EGCE 406: Bridge Design

Praveen Chompreda

Mahidol UniversityFirst Semester, 2010

Bearings & Substructures

1

Class Topics & Objectives Topics

Bridge Bearing

Bridge Substructures Loads on Substructure Abutment Piers

Objective Students can identify and describe

types of bridge bearings Students can describe the loads

involved in the design of substructures.

Students can describe pros and cons for each type of substructure

Parts of the topics discussed in this class can be found in:

Chapter 1-4

2

Load Transfer Loads on the bridge must find a way to the ground

Live Loadon Bridge

Deck Slab Superstructure

Girder Superstructure

Bearing

Substructure(Abutment/ Pier)

Foundation(Footing/ Pile)

Ground

Superstructure

Substructure

3

Components of Bridge

Abutment Abutment

Superstructure

Substructure

Roadway Deck

PierAbutment

Superstructure

Substructure

Roadway Deck

4Source: Nowak (2005)

BearingRole of Bearing

Forces and MovementsTypes

Selection of Bearing

5

Bearing Bearing is a structural device positioned

between bridge superstructure and substructure

Roles of Bearing: Transmit load from superstructure to

substructure Accommodate relative movements

between superstructure and substructure

Types: Fixed Bearing

Rotational movement only Expansion Bearing

Rotational movement Translational movement 6

Forces and Movements on Bearing Forces on Bearing

Vertical forces - from dead loads and live load Horizontal forces - from wind, earthquake

Movements on Bearing Horizontal translation caused by creep, shrinkage, and thermal

expansions. Rotations caused by traffic, construction tolerances, and uneven

settlement of foundations

If no movement is allowed, then the bearing must be able to resist the force due to the deformation

7

Types of Bearing Rocker Bearing Pin Bearing Roller Bearing Slider Bearing Elastomeric Bearing Curved Bearing

Pot Bearing Disk Bearing

8

Rocker/ Pin/ Roller Bearing

Mostly used for steel beams

Can carry large loads Requires high clearance Corrosion can be a

problem need regular inspections high maintenance cost

Source: Chen and Duan (2003)9

Rocker/ Pin/ Roller Bearing

Source: www.mageba.ch (2010)

10

Elastomeric Bearing

Made up of natural or synthetic rubber Very flexible in shear but very stiff against volumetric change Can accommodate both rotational and translational movements through

the deformation of pad Steel or fiberglass is typically used to reinforced the pad in alternate

layers to prevent it from “bulging” under high load, allowing it to resist higher loads

11

Source: Chen and Duan (2003)

Elastomeric Bearing with Slider

Steel slider with Teflon (PTFE – polytetrafluoroethylene) coated surfaces may be used in combination with elastomeric bearing to allow for more translations

12

Source: Chen and Duan (2003)

Elastomeric Bearing

Source: www.mageba.ch (2010)

13

Curved Bearing Curved Surface allows for

rotation Cylindrical Surface can

rotate only about 1 axis Spherical Surface can

rotate about any axes

Slider surface coated with Teflon must be used to allow for the translation

Can resist relatively large loads

14Source: Chen and Duan (2003)

Curved Bearing

Source: www.mageba.ch (2010)

15

Pot Bearing

Pot bearing consists of steel container (“Pot”) with elastomeric pad inside

Can resist much larger loads than conventional elastomeric bearing Rotation is accommodated by deformation of the elastomer Sliding surface is used to allow for translation

16

Source: Chen and Duan (2003)

Pot Bearing

Source: www.mageba.ch (2010)

17

Disk Bearing

Hard elastomeric disk is used with metal key inside Metal key is used to resist horizontal loads Rotation is accommodated by deformation of the elastomer Sliding surface is used to allow for translations

18

Source: Chen and Duan (2003)

Which type of bearing should I use? Consider the following factors when selecting a

bearing to use: Vertical and Horizontal Loads Translational and Rotational Movements

Available Clearance (footprint/ height) Environment (corrosion/ temperature range) Initial Cost Maintenance Cost

Availability Owner’s Preference

19

Bearing Capacity of Common Bearings

20Source: Chen and Duan (2003)

Substructures

21

Types of Substructures Abutment-Type Substructures

Abutment and Retaining Walls Anchored Walls Mechanically Stabilized Earth Walls Prefabricated Modular Walls

Pier-Type Substructures Concrete Pier Steel Pier Composite Steel & Concrete Pier

22

Types of Substructures

Abutment & Pier

PierAbutment

23

Loads on SubstructuresLoads from Superstructure

Loads on SubstructureLoad Combinations

24

Loads from Superstructure Vertical Loads from Superstructures

Dead Load of Structural and Nonstructural Components (DC) Dead Load of Wearing Surface (DW) Live Load (LL) and Impact (IM) Pedestrian Live Load (PL)

Horizontal Loads from Superstructures Wind Load on Structures (WS) Wind Load on Live Load (WL) Earthquake Load (EQ) Vehicular Braking Force (BR), Centrifugal Force (CE), and

Collision Force (CT) Creep (CR), Shrinkage (SH), Friction (FR), and Temperature

(TG/ TU)25

Loads on Substructures Vertical load acting on substructure

Dead Load of Structural and Nonstructural Components (DC) Vertical Pressure from Dead Load of Earth Fill (EV)

Horizontal loads acting on substructure Water Load and Stream Pressure (WA) Ice Load (IC) Wind Load on Structure (WS) Earthquake Load (EQ) Vehicular Collision Force (CT), Vessel Collision Force (CV) Horizontal Earth Pressure Load (EH) Earth Surcharge Load (ES) Live Load Surcharge (LS)

26

Wind Loads (WS, WL)

WS(on Substructure)

WS(on Superstructure)

WL

27

Vehicle Collision Forces (CT) Unless protected, abutments and piers located within a distance of 30.0

FT to the edge of roadway, or within a distance of 50.0 FT to the centerline of a railway track, shall be designed for an equivalent static force of 400 KIP, which is assumed to act in any direction in a horizontal plane, at a distance of 4.0 FT above ground.

CT need not be considered for structures which are protected by: An embankment A structurally independent, crashworthy groundmounted 54.0-IN high

barrier, located within 10.0 FT from the component being protected; Or a 42.0-IN high barrier located at more than 10.0 FT from the

component being protected

28

Load Combinations

29Source: AASHTO (2002)

Load Combinations

30Source: AASHTO (2002)

Design of Abutment and Retaining Substructures

Roles and TypesFailure Limit StatesLoads on Abutment

31

Roles and Types Roles of Abutment

Provide support for bridge superstructure at the bridge ends

Connect the bridge with the approach roadway

Retain the roadway material (soil & rock) from the bridge span

Types Abutment

Open End AbutmentClose End Abutment

Retaining StructuresGravity WallCantilever WallAnchored WallsMechanically

Stabilized Earth Walls Prefabricated

Modular Walls

32

Types of Abutment Open End

Abutment

Close End Abutment

33Source: Chen and Duan (2003)

Types of Abutment Open End Abutment

34Source: Nowak (2005)

Types of Abutment Close End Abutment

35Source: Nowak (2005)

Types of Abutment Open End Abutment

Has some slopes between abutment wall and roadway/ water channel below

Requires relatively larger space Requires longer bridge span Allow for some roadway

widening below bridge More economical

Close End Abutment Has no slopes between abutment

wall and roadway/ water channel below

Requires relatively smaller space (good for urban areas)

Requires shorter bridge span No allowance for future widening More expensive to construct

36Source: Chen and Duan (2003)

Types of Retaining Structures

37Source: Chen and Duan (2003)

Anchored Walls

Types of Retaining Structures

38Source: Chen and Duan (2003)

Types of Retaining Structures Mechanically Stabilized Earth Walls

39

Source: Nowak (2005)

Types of Retaining Structures

40

Source: Nowak (2005)

Types of Retaining Structures

41

Source: Chen and Duan (2003)

Failure Limit States Abutment structures must be checked for:

Global Stability Failure: Bearing Capacity (a) Overturning (b) Sliding Failure (c) Deep Seated Failure (d)

Local Strength Failures: Compression Failure Bending Moment Failure Shear Deflection Etc…

42

Source: Nowak (2005)

Strength Limit States (Global)

NT

(a) (b)

(d)(c)

43Source: Nowak (2005)

Loads on Abutment from Superstructure Vertical loads from superstructures

Dead Load of Structural and Nonstructural Components (DC) Dead Load of Wearing Surface (DW) Live Load (LL) and Impact (IM) Pedestrian Live Load (PL)

Horizontal loads from superstructures Wind Load on Structures (WS) Wind Load on Live Load (WL) Earthquake Load (EQ) Vehicular Braking Force (BR), Centrifugal Force (CE), and

Collision Force (CT) Creep (CR), Shrinkage (SH), Friction (FR), and Temperature

(TG/ TU)44

Loads on Abutment Itself Vertical loads acting on substructure

Dead Load of Structural and Nonstructural Components (DC) Vertical Pressure from Dead Load of Earth Fill (EV)

Horizontal loads acting on substructure Water Load and Stream Pressure (WA) Ice Load (IC) Earthquake Load (EQ) Vehicular Collision Force (CT), Vessel Collision Force (CV) Horizontal Earth Pressure Load (EH) Earth Surcharge Load (ES) Live Load Surcharge (LS)

45

Loads on Abutment

46

Source: Chen and Duan (2003)

Earth Pressure (EH, ES, LS and DD) Earth pressure is a function of the:

Type and unit weight of earth Water content Soil creep characteristics Degree of compaction Location of groundwater table Earth-structure interaction Amount of surcharge Earthquake effects

47

Earth Pressure (EH) Basic earth pressure, p

kh = coefficient of lateral earth pressure At-rest pressure coefficient, Ko Active pressure coefficient, Ka Passive pressure coefficient, Kp

γs = unit weight of soil

z = depth below the surface of earth

Force resultant is assumed to act at 0.4H from the base of wall

h sp k γ gz

48

Earth Pressure (EH)

49

Source: AASHTO (2002)

Surcharge Loads (ES and LS) Constant horizontal earth pressure due to surcharge load

is added to the basic earth pressure

ks = coefficient of earth pressure due to surcharge At-rest pressure coefficient, Ko Active pressure coefficient, Ka

qs = uniform surcharge applied to the upper surface of the active earth wedge

∆p s sk q

50

Loads on Abutment Live Load from Superstructure

51Source: Nowak (2005)

Loads on Abutment Earth Pressure and Surcharge Loads

Passive pressure is ignored

ConcreteApproachslab

O

H’

52Source: Nowak (2005)

Loads on Abutment Earth Pressure and Surcharge Loads

Passive pressure is ignored

Pv

Ph

ConcreteApproachslab

H’

0.4H’

O

Earth Pressure:Ph = ½ (EFPh)H’2

Pv = ½ (EFPv)H’2

Location at 0.4H’ instead of 1/3EFP = Equivalent Fluid Pressure

53Source: Nowak (2005)

Loads on Abutment Earth Pressure and Surcharge Loads

HL

Live load approach

WL

WD

HD

Passive pressure is ignored

Pv

VD

VL

Ph

ConcreteApproachslab

H’

0.5H’

0.4H’

O

Pressures generated by theLive Load and Dead Load Surcharges:HL = KwLH’HD = KwDH’VL = wL (heel width)VD = wD (heel width)wL = heq wD = slab thickness c

54Source: Nowak (2005)

Loads on Abutment Earth Pressure and Surcharge Loads

DLLL

BRCR+SH+TU

HL

Live load approach

WL

WD

HD

Passive pressure is ignored

Pv

VD

VL

Ph

ConcreteApproachslab

H’

0.5H’

0.4H’

O

Vertical Loads at the Bearing:DL and LLHorizontal Loads:BR (braking)CR (creep)SH (shrinkage)TU (temperature)

55Source: Nowak (2005)

Loads on Abutment Earth Pressure and Surcharge Loads

DLLL

BRCR+SH+TU

HL

Live load approach

WL

WD

HD

Passive pressure is ignored

Pv

VD

1

2

3

4

VL

Ph

ConcreteApproachslab

H’

0.5H’

0.4H’

O

Dead Load of theabutment

56Source: Nowak (2005)

Design of Pier Substructures

TypesFailure Limit States

LoadsDesign of RC Columns

57

Piers Pier substructures may be designed using design

procedures of columns Steel Concrete Composite

58Source: Chen and Duan (2003)

Piers Reinforced Concrete Piers

59Source: www.wikipedia.org (2005)

Piers Steel Truss Pier

60Source: www.wikipedia.org (2005)

Piers Piers may be

Solid – usually for short piers Hollow – usually for taller piers to save weight (need large

moment of inertia to prevent buckling and provide larger moment capacity for lateral loads)

Pier Types Solid Wall Pier Single Pier (Hammer Head Type) Rigid Frame

61

Pier Shapes

62Source: Chen and Duan (2003)

Piers

63Source: Chen and Duan (2003)

Pier Types – Steel Bridges

64Source: Chen and Duan (2003)

Pier Types – Steel Bridges Rigid Frame Pier

65

Pier Types – Concrete Bridges

66Source: Chen and Duan (2003)

Pier Types – Concrete Bridges

67

Pier Selection Factors that influences the selection of pier types

includes: Types of superstructures

Steel or Concrete Widths

Location Over land or water Hydraulics

Height (tall piers may be hollow to reduce weight) Space available Aesthetics

68

Pier Selection Guidelines

69

Source: Chen and Duan (2003)

Strength Limit States Pier structures must be checked for:

Global Stability Failure: Overturning

Local Strength Failures: Compression Failure Bending Moment Failure Shear Deflection

70

Source: Nowak (2005)

Loads on Piers from Superstructure Vertical loads from superstructures

Dead Load of Structural and Nonstructural Components (DC) Dead Load of Wearing Surface (DW) Live Load (LL) and Impact (IM) Pedestrian Live Load (PL)

Horizontal loads from superstructures Wind Load on Structures (WS) Wind Load on Live Load (WL) Earthquake Load (EQ) Vehicular Braking Force (BR), Centrifugal Force (CE), and

Collision Force (CT) Creep (CR), Shrinkage (SH), Friction (FR), and Temperature

(TG/ TU)71

Loads on Piers Itself Vertical load acting on substructure

Dead Load of Structural and Nonstructural Components (DC)

Horizontal loads acting on substructure Water Load and Stream Pressure (WA) Ice Load (IC) Wind Load on Structure (WS) Earthquake Load (EQ) Vehicular Collision Force (CT), Vessel Collision Force (CV)

72

Pier Load Analysis for Wind Loads

WS(on Substructure)

WS(on Superstructure)

WL

Investigate High Compressive ForceInvestigate High Bending (Low Compression) 73

Reinforced Concrete Columns Pure Axial (Ø=0.75)

Sprial

Tie

Pure Flexure (beam) (Ø=0.90 for RC)

Combined Axial and Flexure in on direction Interaction Diagram

00.85 0.85 0.85 ' ( )n c g st st yφP φ P φ f A A A f

00.80 0.80 0.85 ' ( )n c g st st yφP φ P φ f A A A f

( / 2)n s yφM φA f d a

74

Reinforced Concrete Columns Spiral vs. Tie columns

75Source: Wang et. al. (2006)

Axial Loads + Bending Moment

76Source: Chen and Duan (2003)

Reinforced Concrete Columns Biaxial Bending + Axial

For high axial load

For low axial load

For slender columns, must also determine the secondary moment due to P-∆ Effect

0.1 'u c gP φf A

0.1 'u c gP φf A

0

1 1 1 1

rxy rx ryP P P P

1.0uyux

rx ry

MMM M

Factored Applied Moment in X and Y direction

Factored Nominal Moment Capacity in X and Y direction

Factored Axial Resistance when has eccentricity only in Y direction

Factored Axial Resistance when has eccentricity only in X direction

77