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Bridge Deck Slab 1

Introduction

• Bridge deck provide the riding surface for traffic, support & transfer live loads to the main load carrying member such as girder on a bridge superstructure.

• Selection of bridge deck depends on location, spans, traffic, environment, maintenance, aesthetic, life cycle cost & others reason.

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Basic types of bridge decks

1. In-situ reinforced concrete deck – most common type

2. Pre-cast concrete deck – minimize the use of local labor

3. Open steel grid deck

4. Orthotropic steel deck

5. Timber deck

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1. In-situ reinforced concrete deck 4

1. In-situ reinforced concrete deck

• Advantages:

• Acceptable skid resistance

• Easier field-adjustment of the roadway profile during concrete placement to provide a smooth riding surface.

• Disadvantages:

• Excessive differential shrinkage the supporting girders & slow construction progress

• Tendency of the deck rebar to corrode due to deicing salts

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2. pre-cast concrete deck 6

3. Open steel deck grid 7

4. Orthotropic steel deck 8

5. Timber deck 9

Materials

1. General requirements

• Reduce concrete distress and reinforcement corrosion and lead to a long service life with minimum maintenance.

• Characteristic: • Low chloride permeability

• A top surface that does not deteriorate from freeze thaw or abrasion damage

• Cracking that is limited to fine flexural crack associated with the structural behavior

• Smooth rideability with adequate skid resistance

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Materials

2. Concrete

• Fly ash up to 35% of the total cementitious materials content

• Silica fume up to 8% of the total cementitious materials content

• Ground-granulated blast furnace slag up to 50% of the total cementitious materials content

• Aggregate with low modulus of elasticity, low coefficient of thermal expansion and high thermal conductivity

• Largest size aggregate than can be properly placed

• Concrete compressive strength in the range of 28 – 41MPa.

• Water reducing and high range water reducing admixture

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Materials

3. Reinforcement

• Epoxy-coated reinforcement in both layers of deck reinforcement

• Minimum practical transverse bar size and spacing

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Materials

4. Construction practice

• Use moderate concrete temp. at time of placement

• Provide minimum finishing operations

• Implement a warrant requirement for bridge deck performance

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Design consideration

ANALYSIS METHOD

Approximate Method of Analysis

Empirical Method of Analysis

Refined Method of Analysis

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1. Approximate method of analysis

• The concrete bridge decks was assumes as transverse slab strips of flexure members supported by the longitudinal girders.

• The maximum +ve moment and the maximum –ve moment to apply for all positive moments regions and all negative moment regions in the deck slab, respectively.

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2. Empirical method of analysis

• Concrete deck slab design based on the concept of internal arching action within concrete slabs.

• In this method, the effective length of slab shall be taken as: • For slabs monolithic with supporting members: the face-to-face distance

• For slabs supported on steel or concrete girders: distance between the webs of girders

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3. Refined methods of analysis

• Usually consider flexural and torsional deformation without considering vertical shear deformation.

• More suitable for a more complex deck slab structure

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Bridge deck deterioration

• Chloride containing deicing salt causes corrosion of rebars and later damage to concrete

• In US over 200 million/year on highway bridge deck repair

• In Canada, Ontario over 20 million/year on bridge repair

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Spalling 19

Deck protection method

• Protection systems

- bituminous waterproofing

- pre-fabricated sheeting

- thin adhesive films

- galvanized rebars

- epoxy coating of rebars

- stainless steel

- cathodic protection

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Cathodic protection 21

Thicker cover

• Use thicker cover and denser concrete

• IOWA method

• slump 12.5 to 25 mm

• Air content 6%

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Composites

• CFRP ( Carbon Fiber Reinforced Polymer) & GFRP (Glass Fiber Reinforced Polymer)

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Composites

• Thermoset

- polyester

- vinyl resin

- epoxy

- phenoic

- polyurethane

• Thermoplastic

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Composites, fibers

• Aramid

• Boron

• Carbon/graphite

• Glass

• Nylon

• Polyester

• Polyethylene

• Polypropylene

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Composites

• Domain of application

- construction of new structures

- renovation, repair of existing bridges

- retrofit of existing bridges

- embedded or externally applied rods

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Composites

• Important issues:

- design to be consistent with limit states design principles

- rigorous material testing procedures

- design provisions for reinforced and pre-stressed components

- site preparation and construction procedure

- fire resistance

- long term durability

- ultraviolet rays, temp, humidity

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Composites

• Testing

• FRP internal reinforcement

- cross sectional area

- anchor for testing FRP specimens

- tensile properties

- development length

- bond strength

• Surface bonded FRP reinforcement

- direct tension pull-out

- tension of flat specimen

- overlap splice tension test

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Composites

• Design

• Flexure

- deformability condition to ensure concrete crushes first

- crack limitations less severe than for steel bars

- deflection limitations similar to conventional members

• Shear

- stirrups fail in corners due to premature fracture at the bends

- few tests show shear resistance is less than predicted

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Composites

• Design

• Thermal stress

- expansion of FRP very different than concrete

- large thermal stresses in harsh climates

- must consider thermal stress in design

• Fire resistance depends on

- critical temperature of FRP varies for various types

- thickness of concrete cover, aggregates

• Ultraviolet

- not concern in embedded bars

- use protective coatings, additive to the resin

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Example 31

Given: nominal parapet loading = 3.5 kN/m

Loaded length = 16m

Surfacing thickness = 50mm

Unit weight of concrete = 24 kN/m3

Unit weight of premix = 22.6 kN/m3

Lane width = 3000 mm

A solid slab highway bridge with cross section as shown in Figure has

slab thickness of 225mm with specific highway loading of HA. Use the

following data to calculate:

a) The total ULS loads in edge girder & inner girder

b) The moment of HA loading for edge & inner girder

Load combination 1 𝛾 fL

Dead load 1.15

surfacing 1.75

parapet 1.15

HA load 1.50

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EXERCISE 33

A solid slab highway bridge with cross section as shown in Figure has

slab thickness of 0.25m with specific highway loading of HA. Use the

following data to calculate:

a) The total ULS loads in edge girder & inner girder

b) The moment of HA loading for edge & inner girder

Given: nominal parapet loading = 1.5 kN/m

Loaded length = 17m

Surfacing thickness = 50mm

Unit weight of concrete = 24 kN/m3

Unit weight of premix = 22.6 kN/m3

Lane width = 3500 mm

Load combination 1 𝛾 fL

Dead load 1.15

surfacing 1.75

parapet 1.15

HA load 1.50