• CE 4241 S4/D  MODULE 1

Part 1

1
 BRIDGE
DEFINITION:
a structure built to span physical obstacles such as bodies of
water, valleys and roads

AASHTO definition:
Any structure having an opening of not less than 6100mm
that forms part of a highway or that is located over or under
a highway

2
 BRIDGE
PURPOSE:
Provide passage over an obstacle

❑ a KEY element in a TRANSPORTATION SYSTEM for 3 reasons:

❖ Controls capacity

❖ Cost per mile is expensive

❖ If bridge fails, transportation system fails

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 BRIDGE as KEY ELEMENT
(a)controls capacity
✓ through volume and weight

✓ insufficient carriage width

❖ cause constriction to traffic flow

✓ Strength deficiency
❖ unable to carry heavy loads (i.e. trucks)
❖ Load limits will cause rerouting of truck traffic

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 BRIDGE as KEY ELEMENT

(b) expensive cost per mile

❖A major investment
✓ Planned carefully for best used of funds

❖Cost is high compared to approach roadways

❖Balance must be achieved between handling future traffic

volume and loads and the cost of heavier and wider bridge
structure

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 BRIDGE as KEY ELEMENT

(c) if the bridge fails, the transportation system fails

❖ When removed or not repaired/ replaced, the transportation

system is restricted of its function
❖ Detours over routes not designed to handle increase volume
❖ Increase travel time and fuel expenses

❖ NORMALCY does not return until the bridge is repaired or

replaced

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 BRIDGE as KEY ELEMENT
Balance must be achieved between

✓ Handling future traffic volume

✓ Loads and
✓ Cost of heavier and wider structure

Strength is the foremost consideration BUT should have measures

to prevent deterioration

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 BRIDGE
❑A structural system that is always exposed
❑MAJOR CONCERNS for Design:
✓ temperature (thermal effect)
✓ Durability (strength)
✓ Cost (inspection and maintenance)

❑ always subjected to large moving and repetitive loads

❑ Fatigue is a primary concern
✓ accumulates damage
✓ results in cracking

8
 BRIDGE ENGINEERING
❑ A field of (structural) engineering that deals with
❑ Surveying
❑ Plan, design, analysis
❑ Construction, management and
❑ Maintenance of bridges

❑ Bridge Engineers MUST ensure that their designs satisfy

given design standard, being responsible to structural
safety and serviceability

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 BRIDGE ENGINEERING
❑ Civil engineering disciplines involved:
❑ HIGHWAY DESIGN
❑ For the overpass and underpass alignment and geometry
❑ STRUCTURAL DESIGN
❑ For the superstructure and substructure elements
❑ GEOTECHNICAL ENGINEERING
❑ For pier and abutment foundations
❑ HYDRAULIC ENGINEERING
❑ For proper bridge span length and drainage of bridge site
❑ SURVEYING AND MAPPING
❑ For layout and grading of proposed site
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 CLASSIFICATIONS of BRIDGE
Based on Span Length BASED ON inter-SPAN
1. Short Span Bridge 1. SIMPLY SUPPORTED
2. Medium Span Bridge 2. CONTINUOUS
3. Long Span Bridge 3. CANTILEVER
** CULVERT BRIDGE

BASED ON MATERIAL BASED ON DECK LOCATION

1. STONE/MASONRY BRIDGE 1. DECK BRIDGE
2. TIMBER/ WOODEN BRIDGE 2. THROUGH BRIDGE
3. METAL / STEEL BRIDGE 3. HALF THROUGH BRIDGE
4. (REINFORCED) CONCRETE BRIDGE
5. PRE-STRESSED CONCRETE BRIDGE

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 CLASSIFICATIONS of BRIDGE
BASED ON STRUCTURAL FORM:
ARCH BRIDGE BASED ON PURPOSE/ USE
TRUSS BRIDGE 1. HIGHWAY
BEAM/ GIRDER BRIDGE 2. RAILROAD
SLAB BRIDGES 3. PEDESTRIAN
SUSPENSION BRIDGE 4. PIPELINE
CABLE – STAYED BRIDGE 5. Aqueducts
6. And more
BASED ON POSITION
BASED ON GEOMETRY
1. BASCULE
1. STRAIGHT
2. SWING 2. SKEWED
3. LIFT 3. CURVED
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 CLASSIFICATIONS of BRIDGE
1. Short Span Bridge (or minor bridge)
▪ Bridges whose end supports spans up to no more than 30 m
Based on Span Length

▪ Slab bridges, prestressed concrete shapes and steel shapes

2. medium Span Bridge (or major bridge)

▪ bridges that has lengths from 30 m to 120 meters
▪ girder bridges( pre-stressed and steel)

3. LONG Span Bridge

▪ cable stayed and suspension bridges
▪ post tensioned concrete and steel bridge with high strength materials

** CULVERT Bridge
▪ Span length is below 6 - 8 meters
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 CLASSIFICATIONS of BRIDGE
BRIDGE VS CULVERT
Based on Span Length

Allow passage OVER an obstacle Permit a body of water to pass

such as a body of water UNDER an obstacle such as road
Provided for the ‘benefit’ of the
Provided for passage of traffic
water
Has a base over which traffic Has a base over which water
can pass flows

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 CLASSIFICATIONS of BRIDGE
SIMPLY SUPPORTED BRIDGE
BASED ON inter - SPAN

❖ are used when the width of gap is small and only single
span of bridge is needed
❖ suitable for short span bridges

CONTINUOUS SUPPORTED BRIDGE

❖ Used when width of gap is quite large and where there is no
chance of uneven settlements
❖ Moments are generally developed at pier supports resulting
to reduction of stress at inner spans

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BASED ON inter - SPAN CLASSIFICATIONS of BRIDGE

CONTINUOUS
SUPPORTED BRIDGE

SIMPLY SUPPORTED
BRIDGE

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 CLASSIFICATIONS of BRIDGE
CANTILEVER BRIDGE
BASED ON inter - SPAN

❖ TYPES OF CANTILEVER BRIDGE

❖ Simple cantilever
❖ Formed by two cantilever arms
❖ Extends from opposite sides of the obstacle to be
crossed
❖ Meets at the center

❖ Balanced cantilever
❖ Cantilever spans counterbalance each cantilever arm
with another cantilever arm projecting the opposite
direction
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 CLASSIFICATIONS
CANTILEVER of BRIDGE
BRIDGE
CANTILEVER BRIDGE
BASED ON inter - SPAN

(simple)

18
 CLASSIFICATIONS
CANTILEVER of BRIDGE
BRIDGE
CANTILEVER BRIDGE
BASED ON inter - SPAN

(balanced)

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 CLASSIFICATIONS of BRIDGE
WOOD/ TIMBER BRIDGE
- Bridges constructed for short
BASED ON MATERIAL

spans
- Not sufficient for heavy loading
- Designed for pedestrians and
low weight transport

MASONRY BRIDGE
- stones and bricks are used as
construction materials
- durable compared to timber bridge
- suitable for shorter spans
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 CLASSIFICATIONS of BRIDGE
STEEL BRIDGE
- Uses steel bars or trusses or steel cables
- More durable and bear heavy loads
BASED ON MATERIAL

REINFORCED CONCRETE BRIDGE

- Reinforce concrete is used as construction material
- More stable and durable
- Suitable for long span and heavily loaded traffic
- Generally used for constructing fly-over and highway bridges
PRE-STRESSED CONCRETE BRIDGE
- Suitable for short to long span bridges
- Has heavy load carrying capacity
- Requires high tensile steel which is more expensive than ordinary
mild steel
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BASED ON MATERIAL CLASSIFICATIONS of BRIDGE

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BASED ON MATERIAL CLASSIFICATIONS of BRIDGE

1st and oldest surviving Key Bridge in Potomac River (1923)

concrete bridge with metal Seven open-spandrel three-ribbed
reinforcement arches designed by Nathan C.
Wyeth
Alvord Lake Bridge (1889) by
Ransome in Golden Gate Park
San Francisco
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 CLASSIFICATIONS of BRIDGE

Deck Bridge
BASED ON DECK LOCATION

- floor is situated on top of

the flange in case of plate
girder bridges
- floor is on the top chord
in case of truss bridge
- top bracing is not
required

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 CLASSIFICATIONS of BRIDGE
Through Bridge
BASED ON DECK LOCATION

- floor is placed at the level of

lower chord of truss type bridge
and on the top chord is braced
laterally

- flooring is provided at the

bottom of the superstructure Chaotianmen Bridge
(China)

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 CLASSIFICATIONS of BRIDGE
Half through type
bridge
BASED ON DECK LOCATION

- floor lies between top and

bottom
- there also double deck bridges
constructed to carry traffic on
both roadways and railways at
same time
- the flooring is located at Bayonee Bridge
intermediate level in the (New York)
superstructure

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 CLASSIFICATIONS of BRIDGE
ARCH BRIDGE
BASED ON STRUCTURE

❖ A bridge with abutments at each end shaped as a curved

arch

❖ Transfer weight of the bridge and its loads primarily into a

horizontal thrust restrained by the abutments at either side

❖ Arches are the primary force resisting elements

❖ Arches resist forces through compression
❖ Thrust is a major consideration

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 CLASSIFICATIONS
ARCH BRIDGE of BRIDGE
ARCH BRIDGE
BASED ON STRUCTURE

Load is distributed along the arch towards the abutments

The ground around the abutments is squeezed and

pushes back on the abutments

The resisting force in the abutments is distributed back

along the arch towards the keystone which supports the
load

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 CLASSIFICATIONS of BRIDGE
Arch Bridge
BASED ON STRUCTURE

Deck Arch Bridge Viaduct Aqueduct

Through Arch Bridge

Corbel Arch Bridge Tied-Arch Bridge

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 CLASSIFICATIONS of BRIDGE
BEAM BRIDGE
BASED ON STRUCTURE

❖ Weight on top of the beam pushes straight down on the

abutments at either end of the bridge

❖ Weight is applied at either end to counteract bending at

center

❖ Beam must be strong in both compression and tension to

resist twisting and bender under load

❖ Usual span is 250 feet maximum

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 CLASSIFICATIONS of BRIDGE
BEAM/GIRDER BRIDGE
BASED ON STRUCTURE

❖ Supported by abutments or piers in between

❖ Consist of vertical piers and horizontal beams

❖ BEAM bridge
❖ Has longitudinal support below the deck

❖ GIRDER bridge
❖ Has both longitudinal and transverse structural members
under the deck

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 CLASSIFICATIONS of BRIDGE
BEAM/GIRDER BRIDGE
BASED ON STRUCTURE

❖ Seldom exceed 500 ft (150m)

❖ Have greater stiffness and less subject to vibrations
❖ Important characteristics in railroads
❖ Resulted in early application of plate girders

❖ PLATE GIRDER BRIDGE

❖ -section assembled out of flange and web plates
❖ Early plate girders, have the webs deeper than
maximum width of plate, resulting to the lengthwise
dimension of web plate in the transverse direction of
the section from flange to flange
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 CLASSIFICATIONS of BRIDGE
BEAM/GIRDER BRIDGE
BASED ON STRUCTURE

❖ Girders are the primary force resisting elements

❖ Forces are resisted through bending

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 CLASSIFICATIONS of BRIDGE
BEAM/ GIRDER BRIDGE
BASED ON STRUCTURE

Railroad Steel Girder Bridge

SLAB-ON-STRINGER (T- GIRDER BRIDGE)

SPANNING FROM 10 TO 25 METERS (33
TO 82 FT.)

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 CLASSIFICATIONS of BRIDGE
BEAM/ GIRDER BRIDGE
BASED ON STRUCTURE

Agas-Agas bridge, Leyte, Ph

Prestressed concrete beam bridge

Manchac Swamp Bridge, Louisiana, USA

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 CLASSIFICATIONS of BRIDGE
Longest bridge in PH at 39.2 km
Skyway (MMSS) Connects NLEX and SLEX
BASED ON STRUCTURE

Huangshi Yangtze River Bridge

Box girder bridge, Prestressed concrete

36
 CLASSIFICATIONS of BRIDGE
SLAB BRIDGE
BASED ON STRUCTURE

❖ Simplest type and least

expensive structures that can be
for small spans up to 12 m

❖ Monolithic flat concrete beams

with twisted or roughened
reinforcing steel rods
concentrated in the lower
Hynds Landspan Deck Slab
portion and at either end of the Bridge
slab, where tensile forces and
sheer are the greatest.

37
 CLASSIFICATIONS of BRIDGE
RIGID-FRAME BRIDGES
❑ Also known as RAHMEN bridges
BASED ON STRUCTURE

❑ Consist of superstructure supported on vertical or slanted monolithic

legs (columns), in which superstructure and substructure are rigidly
connected to act as a unit

❑ economical for moderate medium span lengths

❑ The connections between the superstructure and substructure are

rigid connections which transfer
bending moment,
axial forces and
shear forces
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 CLASSIFICATIONS of BRIDGE
RIGID-FRAME BRIDGES
❑ Also known as RAHMEN bridges
BASED ON STRUCTURE

❑ Superstructure – substructure integral structures with the

superstructure can be considered as girders

❑ include
❑ braced rigid-frame bridges,

❑ V-leg rigid-frame bridges, and

❑ viaducts in urban areas

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 CLASSIFICATIONS of BRIDGE
RIGID-FRAME BRIDGES
Sanpodani Bridge No. 4, Japan Agas-Agas Bridge
BASED ON STRUCTURE

Braced rigid-frame bridge

Pont St Michael, France

Rigid Frame bridge with
V-legs
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 CLASSIFICATIONS of BRIDGE
RIGID-FRAME BRIDGES
BASED ON STRUCTURE

Toyosu Bridge, Tokyo Japan

Second Shibanpo Bridge,
Chongqing China

41
 CLASSIFICATIONS of BRIDGE
TRUSS BRIDGE
BASED ON STRUCTURE

❑ Are kept strong by the stiffness of the structure

❑ All beams/members work together to spread out the
load

42
 CLASSIFICATIONS of BRIDGE
TRUSS BRIDGE
BASED ON STRUCTURE

❑ characterized by the location of its traffic deck

❑ Pony Truss
❑ Travel surface passes along bottom chords
standing to either side not connected to top
❑ Designed for lecture

❑ Through truss bridge

❑ deck is carried along bottom chords BUT trusses to
either sides are higher and connected by cross-
bracing at the tops
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 CLASSIFICATIONS of BRIDGE
TRUSS BRIDGE
BASED ON STRUCTURE

44
 CLASSIFICATIONS of BRIDGE
TRUSS BRIDGE
BASED ON STRUCTURE

❑ characterized by connection of structural members

❑ Pratt Truss
❑ Has vertical members between the
upper and lower members and diagonal
members sloping toward the center

45
 CLASSIFICATIONS of BRIDGE
TRUSS BRIDGE
BASED ON STRUCTURE

❑ characterized by connection of structural members

❑ Warren Truss
❑ uses equilateral triangles
in the framework to spread
out the load on the bridge

46
 CLASSIFICATIONS of BRIDGE
TRUSS BRIDGE
BASED ON STRUCTURE

❑ characterized by connection of structural members

❑ Parker Truss
❑ Pratt truss with a
polygonal top chord

47
 CLASSIFICATIONS of BRIDGE
TRUSS BRIDGE
BASED ON STRUCTURE

❑ characterized by connection of structural members

❑ Camelback Truss
❑ Variation of the parker truss
❑ has a polygonal upper chord
of exactly five slopes

48
 CLASSIFICATIONS of BRIDGE
TRUSS BRIDGE
BASED ON STRUCTURE

❑ characterized by connection of structural members

❑ Pennsylvania Truss
❑ Or petit truss
❑ Variant of pratt truss with
polygonal top chords and panels
subdivided by ties and struts

49
 CLASSIFICATIONS of BRIDGE
TRUSS BRIDGE
BASED ON STRUCTURE

❖ Used for larger spans where the depths of a girder bridge

is not practical due to limitations of
(1) fabrication;
(2) erection and
(3) transportation;
4) economy in case of concrete girders

❖ Rods are the primary force resisting elements

❖ Forces are resisted through tension and compression

50
 TRUSS BRIDGE
BUNTUN BRIDGE
- found in Tuguegarao City
BASED ON STRUCTURE

- 2nd longest bridge in the

Philippines
- Longest river bridge in PH

KEW RAILWAY BRIDGE

-Lattice Truss Bridge
-Spans over River Thames in
London, England

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 TRUSS BRIDGE
Victoria Bridge, Malaysia
Railway truss bridge
BASED ON STRUCTURE

San Juanico Bridge

Arch Truss Bridge connecting
Leyte and Samar

52
 CLASSIFICATIONS of BRIDGE
SUSPENSION BRIDGE
BASED ON STRUCTURE

❖ Allows the longest span for bridges

❖ The bed of bridge can be continuous and is held up by
cables stretched between piers
❖ the load-bearing portion is hung below suspension cables
on vertical suspenders

a) cable stayed:
cables are rigid and directly connected to the bridge
deck
b) suspension bridge
hang vertically off another cable supported by piers
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 CLASSIFICATIONS of BRIDGE
SUSPENSION BRIDGE
BASED ON STRUCTURE

❖ Cables are the primary force resisting elements

❖ Forces are primarily transmitted through tension

54
 CLASSIFICATIONS of BRIDGE
SUSPENSION BRIDGE
BASED ON STRUCTURE

Wheeling Suspension
Bridge (1849)
Still carries traffic up to
now
Wire cable suspension
bridge by John A Roebling

55
 CLASSIFICATIONS of BRIDGE
SUSPENSION BRIDGE
Other bridges by Roebling
BASED ON STRUCTURE

Niagara Falls Suspension Bridge

Cincinnati Suspension Bridge

Brooklyn Bridge
56
BASED ON STRUCTURE CLASSIFICATIONS of BRIDGE

Magapit Suspension
Bridge
57
 CLASSIFICATIONS of BRIDGE
CABLE - STAYED
BASED ON STRUCTURE

❖consists of one or more columns (towers or pylons), with

cables supporting the bridge deck
Two types of design

❖HARP DESIGN
❖cables are made nearly parallel by attaching them to
various points on the tower

❖FAN DESIGN
❖cables all connect to or pass over the top of the tower

58
 CLASSIFICATIONS of BRIDGE
CABLE - STAYED
BASED ON STRUCTURE

❖HARP DESIGN

❖FAN DESIGN

59
 CLASSIFICATIONS of BRIDGE
CABLE – STAYED
Marcelo Fernan
BASED ON STRUCTURE

Bridge connecting
Cebu to Mactan
Airport

60
 CLASSIFICATIONS of BRIDGE
CABLE – STAYED
CCLEX (Cebu –
BASED ON STRUCTURE

Cordova Link
Expressway

1st expressway in central PH

Longest and tallest Bridge over
water (Php33B 8.5km)
61
 CLASSIFICATIONS of BRIDGE
CABLE – STAYED
Penang Bridge, Malaysia
BASED ON STRUCTURE

13.5 km
(Box Girder bridge)

62
 CLASSIFICATIONS of BRIDGE
CABLE – STAYED
Diosdado
BASED ON STRUCTURE

Macapagal
Bridge
Longest bridge in
Mindanao

63
 CLASSIFICATIONS of BRIDGE
MOVEABLE BRIDGE
BASED ON DECK POSITION

❖designed to move out of the way of boats or

other kinds of traffic

❖powered by electric motors, whether operating

winches, gearing, or hydraulic pistons

(a)Bascule (b)Swing (c)Lift (vertical lift)

64
 CLASSIFICATIONS of BRIDGE
MOVEABLE BRIDGE
BASED ON DECK POSITION

(a)Bascule
spans that pivot upward utilizing gears, motors and counterweights

DRAGON BRIDGE,
RHYL WALES

Portland
Broadway Bridge

65
 CLASSIFICATIONS of BRIDGE
MOVEABLE BRIDGE
BASED ON DECK POSITION

(b) swing
a bridge over water
that can be rotated
horizontally to allow
El Ferdan Railway
ships through Bridge in Egypt

Newcastle swing, river

tyne, england

66
 CLASSIFICATIONS of BRIDGE
MOVEABLE BRIDGE
BASED ON DECK POSITION

(c) lift
Or vertical lift bridge;
Portage Lake Lift
span rises vertically Bridge
while remaining parallel
with the deck

PONT JACQUES
CHABAN – DELMAS
BORDEAUZ, FRANCE

67
 CLASSIFICATIONS of BRIDGE
MOVEABLE BRIDGE
BASED ON DECK POSITION

special types: Draw Bridge

Variation of bascule bridge; also known as single leaf bascule bridge
initially used for protection of castles and forts
Slauerhoffbrug
drawbridge, Netherlands

68
 CLASSIFICATIONS of BRIDGE
MOVEABLE BRIDGE
BASED ON DECK POSITION

special types: folding bridge

A three-segment bascule bridge that folds in the shape of an N

Hörnbrücke (Hörn Bridge)

69
 CLASSIFICATIONS of BRIDGE
MOVEABLE BRIDGE
BASED ON DECK POSITION

special types: submerging bridge

movable bridge that lowers the
bridge deck below the water level to
permit waterborne traffic to use
the waterway

Submersible bridge
at the entrance of
Corinth canal

70
 CLASSIFICATIONS of BRIDGE
MOVEABLE BRIDGE
BASED ON DECK POSITION

special types: tilting bridge

rotates about fixed endpoints
rather than lifting or bending,
as with a drawbridge

71
 CLASSIFICATIONS of BRIDGE
MOVEABLE BRIDGE
BASED ON DECK POSITION

special types: transporter bridge

also known as a ferry bridge or
aerial transfer bridge,
is a type of movable bridge that
carries a segment of roadway
across a river

72
 CLASSIFICATIONS of BRIDGE
MOVEABLE BRIDGE
BASED ON DECK POSITION

special types: rolling bridge OR curling bridge

not hinged, and remains horizontal Heatherwick’s
when it is rolled inside the gates of a Rolling Bridge
fort

73
 CLASSIFICATIONS of BRIDGE
MOVEABLE BRIDGE
BASED ON DECK POSITION

special types: retractable bridge

the deck can be rolled or slid backwards Modern versions of rolling
to open a gap while traffic crosses bridge

COPENHAGEN INNER
HARBOUR
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 CLASSIFICATIONS of BRIDGE
PEDESTRIAN BRIDGE
BASED ON PURPOSE/ USE

❖OR FOOT BRIDGE

❖ designed for the use of pedestrians only
“stairway to heaven” EDSA footbridge

RAILWAY BRIDGE
❖Used for the movement of trains
❖Steel bridges are widely used
→ Padre Zamora Bridge. Inquirer 2012

75
 CLASSIFICATIONS of BRIDGE
HIGHWAY BRIDGE
BASED ON PURPOSE/ USE

❖designed for passage of highway

vehicles and pedestrians
❖Designed for heavy rolling loads up to
0.8MN

PIPELINE BRIDGE
❖Used for supporting pipeline on the
deck slab of bridge
❖Used for oil, gas, water,
communication etc.

76
 CLASSIFICATIONS of BRIDGE
AQUEDUCT
BASED ON PURPOSE/ USE

❖Or water bridges

❖are bridges constructed to convey
watercourses across gaps

77
 CLASSIFICATIONS of BRIDGE
(a)Straight (b)Skew (c)curve
BASED ON GEOMETRY

subtended angle is an arch (or bridge) with the line of the arch not at right
less than 90 angles to the abutment.
degrees
78
79
INTRODUCTION TO
BRIDGE ENGINEERING
• CE 4241 S4/D  MODULE 1
Part 2

48
 COMPONENTS of a BRIDGE
1. SUPERSTRUCTURE
▪ Span and directly Receives the live load
▪ Supported by bearings
▪ deck, girders, slab above the main deck

2. SUBSTRUCTURE
▪ Support structures, located below the bearing
▪ Transmits load to ground
▪ piers, abutments, spandrels, caps, bearings

3. FOUNDATION
▪ holds the shallow or deep base of the bridge
▪ Footing; piles
49
COMPONENTS of a BRIDGE

50
COMPONENTS of a BRIDGE

51
 COMPONENTS of a BRIDGE

1 Deck (and overpass) 6 Pile

2 Stringer 7 Underpass
3 Bearing 8 Embankment
4 Pedestal 9 Live Loading
Typical single span slab-on-stringer bridge 5 Footing
site and its representative components
52
SUPERSTRUCTURE

53
 SUPERSTRUCTURE
1. WEARING SURFACE
➢ OR Course

➢ Topmost layer of material

applied upon the deck to
provide smooth riding surface
and to protect deck from effects
of traffic and weathering

➢ In some instances, this is a

separate layer made of
bituminous material, while in
some it is an integral part of the
concrete deck

54
 SUPERSTRUCTURE
2. DECK
➢ The physical extension of the
roadway across the obstruction
to be bridged

➢ Component of the bridge to

which live load is directly applied

➢ Provide smooth and safe riding

surface for the traffic utilizing the
bridge and distribute loads
transversely along the bridge
cross section

55
 SUPERSTRUCTURE
2. DECK

➢ TIMBER DECKS
➢ Normally referred to as
decking or timber flooring
(limited to the roadway
portion that receives
vehicular loads)

56
 SUPERSTRUCTURE
2. DECK

➢ CONCRETE DECKS
➢ Concrete permits casting
in various shapes and sizes
and has provided bridge
designers and builders a
variety of construction
methods
➢ It is used together with
reinforcement to resist
tensile stress (where
concrete is weak)

57
 SUPERSTRUCTURE
2. DECK

➢ STEEL DECKS
➢ Composed of either
➢ Solid steel plate
➢ Steel grids

58
 SUPERSTRUCTURE
3. PRIMARY MEMBERS
➢ Distributes loads longitudinally
and are usually designed
principally to resist flexure and
shear

➢ BEAM TYPE primary members are

also referred to as stringers or
girders

➢ A haunch is placed between the

deck slab and the top flange of
the stringer in order for the slab
not to rest directly on the
member
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 SUPERSTRUCTURE
3. PRIMARY MEMBERS

I – girders: Rolled Beams

▪ Efficient for shorter spans
▪ Limited sizes and shapes

I – girders: Plate Girders

▪ Deep girders can span very
long distances
▪ Vast range of sizes and shapes

Box Girders
▪ Box section efficiently resists
torsion effects
▪ Vast range of shape and sizes
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 SUPERSTRUCTURE
4. SECONDARY MEMBERS
➢ Are bracing between primary members
➢ designed to resist cross-sectional
deformation of the superstructure frame
➢ and help distribute part of the vertical
load between stringers

➢ Other secondary members (like lateral

bracing) composed of crossed frames
at the top or bottom flanged of a
stringer
➢ are used to resist lateral deformation
caused by loads acting
perpendicularly to the bridge’s
longitudinal axis
61
 SUPERSTRUCTURE
4. SECONDARY MEMBERS

CROSS FRAMES
▪ Used on steel girder bridges to
provide torsional stiffness during
construction and in final
condition

62
 SUPERSTRUCTURE
4. SECONDARY MEMBERS

DIAPHRAMS
▪ Used on steel girder bridges to
provide torsional stiffness during
construction and in the final
condition

▪ Typically used on shallow

beams

63
 SUPERSTRUCTURE
4. SECONDARY MEMBERS

LATERAL BRACING
▪ Used to provide lateral stiffness
and limit lateral deflections

64
 SUPERSTRUCTURE
5. BEARINGS
➢ Are mechanical systems which
transmit the vertical and horizontal
loads of the superstructure to the
substructure
➢ Accommodates movement between
superstructure and substructure
➢ Use and functionality vary greatly
depending on the size and
configuration of bridge
➢ Expansion bearings
➢ Allow both rotation and
longitudinal translation
➢ Fixed bearings
➢ Allow rotation only
65
 SUPERSTRUCTURE
5. BEARINGS

Rocker Bearing
Disc Bearing
Elastomeric Bearing

Pot Bearing Mechanical roller

66
 SUBSTRUCTURE

Basic components:
1. Abutments
2. Piers
3. Bearings
4. Pedestals
5. Stem
6. Backwall
7. Wingwall
8. Footing
9. Piles
10. Sheeting

67
 SUBSTRUCTURE
1. ABUTMENTS

➢ Earth-retaining structures which

support the superstructure and
overpass roadway at both ends of
the bridge

➢ Like retaining walls, it resist

longitudinal forces of the earth
underneath the overpass roadway

➢ Connects the bridge with the

approach roadway

68
 SUBSTRUCTURE
2. PIERS

➢ support the superstructure at

intermediate points between end
supports

➢ Bridges consisting of one span, does

not require piers

➢ From aesthetic standpoint:

➢ piers can make a bridge visually
pleasing (or unattractive) since it is
one of the most visible components
of a highway bridge

69
 SUBSTRUCTURE
2. PIERS

Basic Types:

70
 SUBSTRUCTURE

2. PIERS

➢ HAMMER HEAD PIER

▪ Also referred as solid shaft pier or T
pier

▪ Major stream crossings where heavy

loads, tall piers or sizable debris loads
may occur

▪ Looks attractive for bridges requiring

large clearance

71
 SUBSTRUCTURE

2. PIERS

➢ SOLID /GRAVITY WALL PIER

▪ used for most stream crossings
to avoid collecting of debris
and floating ices between
columns

72
 SUBSTRUCTURE

2. PIERS

➢ PILE BENT PIER

▪ well suited for shallow water
crossings

➢ COLUMN BENT PIER

▪ Or also called open Bent

73
 SUBSTRUCTURE
3. PEDESTALS

➢ Short column on an abutment or pier

under a bearing

➢ Directly supports a superstructure

primary member

➢ Bridge seat is used to refer to the

elevation at the top surface of the
pedestal

➢ Normally designed with different

heights to obtain required bearing
elevations
74
 SUBSTRUCTURE
4. STEM
➢ A primary component of the abutment supporting pedestals on top of a
footing
➢ Its main function is to transfer loads from superstructure to the foundation

5. BACKWALL
➢ The component of the abutment acting as a retaining structure on top
of the stem
➢ Also supports the approach slab

6. WINGWALL
➢ Sidewall to the abutment backwall or stem
➢ Designed to assist in confining earth behind the abutment

75
SUBSTRUCTURE

76
 SUBSTRUCTURE

Wingwall

77
 SUBSTRUCTURE
7. FOOTING
➢ As bearing transfer the superstructure loads to the substructure; abutments
and pier footings transfer load from the substructure to the subsoil or piles

➢ A footing supported by soil without piles is called a spread footing

➢ A footing supported by piles is known as a pile cap

8. PILES
➢ When soil under a footing cannot provide adequate support for
substructure (in terms of bearing capacity, overall stability, or settlement),
support is obtained through piles, which extends down from the footing to
stronger soil layer or bedrock

78
 SUBSTRUCTURE
9. SHEETING
➢ Vertical planks driven to the ground to act as temporary
retaining wall permitting excavation

Steel sheeting used as

economical abutment material

79
 APPURTENANCES and SITE-RELATED FEATURES

APPURTENANCE
➢ Any part of the bridge or bridge site which is NOT a major
structural component yet serves some purpose in the overall
functionality of the structure
➢ i.e. guide rails

➢ Bridge site, as an entity, possesses many different

components which, in one way or another, integrates with
the structure

80
 APPURTENANCES and SITE-RELATED FEATURES

EMBANKMENT AND SLOPE PROTECTION

slope protection
- slope that tapers from the abutment to the underpass
(embankment) is covered with a material, which should be both
aesthetically pleasing and provide for proper drainage and erosion control

- form of slope protection varies greatly from region to region and

is mostly dependent on specific environmental concerns and the types of
material readily available

- For water way crossings, large stones are usually used for
foundation scour protection.

81
 APPURTENANCES and SITE-RELATED FEATURES

UNDERDRAIN
- provide proper drainage of a major substructure element, such as an
abutment,
- a drainage system made of perforated pipe or other suitable conduit
that transports runoff away from the structure and into appropriate
drainage channels (natural or man-made

APPROACH
- Section of overpass roadway which leads up to and away from the
bridge abutments
- Helps evenly distribute traffic loads on the soil behind the abutment and
minimize impact to the abutment which can result from differential
settlement between abutment and approach

82
 APPURTENANCES and SITE-RELATED FEATURES

TRAFFIC BARRIERS
- protective device “used to shield
motorists from obstacles or slope
located along either side of roadway
- can range from a guard rail made of
corrugated steel to reinforced
concrete parapets
- On bridges, they are usually called
bridge railings.

GUIDE RAILS
- Designed to keep people or vehicles
from losing their way into dangerous
or off-limit areas
83
 Other Parts
1. BRIDGE TOWER
➢ Sometimes called mast or pylons
➢ Vertical supporting part used for cable stayed or suspension bridge
➢ Made of high strength in-situ concrete

2. SPANDREL
➢ the almost triangular space between the main pillar of the bridge and
decking

3. EXPANSION JOINT
➢ The space between two parts of the structure that allows expansion and
contraction

84
 Other Parts

4. PARAPET
➢ A low wall that forms a barrier around the outer edges of a bridge

5. ANCHORAGE
➢ A point where the supporting elements of the bridge are connected to
the ground

6. APEX
➢ the uppermost portion o a bridge
➢ Called a CROWN for arch bridges

85
Other Parts

86
• Reference:
• Lecture Notes, Engr. YLA Suba,
Saint Louis University
• Bridge Engineering, 2nd Edition,
Tonias, D and Zhao, J

87
MODULE 2: LOADS ON A BRIDGE

LOADS ON BRIDGES: CE 4241 S4/D

DESIGN PHILOSOPHIES MODULE 2 PART 1

1
MODULE 2: LOADS ON A BRIDGE

GENERAL REQIUREMENTS:

AASHTO specifications require highway bridges be

designed for:
constructability
safety
serviceability
With due regard to issues of:
inspectability
economy
aesthetics
2
MODULE 2: LOADS ON A BRIDGE

constructability

➢ Refers to the ability to successfully complete construction of bridge

being designed
DESIGN PHILOSOPHIES

➢ A prerequisite for the bridge to start its design life by entering the
stage of operation

➢ Thus, discussed before other general design issues

3
MODULE 2: LOADS ON A BRIDGE

constructability

➢ New provisions included in LRFD specifications:

DESIGN PHILOSOPHIES

➢ Need to design bridges so that they can be fabricated and built

without undue difficulty and with control over locked-in
construction force effects

➢ Need to document one feasible method of construction in the

contract documents unless type of construction is self-evident

➢ Clear indication of the need to provide strengthening and/or

temporary bracing or support during erection, but not requiring
complete design thereof

4
MODULE 2: LOADS ON A BRIDGE

safety
➢ Public safety is the primary responsibility of the design engineer
STRUCTURAL SURVIVAL
DESIGN PHILOSOPHIES

- structure should not collapse under

design event
LIMITED SERVICEABILITY
- structure should remain stable under
designated emergency vehicular live loading

IMMEDIATE USE
- structure may be reopened to all traffic
after inspection following an extreme event
5
MODULE 2: LOADS ON A BRIDGE

safety
BRIDGE DESIGN SPECIFICATIONS
DESIGN PHILOSOPHIES

PURPOSE:
Ensure bridge safety such that minimum resistances
exceed the potential maximum demands or force
effects due to various loads during its design life

IN TERMS OF:
strength  stiffness 
 stability of structural system (component and the entire
bridge

6
MODULE 2: LOADS ON A BRIDGE

DESIGN METHODS: “Philosophies Of Safety”

1. Allowable Stress Design (ASD by AISC)
❖ Working stress Design or Service Load Design (AASHTO)
DESIGN PHILOSOPHIES

2. LOAD FACTOR DESIGN

❖ Ultimate/ Strength Design

3. LOAD AND RESISTANCE FACTOR DESIGN

7
MODULE 2: LOADS ON A BRIDGE

WORKING STRESS DESIGN (WSD)

❖also known as
❖Allowable Stress Design (ASD by AISC)
DESIGN PHILOSOPHIES

❖ Service Load Design (AASHTO)

❖does not recognize that some loads are more variable
than others
❖treats each load in a given load combination as equal

8
MODULE 2: LOADS ON A BRIDGE

WORKING STRESS DESIGN (WSD)

CONCEPT:
❖the maximum applied stress in a structural component
DESIGN PHILOSOPHIES

does not exceed a certain allowable stress under normal

service or working conditions

❖Based on the premise that one or more factors of safety

can be established based primarily on experience and
judgement that will assure safety of a bridge component
over its design life

9
MODULE 2: LOADS ON A BRIDGE

WORKING STRESS DESIGN (WSD)

EQUATION OF SUFFICIENCY:
DESIGN PHILOSOPHIES

𝑅𝐸
෍ 𝑄𝑖 ≤
𝐹𝑆
WHERE:
Qi = Load
RE = elastic resistance
FS = factor of safety

10
MODULE 2: LOADS ON A BRIDGE

WORKING STRESS DESIGN (WSD)

DISADVANTAGES:
1. Resistance concepts are based on elastic behavior of
DESIGN PHILOSOPHIES

materials
2. It does not embody reasonable measure of strength, which
is more fundamental measure of resistance is allowable
stress
3. Safety factor is applied only to the resistance. Loads are
considered to be deterministic (without variation)
4. Selection of safety factor is subjective, and it does not
provide a measure of reliability in terms of probability of
failure
11
MODULE 2: LOADS ON A BRIDGE

LOAD FACTOR DESIGN (LFD)

❖also known as
❖Ultimate Design ( older ACI code)
DESIGN PHILOSOPHIES

❖ Strength Design (ACI and AASHTO)

CONCEPT:
❖mainly recognizes that the live load (vehicular loads and
wind forces), in particular, is more variable than the dead load

12
MODULE 2: LOADS ON A BRIDGE

LOAD FACTOR DESIGN (LFD)

❖Was developed to overcome drawbacks of ASD method
DESIGN PHILOSOPHIES

❖Loads are multiplied by factors greater than unity and

added to other factored loads to produce load combinations
Type equation here.
for design purposes

EQUATION OF SUFFICIENCY:

෍ 𝜸𝒊 𝑸𝒊 ≤ 𝝋𝑹

Where:
γi = load factor; Qi = load; R = resistance; φ = strength reduction factor
13
MODULE 2: LOADS ON A BRIDGE

LOAD FACTOR DESIGN (LFD)

DISADVANTAGE:
DESIGN PHILOSOPHIES

From a probabilistic design point of view,

➢ load factors and resistance factors were not calibrated
on a basis that takes into account statistical variability of
design

14
MODULE 2: LOADS ON A BRIDGE

LOAD AND RESISTANCE FACTOR DESIGN (LRFD)

➢ Design methodology where applicable failure and serviceability
conditions can be evaluated considering uncertainties associated
with loads by using load factors and material resistances by
DESIGN PHILOSOPHIES

considering resistance factors

15
MODULE 2: LOADS ON A BRIDGE

LOAD AND RESISTANCE FACTOR DESIGN (LRFD)

ADVANTAGE
1. Accounts for variability and uncertainty in both resistance and
DESIGN PHILOSOPHIES

loads

2. Achieves relatively uniform levels of safety different limit states and

material type to possible extent

3. Provides more rational and consistent design method

4. Consistent with other design specifications

16
MODULE 2: LOADS ON A BRIDGE

LOAD AND RESISTANCE FACTOR DESIGN (LRFD)

LIMITATION
1. The most rigorous method for developing and adjusting resistance
DESIGN PHILOSOPHIES

factors to meet individual situations

2. Requires a change in design philosophy (from previous AASHTO

methods)

3. Requires an understanding of the basic concepts of probability

and statistics

4. Requires availability of statistical data and probabilistic design

algorithms

17
MODULE 2: LOADS ON A BRIDGE

LOAD AND RESISTANCE FACTOR DESIGN (LRFD)

SAFETY CRITERION
DESIGN PHILOSOPHIES

AASHTO LRFD EQUATION 1.3.2.1-1

Where:
i = load modifier (ductility, redundancy, operational importance)
i = load factor (statistically based multiplier applied to force
effects)
Qi = force effect
 = resistance factor
(statistically based multiplier applied to nominal resistance)
Rn = nominal resistance
Rr = factored resistance
18
MODULE 2: LOADS ON A BRIDGE

LOAD AND RESISTANCE FACTOR DESIGN (LRFD)

LOAD MODIFIER, 
for maximum i values
DESIGN PHILOSOPHIES

AASHTO LRFD EQUATION 1.3.2.1-2

for minimum i values

AASHTO LRFD EQUATION 1.3.2.1-2

19
MODULE 2: LOADS ON A BRIDGE

LOAD AND RESISTANCE FACTOR DESIGN (LRFD)

LOAD MODIFIER, 
DUCTILITY, D:
DESIGN PHILOSOPHIES

Response of structural components or connections beyond elastic limit

can be characterized by either brittle or ductile behavior

For Strength Limit State

For non ductile :  1.05
For conventional designs : = 1.0
beyond AASHTO requirements:  0.95

For other Limit State = 1.0

20
MODULE 2: LOADS ON A BRIDGE

LOAD AND RESISTANCE FACTOR DESIGN (LRFD)

LOAD MODIFIER, 
REDUNDANCY, R :
DESIGN PHILOSOPHIES

Significantly affects safety margin of bridge structure;

*a statistically indeterminate structure is redundant, that is, more
restraints than necessary to satisfy equilibrium

For Strength Limit State

for non redundant members:  1.05
for conventional redundancy levels: = 1.0
for exceptional redundancy levels:  0.95

For other limit state = 1.0

21
MODULE 2: LOADS ON A BRIDGE

LOAD AND RESISTANCE FACTOR DESIGN (LRFD)

LOAD MODIFIER, 
OPERATIONAL IMPORTANCE, I :
DESIGN PHILOSOPHIES

Bridge of operational importnc are those with shortest path between

residential areas and hospital or schools or provide access for police,
fire and rescue vehicles to home, business and industrial plants

For Strength Limit State

for bridge of operational importance  1.05
for typical bridges = 1.0
for relatively less important bridge  0.95

For other limit state = 1.0

22
MODULE 2: LOADS ON A BRIDGE

serviceability
➢ Ability of a bridge to serve specified functions at an
acceptable level over the design life
DESIGN PHILOSOPHIES

➢ From the specification:

➢ Durability
➢ Inspectability
➢ Maintainability
➢ Rideability
➢ Controlled deformation
➢ Facilitating utilities
➢ Allowance for future widening

23
MODULE 2: LOADS ON A BRIDGE

serviceability
➢ Durability
➢ Contract documents should call for high quality materials and require that those
material subject deterioration from moisture content and/or salt attack be
DESIGN PHILOSOPHIES

protected

➢ Maintainability
➢ Highway bridges need adequate maintenance over their design lives
➢ Maintenance of traffic during rehabilitation or replacement of bridge components
or entire bridge is often required since completely closing the road for such
maintenance operations is unacceptable to the traveling public

24
MODULE 2: LOADS ON A BRIDGE

serviceability
➢ Rideability
➢ Relevant to the bridge deck since it provides driving surface of the bridge.
➢ Deck is required to be designed to permit smooth movement of vehicle traffic
DESIGN PHILOSOPHIES

➢ Facilitating utilities
➢ Bridge shall be made to support and maintain conveyance for utilities

➢ Allowance for future widening

➢ Load carrying capacity of exterior beams not be less than that of an interior
beam unless future widening is virtually inconceivable
➢ When future widening can be anticipated, consideration should also be given to
designing the substructure for widened condition

25
MODULE 2: LOADS ON A BRIDGE

serviceability
➢ Controlled deformation
➢ Bridges should be designed to avoid undesirable structural effects due to
deformations
DESIGN PHILOSOPHIES

➢ While deflection and depth limitations are optional, except for orthotropic plate
decks, any large deviation from past successful practice regarding slenderness
and deflections should be cause for review of design to determine adequate
performance

Recommended deflection limits for steel, aluminum and concrete structure

Load and Structure Deflection Limit
Vehicular load, general span/800
Vehicular and pedestrian loads span/1000
Vehicular load on cantilever arms span/300
Vehicular and pedestrian loads on cantilever arms span/375
26
MODULE 2: LOADS ON A BRIDGE

inspectability
➢ To be assured through adequate means for permitting inspectors to view all
parts of structure that have structural or maintenance significance
DESIGN PHILOSOPHIES

➢ AASHTO specifications also explicitly require inspection ladders, walkways,

catwalks, covered access holes and lightings, if necessary, where other means
of inspection are not practical

➢ Where practical, the specifications also requires access to permit manual or

visual inspection, including adequate headroom in box sections, to the inside of
cellular components and interface areas, where relative movement may occur

27
MODULE 2: LOADS ON A BRIDGE

economy
➢ Economic consideration is required at every stage and step of bridge design

➢ Starting from preliminary design to taking into account the location and
DESIGN PHILOSOPHIES

dimensions of members and amount of reinforcement in concrete components,

➢ COST SAVING IS ALWAYS A SIGNIFICANT FACTOR

aesthetics
➢ Bridges due to their significant geometric dimensions, become part of
environment or landscape after construction

➢ Design engineer should be conscious about possible impact of bridge to the

surrounding
28
MODULE 2: LOADS ON A BRIDGE

aesthetics
➢ Aesthetic qualities of design are intangible, perceived qualities arising from
relationships of design elements
➢ Properties of aesthetic qualities are:
DESIGN PHILOSOPHIES

➢ Proportion
➢ Rhythm
➢ Order
➢ Harmony
➢ Balance
➢ Contrast
➢ Scale
➢ Unity

These properties are basic elements of creative design compositions common to all fine arts as well as bridge architecture
29
MODULE 2: LOADS ON A BRIDGE
Bridge inspections
DESIGN PHILOSOPHIES

Utilities

Wide Sidewalks for accessibility

30
MODULE 2: LOADS ON A BRIDGE
DESIGN PHILOSOPHIES

Color complements the

natural surroundings

31
MODULE 2: LOADS ON A BRIDGE
DESIGN PHILOSOPHIES

32
MODULE 2: LOADS ON A BRIDGE
DESIGN PHILOSOPHIES

33
MODULE 2: LOADS ON A BRIDGE
DESIGN PHILOSOPHIES

34
MODULE 2: LOADS ON A BRIDGE

LOADS ON BRIDGES: CE 4241 S4/D

LIMIT STATES MODULE 2 PART 2

35
MODULE 2: LOADS ON A BRIDGE

LIMIT STATES

❖ AASHTO codes intended to provide buildable and serviceable

bridge capable of safely carrying design loads for specified
Limit states

life span

❖ Bridge Life span = 75 years

36
MODULE 2: LOADS ON A BRIDGE

LIMIT STATE

❖ A condition which represents the limit of “structural usefulness”

(AISC LRFD, 1968)
Limit states

❖ A boundary between desired and undesired performance of

structure (Nowak and Collins)

❖ A condition beyond which the bridge or component ceases to

satisfy the provisions for which it was designed

37
MODULE 2: LOADS ON A BRIDGE

▪Ensure that (local and global) strength and stability are

STRENGTH
capable to resist statistically significant load combinations
LIMIT STATE experienced during its design life
▪used to control stress, deformation, deflection,and crack
SERVICE LIMIT
width under normal service conditions to ensure structure
Limit states

STATE serviceability
FATIGUE & ▪Restrictions on stress range under regular service
FRACTURE conditions reflecting number of expected stress range
LIMIT STATE excursions
EXTREME ▪Ensure structural survival of bridge component or system
EVENT LIMIT during rare events
STATE
38
MODULE 2: LOADS ON A BRIDGE

LIMIT STATES:
❖Strength
❖ defines Safe operation and adequacy of structure under
Limit states

normal or extreme load condition

❖Defined by
Yielding strength  ultimate strength
 buckling  overturning

39
MODULE 2: LOADS ON A BRIDGE

LIMIT STATES:
❖Serviceability
❖Defines performance and behaviour of structure under
Limit states

nominal service condition

❖Defined by
 Stress  Fatigue  Deflection
 Vibration  Crack width

40
MODULE 2: LOADS ON A BRIDGE

▪AASHTO LRFD SPECIFICATIONS

**each member and connection satisfy:

▪Strength I
▪Basic load combination
Limit states

▪Relates to normal vehicular use of structure without

wind or any extreme event loads (Earthquake)

▪Mostly applied to control superstructure member

41
MODULE 2: LOADS ON A BRIDGE

▪AASHTO LRFD SPECIFICATIONS

**each member and connection satisfy:

▪Strength II
▪Used for owner-specified special design vehicles or
Limit states

permit vehicles

▪No wind or any extreme event loads considered

▪Not commonly used

▪Reduced dynamic load allowance may be allowed

42
MODULE 2: LOADS ON A BRIDGE

▪AASHTO LRFD SPECIFICATIONS

**each member and connection satisfy:

▪Strength III
Limit states

▪Used on bridges exposed to maximum wind velocity

▪No live loads is assumed present on the bridge

43
MODULE 2: LOADS ON A BRIDGE

▪AASHTO LRFD SPECIFICATIONS

**each member and connection satisfy:
▪Strength IV
▪Used for structures with very high dead-live load force
effect ratios
Limit states

▪Control load combination for certain elements if

▪structure has long span length and/or large dead
load
▪Bridges under construction
▪Make sure that various type of bridges have similar
failure probability

44
MODULE 2: LOADS ON A BRIDGE

▪AASHTO LRFD SPECIFICATIONS

**each member and connection satisfy:

▪Strength V
▪Relate to normal vehicular use of bridge with wind
Limit states

velocity of 55mph (90kph)

▪Live and wind load combined – both values reduced

because probability is very low to experience very
heavy live load and extremely high wind load

45
MODULE 2: LOADS ON A BRIDGE

▪AASHTO LRFD SPECIFICATIONS

**each member and connection satisfy:

▪Service I
▪Used for normal operational use with 55mph wind
Limit states

▪All loads are taken at nominal values

▪Extreme loads are excluded
▪Used to control deflection, crack width (for RC),
compressive stress (prestress), and soil slope
stability

46
MODULE 2: LOADS ON A BRIDGE

▪AASHTO LRFD SPECIFICATIONS

**each member and connection satisfy:

▪Service II
Limit states

▪Is for preventing yielding of steel due to vehicle live

load

▪Live load used is approximately halfway between

service I and strength I

47
MODULE 2: LOADS ON A BRIDGE

▪AASHTO LRFD SPECIFICATIONS

**each member and connection satisfy:

▪Service III
Limit states

▪Relates only to tension in prestressed concrete

superstructure

▪Load factor of 0.80 is applied to live load → If nominal

design live load is used, superstructure is overdesigned
for concrete tensile areas

48
MODULE 2: LOADS ON A BRIDGE

▪AASHTO LRFD SPECIFICATIONS

**each member and connection satisfy:

▪Service IV
▪Relates only to tension in prestressed concrete
Limit states

substructure to control cracks

▪Load factor of 0.70 for wind (represents 84mph)

▪Reflects probability of PC substructure will be
subjected to tensile stress once every 11years

49
MODULE 2: LOADS ON A BRIDGE

▪AASHTO LRFD SPECIFICATIONS

**each member and connection satisfy:
▪Fatigue
▪Fatigue and fracture load combinations
▪Relate to repetitive gravitational vehicular live load
Limit states

and dynamic responses

▪Live load factor of 0.75 represents cumulative effects
of majority truck population
▪Only a single 32k loads (30ft constant spacing) is
applied

50
MODULE 2: LOADS ON A BRIDGE

▪AASHTO LRFD SPECIFICATIONS

**each member and connection satisfy:

▪Extreme Event I
▪Related to earthquake
Limit states

▪Live load considered shall be based on daily traffic

volume of bridge
▪Normal bridge: Live load Factor, 0.5
▪Implies low probability of maximum live load at
time of large earthquake may occur

51
MODULE 2: LOADS ON A BRIDGE

▪AASHTO LRFD SPECIFICATIONS

**each member and connection satisfy:

▪Extreme Event II
Limit states

▪Used for extreme conditions (ice load, collision by

vessels and vehicles)

▪Only one should be considered at a time

▪reduced live loads are considered

52