability of strata at the
founding level.
FIG4. FORCES ON BRIDGE
Beam
Pier
7. TYPES OF FOUNDATIONS
The type of foundation is designed when subsoil data of
bridge site is obtained. The different types of foundations
for bridges are given following;
Shallow Foundation (D<B)
Spread Foundation and Raft foundation
Deep Foundation (D>B)
Pile and Well foundation B
D
FIG5. DEPTH AND WIDTH OF
FOUNDATION
8. SHALLOW FOUNDATION
A shallow foundation is sometimes defined as one whose
depth is smaller than its width. Shallow foundations can be
laid using open excavation by allowing natural slopes on all
sides. This is normally convenient above the water table and is
practicable upto a depth of about 5m. Shallow foundation
transfer the load to the ground by bearing at the bottom of the
foundation.
FIG6. SHALLOW FOUNDATION
9. DEEP FOUNDATION
A deep foundation is defined as
one whose depth is larger than its
width. Deep foundations can not be
laid using open excavation.
Deep foundation transfer the load
to the ground partly by end bearing at
the bottom of the foundation and partly
by skin friction with the soil around
the foundation along its embedment in
the soil.
Piles are preferred over wells as
they are more economical than wells.
FIG7. DEEP FOUNDATION
10. Bridge Bearings
The devices which are provided over the support of bridge
to accommodate the change in the main grinder due to
deflection, temperature, vertical movement due to sinking
of the support,shrinkage ,prestressing creep. The bearing
are provided for the distribution of the load evenly over
the substructure material which may not have sufficient
bearing strength to bear or take up the load superstructure
directly
10
11. TYPES OF BRIDGE BEARING
ROCKER
BEARING
PIN BEARING
ROLLER
BEARING
LAMINATED
ELASTOMERIC
BEARING
POT
BEARING
KNUCKLE
BEARING
12. ROCKER BEARING
A rocker bearing is a type of expansion bearing that
comes in a great variety. It typically consists of a
pin at the top that facilitates rotations, and a curved
surface at the bottom that accommodates the
translational movements. Rocker and pin bearings
are primarily used in steel bridges
13. PIN BEARING
A pin bearing is a type of fixed bearings that
accommodates rotations through the use of a steel.
Translational movements are not allowed. The pin
at the top is composed of upper and lower
semicircularly recessed surfaces with a solid
circular pin placed between. Usually, there are
caps at both ends of the pin to keep the pin from
sliding off the seats and to resist uplift loads if
required.
14. POT BEARING
A POT BEARING consists of a shallow steel
cylinder, or pot, on a vertical axis with a neoprene
disk which is slightly thinner than the cylinder and
fitted tightly inside. A steel piston fits inside the
cylinder and bears on the neoprene. Flat brass
rings are used to seal the rubber between the
piston and the pot. The rubber behaves like a
viscous fluid flowing as rotation may occur
15. PIERS
• The intermediate supports of a bridge
susperstructure are known as piers.
• FUNCTION:-
• The only purpose of providing piers is to
divide the total length of bridge into suitable
spans with minimum obstruction to the
stream or rivers.
17. Choice of Pier
Wherever possible slender piers should be used so
that there is sufficient flexibility to allow
temperature, shrinkage and creep effects to be
transmitted to the abutments without the need for
bearings at the piers, or intermediate joints in the
deck.
A slender bridge deck will usually look best when
supported by slender piers without the need for a
downstand crosshead beam.
18. Types of Bridge Decks
Simply defined, a bridge deck is the portion of a
bridge that acts as the roadway in the support of
vehicular or pedestrian traffic. While deck parts like
trusses, girders, rails, arches, posts and cantilevers
assume a number of forms and types, there are
relatively few bridge deck types given the utilitarian
nature of the component. Deck types are defined
by the materials from which they are made and the
manner in which those materials are fit together.
Bridge decks must be sturdy enough to withstand
constant pressure and extreme weight.
19. Concrete Decks
Concrete bridge decks are much what they
sound like: flat roadway surfaces made of
poured concrete that is laid in sections on
large bridges or in one fell swoop on small
bridges. Thin steel beams are laid into the
concrete to provide both strength and
flexibility. Concrete is a rigid material that will
break if under overburdening pressure. Steel
laid into concrete bridge decks permit the
deck to bow and sway gently under the
20. Reinforced Decks
Reinforced bridge decks are similar to concrete decks in that
they are poured of reinforced concrete and interwoven with
steel support bars for added strength and flexibility. Such
decks differ from standard concrete decks in that they apply
further support systems beneath the concrete for additional
support. A typical reinforced bridge deck consists of a thick
layer of concrete to form the roadway and solid steel sheets
laid beneath the concrete to offer additional relief from the
pressure of weight. Distribution bars and support beams are
laid beneath the steel sheets. Distribution bars relieve
pressure from the deck incrementally and transfer weight-
bearing responsibility to support beams, much like flying
buttresses do for buildings.
21. Beam and Girder Decks
Beam and girder decks are those that employ side
reinforcement. Girders are support beams made from
steel that are divided into sections, or plates, and
affixed to the sides of a concrete bridge deck for
added support. Beams work much in the same manner
but are generally one enormous piece of steel that
provides structural support by helping a bridge
maintain its shape in the face of elements that may
cause the concrete to bow or flex. Girders help
alleviate deck weight by segmenting the deck and
relieving pressure from the structure as a whole.
