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T6 bridges tubbs jb

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  • Arches, trusses, beam, cable-supported
  • Inhabited: Operator, concessions, security buildings. LRT Systems: Signal, Communication, substation buildings
  • Types: Mined or Cut and Cover. Fire, life, and safety considerations generally for tunnels over 300 ft in length
  • Platform amenities, stairs, ramps, parking garages, platform walls. Stations most often constructed at grade or on retained fill, less frequently on bridges. Pictures of Den station on bridge?
  • Updated renderings of WRB? Other LRT crossings over water?
  • Disadvantages: Short spans, doesn’t accommodate curvature well, aesthetic limitations
  • Disadvantages: more expensive, construction duration, falsework expense and safety considerations
  • Disadvantages: Cost, higher degree of dimensional control during construction,
  • Picture of Johnson Creek
  • Disadvantages: initial and life-cycle costs, lead time,
  • Other types of mention: Steel truss, steel or concrete arch, cable supported – typically used for major crossings with longest spans or where signature spans are required.
  • Other types of mention: Steel truss, steel or concrete arch, cable supported – typically used for major crossings with longest spans or where signature spans are required. Closely follows highway loading S/D ratios – ONLY approximations
  • Other types of mention: Steel truss, steel or concrete arch, cable supported – typically used for major crossings with longest spans or where signature spans are required. Closely follows highway loading S/D ratios – ONLY approximations
  • Use updated graphic with TriMet loading and HL-93 Loading
  • Show updated covers of both, discuss LRFD as current TriMet design critieria
  • Update graphic
  • Update graphic
  • Update graphic
  • Update graphic
  • Transcript

    • 1.  
    • 2.  
    • 3. OVERVIEW
      • Structure Layout and Type Selection
      • LRT Loading Requirements
      • Special Considerations
      • Constructability Considerations
    • 4. Basic types of structures - Bridges Structure Layout & Type Selection
    • 5. Basic types of structures - Buildings Structure Layout & Type Selection
    • 6.
      • Basic types of structures
      • Tunnels
      Structure Layout & Type Selection
    • 7.
      • Basic types of structures
      • Stations
      Structure Layout & Type Selection
    • 8. Basic types of structures - Walls Retaining Walls Sound Walls Structure Layout & Type Selection
    • 9. What does a structure do? - Provides infrastructure for system - Separates facility from other features Structure Layout & Type Selection
    • 10. What does a structure do? - Solves safety concerns Structure Layout & Type Selection
    • 11. Crossing Types - Bridge over road Structure Layout & Type Selection
    • 12. Crossing Types - Bridge over water Structure Layout & Type Selection
    • 13. Crossing Types - Tunnel under road Structure Layout & Type Selection
    • 14. Crossing Types - Tunnel under geographic feature Structure Layout & Type Selection
    • 15. Modern Bridge Types - Pre-stressed Concrete Structure Layout & Type Selection
    • 16. Modern Bridge Types - Pre-stressed Concrete Structure Layout & Type Selection Advantages - Lowest cost bridge alternative - Good for shorter crossings - No falsework required in roadway or stream - Fast, simple installation, saving construction time - Shallow depth providing greater clearance to stream or roadway surfaces below
    • 17. Modern Bridge Types - Cast-in-Place Concrete Structure Layout & Type Selection
    • 18. Modern Bridge Types - Cast-in-Place concrete Advantages - Good for longer spans - Resistance to seismic forces - Accommodating horizontal curves, gradelines, or superelevations - More aesthetically pleasing Structure Layout & Type Selection
    • 19. Modern Bridge Types - Concrete ~ Segmental Structure Layout & Type Selection
    • 20. Modern Bridge Types - Segmental Concrete Advantages - Good for longest spans - Highly aesthetic - Limited surface-level disturbance - Geometric flexibility Structure Layout & Type Selection
    • 21. Modern Bridge Types - Steel Structure Layout & Type Selection
    • 22. Modern Bridge Types - Steel Advantages - Longer spans - Can accommodate track geometry - Lighter foundation & seismic loads Structure Layout & Type Selection
    • 23. Modern Bridge Types - Signature Bridges Structure Layout & Type Selection
    • 24. Modern Bridge Types Typical span ranges (order by superstructure cost) - Precast concrete slabs up to 80 feet - Precast concrete box beams up to 120 feet - Precast concrete girder up to 180 feet - CIP post-tensioned box girder 100-600 feet - Steel plate girder 60-300 feet - Steel box girder 60-500 feet - Segmental concrete ~ Span-by-span 80-150 feet ~ Balanced Cantilever up to 800 feet Structure Layout & Type Selection
    • 25. Modern Bridge Types Typical Span-to-Depth ratios (structure thickness only) - Precast concrete slabs/boxes Span/33 - Precast concrete girder Span/23 - CIP post-tensioned box girder ~ simple span Span/26 ~ continuous, uniform depth Span/29 ~ continuous, variable depth Span/35 - Steel plate girder ~ simple span Span/25 ~ continuous Span/31 Structure Layout & Type Selection
    • 26. Modern Bridge Types Structure Depth Don’t Forget!! Structure Layout & Type Selection Overall Structure Depth = Structure thickness + Superelevation + Track section depth
    • 27. Retaining Walls
          • Cut Walls
          • Fill Walls
      Structure Layout & Type Selection
    • 28. Retaining Walls Common Types Structure Layout & Type Selection
    • 29. Retaining Walls Common Types Structure Layout & Type Selection
    • 30. Retaining Walls Common Considerations - Excavation for reinforcement/footings - Easements for subterranean elements - Increased design height on slopes - Proper consideration at wall terminations - Drainage conveyance Structure Layout & Type Selection
    • 31. Common bridge layout considerations: - Site conditions - Bent locations and required span lengths - Cost - Material availability - Aesthetics - Vertical clearance - Horizontal alignment - Schedule - Seismic resistance - Maintenance, future widening, and more... Structure Layout & Type Selection
    • 32. Bent location considerations: - Proximity to facilities - Right of way - Span length - Constructability - Required clearances - Environmental concerns Structure Layout & Type Selection
    • 33. LRT Loading Requirements
    • 34. Load effects of DL - Not much variance in stresses over time LRT Loading Requirements Load effects of LL - Transient loads produce variable stresses
    • 35. General Design Criteria: - Agencies allow both AASHTO & AREMA - Most light rail loads are greater than the HL93 used by AASHTO LRFD, but much less than AREMA’s Cooper E80 LRT Loading Requirements
    • 36. General Design Criteria: AREMA - Restrictive for light rail transit structures due to the great differences in loading - Wheel spacings don’t correspond to those found on LRV’s - Impact criterion is not consistent with the suspension and drive systems used on LRV’s - Types of loading not consistent with LRV’s LRT Loading Requirements
    • 37. General Design Criteria: AASHTO - Ratio of LL to DL more closely approximates that of highway loadings than heavy rail loadings - Axle loads and car weights are similar to LRV’s - Results in conservative design that is not overly restrictive or uneconomical LRT Loading Requirements
    • 38.
      • Loads and Load Combinations (TriMet 2010):
      • Dead load
      • Live load
      • - LRV-specific
      • - Highway Pedestrian
      • - Seismic loads
      • - Earth loads
      • - Wind loads
      • - Thermal Loads
      LRT Loading Requirements
    • 39. Loads and Load Combinations (TriMet 2010): Dead loads (DC) - Superstructure weight - Superimposed loads - Cross Beam weight - Column weight - Footing weight - OCS poles - Ductbanks - Plinths/Ballast - Rail LRT Loading Requirements
    • 40.
      • Loads and Load Combinations
      • (TriMet 2010):
      • Live Loads (LL)
      • - Highway (AASHTO)
      • - Pedestrian (AASHTO)
      • - LRV-Specific
      • ~ 1 to 4 car train
      • ~ Single or multiple
      • tracks loaded
      LRT Loading Requirements
    • 41. Loads and Load Combinations (TriMet 2010): Other LRV-specific live loads: - Vertical impact (Iv or IMv) ~ Max between AASHTO and AREMA but generally not exceeding 30% - Horizontal impact (Ih or IMh) ~ 10% of each axle load applied transversely at 4 ft above TOR - Impact applies generally only to structural elements above ground for trains that are not stationary LRT Loading Requirements
    • 42. Loads and Load Combinations (TriMet 2010): Other LRV-specific live loads: - Longitudinal forces (BR): ~ Acceleration = 16% of LRV load ~ Deceleration = 21% of LRV load ~ Combine as necessary to obtain max force effect (e.g., one track accelerating while other track decelerating) LRT Loading Requirements
    • 43. Loads and Load Combinations (TriMet 2010): Other LRV-specific live loads: - Centrifugal forces (CE): ~ 10% of axle load for track CL radius <= 2450 ft ~ Axle load*0.0875*(V^2)/R for larger radius ~ Applied transversely at 4 ft above TOR LRT Loading Requirements
    • 44. Loads and Load Combinations (TriMet 2010): Special LRV-specific live loads: - Emergency Braking (EB) ~ 46% of LRV on one track ~ Combine with BR loads on other tracks as necessary to obtain max force effect ~ Considered only for Strength II limit state, and is not combined with derailment loads LRT Loading Requirements
    • 45. Loads and Load Combinations (TriMet 2010): Special LRV-specific live loads: - Derailment Loads (DR) ~ Vertical – 100% impact applied for any truck ~ Horizontal – 10-30% of single LRV vehicle applied at 2 ft above TOR over 10 ft distance ~ Only one track assumed to derail, other tracks unloaded or loaded with stationary train ~ Considered only for Strength II limit state, and is not combined with EB loads LRT Loading Requirements
    • 46. Loads and Load Combinations (TriMet 2010): Other Special LRT Loads: - Thermal forces ~ Radial rail forces ~ Rail break LRT Loading Requirements
    • 47. Special Considerations
    • 48. Ballasted Track versus Direct Fixation (DF) Special Considerations
    • 49. Ballasted track versus direct fixation on structures Ballasted track - Greater DL requires larger structural members - Flexible track structure support - Most prevalent track type used at grade - Must contend with electrical isolation & acoustic attenuation - Results in deeper bridge structure Special Considerations
    • 50. Ballasted track versus direct fixation on structures Direct Fixation - High initial cost - Rail interacts with structure - Standard method of construction on aerial structure - Much stiffer vertically than ballasted track - Lower maintenance costs Special Considerations
    • 51. Continuously Welded Rail Rail Break Gap - Occurs when a thermally induced tensile force exceeds the ultimate tensile strength of the rail. - Likely to occur at or near ~ Bridge expansion joints ~ At a bad weld ~ A rail flaw ~ Weak spot in rail Special Considerations
    • 52. Continuously Welded Rail Rail Break Gap - Established limits on gap size ~ Usually based on LRV’s wheel diameter ~ Decreasing the fastener’s longitudinal stiffness results in increased gap size Special Considerations
    • 53. Continuously Welded Rail - Rail-Structure Interaction ~ Thermal deformations of bridge induce stress on rails ~ Restraint of CWR and DF fasteners induce stresses on rails and structure ~ Rail break forces transferred through DF fasteners to structure and to remaining unbroken rails according to relative stiffnesses Special Considerations
    • 54. Continuously Welded Rail Rail-Structure Interaction DF Fasteners: ~ Proprietary devices that allow differential movement between structure and rail ~ Full lateral restraint ~ Provide varied levels of longitudinal restraint Special Considerations
    • 55. Continuously Welded Rail Rail-Structure Interaction DF Fasteners: - Lower restraint fasteners often used at locations of highest structure thermal deformation (i.e., near expansion joints) - Higher restraint fasteners used near middle of frame Special Considerations
    • 56. Mixed modes on bridge Special Considerations
    • 57. Stray current protection - Stray currents are leaking current from the rails that return to the ground grid of the substation - Corrosion is the most common result of stray currents Special Considerations
    • 58. Stray current protection To minimize stray currents: - Insulate rails from their fastenings and encase rails in embedded track with extruded boot - Continuously weld reinforcement in underlying slab - In ballasted track areas the ballast should be clean, well-drained and not in contact with the rail - Conduct corrosion surveys and perform regular monitoring and maintenance Special Considerations
    • 59. Pedestrian considerations: - Restriction to trespassing - Emergency access/egress Special Considerations
    • 60. Constructability Considerations
    • 61. Basic bridge construction issues Constructability Considerations
    • 62. Basic bridge construction issues - Maintenance of traffic - Adequate easements for construction equipment and laydown areas - Detailing with construction tolerances in mind - Staged construction - Concrete pour sequences - Work site access Constructability Considerations
    • 63. Deck/Plinth Construction - Method of plinth construction can have significant impact on cost and constructability Constructability Considerations
    • 64. CWR welding and setting track Constructability Considerations
    • 65. Downdrag on foundations & long term settlement: - Downdrag ~ Occurs as layers of soil consolidate ~ Causes: Additional fill, liquefaction, secondary compression ~ Can introduce substantial vertical load on piles ~ Can create settlements in shallow foundation systems - Mitigation ~ Coat piles to create slip-plane ~ Design for additional loads ~ Surcharge prior to construction to pre-consolidate soils Constructability Considerations
    • 66. Temporary works Shoring existing facilities Constructability Considerations Temporary work bridge
    • 67. Temporary works Falsework Constructability Considerations
    • 68. Foundation construction in water (cofferdam) Constructability Considerations
    • 69. Foundation construction in water (cofferdam) Cofferdam subject to high water pressures Constructability Considerations Pile driving through template in flooded cofferdam
    • 70. Foundation construction in water (cofferdam) Subgrade stabilization below concrete seal Subgrade excavation of footing in dry cofferdam Constructability Considerations
    • 71. Foundation construction in water (drilled shaft) - Drilled shaft with temporary casing negates need for cost prohibitive cofferdam and reduces environmental impacts Constructability Considerations
    • 72. Foundation construction in water (drilled shaft) Temporary Work Bridge Covered With Plastic to Keep Dredged Materials from Entering Slough Dredged Materials Removed Safely From Site Constructability Considerations
    • 73. Girder shipping and setting - Crane placement - Girder delivery - Shipping/handling weights Constructability Considerations
    • 74. QUESTIONS?

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