Basic types of bridge decks

Transcription

1 Bridge Deck Slab 1

2 Introduction 2 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.

3 Basic types of bridge decks 3 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

4 1. In-situ reinforced concrete deck 4

5 1. In-situ reinforced concrete deck 5 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

6 2. pre-cast concrete deck 6

7 3. Open steel deck grid 7

8 4. Orthotropic steel deck 8

9 5. Timber deck 9

10 Materials 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

11 Materials 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

12 Materials Reinforcement Epoxy-coated reinforcement in both layers of deck reinforcement Minimum practical transverse bar size and spacing

13 Materials Construction practice Use moderate concrete temp. at time of placement Provide minimum finishing operations Implement a warrant requirement for bridge deck performance

14 Design consideration 14 ANALYSIS METHOD Approximate Method of Analysis Empirical Method of Analysis Refined Method of Analysis

15 1. Approximate method of analysis 15 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.

16 2. Empirical method of analysis 16 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

17 3. Refined methods of analysis 17 Usually consider flexural and torsional deformation without considering vertical shear deformation. More suitable for a more complex deck slab structure

18 Bridge deck deterioration 18 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

19 Spalling 19

20 Deck protection method 20 Protection systems - bituminous waterproofing - pre-fabricated sheeting - thin adhesive films - galvanized rebars - epoxy coating of rebars - stainless steel - cathodic protection

21 Cathodic protection 21

22 Thicker cover 22 Use thicker cover and denser concrete IOWA method slump 12.5 to 25 mm Air content 6%

23 Composites 23 CFRP ( Carbon Fiber Reinforced Polymer) & GFRP (Glass Fiber Reinforced Polymer)

24 Composites 24 Thermoset - polyester - vinyl resin - epoxy - phenoic - polyurethane Thermoplastic

25 Composites, fibers 25 Aramid Boron Carbon/graphite Glass Nylon Polyester Polyethylene Polypropylene

26 Composites 26 Domain of application - construction of new structures - renovation, repair of existing bridges - retrofit of existing bridges - embedded or externally applied rods

27 Composites 27 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

28 Composites 28 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

29 Composites 29 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

30 Composites 30 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

31 Example 31 Given: nominal parapet loading = 3.5 kn/m Loaded length = 16m Surfacing thickness = 50mm Unit weight of concrete = 24 kn/m 3 Unit weight of premix = 22.6 kn/m 3 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

32 solution 32

33 EXERCISE 33 Given: nominal parapet loading = 1.5 kn/m Loaded length = 17m Surfacing thickness = 50mm Unit weight of concrete = 24 kn/m 3 Unit weight of premix = 22.6 kn/m 3 Lane width = 3500 mm 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 Load combination 1 γ fl Dead load 1.15 surfacing 1.75 parapet 1.15 HA load 1.50