bridge deck slab - universiti malaysia...
TRANSCRIPT
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
solution 32
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